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SUMMER HEAT TOUGH ON PLANTS NOT WELL ADAPTED TO OUR HOT SUMMERS

GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written Septembe 13, 2015

SUMMER HEAT TOUGH ON PLANTS NOT WELL ADAPTED TO OUR HOT SUMMERS
Two years of record heat is just too much. I am tired of seeing samples of crispy brown plants and being asked the cause of the problem. Quite simply, it has been hot and difficult for plants to survive, especially plants that are not well adapted to our climate.

Several weeks ago I took a look at some local Norway and Colorado spruces that were turning brown and dying. While not always the best clue to the origins of a plant, these spruces’ common names do give us a hint that they may not be well suited well to the hot, dry summer weather of the mid-Columbia. Norway spruce is native to northern and central Europe and prefers a cool, moist, humid climate. Colorado spruce, native to the central and southern Rocky Mountains of the US, is also best adapted to a cool, humid climate.

In their publication on “Spruce Problems” the University of Illinois points out that spruces as a group “prefer locations with acidic, well drained soils” and that “spruces are not well adapted to hot dry locations and often suffer when planted in the warmer regions of the US.” In this publication they also discuss heat injury of spruces, indicating that high temperatures can cause heat damage, especially when the high temperatures are preceded by cool weather. Heat damage on spruces is expressed as browning and dropping of new needles, leaving dead branch tips. After two or three years of this, a spruce is pretty much dead.

Just because spruces are not well suited to our climate does not mean that you can not find healthy spruces growing locally. However, our climate does stress them and make them more vulnerable to attack by a number of pests, like spruce mite, bud scale, and needle miner. I did find spruce bud scale on one of the browning Norway spruces, but the infestation was not severe enough to kill the tree. At least we can be thankful that our dry climate keeps fungal diseases that infect spruce from being a problem here.

Flowering dogwood is another tree that suffers when faced with hot, dry, windy summer weather. In its native habitat, it is an under-story tree that grows in the filtered shade of other forest trees. It grows best in a moist, well-drained, slightly acidic soil that is high in organic matter.

Dogwoods become stressed when planted in full sun and subjected to high temperatures, reflected heat and light from pavement and structures, wind, compacted soil, and poor watering practices. This stress shows up as curled leaves and crispy brown leaf edges. Nevertheless, many of these trees still put on a beautiful display of flowers each spring. To help dogwoods better cope with mid-Columbia conditions, plant them where they will have filtered shade and will not be subjected to a southern-western exposure or drying winds.

Dogwoods and spruce have very shallow root systems, making them more subject to drought and heat stress. It is advisable to keep the roots cooler and moist by mulching the roots with wood chip or shredded bark mulch. Apply a 3 to 4 inch layer of mulch all the way out to the tree’s dripline and beyond. Keep the soil moderately moist, but avoid excessive soil moisture. Be sure to water the spruces during the winter if the weather stays dry and mild.

I hope next summer is a little cooler, don’t you?

FLOWERING DOGWOODS DON’T DO WELL HERE?

written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

The flowering dogwood (Cornus florida) isn’t a tree that should thrive in the Tri-Cities. It’s a tree that’s native to eastern and central U.S. forests. It’s considered an understory tree which means that in it’s native habitat it grows beneath the canopy of bigger forest trees, such as oak, beech, and maple trees.

Flowering dogwood prefers a cool, moist acidic soil that’s fairly high in organic matter. It doesn’t tolerate stress, heat, or drought well. These don’t sound like conditions in Tri-Cities landscapes where soils are slightly to very alkaline. Our local summer sun and heat are very intense and stressful on landscape plants, especially flowering dogwoods.

While the flowering dogwood shouldn’t grow well here, it does. Everywhere I looked around the Tri-Cities this week, I saw gorgeous white, pink, and dark pink dogwoods in full bloom. They were glorious to behold.

The flowering dogwood is relatively small, about 30 feet tall, with an equal or larger spread. It has a somewhat horizontal branching structure, developing a flat-topped form as it matures. If it hasn’t been trained into more of a tree form, it can be shrubby in appearance with its main branches forming fairly close to the ground.

Despite their magnificent show of flowers in the spring, dogwoods do have a tough time growing in our region, especially with the wind, intense summer sun and extreme summer heat. Towards the end of summer, worried owners of dogwood trees often bring me branches of their sick dogwoods. These trees have developed a problem called “dogwood leaf scorch.” The leaves are puckered and partially rolled upwards along the mid vein. Usually, the leaves also have developed dry brown tips and margins along with a reddish color. If the scorch is severe, the brown, dry tissues may extend into the leaf area between the veins.

Dogwood leaf scorch is a sign of stress that develops when water is lost from the leaves faster than the tree can replace it. This can be the result of several factors including high heat, windy weather, drought, intense full sun, compacted soil, excess soil moisture, excess salts from fertilization, or a combination of these factors. This leaf scorch problem is common on young and recently planted dogwoods because their roots have not become well established and aren’t able to absorb enough water for the trees’ needs.

Flowering dogwoods are very prone to leaf scorch because they have shallow roots and are adapted to a more moderate climate and partial shade. To minimize dogwood leaf scorch, there are some things that you can do to help your tree. First plant flowering dogwoods where they will be protected from drying winds and hot afternoon sun.

Keep the tree’s shallow roots cool and moist, by mulching with bark, being sure to keep the mulch about six inches away from the trunk. Water the tree deeply to encourage deep rooting, providing enough water to keep the soil lightly moist, but not excessively wet. With recently planted trees, pay special attention to keeping the root ball and surrounding soil moist.

I’m partial to white flowering dogwoods, but there are many lovely pink and dark pink varieties. Check to see which ones are available from your favorite local nursery. Cater to the needs of these tender trees and you’ll be rewarded with a spectacular display of flowers every spring and attractive red to purple leaves each fall.

Garden Note: In western Washington and other wetter regions, flowering dogwoods are attacked by a fungal disease called dogwood anthracnose. This disease attacks the leaves and flowers and causes twig dieback. Thankfully, it’s seldom a problem in our arid region of eastern Washington.

Published: 5/1/2010 11:15 AM

DIFFERENT DOGWOODS FOR LANDSCAPE USE

written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

It would be boring if everyone created a painting using the same exact color. That’s pretty much what gardeners do when they only utilize one type of dogwood, the flowering dogwood (Cornus florida), in their plantings. It’s arguably the most beautiful of the dogwoods, but there are also other dogwoods that can be utilized to lend interest and diversity to landscape designs.

One of my favorite dogwoods is the Kousa dogwood (Cornus kousa), also known as the Japanese or Oriental dogwood. It’s native to Japan, China, and Korea. This small shrubby tree is vase-shaped when young, developing a horizontal branching structure as it matures. Growing only 15 to 20 feet tall, this dogwood can be very striking when in bloom. It flowers in late spring, about a month after the flowering dogwood. The “flowers” are typically white, consisting of four pointed bracts, and last almost an entire month. Many of the popular Kousa dogwood cultivars flower profusely and surpass the display of its more popular cousin.

The tree grows in sun to partial shade and prefers a well-drained, acidic soil. It’s not very heat tolerant, so its best planted where it gets partial shade or afternoon shade… and where it’s not surrounded by paving or buildings. It’s reported to be a little more drought tolerant than flowering dogwood, but it isn’t considered drought tolerant. It’s hardy to USDA Zone 5, making it winter hardy in our region. The bark on a mature tree is exfoliating, creating a pleasing tan and brown mottled pattern.

Another interesting feature of the tree is the fruit that follow the flowers. About an inch in diameter, the round green fruit turn red to pinkish-red in the fall. These fleshy fruit look like a big raspberry and are edible, but mealy and not very tasty… except to birds. The fruit can be a litter problem if planted next to a walk or driveway. The leaves turn to varying shades of dull red, scarlet, or maroon in the fall.

There are a large number of Kousa dogwood cultivars available to home gardeners with some of the best “bloomers” being Cornus chinensis hybrids, such as ‘Milky Way’ which is very free flowering,

Lustgaren Weeping

with a weeping habit, or

Satomi

(

Rosabella

) with red- pink flowers.

Another dogwood to consider is the Cornelian Cherry dogwood (Cornus mas). This shrubby tree was once a popular landscape plant, but is not used much anymore. That’s probably because it’s not as spectacular as its more popular flowering cousins, the flowering dogwood and Kousa dogwood. It grows to a height of 15 to 25 feet and a width of 15 to 20 feet wide. Branching close to the ground, the Cornelian Cherry is usually grown as a small tree with multiple trunks and tends to shade out any grass growing beneath it. As it grows, the branches tend to droop and the crown develops a round shape.

The flowers are yellow , but only about one sixth inch in diameter and are borne in umbels (groups) providing a showy display, especially if seen against a dark background . Flowering occurs in late winter to early spring… definitely a time of year when color is appreciated in the landscape. The flowers are followed by one-half to one inch oval red or yellow fruit that attract birds. While not very palatable to humans, the fruit can be used to make jelly or syrup.

The fall color is sometimes red to purple-red, but is usually not spectacular. The Cornelian cherry is not as dramatic as its cousins, but its early yellow flowers, exfoliating gray-brown to dark brown bark, small size, and typically multiple-stemmed trunk make it a good choice for use in the landscape.

Don’t be boring and use only one type of dogwood for “painting” your landscape. Consider the Kousa or Cornelian Cherry dogwoods. They can help you paint a pretty picture too!

Published: 8/12/2006 11:09 AM

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