July 11, 2002

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: Can you tell me why my mother’s cucumber leaves are turning yellow? (Napoleon, N.D.)

A: She could be overwatering, or she simply could be seeing the cotyledons (seed leaves) drying up, which is natural. As long as the rest of the plant looks normal, she need not worry. If it continues, tell her to give them a shot of nitrogen.

Q: I have a honeysuckle that is 4 years old and has done beautifully. It was coming good, but noticed last night that the leaves are turning brown and curling up. Earlier this spring it froze, and it seemed to come out of that. We have had lots of rain so it was wet, but other years it has been wet and it never looked like this. I have another one I just planted last year and it is doing okay so far. Second question. A gentleman wants to put a hedge up on the south side of his place as he gets lots of wind. He wanted to know how fast growing spirea and caragana are? Any suggestions on this? (Cavalier, N.D.)

A: My only guess is the use of an herbicide around the particular honeysuckle, if there is no evidence of insect activity. The bridal wreath spirea is a good choice. It’s tough as nails and will grow rather quickly, given some water and fertilizer.

Q: I have lilacs that are over 70 years old and perhaps older. My brother thinks they may be closer to 100 years old. Is it a lilac tree or a lilac bush? Are there both trees and bushes or are lilacs all trees or all bushes? (E-mail reference)

A: When is a plant a tree and when is it a bush? The eternal question. As in many things where beauty and definition have different meanings, it is sometimes difficult to say. But here is how I bail myself out: If it is a multiple stemmed plant and is under 15 feet tall, then it is a bush. Anything larger starts getting into a small tree category. By the same token, if the same plant is not allowed to go into a multi-stemmed growth, it could be said to be a "tree form." Either way, lilacs are considered shrubs (bushes) rather than trees, although there is the Japanese tree lilac - Syringa reticulata - that gets 20 feet or more tall and is considered by many "experts" to be a small tree, although some hedge and call it a large shrub or small tree! Take your pick! What you call it makes little difference to the plants.

Q: I planted a shrub rose ("Morden Blush") this spring and it has flowered nicely, but the canes are so weak they can't hold the flowers up. The same thing happened last year with another variety. Is the soil lacking something? Or do you know what I can do? I have several shrub roses (all about 2 years old) and all of them do not do this. (Vergas, Minn.)

A: They might not be getting enough sun, but if they are flowering, you've got it made. Put some tomato or peony cages around them for support for now.

Q: I have a client who wants to plant some trees near his house. He had some pine and spruce trees planted, and they did not fare well at all. We examined the area and tested the soil. There is very little topsoil (1 or 2 inches, tops), hard sandstone and calcium, and I think it was salty, too. Are there any varieties of trees that may thrive here? It is a hillside, and some Russian olives are doing OK, but are quite short. (Bowman, N.D.)

A: They might try some of the Ponderosa pines or limber pines, both of which are native to your part of the state. High salts are going to have an impact on the growth of all plants, even those that are salt tolerant. You might also consider suggesting the larches. Since they are deciduous in winter, they would be under less stress.

Q: I have a couple of aborvitaes in front of the house and they are just loaded with flies. Could you tell me why and what I can do to get rid of the flies? (E-mail reference)

A: The flies are getting some nectar or exudate from your tree. You can get rid of them with a spray of Sevin insecticide.

Q: We are looking for a tree that provides: good rate of growth, shade for a 1 1/2 story home within a couple of years, a rustle sound in the wind, minimal care, clean droppings, large leaves. And has NO sap dropping, NO seed dropping, NO helicopter leaves, NO cottonwood droppings. What do you think? (Grand Forks, N.D.)

A: There is nothing that meets all of your requirements, that's my first answer. Now, for selections that come close, here they are:

• 'Fallgold' black ash
• 'Skyline' honeylocust
• American hornbeam
• 'Macho' Amur corktree
• 'Prairie Gem' Ussurian pear
• Laurel willow

Have fun shopping!

Q: A lady called in with a rose bush that is 10 to 12 years old and about 6 feet tall and 6 feet wide that has a bright orange looking fungus or mold. She says she has seen it one other time but not very much. The ground is sandy where she is but has had quite a bit of rain. Any ideas on what could be wrong and how to treat it? (Cavalier, N.D.)

A: What you are seeing is a stage of the cedar-apple rust. Apples and roses are in the same family and are subject to this same fungus. All that needs to be done is interrupt the life cycle by removing the infected leaf or leaves. There are several protective fungicides that can be applied as well.

Q: I am still confused on just how severe a trimming you can give lilacs. I have a small hedge consisting of eight lilac shrubs. They are placed approximately 6 feet apart. I wanted them to fill in as a solid row. After 25 years, they are shabby and are not filling in the spaces. They are approx. 6 feet high and are planted in well drained soil with sunshine all day. I want to trim then back to maybe 2 feet high to see if they will balloon out. Is that too severe a trimming? They have just finished blossoming. (E-mail reference)

A: Do that and you will have an ugly looking hedge, with everything starting at 2 feet. Basically, to thicken up your hedge leave them alone for now, and then cut them back to as close to the ground as possible next spring before leaf out. You will not get any blossoms that summer, but you should get a flush of thick, lush growth that will make a nice dense hedge. In future years simply thin out the thickest canes right back to as low as you can cut them and you should continue to have an attractive hedge.

Q: Would you have any suggestions other than caragana or lilac for a hedge that people want to grow 6 to 8 feet tall and kind of act as a fence for their property? They also want something that's not too disease prone. The soils are mostly gravelly with shale below the top 6 to 12 inches. (Cando, N.D.)

A: Look into the viburnums. The nannyberry viburnum is a beauty that is native, and attractive to birds as well. Freedom honeysuckle is another, and there is always cotoneaster.

Q: I have an ash tree (Marshall I think) that is about 20 years old. Last year, and more so this year, there are not too many leaves and a lot of dead branches. It looks like it is dying. Is there any hope for it? The rest of the ash trees are doing very nicely in my neighbor's yard. This is in the front yard so hate to lose it. (Groton, N.D.)

A: The tree could be suffering from borer damage. Check the dead branches to see if there is evidence of borer activity at the base, and peel the bark back to see if there is evidence of bark beetle damage. I suspect either or both could be causing the problem. If you can, get a certified arborist or horticulturist out to check over the tree. Something may be getting started here that you don't want spreading to the other trees on your property.

Q: A few years ago I had to have our American elm tree removed because of disease and the stump was ground out. The year after, and every year since, mushrooms come up around the base of the former tree, in increasing numbers and in a widening circle. Is there any kind of herbicide I can spray on them to kill them without doing damage to the lawn? And how about some kind of sporicide to take care of the released spores so they won't sprout? Or is this just something I have to live with? (Hatton, N.D.)

A: Live with it, unless you want to do a lot of digging. Sorry! It should pass in a few more years when everything is broken down.

Do you have a gardening or houseplant question? Write to Hortiscope, Box 5051, NDSU Extension Service, Fargo, ND 58105 or e-mail to Ron Smith at ronsmith@ndsuext.nodak.edu. Note to e-mail correspondents: please identify your location (city and state) for most accurate recommendations.

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Source: Ron Smith, (701) 231-8161, ronsmith@ndsuext.nodak.edu
Editor: Gary Moran, (701) 231-7865, gmoran@ndsuext.nodak.edu