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GARDEN TIPS – Written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Published June 26, 2016

The weather this spring has certainly been erratic going from calm and sunny to windy and stormy and back again. These winds have created havoc for outdoor events and celebrations, but they have also impacted our yards and gardens.

Wind beats plants up. The wind flails leaves about, tearing the tissues and creating small holes in young, tender leaves. As the leaves grow bigger, the holes get bigger too, looking very much like chewing insects are doing the damage. When the wind is severe, some leaves may actually become shredded.

The leaves of squash, melon, and cucumber leaves are very bristly. When beaten about by wind, these bristles puncture leaf surfaces. This leads to small crusty patches that resemble a plant disease instead of typical wind injury. In sandy areas, the wind combined with fine sand particles can “sandblast” the stems and leaves of seedlings or transplants. This sandblasting abrasion can seriously damage young plants or outright kill them.

Desiccation is another problem that occurs as a result of windy weather. Wind increases the loss of moisture through plant leaves. Even if the soil is adequately moist when a wind event occurs, the plant roots may not have grown enough to absorb all the water needed to keep up with what is being lost through the leaves. The result can be brown, crispy leaf margins or similarly necrotic spots between the veins on the leaves.

The drying effect of wind can also cause the desiccation of flowers, leading to a lack of fruit set. In addition, the activity of bee and other pollinating insects decreases when it is windy, also leading to a decrease in the number of fruit that develop.

Severe winds and hail can cause wounding and bruising of fruits and vegetables. Bruising is usually worse when the fruit is ripe or nearly ripe. If the fruit is soft, these injuries can easily provide entry to bacterial rot organisms. Remove and dispose of fruit with significant large bruises or soft spots so that potential rot diseases will not spread to healthy, unblemished fruit.

Herbicide injury is an unnatural consequence of winds. When a gardener applies an herbicide spray in their yard, even a very slight breeze can pick up the spray droplets and move the herbicide to unintended nearby plants or even plants much further away.

The phenoxy herbicides, such as 2,4-D, dicamba, and mecoprop, commonly used for killing broadleaf weeds like dandelions are often the cause of herbicide damage found in local yards and gardens. These materials distort plant growth, causing twisted stems, cupped, feathered, or distorted leaves, and curling of growth. The best way to avoid this type of damage is to use these herbicides only if needed, apply them when the wind is calm, and use a sprayer that applies large droplets instead of a fine mist.

It is interesting to point out that while wind can cause damage to our garden plants, slow their growth, and reduce production, some wind stress can be helpful. Researchers have found that light wind, less than five miles per hour, can lead to plants with stronger, stockier stems. We can only hope we have seen the last of the extreme winds for this season, but what are the chances of that?


GARDEN TIPS – Written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Published May 29, 2016

In our region, it seems like abnormal weather has been the norm in recent years. This is so frustrating for gardeners like me and you. My tomatoes are just sitting in the garden and hardly growing. At the beginning of the month it seemed like the weather was turning hot, so I removed the protective water-wall cylinders that were providing extra heat to the plants. A week later the weather has turned cooler and unsettled.

Tomatoes, peppers, cucumbers, melons, and squash all grow best in warm weather. These warm-season crops have been stalled by our recent cool weather. Because of the cooler temperatures and rain in some areas, watering everyday or every-other-day may be keeping plant roots too wet. This can lead to root damage and impair plant growth. It also encourages various plant diseases and leaches away valuable nutrients needed for growth. Before you irrigate, check the soil moisture in your garden and landscape by digging down a few inches. If the soil feels moist, do not water.

Also related to our spring weather is the appearance of a bacterial disease called fire blight. This disease attacks certain members of the rose family. It is favored by mild (65 degrees F or warmer) and moist spring weather. The bacteria enters the plant through wounds or natural plant openings like the ones that occur in flowers. A common means of transmission is via bees or other insects that pick up the bacterium from an infected plant and carry it unsuspectingly on their bodies to uninfected plants.

Typically, susceptible members of the rose family that become infected are the ones that are in bloom at the time the conditions are “right” for infection. Apples, pears, crabapples and flowering pear are prone to infection in our region. Other members of the rose family that are candidates for severe fire blight infections are photinia, pyracantha, cotoneaster, mountain ash, flowering quince, and hawthorn.

How will you know if your plant is infected? Leaves, twigs, and branches will become blackened as if scorched by fire. A closer look may reveal twig tips bent over to form the shape of a shepherd’s crook. These symptoms start where the bacterium enters the plant and move downward. If allowed to progress unchecked, fire blight can kill the plant.

If you detect fire blight on any of your plants, you should act quickly. Because the infection is within the plant, your main means of stopping fire blight is to remove the infected portions of your plant with pruning. Prune at least a foot or more below the visible symptoms. Dispose of the infected materials in the garbage.

To avoid spreading the disease, your pruning tools must be disinfected between each cut you make on the infected plant. You can do this by dipping the blades in registered household disinfectants, such as Lysol or Pine Sol, and then wiping them off. While a bleach solution can be used, it tends to be corrosive on both the blades and clothing.

Copper fungicide sprays applied when a plant is in full bloom next spring can help prevent reinfection of the plant and infection of susceptible plants in the area. Remember to read the label before using any pesticide. Another line of defense against fire blight is the selection of fire blight resistant cultivars when available. It is also advisable to avoid wetting the leaves and branches of the plant by using drip irrigation.


GARDEN TIPS – Written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written December 27, 2015

Now that we have almost closed the book on 2015, let us reflect a bit on the extraordinary weather of this past year and years past. It is no surprise that the summer of 2015 was the hottest on record in the region with a total annual precipitation of 3.72 inches. That is not much considering that 9.16 inches of moisture were lost through evapotranspiration (ET) during the month of August. Plus, some areas experienced limited irrigation water.

This extraordinary year was compounded by the fact that until 2015, 2014 was the hottest on record with 3.44 inches of precipitation, a total ET of 9.02 inches in August, and an unusually mild December. Also consider that 2013 was the 2nd hottest summer on record until 2015 with a total annual precipitation of 2.79 inches. Plus, the summer of 2013 was the 6th year of summer weather with near or above average temperatures.

That is a great deal of summer heat. Heat stresses plants, especially ones not well adapted to our hot summer climate. Heat stress is compounded by drought stress that results from limited irrigation water or improper watering practices. Drought stress may also be inflicted on a tree due to a lack of an adequate root system, physical injury to the trunk, restricted or girdling roots, compacted soil, or other factors that affect the tree’s ability to absorb or transport water to the top of the tree.

Stress on trees makes them more vulnerable to attack by certain insects, especially boring insects. As a result of the several years of summer heat stress that local trees have endured, we are seeing an increasing number of wood borers attacking local ornamental trees.

Even if a tree looks fairly healthy to you and me, it may become fodder for borers because it is stressed. Stressed trees are more vulnerable to attack by borers because stress causes them to produce volatile chemicals, such as terpenes, that attract boring insects.

In addition, some borers (such as bark beetles) will emit an aggregation pheromone (a chemical compound that elicits insect behavior) once it locates a stressed tree. This insect pheromone lets other bark beetles in the area know of a stressed tree’s presence. One bark beetle might not significantly harm a tree, but a bunch of them feeding spells trouble.

Once the volatile chemicals emitted by the tree and the aggregation pheromone gets a gang of bark beetles to the tree, they still have to get under the bark. As they start to eat their way into the tree, the sap pressure in a healthy tree will often drown or push them back out. However, in a stressed tree the sap flow is lower and they can successfully eat their way in.

The quote of “the best defense is a good offense” may or may not be true in sports, but it is very true when it comes to protecting your trees from boring insects. Keeping a tree healthy is not just its best defense against borers, in many cases it is the only defense.

We no longer have the long-term residual insecticides that were once used to protect trees from borers. Insecticide applications as a spray to the trunk are generally not a good “offense” and even the systemic insecticides applied to the soil or injected into the trunk are only effective against a few types of borers.

Hopefully in 2016 we will not experience another summer of extraordinary heat and limited irrigation water. If we do, make every effort to keep your trees healthy and “unstressed” to protect them from attack by borers.


GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written November 29, 2015

You probably have heard about the many trees that came down around our state in the windstorm last week, but you may not have heard about one tree in Spokane that snapped off and speared the house below. It entered the roof, went through the crib of a six-week old baby, and stopped only when it reached the basement floor. Thankfully, the baby was with his mother who was in the kitchen fixing dinner and the rest of the family was safe too. This hazardous tree story literally hit home for me because that little baby is my grandson.

I have talked often about not topping trees, but this story stresses why it is important to prune trees properly and to periodically assess large trees for the potential hazard that they may pose.
What qualifies a tree as “hazardous?” A tree is considered “hazardous” when all or part of the tree could “fail” and damage a “target,” such as a building, a vehicle, or people. Common failures are the breaking off of a tree limb, a tree splitting apart, or a tree uprooting and falling over.

There are a variety of reasons for failures including wood decay from past topping, other bad pruning cuts, or injuries to the bark and trunk; a lopsided crown; competing central leaders or main branches that are weakly attached at a less than 45 degree angle; the severing within the drip line of more than 50 per cent of a tree’s root system; and the development of significant girdling roots at the base of a tree.

The failure of a small tree is usually not significant, but the failure of a large tree can be catastrophic. When I first moved to this area in 1980 we didn’t have many large mature trees in our home landscapes, now there are many more. This is good, but it has also increased our potential for hazardous trees.

If you have a larger older tree, I urge you to check for any signs of potential failure in your shade trees and then consult an ISA certified arborist if you think there might be a problem. A certified ISA (International Society of Arboriculture) arborist can give you reliable advice regarding your tree and its health.

Signs of potential tree failure include:
– trees that have been topped in the past
– a tree that is leaning
– a tree with multiple trunks or with competing leaders
– trees with lopsided crowns
– trees with dead or broken branches
– trees with dead areas of trunk or signs of wood rot

If you have smaller tree that will grow into a big one, also consider having an arborist check it for any corrective pruning that is needed to avoid future problems. It is better and less expensive to take care of these problems when the tree is young.

It is possible that a consultation with an arborist prior to last week’s extraordinary wind event might have avoided the damage to my family’s home, the deaths of several people, and the property of many others, but there is no way to know for sure. Hindsight is always better than foresight.

Hiring an certified to take corrective action before a tree becomes a hazard is not inexpensive, but it is much less costly than having a tree come through the roof your house and potentially harming your family. A search of the yellow pages in the phone book or on-line will help you find a qualified ISA certified arborist. Please do this now before the next big windstorm.


GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written July 30, 2015


We had a brief respite from the hot weather this past week, but now it is back. I am hoping that my garden tomatoes will have set more fruit during the cooler weather. I have been able to start harvesting a few ripe tomatoes, but alas many of these tomatoes are cracked.

Cracked Tomatoes: After a long wait for ripe tomatoes, it is disappointing that many have radial cracks or splits in the skin starting at the stem. This occurs because the flesh of the fruit grows faster than the skin. Temperatures over 90 degrees or temperatures fluctuating widely between day and night can lead to cracking. It also can be attributed to heavy pruning when staking tomatoes. This exposes the fruit to light and increases the temperature of the fruit.

Uneven watering, fluctuating between very dry to very wet soil, can also give rise to tomato cracks. Heavy nitrogen fertilization causes very fast vine growth, also causing more fruit to crack.

Finally, some varieties are more prone to cracking. A number of the heirloom varieties, like Brandywine, are notorious for their tendency to crack. That is one of the reasons why modern hybrids were developed. For example, Burpee developed their hybrid Brandy Boy to have the same great taste of Brandywine without the problems, including cracking, associated with growing this heirloom.

The problem with cracked tomatoes is that the cracks in the skin make it easy for secondary fungi and bacteria to infect the fruit. The appearance of mold, extremely soft fruit, or liquid leaking from the tomato are sure signs of infection. Discard them. You can eat cracked fruit that are not infected, but do so quickly because they will not last long.

Blossom Drop: Astute veggie gardeners have noted the lack of beans on their bean plants and attributed it to the heat. When temperatures climb well above 90 degrees, beans and peas will drop their flowers without setting fruit. The same often happens with tomatoes and peppers too. The reason for “blossom drop” and the lack of fruit involves pollination and the subsequent fertilization of the embryo in the ovary within the flower.

You might think the reason for this is that bees are not active in the garden when temperatures are above 100 degrees, but beans, peas, tomatoes, and peppers are self-pollinating and thus do not depend on bees or other insects to enable pollination and fertilization. However, these self-pollinating flowers do need wind or insects to shake the pollen from a male part of the flower (anther) onto a female part of the flower (stigma).

What about the veggies that do require an assist from bees and other pollinating insects? Fruit production of cucumbers, melons, and squash seems to slow in hot weather too. Aborted or misshapen fruit are because bees are not very active in the hot weather and because pollen does not remain viable for very long.

We can not do anything about the hot weather, but we can reduce plant stress and minimize cracking and blossom drop by keeping the garden soil evenly moist, mulching to cool the soil and conserve moisture, and not applying excessive amounts of nitrogen fertilizer. It’s also a good idea to provide bees with some moisture. Turn a bird bath or large pot saucer into a bee bath by filling it with coarse gravel or river rock and adding water. The stones are used as perches, so the bees will drown in the open water.


GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written July 23, 2015


Did you ever wonder why it seems like some weeds grow even faster in hot weather? It is because they do!

Growth of cool-season turfgrasses, like Kentucky bluegrass and fine fescues, slows during the sweltering heat of summer. However, some weeds are able to make the most of the heat and sun because they have a different type of respiration and function better when temperatures are between 85 to 117 degrees. Some of these warm-season weeds are Bermuda grass, crabgrass, foxtail, goosegrass, purslane and prostrate spurge.

I hate crabgrass because it sticks out like a sore thumb with its lighter green leaves and rapid growth, making it very obvious that there are major crabgrass infestations in many local lawns this summer. How could this happen despite applying a crabgrass “preventer” or preemergent herbicide? Even if the herbicide was applied at the recommended time, spring temperatures fluctuated up and down and may have thrown off the timing and resulted in applying the material too late or too early. If applied too early, the material may have lost its effectiveness before the crabgrass germinated.

Failure to control crabgrass could also be due to a lack of good coverage or not using the right rate. Always be sure to calibrate your sprayer or spreader before application. For more even coverage, apply half the amount of herbicide in one direction and then apply the other half in the direction perpendicular to your first pass.

A healthy dense turf is the best protection against crabgrass. Last summer’s extraordinary heat was tough on lawns and resulted in thinner turf that is now being stressed again by excessive summer heat and in some areas severe drought stress. Keep in mind that the grass in most lawns is comprised of cool-season turfgrasses that actively grow during the cooler months (March, April, May, October, and November) of the growing season. With the extraordinarily warm fall last year and very warm spring this year, many lawns have not been able to fully recover.

When (and if) cool fall weather arrives, fall fertilization at the recommended times of early September and early November will be important for green lawns that have made it successfully through the summer. However, only fertilize if there is adequate water available and the grass is green and growing.

A number of local residents have also been noting the proliferation of prostrate spurge in their lawns and gardens. There are four types of prostrate spurge, with spotted spurge being the most common in this area. These low-growing plants have tiny leaves and form a prostrate mat along the ground. As members of the Euphorbia family they have a milky sap that can cause skin irritation.

Spurge grows best in dry open areas and takes advantage of bare garden soil and dry lawn edges. In the garden or landscape, I recommend pulling or hoeing for spurge control. In lawns, you can kill spurge with an application of a “spurge killer” herbicide containing triclopyr, but you may find it easier just to dig up the plants if you only have a few here and there.
Of course, the weeds are the only green plants in some lawns where there has been restricted watering this summer. In a few weeks we will discuss what, if anything, can be done to bring these lawns back from the brink of doom.


GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty for the Tri-City Herald, Kennewick, WA
Written July 2, 2015


I was trying to be optimistic and have avoided talking about the affects of all this extremely hot weather on our landscape and garden plants. However, continued record high temperatures in the region and some of the “warmest months” on record have compelled me to talk about the affects of heat on plants.

Perhaps you can recall learning about how plants take the sun’s energy via the process of photosynthesis to create carbohydrates. The carbohydrates provide the energy for plant growth. The rate of photosynthesis increases with increasing temperatures up to a point. Once temperatures reach about 95 degrees, the rate of photosynthesis decreases.

At the same time, higher night temperatures increase a plant’s rate of respiration. Respiration is the process that breaks down carbohydrates to provide the plant with energy. As a result of decreased photosynthesis and increased respiration, the plant has to start using its energy reserves. Sugars and other carbohydrates that would ordinarily be used for plant growth and the development of fruit are used to keep the plant alive. Plant growth slows to a stop along with the production of flowers and fruit.

However, there is more to the story. Plants use the process of transpiration to cool themselves, similar to our bodies producing sweat. Transpiration involves the absorption of water by the roots. The water then moves up through a plant into the leaves where it changes to water vapor and exits through pores, called stomates, in the leaves.

If a plant does not have an adequate root system or there is little available water, transpiration stops and the stomates close. When this happens, a plant has no way to cool itself. As a result, damage can occur to plant tissues in the form of sunburn or sunscald (large brown blotches), especially on a plant’s south and west sides. Other symptoms of heat damage include stalled growth, leaf drop, and even death.

In addition to the extraordinarily hot weather, many area gardeners are faced with a limited supply of irrigation water. Plus, the hot weather arrived so early in the season that some transplanted trees, shrubs, flowers and vegetables may not have had the chance to grow a root system capable of absorbing adequate amounts of water to keep transpiration going.

The problems brought on by high heat are exacerbated when plants are surrounded by materials that absorb heat, such as dark rock mulches or brick walls, or situated next to surfaces that reflect light onto the plant, such as light colored building walls or white rock mulches.

What does this all mean? If hot weather persists, it means we may see sunscald on vegetable plant leaves and fruit, especially if gardeners are not able to keep the soil moist. Woody plant leaves may exhibit sunscald or leaf scorch (browning of leaf edges and tissues between the veins.) It also means plants are stressed. Woody plants will be vulnerable to attack by borers and other insects. Tree and shrub roots may succumb to dessication leading to dieback of branches from the top of the tree downwards now and in future years.
What can be done? If irrigation water is available, keep garden soil and container mixes evenly moist. Deep water trees. Apply a mulch of wood chips or bark in landscape beds if you don’t already have mulch in place. Mulch veggie gardens with compost or newspaper. Where practical, shade recent transplants during the heat of the day. Finally, hope that this weather moderates and cooler temperatures come quickly.

Local Evergreens Turning Brown and Dying

GARDEN TIPS – written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written June 11, 2015

Several weeks ago I noted that a number of our local landscape plants were showing signs of problems related to last year’s hot summer and other extraordinary weather events. Now hot weather has arrived much too early and local pines, arborvitae, juniper, and other evergreens are “dropping like flies” causing shock and dismay. Both old mature trees planted 20 years ago or more and younger ones planted less than five years ago are turning brown and dying.

There are a number of factors that have led to this widespread browning and dieback of local evergreens. One is the watering habit of many tree owners. Despite me frequently urging owners to deep water trees and shrubs weekly during hot weather, few actually do this. Instead they rely on lawn watering during the growing season to meet the needs of their trees. This is typically very shallow watering and has subjected a number of trees to years of chronic drought stress. The cumulative effect of this stress has weakened the trees and made them more vulnerable to the weather extremes we experienced last year.

Past winter drought stress is another likely factor in evergreen dieback. While this past winter was fairly “wet” for us, in recent years the winter weather has been mild with little precipitation. That is why I also urge tree owners to take on the burdensome task of deep watering trees, especially evergreens, in October before irrigation water is turned off and monthly during dry, mild winter weather. Again, few do this resulting in additional drought stress.

At this point we might assume that last summer’s heat was the proverbial “straw that broke the came’s back,” but other factors could be contributing to the current dieback problem.

1. Girdling roots restrict the uptake of water. They are caused by a failure to adequately loosen and spread the roots at planting time.

2. In addition to loosening roots at planting time, proper planting techniques are important. Planting too deeply smothers the roots. Leaving plastic pots, biodegradable containers, and even treated burlap around the roots can delay or restrict root growth out of the original root ball.

3. In many landscapes, soil becomes compacted from lawn use or was compacted during home construction. Soil compaction prevents air and water from getting to the roots.

4. Sandy soils and shallow soils are not capable of retaining as much water as heavier or deeper soils, limiting the availability of soil moisture.

5. Physical damage to tree trunks from weed trimmers or mowers impedes the transport of water from the roots to the top of the tree, causing water stress in the top of the tree.

6. I am a strong advocate of mulches, but rock mulches and close proximity to concrete walls put additional heat stress on a tree and increase its need for water. Bark or wood chip mulches are recommended, but when applied in layers thicker than 3-4 inches, they restrict air and water movement.

The are many lessons to be learned from our current situation, but deep watering and keeping our trees and shrubs in good health is one of the most important. There is no one cause for the widespread browning and dieback of local evergreens, but the primary factors are watering, weather, and root problems.

Next week I’ll talk about wood boring insects that are exacerbating the dieback problem by attacking stressed trees and quickening their demise.

The Results of Last Year’s Abnormal Weather

GARDEN TIPS – written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written May 21, 2015

I wondered what the repercussions would be from our record breaking hottest-summer-on-record last year. Did you know it reached a high of 109 degrees in mid-July?  I knew this heat strained both us and our electric bills, but it also stressed our landscape plants.

One reason that many of our landscape plants are stressed by high temperatures is because they are not well adapted to our climate, growing better in more temperate regions with higher humidity, like conditions found west of the Cascades. Even in normal summers, these plants are subjected to stress, but the high temperatures experienced here last summer were even more burdensome. At the time I worried, knowing that extremely stressed plants are more vulnerable to attack by insect pests and winter injury from cold temperatures.

In addition to heat stress, many trees and shrubs also likely experienced drought stress last summer because the majority of tree owners habitually fail to provide them with adequate water. They rely on lawn watering for irrigating their large trees and shrubs. As I noted last week, large trees and shrubs should receive additional water with deep watering and moistening the soil to a depth of 12 to 18 inches at least once a week during hot weather. With the extremely high temperatures of last summer, the water needs of these plants were even greater.

The severe heat of last summer was followed by an extraordinarily mild, warm October. Nice for us, but woody plants are cued into the oncoming winter by lengthening nights (shortening days) and gradually cooler weather. The extended warm early fall weather delayed plants from “acclimating” or going through the physiological changes that make them resistant to damage from cold temperatures.

This might not have been a significant problem if temperatures had cooled gradually in late fall, but in the middle of November temperatures suddenly dropped from temperatures in the 60s and 70 into the teens. It was obvious that many trees and shrubs were not prepared for severe cold temperatures, because the leaves were frozen on the trees instead of going through the normal process of leaf fall. Because many plants were not fully acclimated, making them ready for winter temperatures, the severe freeze had the potential to damage buds, twigs, and branches.

So what have been the results of this extraordinary sequence of climatic abnormalities?  Here is a list of the plant problems I have seen so far:

– Flowering cherries that were healthy last year failing to produce flowers or leaves is attributed to cold temperature damage and heat stress.

– Dieback on a number of arborvitae is being caused by the flatheaded cedar borer that attacks heat and drought stressed arborvitae, juniper, and cedar.

– Excessive needle drop, dieback and death of mature pines and other needled evergreens is being noted. It looks like many of these trees were already compromised and on the edge of fatal drought stress from shallow watering practices, past winter droughts, compacted soil, restricted roots, or other factors that restricted water uptake. Last summer’s heat appears to have pushed a number of them over the edge.

In addition to twig dieback, some woody plants have been slow to leaf out and have undersized leaves. As the weather warms, I suspect we will see more plants start to fail. All we can do now is provide the plants with the best growing conditions possible, watering correctly, pruning out obviously dead tissues and hoping for a cooler summer and enough water to keep our plants alive.

Helping Landscape and Garden Plants Cope with Drought

GARDEN TIPS – written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA

Written April 2, 2015

With the prospect of limited irrigation water in the coming months, we may have to make agonizing decisions regarding which plants in our yards and gardens to save and which plants to let go. To me, it is like making ASophie=s Choice.@  Before making these difficult decisions becomes a necessity, there are some things we can do to make the most of the water that will be available.

As much as 50 percent or more of the water that is applied to bare soil is lost to the atmosphere through evaporation from the soil. The rate of evaporation increases with increasing air temperatures, solar radiation, and wind. In addition, the lower the humidity, the faster the evaporation. By applying a mulch in our landscape and garden beds we can reduce the amount of soil moisture lost through evaporation by as much as 50 per cent, depending on the type of mulch.

For landscape plants and perennial flower beds, I recommend using shredded bark or wood chip mulches applied on top of bare soil and maintained at a depth of 3-4 inches. Bark and wood chip mulches should not be used in vegetable gardens and annual flower beds because they will become incorporated into the soil. This causes a problem because soil microbes will use the nitrogen in the soil for the decomposition process, thereby tying up the nitrogen and making it unavailable to garden plants.

Where annual crops are grown and the soil is regularly tilled or disturbed, organic mulches that break down more quickly are advisable. I recommend applying well-rotted compost, lawn clippings mixed with compost, or lawn clippings as mulches. Keep in mind that the general recommendation is not to collect lawn clippings, but if you do have them available they can be recycled as a mulch. However, you should never use clippings if they have been treated with an herbicide without waiting the amount of time specified on the product label.

Never apply more than a one-inch layer of fresh grass clippings at one time because they mat down and start to decompose anaerobically, making a gooey mess. Instead, wait until the clippings last applied have dried, and then apply another one-inch or less layer. The clippings can be tilled into the soil at the end of the season, adding organic matter to the soil.

To increase the effectiveness of a grass or compost mulches, place one to two moistened sheets of newspaper on top of the soil, overlapping the sheets as you place them in the garden, and then cover the paper with a layer of mulch. (Without a cover of mulch, the newspaper will easily be blown away by wind.) Do not use glossy color sections of newspaper, as they may contain heavy metals or other chemicals that will contaminate the soil. The newspaper will decay over the growing season and then can be tilled into the soil along with the layer of mulch on top.

Rock mulches are suitable for areas vulnerable to wildfires or non-plant areas, but they should generally be avoided around landscape plants because they are heat sinks. The rocks absorb heat during the day and then radiate that heat back at nighttime, increasing the heat stress and water needs of plants. Light-colored and white rock also reflects light back onto plants compounding

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