When Snow or Ice Bows and Breaks Tree

When Snow or Ice Bows and Breaks Tree

Marianne C. Ophardt
Washington State University Extension
Area Horticulture Specialist

Heavy wet snow, freezing rain and ice can mean bowed and broken tree limbs and trunks.  What causes limb and branch breakage?  Certain types of trees, especially fast growing species, have "brittle" wood that is prone to breakage.  This includes Chinese elm, silver maple, boxelder, and poplar.  Some tree species have narrow branch angles, making them structurally weaker in situations like these.  The `Bradford' cultivar of callery pear is a good example of a tree with a weak structure due to narrow branch angles.

Another reason for structural weakness in a tree is past pruning practices.  Improper pruning practices, such as topping or stub cutting, leads to the development of poorly attached branches.  There is a great tendency for these branches to break off the tree as they grow larger and heavier, especially when stressed by strong winds or a load of snow and ice.

Trees also become structurally weaker when wood rot develops in the trunk and main branches.  Wood rot is the result of fungi, which invade the tree after physical damage occurs... through wounding, bad pruning cuts, and severe temperature damage.  Severe wood rot can develop through repeated wounding and large branches that have been topped.

Some trees broke under the recent heavy snow-loads but some only bent... bending or bowing was common on young deciduous trees, as well as on certain types of evergreens trees and shrubs.  The wood in these plants is more elastic, with wood bending instead of breaking.  In these cases, it was merely a factor of the snow and ice and the branches yielding to the weight.

Now what can be done about the injured trees and shrubs?  Let's deal with the "bent-out-of-shape" plants first.  According to Dr. Ray Maleike, Washington State University Extension Horticulturist Emeritus, "When snow or ice bend branches and entire trees out of shape, the offending snow or ice should be removed immediately and an attempt made to straighten the bent branch or trunk.  If the plant part isn't straightened very soon after the snow has stopped, the plant may remain bent over... permanently."  Collected snow can be removed with a broom.  Sweep upward to lift the snow off.  However, don't disturb the branches if they're heavily weighted and brittle with ice or you have a concern about the structural integrity of your tree.

Maleike suggests trying to physically straighten the plant or branch once you remove the snow.  He notes, "This doesn't always work, but it does occasionally.  If the young tree or shrub has been squashed down to where it extends into traffic areas, it may have to be pruned."

Around our area there a number branches on multi-stemmed, columnar-needled evergreens, like arborvitae, that have been bent out away from the plant.  Maleike indicates that these may be tied back to the main plant with a soft, non-chafing material like cotton clothesline or nylon pantyhose.  The tying materials may have to be left on for 6 months or more.  He notes, "Tying the plants together before the winter starts is a good preventative for this problem."

What can be done for small trees which have bowed over but have not broken or cracked?  These trees can be staked until they can stand on their own again.  Maleike recommends this procedure, "Drive two stakes, about six to eight inches away from the trunk, into firm ground. (Be careful not to severe major roots.)  Then tie the trunk to the stake at the lowest height, which stabilizes the tree in an acceptable upright position.  A nonchafing tying material must be used."

The stakes should not be left on indefinitely.  They should be removed as soon as the tree can stand by itself again.  This should be within the first growing season after the "bowing" occurred.

Trees with broken branches don't need immediate attention.  However, it's advisable to prune off broken branches as soon as the weather and circumstances allow.  Prune damaged branches back to another branch or the main trunk if necessary... don't make flush cuts and don't leave branch stubs.  On large branches this cut should be made to just outside the branch collar.  Be sure to follow recommended tree pruning practices.  When power lines, large limbs, or main branches complicate the matter, contact a trained and certified arborist.

With the breakage of limbs, sometimes bark is torn on the larger limbs or the main trunk.  To help the tree, the torn bark should be carefully trimmed with a sharp knife to make a smooth, rounded edge to the wound.  Cut only the bark and not into the wood.  No wound dressing materials are recommended for bark wounds or pruning wounds.

Cold Temperatures Can Damage Plants

Cold Temperatures Can Damage Plants

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent

How cold can it get before plants suffer cold temperature injury? It’s important to keep in mind that a plant’s potential hardiness is genetically determined.  Plants that are native to a geographic region have evolved in response to that area’s climate and weather patterns.  It can be thought of as “survival of the fittest”... the hardy plants that can survive the winter weather of a region produce offspring that are also hardy.  Through this natural selection process, native plants are usually able to survive the winter cold of their particular native region.

However, a hardy plant in the middle of summer can’t withstand the same amount of cold that it can in mid-winter.  This is because hardiness to cold develops as a series of physiological changes within the plants.  The first change to occur is a response to the shortening days of late summer and early fall.  Plant hormones are produced in response to the shorter days.  These tell the plant that winter is coming and plant tissues develop greater resistance to damage from freezing temperatures. 

As fall proceeds and temperatures become increasingly cooler, the plants develop even greater hardiness.  The rate at which plants develop hardiness varies from species to species.  The rate also is dependent on the degree of cooling that occurs in the fall.  If fall temperatures remain mild, plants may fail to acclimate fully to cold temperatures.  Because our late fall and early winter has been so mild, it’s very possible that some plants sustained some cold temperature damage from the recent deep freeze. 

At some time in the middle of winter, plants develop their ultimate mid-winter hardiness.  This point is genetically determined.  It’s interesting to note the part that genetics and geographics play in plant hardiness.  The ultimate mid-winter hardiness can be quite variable even within the same species.  For example, Douglas firs that evolved in the Rocky Mountains are hardier than Douglas firs that evolved in the Cascades.  Similarly, a flowering dogwood that is native to the New York state region is hardier than one from the Florida or Georgia regions.  In both cases the plants are exactly the same genus and species, they just evolved in a different climatic region.

After the plants receive their ultimate mid-winter hardiness they begin to deacclimate or lose some of their hardiness.  Like the acclimation process, deacclimation is usually gradual.  However, deacclimation can occur quite rapidly during an extended warm spell.  Plants have the potential to acclimate to colder temperatures again and again when temperatures drop, but they lose this potential as spring approaches and growth begins.

Many gardeners ask how they can protect their plants from cold temperatures.  Plants aren’t “warm blooded” creatures.  Putting blankets around a tree trunk won’t keep them warm.  Blankets can’t help, but other things can be done to provide a measure of protection:

1. Select plants that are hardy for the local climate.  Nurserymen will indicate a plant’s hardiness by noting the USDA hardiness zones for which it’s suitable.  The zone for the Tri-Cities area is Zone 6.  Gardeners close to the river or in the Walla Walla area might be able to push it to Zone 7.  You may see “borderline hardy” plants in area landscapes that do well here for several years when the winters are relatively mild winters, but then they succumb to a particularly cold winter.  That’s because they’re not truly hardy for this area.
2. When planting conifers (evergreens) in the landscape, situate them to limit their exposure to sun and wind.  If you live in a particularly exposed location where there is no “protected location,” plant a windbreak to protect them in winter months.
3. Keep plants in a healthy condition.  Healthy plants are better able to withstand the rigors of winter.  Stressed plants are more susceptible to winter injury.
4. Plants that are actively growing late in the season fail to acclimate as winter approaches.  Avoid fertilizing, pruning, or irrigating excessively towards the end of the summer and in early fall.  Keep in mind that the fall fertilizer that you put on the lawn may well be reaching tree roots and encouraging late season growth.  Try to avoid fertilizing trees and shrubs in the fall, especially those that are not extremely winter hardy or ones prone to winter injury.
5. While you don’t want to water plants excessively and encourage late season growth, it’s also important to note that water stressed plants are less hardy.  Don’t let your plants go into winter with dry soil.
6. Mulch the roots and crowns of tender plants, plants prone to winter injury, and recently planted trees, shrubs, and perennials.  Use loose mulch, such as finely shredded bark, that won’t mat down or exclude air from the roots.  Roses will usually benefit from an application of bark to the crown to protect them from cold and dessicating winds.
7. Protect the trunks from sunscald.  Sunscald damage happens when bark surfaces on the south and west sides of a tree are warmed by bright winter sun and then the temperature drops rapidly when the sun goes down.  This abrupt temperature change can damage the bark and cambium underneath.  Newly planted trees; trees with dark bark, such as cherries; or young trees with thin bark, such as maples, ash, crab apples, and tulip trees are particularly susceptible to this type of injury.  Wrap the tree trunk with a commercial trunk wrap or paint it with an inexpensive interior white latex paint to reflect the sun and prevent damage.  Bark wraps should be removed in the spring.

Early Fall Cold Snap Can Lead to Damage on Landscape Plants

Early Fall Cold Snap Can Lead to Damage on Landscape Plants

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

In our area we typically have relatively long periods of mild fall before we finally get a hard freeze.  In most years, the leaves senesce and normally fall off the tree as leaves do in autumn.  However, occasionally an early cold snap will take us and our trees and shrubs by surprise.  One very obvious sign of the sudden end to the growing season is all the leaves left hanging on the trees.  Just like us, they weren’t ready for the severe cold.  They didn’t have time to form the “abscission layer” that develops at the base of the leaf stem and causes the leaf to fall. The leaves stay attached to the trees.  This is a common trait of trees such as oaks, but unusual for many other trees and shrubs.  Some of these leaves will hang on for most of the winter, but others will fall every time we have a strong windy day. All will drop off by spring when the new leaves start to develop.

How Plants Get Ready for Cold Winter Temperatures

While these persistent leaves are not harmful to the plants, they are a sign that many trees and shrubs were not ready for record breaking severe cold temperatures.  Plants go through a physiological process to be able to avoid damage from cold temperatures.  This begins in late summer and early fall as the days grow shorter and the temperatures begin to decline.  Plant hormones formed in response to these changes trigger the cessation of plant growth, stimulate the formation of the abscission layer, and bring about physiological changes that allow the plant to withstand colder and colder temperatures.  In response to gradually cooling temperatures, the plant attains its winter hardiness through this physiological process called “hardening” or “acclimatization”.  By midwinter it has attained its ultimate hardiness, which is genetically determined.

The potential problem caused by our recent record-breaking cold spell is that many plants were not fully acclimated and hadn’t achieved their ultimate winter hardiness.  While they might be able to withstand 15 degrees, 10 degrees, or even 5 degrees in mid-winter, they may have sustained damage with the cold temperatures coming so early.  It won’t be until the next spring and summer that the amount of potential damage can be assessed.

Symptoms of Damage

For gardeners, the next spring and summer are the “moment of truth” for appraising the extent of possible damage.  The first clue that damage actually occurred will be the failure of a plant to leaf out and grow.  In some cases, leaves may form while flowers fail to develop because of injury.  There may also be plants that die abruptly after appearing unscathed with leaves and flowers growing normally.  On these plants, the buds were not injured but stem and branch tissues were severely damaged or killed.

When cold is sudden and sustained over a period of several days, roots of plants also may be damaged.  This usually takes longer, perhaps several months or more, to become evident on established plants.  Symptoms include outright plant death or gradual thinning and dieback of the crown.

Help for Injured Plants

Once spring arrives, there are some things gardeners can do to help an injured plants. First, be patient. Wait until late spring, after there has been sufficient time for the plants to fully leaf out, and then prune out dead wood.  Be sure to prune properly.  Don’t make stub cuts.  Prune back to a bud, stem or trunk with live green healthy wood.  Only remove dead and severely damaged wood.  Follow that with tender-loving care, proper watering, and mulching to retain soil moisture.  Injured plants are already stressed; so don’t add to their stress. 

Experts disagree about fertilizing winter-injured plants.  Some advise against it, others recommend it. One thing you don’t want to do is encourage excessive growth with heavy fertilization because injured roots and transport tissues may not be able to support this growth.  I recommend watering properly and fertilizing only lightly in the spring.

Minimizing Cold Temperature Damage

There’s not much we can do to protect our plants from record-breaking low temperatures in the fall or winter.  But we can minimize losses to our landscape and gardens by selecting plants hardy to our region.  Many landscape plants that we commonly use are “exotics” and are better adapted to climates where they’re considered natives.  Exotic plants respond differently to local climatic clues than do native plants.  Native plants have a greater chance of surviving winter cold temperatures.  However, gardeners like to test the limits and try growing many different plants... so even if we are planting “exotic” trees, shrubs, and perennials, we should make sure they’re hardy for our zone.

Several late-season gardening practices can help plants avoid winter injury, whether they’re natives or exotics.   It’s important not to promote late-season growth. Avoid fertilizing trees, shrubs, and perennials late in the growing season.  Don’t prune plants late in the growing season.  Wait for trees and shrubs to become fully dormant.  Late winter is the best time to prune.  Don’t drought stress your plants, but do cut back on the watering as the weather cools.  They certainly don’t need as much water in late summer and early fall as they did during 100-degree heat.  (It’s still important though not to drought stress your plants, especially needled and broad-leaved evergreens, as they go into winter.)

Fall and Winter Watering

Fall and Winter Watering

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

When irrigation water is turned off and systems blown out in the fall, your landscape plants still need water.  Foggy mornings, heavy frost, and cloudy skies often give a false impression that plants have adequate soil moisture.  Relatively dry air and low or no measurable precipitation lead to dry soils.  This means that even in the fall and winter... trees, shrubs, and lawn grasses need water to avoid drought stress.  This is particularly true during the fall and early winter when there is little or no snow cover... or when there is an extended warm fall.

Fall and winter watering can be crucial to having healthy plants in the landscape.  During the summer we are clued in to water stress by wilting and dropping leaves.  Plants that experience fall and winter drought can’t tell us something is wrong until the next year when they fail to thrive the next year.  Fall and winter drought can lead to root injury or death.  These drought-injured plants may not show symptoms of the problem until the next season or even the next year.  In fact they may leaf out and flower just fine in the spring, relying on stored food reserves.  Once that energy supply runs out plants weaken and start dying back.  Even if a plant isn’t killed outright, it is made more susceptible to insect and disease attack.

This type of “winter” injury seems to be more common than we realize in this area.  For the past several years, we have been losing many of our area birches.  This has been attributed to past winter droughts and cold temperatures without the benefit of insulating snow cover.  Birches are particularly sensitive to fall and winter drought.  Weakened by this, the birch trees that weren’t killed outright have become increasingly susceptible to attack by the bronze birch borer, which attacks and eventually kills weakened birch trees. 

Other shade trees are also susceptible to winter drought damage, especially those with shallow root systems.  This includes Norway maple, silver maple, linden, Colorado blue spruce, Norway spruce, and many other evergreens.  Shrubs are also vulnerable to winter drought damage, especially those growing up close to the house or in a warmer location.  This includes junipers, Oregon grape-holly, and euonymus.

So what’s the answer?  It’s simple.... water the landscape in the plants and the fall.  Yes, it will be work and you’ll have to use your domestic water but, the effort will be worth it when you see that your plants survive and others around you don’t do as well as yours.  I’m not talking about watering plants every day.  .... you’ll probably only have to water a couple of times in the fall to prevent damage. 

The most critical time to water is in the fall just before cold weather hits or during extended warm weather.  It’s interesting to note that not so many years ago, horticulturists thought it was a good practice to insure dormancy by drought stressing plants in the fall and this decreased the chance of winter injury.  Research since then has indicated that the reverse is true... so now we try to insure plants aren’t drought stressed in the fall.  The soil should be kept slightly moist down to a depth of 18 inches for most shrugs and a depth of 18 to 24 inches for trees.  Water only when the air temperature is above freezing and the soil isn’t frozen... which isn’t usually much of a problem during the fall but can be during winter dry spells.  Water early in the day to allow water time to drain away from the bases of plants.  (Frozen water next to the bark can physically damage trees and shrubs.)  Soaker hoses work well for applying the water slowly and where needed.

Since fall and winter watering will be more labor intensive for you, apply the water where it counts the most... in the root zone.  Consider that established trees have roots that go out at least as far as the tree is tall and usually further.  It is in the “dripline” and just beyond where most of the water should be applied.  The “dripline” is an imaginary vertical line that is perpendicular to the longest side branches of the tree and perpendicular to the ground.  Water applied at the tree trunk base is wasted because there are no water absorbing roots there.

Watering recently planted trees and shrubs is a different story.  Their roots don’t go out that far yet.  In this case you will want to water the root ball zone and just beyond.  The aim is to water where the roots are.  This makes sense doesn’t it?

Keep in mind that even if we do get lots of rain during the fall, shrubs and trees close to the house foundation or located under eaves may still need watering.  Located in these areas, they receive little precipitation and they lose more moisture than other plants because of their proximity to the structure and reflected heat from the walls.

Trunk Cracks and Wood Rot

Trunk Cracks and Wood Rot

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent

Have you ever seen cracks in tree trunks?  Radial separations of bark and wood are usually referred to as frost cracks.  Almost every reference you’ll look at on tree care blame frost cracks on extremes fluctuations of temperature in the winter.  In fact, most sources blame frost cracks on the phenomenon of “southwest winter injury.”  This type of injury is attributed to the bark and wood of trees warming up on the southwest side on a sunny but cold winter day.  The tissue deacclimates, coming out of its complete winter dormancy.  When the sun goes down and the temperature drops rapidly, the tissues can’t reacclimate quickly enough and the water in the tissue freezes, causing cell damage.  The theory has been that sometimes this tissue damage can result in wood and bark cracks.

For many years bark cracks and trunk splits were attributed only to frost.  It wasn’t until the last twenty years, under the guidance of former U.S. Forestry Service scientist and author, Dr. Alex Shigo, that researchers have realized the real cause of split trunks and bark cracks.  Apparently “frost” cracks start from a wound that may have happened much earlier in the tree’s life.  These wounds are believed to be formed at the death of a root or branch.  This wound can create an internal “crack” that develops as a result of stresses from drying, wind, or temperature extremes.  When other pressures occur, such as the thawing and freezing that occurs in the “southwest winter injury” scenario, the internal cracks develop outward.

While the frost leads to a visible crack and open wound, it’s not the real cause of “frost cracks.”  The real cause of the cracks are the death of major roots at planting time; physical injury to roots from construction or soil compaction; wounds created by flush cut pruning; dead limbs resulting from topping cuts, physical injury to the tree trunk, and poor graft unions.

What is the problem with cracks in the tree wood?  Even though callus forms at the edge of the crack and may appear to close it, the wood will never re-knit together.  It’s not like broken bones on humans.  Once those wood fibers are split, they are split forever.  This weakens the mechanical support of the trunk or limbs involved. 

Which came first the chicken or the egg?  It was thought that trunk cracks developed first and then the decay developed in the center due to the opening created by the cracks.  Shigo discovered that the decay is there before the crack, coming from the dead roots, branches, or wounds which instigated the crack.  Additional fungi and insects may attack the tree as a result of the outward crack, but decay organisms are already present before the outward crack develops.

What can be done about split trunks?  Not much really.  One must realize that most of the wood cells of a tree are dead cells.  As I mentioned, they will not “knit” or grow back together.  In the case of most trunk cracks, the internal wood of the tree is already subject to wood decay from fungi.  The tree may function quite well with little effect from the crack or internal decay, since    the vital functions are carried out in the outer few inches of the tree's circumference.  The real concern is for the tree’s structural integrity.  If wood decay becomes substantial, the tree will become a hazard.

Don’t try to paint or seal the split with any type of compound.  They don’t help and they can aggravate the wound.  The best you can do is clean or smooth the edges of the wound with a sharp knife.  Start at one end of the split, smooth around one side of the wound, going no more than one‑half to one inch back from the split bark.  Stop at the other end and do the same procedure on the opposite side of the split.  This aids in callus development.  Sterilize the knife between cuts by dipping for several minutes in a 1:10, bleach:water solution or a 70 percent alcohol solution.

Occasionally “bleeding” or slimy seepage occurs from cracks and wounds.  This is called wetwood or slimeflux.  It is caused by an infection of the wood by a bacterium.  This bacterium feeds on the sugar in the wood and produces a foul-smelling gas and liquid basically through a fermentation process.  The infection can kill some of the bark cambium and can stunt growth but, usually doesn’t kill the tree.

Not all “cracks” are serious cracks that form in the wood.  Some cracks are simply bark splits and are not likely to be fatal to trees, although they will, in some cases, allow entry of disease organisms which can lead to wood decay.  Most of these bark splits are fairly superficial, forming mainly in the outer bark.  Splits occur vertically along the trunk or main branches.  In many cases, bark splits will often close or callus over completely leaving only a slight ridge in the trunk.

Causes of these splits include various environmental factors, such as rapid growth spurts, drought, fluctuating conditions of excessive and deficient, temperature extremes, southwest winter injury, late fall growth, and sun scald.  Trees that are most susceptible to this type of injury are those with thin bark, such as Kwanzan cherry, maple, and certain fruit trees.  Young trees also seem more prone to bark‑splitting than older, established trees.

So the next time you see a bark split or a crack in the trunk of a tree be aware that the real cause of the problem is not frost.  They are reminders that tree care from the time of planting to pruning all contributes to a tree’s health, now and in the future.

Hot Weather and Leaf Scorch on Trees

Hot Weather and Leaf Scorch on Trees

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

It takes longer for trees and shrubs to show signs of distress from lack of water or improper watering practices than other smaller plants in vegetable and flower gardens..  Leaf scorch is a possible sign of water stress.  Mild leaf scorch appears as the yellowing and then browning and drying of the tips and margins of leaves.  More severe scorch appears as the yellowing and then browning of tissues between the main veins of the leaf or large angular blotches of brown tissues between the veins. (In many cases no yellowing occurs at all, tissues just turn brown.) Extremely severe scorch involves the browning and death of entire leaves.

Leaf scorch is a physiological problem related to watering.  The leaves are telling us that they’re losing water at a faster rate than can be replaced by the plant.  Leaf tissues that are furthest from the veins (the margins and areas between the veins) are the first ones affected by the lack of water. Environmental conditions that increase the water demands on a plant tend to increase the severity of leaf scorch.  Hot temperatures, low humidity, high light intensity, and wind all increase the rate of water loss from the leaves.

Sometimes leaf scorch is simply due to a lack of adequate irrigation during the demanding summer weather.  However, anything that interferes with the uptake and transport of water to the leaves can lead to leaf scorch.  Compacted soils; girdling, choking, or underdeveloped root systems; root damage from excavation; and trunk injury from mowers and weed trimmers are often involved. Certain disease and insect problems may also be part of the problem.   Recently transplanted trees with unestablished root systems are frequent victims of leaf scorch.  

Some types of trees and shrubs, such as Japanese maple and flowering dogwood, are not well adapted to hot summers in an arid climate like ours.  To survive and thrive in our region, they do best where they’re protected from excessive heat, afternoon sun, and drying winds.  In more exposed locations or surrounded by reflected heat from buildings and pavement, they will often develop leaf scorch.  They also benefit by having their roots kept cool with a layer of bark mulch. 

Strangely enough, leaf scorch can also be caused by too much water. Saturated soils don’t allow roots to get the air that they need.  Suffocated roots die and the plant can’t take up water... creating the same symptoms that appear if there isn’t enough water.  Saturated soils can lead to fungal and bacterial root rots and eventual death.

If leaf scorch develops on a tree or shrub of yours, try to determine the cause.  Don’t simply start dumping more water on it, assuming that too little water is the problem.  Check the roots and trunks for problems.  Consider all the possible factors that might be involved, but don’t forget to check soil moisture too.

It’s easy at this time of year to be derelict in your watering duties. Contrary to the belief of many, most trees don’t have tap roots and aren’t able to make use of the water in the water table. Most tree and shrub roots that absorb water are located in the top 18 to 24 inches of soil.   Trees growing in our region depend upon us and irrigation water to supply their moisture needs.

During the hot part of summer, trees and large shrubs should be watered with “deep” watering about once a week.  More shallow lawn watering is inadequate to supply their needs. Use a soaker hose to provide this deep watering.  Soaker hoses are made of porous canvas, plastic, or rubber. They allow water to seep out slowly and are useful in watering trees, flowers, vegetables, and shrub beds. Don’tprovide the water at the base of tree trunks where it’s wasted.  Apply water to the area known as the “drip line”, the outer edge of the branch spread.

Special attention should be given to trees and shrubs planted within the last two years.  Make sure they’re getting enough moisture by checking their root balls.  They can’t “tap” into surrounding soil moisture until their roots grow out of the original root ball. It’s important to keep their root zone moist... but not wet.

How much water does a tree need to keep it “happy”. Research has shown that a mature silver maple can lose over 000 gallons of water a day through its leaves, and a mature oak tree can lose over 400 gallons a day.  However, rather than worrying about how many gallons of water to give your tree, you should be checking the soil moisture in the root zone.  Use a spade, shovel, or probe to see if the soil is moist in the top two feet of soil. 

Prevent hot weather stress in your yard and garden by watering the right way!

Watering Trees

Watering Trees

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

Proper watering is always important, but it becomes crucial when the temperature hits triple digits and stays there.  If plants are only provided with shallow waterings every day, they’re probably only getting a fraction of what they need.  Let’s look at the water needs of trees.  Large amounts of water evaporate through tree leaves.  This “pulls” water through the plant.  Water is the “vehicle” that nutrients use to enter the plant.  These nutrients are needed for plant functions and growth.  Water is also needed for vital physiological plant processes.  A lack of water means stress and disruption of plant functions.

While humans are supposed to drink at least eighty ounces of water a day and more in hot weather, trees need gallons of water.  A mature silver maple can lose up to 58 gallons of water per hour on a hot summer day!  This translates to over1000 gallons in a twenty four hour period.  Wow! Watering your tree for 10, 15 or 20 minutes a day just isn’t going to give that big old maple the water that it needs.  It’s like getting only a little glass of water after standing outside all day.

To water trees adequately, water should be applied over a longer period of time that will thoroughly moisten the soil to a depth of 18 inches or more.  Water should be applied slowly enough so that it soaks into the soil without running off down the driveway, sidewalk or street.  An excellent way to apply water slowly is with a soaker hose.  Soaker hoses are made of porous canvas, plastic, or rubber.  They allow water to seep out slowly and are useful in watering trees, flowers, vegetables, and shrub beds.

If you have a solid set irrigation system and numerous trees, soaker hoses might not be practical for you.  You’ll need to work with your system’s timer so that you can apply water for a longer period of time in the same location.  You may want to “pulse” the water, applying it several times with “resting” periods between applications to allow the water to soak in.  Check the soil several hours after you water to make sure that it’s moist to a depth of 18 to 24 inches.

It’s important to point out that the tree roots that absorb water are not right next to the trunk of established trees.  Water applied in the tree trunk area is wasted water.  The fine feeder roots that absorb most of the water for the tree are located at and beyond the “dripline.” The “dripline” is the outer edge of the branch spread.   Newly planted trees are an exception to this rule.  The water absorbing roots of recent transplants will generally be in the area of the root ball.  Care should be taken to keep that root ball moist and water may have to be applied close to the trunk to accomplish this task.

What’s the best time of day to water during the hot weather? It’s probably best to water in the very early morning, but irrigation water isn’t always available when you need it.  If you have a choice, water during the cooler part of the day, morning or evening.  If you water during the hottest times of the day, you lose considerable moisture from evaporation before the plants even get a chance to use it.

It would be a good idea to check out all your sprinkler heads and make sure they’re working properly.  During hot weather, a broken or clogged head might mean a stressed tree, a dead garden plant, or a brown patch of lawn.  If you rely on drip systems to water trees and landscape beds, make sure all the emitters are functioning correctly.

Caution: Even though you want to keep your plants supplied with the water they need, you shouldn’t drown them.  Saturated soils can lead to root rot and the eventual death of trees.

Leaf Scorch

Leaf Scorch

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

Hot weather or drought conditions sometimes lead to a physiological problem called leaf scorch. Leaf scorch shows up as a browning and drying of the leaf edges. In severe cases the brown areas will extend into the leaf tissue between the main veins. In extreme cases, the entire leaf turns brown.

Leaf scorch is often more severe on the side of the plant where the heat stress was greater, usually the south or southwest sides. Reflected light from light-colored surfaces and heat radiated from cement or asphalt put additional heat stress on plants and can increase the severity of leaf scorch. Rock mulches also absorb and radiate heat causing plant stress.

Leaf scorch is associated with inadequate amounts of water being available for the plant to use, especially during hot weather when plants have higher water demands. However, the cause is not always a matter of heat stress and too little water in the soil. A number of other factors may contribute to the development of leaf scorch. These factors include:

Inadequate or poorly developed root systems due to recent transplanting or poor planting practices.

Girdling roots choking the tree.

Injury to the roots or trunk, especially mower and weed trimmer injury.

Vascular disease.

Root disease, especially root rot.

Interference with water uptake and utilization due to soil compaction, poor penetration of water into the soil, water run off on slopes; and high salts in the soil.

Excess water and saturated soils exclude oxygen from the roots and also interfere with root function and water uptake. The result of too much water can be the same as too little!

Leaf scorch is a sign that a tree is under some sort of stress. When scorch develops on tree leaves, it's important to analyze the cause and then take remedial action to alleviate the stress and keep the tree as healthy as possible.

When Strong Winds Uproot Trees

When Strong Winds Uproot Trees

Marianne C. Ophardt
Washington State University Extension
Area Horticulture Specialist  

It’s not unusual in this region for strong winds to sometimes blow trees over and or at least cause them to lean a bit more than they had been before the windstorm. Why do trees fall over in the wind? It’s usually due to the failure of the root system to keep the tree upright, not the size of the tree.  In addition to absorbing water and nutrients, roots have the task of job of anchoring the tree along.

There are many diagrams of trees that show large trees with a big tap root directly beneath the trunk. This concept has been proven wrong by many different studies of tree root systems. Most trees do not have tap roots, especially in urban situations where the soil is compacted or where the there is a high water table.  You will not find tap roots on most of the trees in your yard. 

Most tree roots are in the top 6 to 24 inches of soil.  Tree root system consists of larger, woody perennial roots and smaller, fine feeder roots.  The woody perennial roots horizontally, radiating outward from the trunk.  Most of these roots will be found in the top six inches of soil, but vertical anchoring roots along this horizontal network may grow several feet deep or more.  The function of the woody perennial roots is anchorage, water conduction, mineral transport, and food storage. 

The fine feeder roots are much smaller than the perennial roots.  Their function is to absorb water and nutrients. They grow outward and upward from the perennial roots and are predominantly located in the top several inches of soil.  Feeder roots die and are replaced on a regular basis.  These feeder roots are only about 1/16 of an inch in diameter or smaller and increase the root system's surface area.  This is important because, the greater the surface area, the greater their capacity to provide water and nutrients to the tree.

Major perennial tree roots may not be as deep as we've imagined in the past but they are longer than most people think. The framework of roots often grows outward to a diameter one to two times the height of the tree.  This is much further than the simple branch spread or "drip‑line", where they were once thought to terminate.  On average, tree roots spread about three times the spread of the branches.  Studies have indicated that over 50 per cent of the roots are outside the drip‑line.

The major perennial roots have the job of anchoring the tree.  In order for a root system to support a large, long‑lived plant like a tree, it must be free of structural defects and the main structural roots should be distributed evenly around the trunk.  Wind‑throw results most often from poorly distributed roots or poorly developed root systems. 

Poorly distributed roots can result from kinks and circling roots; improper planting practices; physical damage or severing of roots; restriction of root growth; or death of roots from cultural or climatic factors.  Poorly developed root systems can result from improper planting practices; compacted and shallow soils; and poor growing conditions.

Roots fail to hold a tree upright when there isn't a healthy, well‑distributed root system.  When a tree uproots and falls over in the wind, we have to ask ourselves what caused its failure.  This takes examining the roots and trying to detect the cause.  It also involves reviewing the trees situation and history.  Were major tree roots severed recently or years ago?  Were there any girdling or kinked roots evident?  Was there a poorly developed system?  What might have been restricting root growth on one or more sides? 

Can fallen trees be uprighted and saved?  Large trees, over eight feet tall, can't and shouldn't be saved.  Removal is the only option.  Even if you can successfully upright the tree, it may become a hazard because of the damage that has occurred to woody roots anchoring the tree.  Uprighted trees can pose a serious hazard, especially as they grow in size and girth.

For trees smaller than eight feet, it may be possible to upright the tree and save it.  However, it will probably only be successful if one‑third to one‑half of the roots are still in the soil and not exposed and if the roots which are exposed are fairly compact and undisturbed. 

The process of “uprighting” the tree may require some type of lift equipment to pull the tree upright.  Before pulling it upright, you should remove some of the soil beneath the exposed root mass to allow the root mass to be situated at soil grade level.  Once you have the tree back in place, fill in the soil around the roots as needed, being sure to keep the tree at the same soil level as it had been growing.  Water the tree thoroughly to get rid of air pockets and settle the soil around the roots.

Since the tree has lost a portion of its anchoring roots when it blew over, you will need to provide some support in the form of staking.  Drive two stakes into firm ground about six to eight inches away from the trunk.  Then tie the trunk to the stake at the lowest height which stabilizes the tree in an acceptable upright position.  The stakes should be removed when the tree can stand by itself.  Check the tree every year to make sure it's still stable.  If it's not, removal may be needed to maintain safe conditions.

Winterizing Trees and Shrubs

Winterizing Trees and Shrubs

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent

Avoiding drought stress with adequate fall irrigation is also important in winterizing your trees and shrubs. Be sure to give your landscape plants a deep watering before your water supply is cut off for the season.  Don’t neglect watering the trees, especially birches, situated in your in the lawn. 

Fall watering is critical for the broadleaf evergreens, such as rhododendrons, and needled evergreens, such as like pines and arborvitae, in your landscape.  They may not be actively growing, but evergreens still lose moisture through their leaves and needles during the winter.  They’re prone to damage from winter drought... another reason to keep a hose and sprinklers handy during the winter months.  Don’t let them go dry, especially during mild winter weather.

Fall fertilization may also give some protection to trees and shrubs against cold winter temperatures.  If you decide to fertilize your plants, place the fertilizer in the root zone area after they have gone dormant, but before the soil in the beds drops below 45 degrees.

Mulching the root zone of trees and shrubs is frequently recommended for weed management and to help reduce the loss of moisture from the soil, but it can also provide some insulation to tender root systems. This is particularly important for plants that are only “borderline” hardy in this region, as well as for young or recently planted trees and shrubs. 

Loose mulches can be applied to the root zone to provide some insulation from cold temperatures and to moderate the effects of freezing and thawing.  Apply a several inch layer of a mulch material that allows good air and water movement.  Use mulches like shredded bark, pine needles, or coarse compost.  Keep any mulch several inches away from the trunk of the tree or shrub to discourage mice and to avoid problems from excess moisture close to the base of the plant.

Trunks of young or recently transplanted trees can be protected against splits by shading the south and west sides of the trunk.  Some gardeners shade the trunk of their trees with a commercial bark wrap or they simply use a board on the sunny sides.  The shading or wrap keeps sunlight off the trunk, preventing the bark from warming up too much on a cold winter day and reducing temperatures fluctuations that can lead to trunk or bark splitting.