Washington State University Extension

Garden Tips

Archive for November 2013


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 10/18/2013

There was frost on my lawn Monday and Tuesday mornings which tells me the gardening season is just about over. It is a wistful time of year for gardeners, but also a good time to reflect on this past season’s successes and failures. I wish I could get into the habit of using a garden journal to record my end-of-season thoughts, but mostly I make mental notes. By the time next year rolls around there are some ideas that I will remember and others forgotten.

Container Vegetable Gardening: My container vegetable “garden” did better than expected. I grew a variety of different vegetables in four wine barrels. I was most happy with my yellow summer squash, zucchini, and cucumbers. The main problem here was that I had planted too many plants in each container and this led to crowding, even though I used compact varieties of zucchini and cucumbers recommended for container growing. One total failure was planting carrots and lettuce in the same container at the same time with the yellow squash. The squash plants became large quickly and shaded them out. Next year I plan to plant the lettuce and carrots early enough to harvest these cool season crops before I plant the squash.

I planted four pepper plants and three eggplants in another barrel. Again, too many plants led to crowding. In my fourth barrel I planted Beaverlodge, a cold tolerant early season tomato. The Beaverlodge fruit produced long before my garden tomatoes, but they weren’t very tasty. I’ll try another type of early patio tomato next year or maybe I’ll plant herbs instead.

Tomatoes: I planted six other tomato plants in my garden. After warm weather finally arrived, they took off and produced fairly well. The plants ended up over five feet tall. That was a problem because the plants fell over during one of our wind storms. I had tried several different types of cages that were three feet tall and secured to a fence, but the plants were just too big and heavy. (It is very difficult to harvest tomatoes from plants that have flopped over.) There has to be a better way to support tomatoes. Any ideas? Share them with me and others on our Master Gardener Facebook page at Be sure to include pictures if you have them.

For the past two years, a great many gardeners have bemoaned the lack of tomatoes on their plants. This was primarily due to extended cool spring weather followed by extremely hot weather, both conditions that are not conducive to good tomato fruit set. Next year I want to plant at least one variety that sets well in cool weather and another variety that’s heat tolerant to “cover my bases.”

Local gardeners can usually find transplants of early cold tolerant tomatoes like Oregon Spring or Siletz, both developed at Oregon State University for short season climates. Heat tolerant varieties that will set fruit when the temperatures are above 85 or 90 degrees are harder to find. You may have to start your own transplants, but it could be worth it. Heat tolerant varieties include Heatwave II, Sun Master, Bella Rosa, and Solar Fire. You can find these and other heat tolerant varieties from a number of seed companies.

That pretty much covers my 2013 vegetable gardening endeavors. Sometime I’ll tell you about this year’s flower container hits and misses.

Published: 10/18/2013 2:39 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 10/25/13

For the past month, we’ve been bombarded with a variety of messages in support or against labeling products that contain GM or genetically modified ingredients. That’s not a discussion I’m qualified to address, but I find it interesting that a number of seed catalogs, especially those specializing in heirloom veggies, note that they don’t offer seed of any genetically modified crops. I imagine that allays concerned gardeners’ fears, but the truth is that currently there is no GM home garden vegetable seed readily available to home gardeners. Most of the GM crops grown in this country are major agricultural crops that bring seed companies big money. These are marketed to commercial farmers and include wheat, soybeans, corn, and canola.

That doesn’t mean that scientists haven’t tinkered with the genes of some vegetables and fruits. Gardeners may remember the “Flavr Savr” tomato introduced in 1994. It was intended to be a grocery store tomato with a longer shelf life and better flavor. The FDA indicated that they didn’t pose a health risk and allowed the tomatoes to be sold without special labeling.

At the time it sounded like we would benefit from having better tasting grocery store tomatoes. Fortunately or unfortunately, depending on where you stand on the GM food issue, the company marketing, growing, and shipping Flavr Savr failed to capitalize on this groundbreaking tomato. Their field production was much lower than that of other tomato growers and a large percentage of fruit were damaged during harvesting, making this new tomato less profitable than anticipated. Plus, there was strong competition from other new tomatoes, called long-shelf-life tomatoes, developed by conventional plant breeding methods.

However, scientists are still working towards bringing other GM tomatoes to commercial markets. Their efforts are aimed at making the fruit tastier, more nutritious, and easier to handle, as well making the plants more insect and disease resistant and more tolerant of stressful environmental conditions. Tomatoes and other crops are also being looked at as vehicles to deliver vaccines to protect humans against a variety of diseases such as cholera, rabies, hepatitis B, norovirus, Alzheimer’s, and HIV.

There are GM squash grown in some commercial fields in the US and Mexico. These squash have been modified to better resist virus diseases that attack squash. However, an unforseen problem has resulted from genetic modification. The plants are healthier, but this makes them more attractive to cucumber beetles. The cucumber beetles spread a bacterial wilt disease to the plants in their feces that they drop on the leaves while feeding. This sounds like both a GM success and failure.

As the Washington debate on GM labeling rages on until election day, scientists are in their labs working away. Keep in mind that a large number them are still developing new cultivars (varieties) with conventional plant breeding methods. These methods date back to the work of Gregor Mendel who experimented with pea breeding in the 1800s and provided the foundation for modern plant and animal breeding.

Monsanto, well known for its GM crops, owns Seminis Vegetable Seeds, Inc. Seminis is one of the largest developer, grower and marketer of vegetable seed in the world. They market seed to both commercial farmers and home gardeners. Monsanto indicates that none of the vegetable seed Seminis sells for home gardeners are GM vegetables.

For now it appears that gardeners do not need to worry that the vegetable seeds they are buying are GM, but who knows what the future will bring?

Published: 10/25/2013 2:35 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 9/6/13

As the garden season winds down, many gardeners may be thinking it is time to relax. It is not. Now is the time to make a checklist of fall gardening chores that should be done before fall’s end.

First on the list should be fertilizing the lawn. Early September and late October are the two most important times of year to fertilize your lawn. During the hot part of summer cool season grasses become stressed. Grass shoot and root growth slows to a stop. As the weather cools in fall, the grass begins to grow well again, establishing new roots and putting on sideways growth that increases lawn thickness. Nitrogen applied in the fall helps the grass recover from the stresses of summer.

Fertilizer applied now helps stimulate shoot growth. A late fall fertilization, applied after the grass stops growing, promotes root growth and the storage of food reserves needed for spring growth. This late fall application also keeps the grass looking greener through the winter and you should not need to fertilize again until April or May.

WSU recommends using a top-quality lawn fertilizer that contains some slow-release or controlled-release nitrogen, such as IBDU, sulfur-coated urea, or urea formaldehyde. These fertilizers release nitrogen over an extended period of time and allow for more even growth during the growing season. Fertilizers with soluble nitrogen, such as ammonium sulfate or urea, with nitrogen in a quickly available form are best for late fall fertilization.

Next on your list should be taking care of lawn weeds. If you just have a few weeds here and there, take them out with a weed digger. If the problem is more serious, you may want to consider the application of a broadleaf weed killers. October is a good time for applying these materials.

For weeds like black medic, bindweed, mallow, dandelions, plantain, and clover a combination herbicide product containing 2,4 D and MCPP should provide good control. A lawn product containing triclopyr will help with tough-to-control broadleaf weeds, like oxalis, prostrate spurge, henbit, ground ivy, and lawn violets. As with any pesticide product, be sure to read and follow label directions.

Now is also a good time to order or purchase spring flower bulbs for planting next month after the weather cools. Keep in mind that bigger (more expensive) bulbs produce bigger flowers. If your bulbs are packaged in a plastic or closed paper bag take them out and place them in an open well ventilated tray located in a cool (50 to 60 degrees Fahrenheit) spot.

Wait to plant the bulbs until the soil temperature drops below 60 degrees Fahrenheit. This temperature allows for root growth without stimulating leaf growth. Don’t forget the bulbs need water, so water them in right after planting and whenever needed during mild fall and winter weather to keep the soil slightly moist.

Other tasks to put on your list include:

raking up leaves

building a compost pile

dividing spring and early summer flowering perennials that have become crowded

cutting back to the ground the dead tops of perennial flowers

weeding and cleaning away plant refuse in garden and landscape beds

aerating your lawn if the soil is compacted

giving all your trees, shrubs and perennials a good deep watering before the water is shut off for the season


Whew! That’s a lot of work. You and I should get busy.



Published: 9/6/2013 2:28 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 9/13/2013

Last year at this time I talked about planting tulips and pointed out that tulips don’t “perennialize” well, coming back year after year and blooming again like daffodils. Even tulips sold as “perennial tulips” only bloom for a couple of years before declining. That’s why I wasn’t too upset when one third of the supposedly pink tulips we planted in our landscape last year turned out to be dark purple. If I want an attractive pink tulip display next spring, I should buy more bulbs (from a reputable bulb nursery this time) for planting this fall.

This isn’t good news for my husband who did all the hard work of planting the tulip bulbs in our landscape beds. I did buy a hand bulb planter for him to use, but even in our sandy soil it was a tough job cutting out the holes for all the bulbs.

To make the job easier this year I’m thinking about buying a different bulb planter. A. M. Leonard company (< offers a bulb planter with a 36 inch handle. The planter allows gardeners to pull out a 6 inch deep 2.75 inch round core of soil, creating a hole for a bulb. It also has a plunger that allows the user to push the core of soil back into the hole on top of the bulb. No bending over or kneeling is needed for planting bulbs.

Similar to this is the Badger Semi-Automatic Planter ( This bulb planter removes a plug of soil to a depth of 3 to 6 inches. Their other planters make holes the size of a three-inch and five-inch pots. They are designed to help dig holes in the garden for planting flower or vegetable transplants in the spring.

The DeWit Double-Handle Bulb Planter is another type of long-handled planter available from Lee Valley ( This planter is a smaller version of a post-hole digger with two 30 inch long wooden handles each with a blade at their base and attached together with a hinge. When the blades are plunged into the soil, this hinge can be used as a step for pushing down on the blades. When pulled up, the blades remove a core of soil.

Power tool enthusiasts should find power augers a handy tool for making the needed holes. One company ( sells bulb and garden augers for use with everyday household drills. They offer 1.75, 2, or 2.75 inch diameter augers, each with a 24 inch long 3/8 inch diameter steel shaft. The company points out that their augers can be used for digging holes for transplants, deep root watering, aerating the soil, and turning compost piles.

There’s also the Bulb Bopper sold by the Garden Supply Company ( It also attaches to your power drill. This is a steel auger cylinder that can make holes 9 inches deep and 2 inches in diameter, but does not have a long shaft.

I’m don’t really know how well any of these work, but hopefully whichever one I buy will make the job of planting bulbs easier.

Published: 9/13/2013 2:23 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 9/20/13

One of the most interesting trees that can be grown locally is a ginkgo tree. It was called a “living fossil” by Darwin because it is basically the same tree found in fossils from over 200 million years ago when dinosaurs roamed the earth. Most other plants of that time were wiped out by drastic climate change and the ice age. The ginkgo tree that we know today, Ginkgo biloba, has survived over time with few evolutionary changes for at least 56 million years. How awesome!

The ginkgo tree grew in America until the ice age came along about seven million years ago. The only place in the world where Ginkgo biloba survived the ice age was in China, preserved possibly by Chinese monks in two areas and by natural geographic features in another area.

Scientists believe the ginkgo tree has been cultivated in China for 1,000 years, making its way out of China into Japan and Korea in the 14th or 15th century. In Asian cultures it is a revered symbol of strength and longevity. A member of the Dutch East India Company introduced the ginkgo to the West in 1692,

The ginkgo tree is unique. It has no close or distant relatives. The fan-shaped leaves are distinctly different from other trees with a notch at the top and raised parallel veins. The tree is dioecious, meaning that there are separate male and female trees, with only the female producing a small plum-shaped fruit… more about these distinctive fruit later.

Some gardeners like the ginkgo for its status as a living fossil. Others simply like it for its unique form and leaves. As a young tree, the ginkgo has a columnar growth habit, eventually spreading out and developing an irregular oval shape. A slow grower, it takes a long time to reach its full potential of 70 to 80 feet tall. In the fall, all the leaves of the ginkgo tree turn a brilliant yellow and flutter to the ground seemingly overnight.

Ginkgo grows best in well-drained moist, sandy soils, but is tolerant of a variety of stressful conditions including heat, drought, compacted or alkaline soil. It is a long-lived tree that is resistant to storm damage. Better yet, it has no significant pest or disease problems and is very winter hardy (USDA Hardiness Zone 3A).

Gingko has one objectionable drawback… the fruit. The nut inside the fleshy fruit is considered an Asian delicacy and served for special occasions. However, the fleshy part of the fruit stinks, many likening it to the smell of dog manure. It may take 20 years for a female ginkgo tree to produce fruit, but when it does the fruit can be prolific and smelly. Reputable nurseries only sell male ginkgos that do not produce fruit.

The are numerous named selections of ginkgo available including Autumn Gold that only grows 50 feet tall and has a broader, rounder crown, Jade Butterfly which is a slow growing dwarf half the size of the species, Pendula with a weeping habit, and Princeton Sentry with a narrower columnar form and growing 60 feet tall. I have a newer selection of ginkgo in my yard called Presidential Gold. It does grow slowly but I like how its leaves flutter in the slightest of breezes and its fleeting beautiful yellow color in fall. Watch for the ginkgos this fall as their leaves turn bright yellow.

OPTIONAL SIDEBAR: There is evidence that ginkgo and other tree species grew long ago in our region of Washington. Petrified wood of ginkgo and these other trees was discovered in 1927 by highway workers. The petrified wood is estimated to be over 15 million years old. This wood was excavated by a geologist and l in 1938 a park and a museum were established there. The area became a National Natural Landmark in 1965. Interested in seeing some of this ancient ginkgo wood? Near Vantage, the Ginkgo Wanapum Interpretive Center, the Ginkgo Petrified Forest State Park and Wanapum Trails area is only a 90 minute drive from the Tri-Cities.

Published: 9/20/2013 2:15 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 9/27/13

Some of you may know that year after year I have raved about the super performance of the “Wave” line of petunias. The Waves are still great, but there are many more petunias that are matching and maybe even surpassing them. I am so excited to tell you about the newest petunias on the market or coming to the market soon.

I am enthralled by the mini-petunias, also known as milliflora petunias . These are petunias with small, petite flowers about 1.5 inches in diameter. I tried two of Proven Winners’ Charm series of mini-petunias in my containers this year. I was astounded at the mass of color these little charmers provided. Pink Charm grows 10 inches tall with a trailing habit up to 48 inches long. The soft pink flowers have white throats and cover the plants with a mass of color. The Charm series is heat and drought tolerant and also includes Sangria Charm with rosy purple flowers, Indigo Charm with purple flowers, and Watermelon Charm with red flowers.

New this year to the Proven Winners’ Supertunia line is Picasso In Pink, joining Pretty Much Picasso already on the market. Both these petunias have a striking chartreuse edge around the flowers, but the new Picasso in Pink is more compact and less vigorous with a more mounded habit.

The “Picassos” aren’t the only line of petunias with green-edged flowers. Just coming on the market is the “Kermit” series from Westflowers. This line includes Baby, Piggy, and Rose with unique pink and green flowers. They are touted as being abundantly floriferous and weather tolerant.

The Kermit petunias were bred by a German breeder who has also developed a line of petunias called “Crazytunias.” One of these is Black Mamba, a black petunia that is said to be one of the best black petunias available because the flowers don’t fade or develop stripes. Another Crazytunia is ‘Cherry Cheesecake’ with an intense red and white candy cane star patterned flower. It will be exciting to see others from this line of unusual petunias.

It took a while for plant breeders to come up with some truly nice yellow petunias, but what about orange? Danziger just might have it with their Cascadias Indian Summer. It’s a vigorous semi-trailing petunia with blooms that open to yellow and then turn to a peachy orange.

First new colors and sizes in petunias and now there is a new shape too! “Sparklers,” the first star-shaped petunias, were introduced by Thompson & Morgan. They recently introduced ‘Sparkler Mixed’ with star-shaped flowers with both pointed petals and leaves. This mix contains flowers in pastel and jewel toned pinks and purple. The plants have a 12″ tall mounding habit and a spread of 14 inches.

I can’t wait to try some of these new petunias and this season isn’t completely over yet!

Published: 9/27/2013 2:10 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 10/11/13

I often get asked when is the best time to plant or transplant trees and shrubs. It’s a question that I have to answer with, “it all depends.” Mid-fall, after trees and shrubs are dormant, can be a good time to plant or move trees and shrubs.

There are several reasons why fall planting is frequently recommended. One reason is that the soil temperature is warmer in fall than in early spring. This is an advantage because roots of woody plants will grow when the soil temperature is above 40 degrees. This allows fall planted trees and shrubs to become established before the stress of summer heat next year. When planted in early spring, roots don’t have as much time to grow and adequately support the plant when hot weather arrives.

Another reason for recommending fall planting is that as plants go dormant in autumn, there is less competition for the carbohydrates needed for growth. In the spring, carbohydrate reserves are needed for both top growth and root growth. This results in a fight between the roots and the top of the plant for those reserves.

If you are considering moving a tree or shrub that is already established in your landscape, fall is the best time to do this. The stress caused by the root damage and the shock of moving the plant will be less when done in the fall when the plant is dormant. The most important thing whenever moving a plant is to get as many of the roots as possible. It is estimated that when woody plants are dug up in a nursery as much as 95 per cent or more of the root system is lost. It is likely that even more roots are lost when we move landscape plants.

Those were the “pros” for fall planting, but there is one significant “con” or reason against it. Water. Fall planting is great for the regions of the Pacific Northwest that can depend on natural fall and winter rains to keep the soil moist. We can not. Fall transplanted trees and shrubs should be watered in with a thorough watering at planting time and then the soil should be kept moderately moist to help the roots grow.

If you plant or move a woody plant in the fall, you must find some way to provide it with water through the fall and winter months when the weather is mild and dry. Hauling out a hose during the winter is a nuisance, but the advantages gained by fall planting will disappear if the soil is not kept moist. Check the soil regularly to monitor the moisture situation even when foggy and overcast weather predominates.

I also recommend that you mulch your newly transplanted tree or shrub with a three to four inch layer of shredded bark or wood chips to help retain soil moisture and discourage weed growth next year.

Fall is a good time to take advantage of sales held by local nurseries to reduce the volume of woody and perennial plants they need to hold over the winter. However, before you buy make sure you have a suitable site where you can provide water through the fall and winter months.

Published: 10/11/2013 2:05 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 10/4/2013

There are three types of hand pruning tools that every gardener should own. First, a quality pair of bypass hand pruners for cutting woody branches is a “must.” These are generally intended to cut woody stems up to .75 inches in diameter, although some are rated for larger diameters. Bypass pruners have two curved blades that cut with a scissor-like action. If properly sharpened, the pruners can make clean cuts close to stems.

I recommend investing in a high quality pair of bypass pruners that will last for years and can be handed down to the next generation of gardeners in your family. Felco, ARS and Bahco brands offer exceptional quality bypass hand pruners. A good pair of these brands will typically cost $40 or more. Each brand’s high-end pruners typically have replaceable parts, like blades and springs that help keep them working even when heavily used.

Anvil pruners are another type of hand pruners. They have a top blade that cuts a stem against a lower bottom plate. Gardeners are often discouraged from buying these pruners because they tend to crush woody stems rather than make a clean cut and because they are often too wide to allow making close cuts at narrow angles.

While anvil pruners aren’t the best for most tree and shrub pruning jobs, I have found that a good pair of anvil pruners is an indispensable tool for deadheading and cutting back tough perennials in the garden. Because my hand strength isn’t as good as it once was, I favor a Florian Ratchet Pruner. My current pair is over 7 years old and I have yet to replace it.

My Florian pruners have a Teflon coated high carbon steel top cutting blade. The handles and cutting platform are made of fiberglass-reinforced nylon. The ratchet mechanism “increases hand strength 700-percent” and its light weight makes the repetitive task of snipping and cutting much easier on my hand and wrist. The Florian ratchet pruner is not inexpensive, usually costing $30 or more with a holster. As with bypass pruners, you can find cheaper pairs but they are not likely to last as long. The holster is a good idea for protecting the blade and keeping the pruners handy.

Löwe, a German company, also offers high quality anvil hand pruners. Their Series 8 anvil pruners have a strong steel top blade that is curved, allowing it to make a drawing cut against the anvil. The design of the blade cuts woody stems without needing much force and without crushing the stem. Costing over $50 a pair, the Löwe Series 8 pruners have replaceable parts available.

The third pruning “pruning tool” I couldn’t live without are my Fiskars Softouch Micro-Tip Pruning Snip. These little pruners have sharp pointed 1.5 inch stainless steel blades. I use them more than any other tool in my garden. They are best for snipping flowers, trimming transplant roots, and a variety of other light garden tasks.

If you are looking for a new pair of pruners, consider what their main task will be and choose accordingly. Look for pruners that are ergonomically designed and be sure they fit your hand. I have small hands and some pruners are too large for me to operate. Once you invest in a good pair of pruners, be sure to protect your investment by caring for them properly. More on that another time.

Published: 10/4/2013 1:58 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 11/1/13

My birthday is in September and I like having sapphires as my birth stone, but as a young girl I was disappointed that asters were my official “birth flower.” To me they lacked the beauty of roses, carnations, or other birth flowers. I’m happy to say that the garden asters of today have changed my feelings about asters. These fall flowering perennials bring color to the fading perennial garden and are great companions to chrysanthemums blooming at the same time.

The name aster is derived from the Greek word for “star” which is attributed to the centers of these small daisy-like flowers. In the language of flowers, asters supposedly symbolize love, faith, wisdom and color.

Asters are an easy-to-grow perennial that has few serious insect or disease problems. Like so many flowering perennials, they grow best when located in a full sun site with a well-drained, loamy soil.

There are two main types of aster along with a few minor types. The major types are New England asters and New York asters and they look very much the same. Both are very winter hardy and both are native to eastern North America. They are not considered aggressive or invasive.

Depending on the cultivar, New England asters (Aster novae-angliae) tend to be taller, growing from 3 to 6 feet tall. New England asters have thick hairy stems and hairy leaves. The hairs are irritating to the skin of some people. There are cultivars with red, blue-purple, violet, white or pink flowers produced above the leaves in late summer to early fall.

Because of their upright growth and height it is advisable to stake or provide some other type of support, especially considering our windy weather. To avoid staking the taller New England cultivars, pinch them back early in the growing season to encourage branching. Pinched plants will be shorter and bushier.

(What is meant by “pinching back? This is a gardening term that means using the fingernails on your thumb and forefinger to pinch off the tips of tender plant shoots. It is typically done to encourage branching below the shoot ends to make a plant more compact and to encourage more blooms.)

New York asters (Aster novae-belgii) are generally more popular and a bit shorter. Depending on the cultivar, they grow from 2 to 4 feet tall. Their stems are thinner and without the irritating hairs. You will want to stake taller cultivars. There are many purple to blue cultivars, but there are also ones in white and pink. They tend to bloom fairly late, often around the end of September and are sometimes referred to as the “Michaelmas daisy” because the Feast of St. Michael is observed on September 29th.

While New York asters are generally more popular than the New England ones, there is a notable exception. A real “star” of the garden is Purple Dome New England aster. Purple Dome is a compact mounded plant that grows 18 inches tall and 36 inches wide. It is a true “purple dome” in the fall, covered with bright purple semi-double flowers.

Once planted in your garden, asters don’t need much attention other than staking. If they grow well, they may need dividing every couple of years. If so, divide them in the spring. Problems to watch for include powdery mildew and aphids.

Published: 11/1/2013 1:52 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 8/30/13

While severely cold winters have become less and less common in our region, it is obvious that we can still count on our extremely hot summers. When selecting trees, shrubs, or perennial plants for local landscapes, a plant’s ability to withstand the stress of multiple days of high temperatures during the summer should be considered along with a plant’s ability to survive cold winter temperatures.

The late Dr Marc Cathey, American Horticulture Society (AHS) president emeritus, noted that heat damage is not as obvious as severe cold temperature injury that can outright kill or damage a plant. Heat damage is typically more of a chronic condition with plants failing over time from accumulated stress that leads to poor growth and attack by insects or disease.

That’s why in 1997 the American Horticulture Society under the direction of Dr Cathey developed the AHS Heat Zone Map. Similar to the USDA Hardiness Zone Map, the AHS Heat Zone Map is divided into zones. The Heat Zone map has 12 zones that are based on the average number of days that “zone” experiences with temperatures over 86 degrees Fahrenheit. Above the suitable zones, a plant will suffer heat damage.

Most of Benton and Franklin counties is rated as being in AHS Heat Zone 6 with greater than 45 days and less than 60 days over 86 degrees. However, the immediate area around the Tri-Cities is rated in AHS Heat Zone 7 with greater than 60 days and less than 90 days above 86 degrees. Thank goodness we aren’t in Zone 1 with less than one heat day or Zone 12 with greater than 210 days!

It is important to note that the AHS Heat Zone Map assumes “that adequate water is supplied to the roots of the plant at all times. The accuracy of the zone coding can be substantially distorted by a lack of water, even for a brief period in the life of the plant.” Most plants we place in the our area home landscapes are not native to our region and require adequate supplemental watering. Indicating a plant is heat tolerant in our “zone” doesn’t mean that it is drought tolerant.

Water isn’t the only factor that could skew a plant’s ability to thrive in a particular heat zone. Soil aeration and drainage; exposure to light; air circulation; exposure to radiant heat from mulches, structures, and paving; soil fertility; and soil pH all affect a plant’s ability to thrive in a particular heat zone.

I am seeing more and more trees and shrubs rated with both their USDA Hardiness Zone Map rating and their AHS Heat Zone Map rating in catalogs and on plant labels. When you go plant shopping, look for these ratings to help insure that your plants will have a long and happy life.

Reminder: Our area is located in USDA Hardiness Zones 6B to 7A.

Published: 8/30/2013 1:43 PM



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