Don Gordon's articles - August 2003

Don Gordon is professor emeritus of botany at Minnesota State University. Send questions concerning horticulture or the environment with a stamped self-addressed envelope to him at 52794 Deerwood Trail, North Mankato, MN 56003 or e-mail to osokato@aol.com. Professor Gordon is author of Growing Fruit in the Upper Midwest.

"Becky" shasta daisy

(August 30, 2003)

Q: Over the years I have grown several different varieties of shasta daisy, but most seem to die out after a few years. Are there any good varieties that you can recommend?

A: Luther Burbank was probably the first botanist to work on shasta daisy. He conducted hybridization experiments not too far from Mt. Shasta in California, hence the name. Since that time scores of varieties have been introduced, but many lacked sufficient cold tolerance for the North or had a relatively short blooming season. I am hoping that the 2003 perennial plant of the year, Leucanthemum x surbum ‘Becky’, will turn out to be a superior shasta daisy for the North.

To date, performance of this cultivar in our garden has been outstanding. This cultivar is not the product of hybridization or selective breeding. It was discovered in an Atlanta garden and ultimately was passed on to Wayside Gardens who named it. In contrast to other types of shasta daisy, ‘Becky’ blooms from June to September. The plant has sturdy upright stems that grow 40 inches tall with a similar spread and is recommended for USDA hardiness zones 4-9.

Q: Have you grown the ornamental pepper called ”chilly chili”?

A: Yes, I am very impressed with this 2002 All-America award winter. The “fire” has been breed out of this ornamental pepper so there is no need to worry about children being harmed from eating the fruit. Like all peppers, this variety loves hot weather and is extremely drought tolerant. This variety can be enjoyed long after the growing season is over if the colorful red and yellow fruit is dried and used for indoor decoration.

Q: We recently camped at a State park and went on a nature walk with the park ranger. He told our group that Norway maple and Amur maple were invasive trees and were not the best choices for home landscaping. I know you have recommended these trees in the past, so I am wondering what you think of these trees now?

A: Name any tree species and I can probably find at least one undesirable feature. In other words, there are no perfect trees. Both Acer ginnala, amur maple and Acer platanoides, Norway maple, are non-native species and can sometimes be invasive. In contrast, in the right location, they are still considered desirable trees for home landscaping and are readily available from nurseries throughout the State. Of the two, my least favorite is the Norway maple. This species and its numerous cultivars are planted far too often. In addition, once the trees start to increase in size, it is practically impossible to grow grass beneath them.

Q: I have tons of crabgrass this year and next spring I would like to use corn gluten meal, but I also will need to reseed a number of bare spots. What can I use that will prevent more crabgrass yet not harm germinating grass seed?

A: Corn gluten meal will inhibit germination of bluegrass, but I would recommend that you reseed the bare spots this fall (before the end of September). Another less desirable option for spring is to use a lawn starter fertilizer that contains siduron (Tupersan). This chemical inhibits germination of crabgrass but does not affect desirable lawn grasses such as creeping fescue, perennial rye or Kentucky bluegrass.

Arborvitae varieties

(August 23, 2003)

Q: Many people are looking for small globe arborvitae that don’t need a lot of trimming. I am looking for just the opposite. What is the largest globe arborvitae out there? I was looking at specifications for the variety Woodwardii and saw widths listed for everything from 5’ to 15’. Are there different subvarieties? How will I know which one I am buying? I’m also hoping that my shrub of choice will stay green all winter, as some apparently change color.

A. In milder regions of the United States arborvitae are grown for timber, and some reach a height of 50’ for more. Here in Minnesota, the best arborvitaes are cultivars or named varieties of Thuja occidentalis. The best of these varieties is “Techny” which is also sometimes named “Mission”. This variety is sometimes trimmed and sold as a globe arborvitae, but if left untrimmed it will reach a height of 10-15 feet. Techny remains dark green all winter long, and it is extremely resistant to winter burn. It would be my choice. In contrast, the variety that you mention called “Woodwardii” has a natural globe shape and is larger than Techny, but it lacks good winter color and is more susceptible to winter burn. Dirr in “Manual of Woody Landscape Plants” reports that Woodwardii is commonly planted in cemeteries in the Midwest, but he thinks it is “not the most appealing plant for placing by a loved one.”

Q: A few weeks ago you had a column on coffee trees. I have two questions about this plant. Are some plants male and others female? Also, are these plants poisonous?

A: The scientific name of Kentucky coffee tree is Gymnocladus dioica.The name dioica refers to the fact that the tree is dioecious. This simply means there are separate sexes on separate plants. This week I received a “confessional” letter regarding the sex of these plants. It seems that the neighbor of the letter writer had four beautiful 60’ coffee trees that had never produced a pod in 30 years. Suddenly, after all these years, her trees were loaded with fruit, and she was whooping mad and just could not understand it. It seems her female trees must have gotten pollinated by some nearby new male trees. Guess who planted those male trees?

There are several reports that livestock have been poisoned after eating Kentucky coffee trees, and Kingsbury (Poisonous Plants of the United States and Canada) reports one woman was poisoned after mistaking the tree for honey locust (Gleditsia) and eating some fruit pulp from it.”

The latest issue of the publication Arbor Day has a warning about the hazards of what they call “volcanic mulching.” This simply refers to the piling up or stacking up of wood chips, peat or other types of mulch around the base of a tree. Stacking mulch around the trunk is not good horticultural practice because it may foster basal shoot growth, encourage collar rot , and provide a habitat for rodents. Mulching is great idea, but keep it a few inches away from the trunk.

Canna culture

(August 9, 2003)

Q: Last week I went on the pond tour and was surprised to see some cannas growing in water. My plant books all say that cannas like a well drained soil. Were these some type of special “aquatica” cannas? Also, I wonder if you can tell me why my cannas do not bloom?What is the best way to store these plants?

A: There are several cultivars of the common garden canna, Canna x generalis, and all will grow in a pond type environment. For pond culture it is best to plant the rhizomes in a 8 inch azalea pot and have the water level just at the top of the pot. In water, no fertilization is necessary.

For a terrestrial environment, cannas do best in full sun, but will flower with a minimum of 4 hours of direct sun. The soil should be fertile and well drained. Thoroughly mix in a half cup of 5-10-5 at planting time and then use a liquid fertilizer such as Miracle-Gro every 2-3 weeks during the growing season. Give the plants a good soaking once a week. Dig Canna rhizomes after the first hard frost. Wash off the excess soil and store at 45-50 degrees over the winter. My plants are placed along with Dahlia roots in a garbage can filled with slightly moistened shredded leaves and then stored in our root cellar.

Q: We recently purchased a unique specimen plant for zone 3 from a nursery in Eau Claire, Wisconsin . The tag reads: Dappled willow, Salix integra “Hakuro Nishiki.” The leaves are a combination of pink, white and green. We can’t find this plant in our tree and shrub book. Do you have any information on this plant?

A: The Dappled or Nishiki willow reaches a height of about 4-6 feet with about the same spread. It is called “dappled” because the buds open to produce green, pink and white leaves. Some of the leaves also may be all white. Like all willows, this variety is not that difficult to grow except that it will perform best in partial shade.

Worldwide there are perhaps 300 species of willows and countless hybrids. This is one of the most confusing taxonomic groups in the plant kingdom, and it also one of the most troublesome with respect to pests. Michael Dirr, in Manual of Woody Landscape Plants reminds us that “the use of any willow should be tempered with the knowledge that serious problems do exist. Many are short lived and require much maintenance to keep them presentable.”

Q: Do you know of a nursery where I can purchase the new “Endless Summer” Hydrangea?

A: Some of the local nurseries have received limited quantities of this cultivar, but they are disappearing quickly. For example, Traverse Des Sioux was allotted 20 of the plants, and they were gone in a couple of hours. I picked up three of these plants from a local nursery this week, but they were not advertised. You will have to ask for this variety. Don’t confuse it with “Nikko Blue” which is not hardy here. I congratulate Bailey Nursery, who discovered this plant and all the other wholesalers for a near genius marketing effort.

If you want to create a demand for a product, follow this time tested method. Hype the product to the hilt and then limit the supply. This has seen a very successful advertising campaign and it reminds me of the early Twentieth Century peony craze. At that time, a bushel basket of “scarce” peony roots sold for around $700.

Just two years ago we had another advertising hoopla for a new mum called “My Favorite.” I won’t call this mum a dud, but the expectations did not live up to the hype. Based on the research I have read, I believe “Endless Summer” will live up to hype. Hope I don’t have to eat crow. If you don’t locate an “Endless Summer” Hydrangea this year, be patient. Next spring, they will be available from virtually every nursery in zones 4-9.They will be sold by the millions. One of the local nursery owners joked that they may become so common that in a few years we will be sick of pink and blue hydrangeas.

Black snakeroot culture

(August 2, 2003)

Q: This spring I purchased a black snakeroot plant from one of the local nurseries. I have the plant in partial shade, but it seems to be struggling.What am I doing wrong?

A: Cimicifuga racemosa, known commonly as black snakeroot, black cohosh and bugbane is a tall (4-6 ft.) white flowered perennial that is used as a specimen plant or is grouped in mass at the back of the perennial border. The natural habitat of these plants is a woodland setting; thus, they seem to grow best in partial shade. In full sun, the soil must be kept cool and moist. These plants reportedly have insecticidal properties hence the name bugbane. Extracts from the root have also been used for post menopausal hot flashes.

Q. Have you ever grown Comfrey? A friend has offered to share some of her plants, but we are not sure when would be the best time to transplant.

A. I would urge you to think twice about planting Comfrey, Symphytum grandiflorum. Thirty years ago a friend gave me a start of this plant, and it still persists in my garden despite mowing, rototilling and plowing under. Comfrey is easily transplanted by division practically anytime, and once established, it will persist a lifetime. Steven Still, in Manual of Herbaceous Ornamental Plants reports that "few weeds will find their way through a massed grouping of Symphytum." I could not agree more.

Q. Our Japanese lilac did not flower this year. The leaves looked dried and shriveled. Any ideas what might have happened?

A. First of all, Japanese tree lilac, Syringa reticulata, typically flowers every other year. Of all the lilacs grown here, this is probably the most trouble free species, but rarely there may be insect, fungal, bacterial, or viral problems. Chemical treatments are rarely warranted. Dried and shriveled leaves may also be caused by environmental problems.

Q. I planted a 2-clump birch that I transplanted from my daughter's wooded land in Wisconsin. The birch is doing just great, but the trunks are very thin (about the size of a garden hose). One of the trunks is about 3 feet higher than the other. I have been advised to cut off the top of one so that the two trunks are about the same size. Supposedly, this would also make the plant fill out quicker. I do not agree with this assessment, but I would like your opinion.

A: I am not a fan of topping trees. I suggest you do nothing. So what if one branch is a little higher than the other? Nature's natural symmetry is usually the most aesthetically pleasing.

Q: A friend of mine now has a lilac in bloom. Is this unusual?

A: Every few years I get reports of lilacs, apples, flowering crabs and other trees blooming in July or August. I am not sure why this happens, but I think we can blame it on the weather, Bill Clinton or Martha Stewart.

Q: My black currants in Calgary, Alberta, Canada show an infestation of tiny white maggots inside the ripening fruit. I can't figure out what they are called or how best to treat them. What do you advise?

A: There are a number of great internet sites that have photos and remedies for black currant problems. Just type in "black currant pests." Nearly 30 years ago when I started this column, requests for information almost always came from a 50-70 mile radius of Mankato. Today, thanks to the world wide web, it is not unusual to get questions from some pretty distant sites. Welcome to the information age.

Q: I have noticed the beautiful roses that the city has planted in the downtown area. Could you please advise me of the names of these roses?

A: The city has been doing a great job not only with the roses but also with their annual flower beds in the Downtown area and in Sibley park. Park Superintendent, Tom Severns, credits the effort to his staff, and he reports that there are a number of roses being grown. Examples of the reds include John Cabot, Cuthbert Grant, Ramblin Red, Henry Kelsey , and John Franklin. Simon Fraser and Carefoot Beauty are the pinks. For information on a rose in a specific location, phone the Park Department at 387-8649.

All articles © Don Gordon 2003. For information about reprints, copies, or use of the material, contact Don Gordon, 52794 Deerwood Trail, North Mankato, MN 56003 or e-mail to osokato@aol.com.