July 18, 2002

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: Is there a way to make my cottonwood trees stop producing cotton? I have three of them that are around 40 to 50 years old and any information about stopping the cotton would be helpful. (E-mail reference)

A: Short of cutting them down, nothing. Sorry!

Q: What do you know about Zoysia grass? My son ordered some of the plugs for me as a gift. After reading some of the information, I am wondering if it is as aggressive as they say. I am concerned about it spreading into my neighbors’ yards. (Breckenridge, Minn.)

A: In Minnesota you have nothing to worry about Zoysia spreading in your own yard, let alone your neighbor's. It is a warm season grass, which means that it is active during the warm weeks of the summer and goes dormant with the first 40 degree day in the fall. It will simply be a novelty in your yard if it doesn't winter-kill.

Q: A friend of mine has a garden and is trying to raise zucchini squash, with not much luck, I am afraid. The plants look great, but the fruit that sets on does not mature. When the fruit is about ready to be picked the bloom end gets yellow and soft and is not useable. He asked me what I thought it was. I said I am not sure but that I will e-mail you. I do know that last year he had a worm or bug of some kind that bored into the stem. He said he has looked and has not seen that this year and I know he did not plant in the same place in his garden. He does water quite often, not a lot at one time, We hope you can help. (Armour, S.D.)

A: You are going to probably find this hard to believe, but it sounds like your friend's zucchini is suffering from blossom end rot. We often hear of this on tomatoes and peppers, but it can occur on squash as well. I suggest mulching around the plants with peat moss or something similar to keep the soil evenly moist and the roots undisturbed from hoeing. Generally this malady shows up on early fruit setting, which yours is doing, and as the plant's root system matures, delivery of calcium to the blossom end of the fruit is more assured, resulting in a decrease or elimination of the problem.

Q: I have a magnolia tree/bush on the north side of my house. It blooms very early spring and the blooms never last long. My question is, the bush is becoming quite large and needs to be pruned back. When can I do this and how much can I prune? (Jamestown, N.D.)

A: Summertime is the best time to prune magnolias. Never take off wood any larger than you can prune with a hand clipper. Never make a cut where a saw is needed.

Q: I have a jade plant I repotted and it has exponentially developed white gooey junk around all of the nodes and at the base of the plant. I sprayed all the junk off with a water bottle and will try the alcohol method at the base of the plant. First question, should I use isopropyl alcohol and will the alcohol harm the plant? Second, can this fungus/parasite come into contact with humans, i.e., like live on your eyelashes and cause them to fall out? Silly question I know, but I live in an apartment and there's not much ventilation except through the wall air conditioning units. I can't figure out where the fungus came from and how to get it out of my apartment. (Minneapolis, Minn.)

A: Not to worry. If plant fungi were to attack human hair, I would be totally bald, beardless, and have no eyelashes! I have a pretty full head of hair, a full beard, and normal eyelashes. The isopropyl (rubbing) alcohol will not hurt the plant, just the fungus. Fungal spores are air borne and can travel through air conditioner openings and are usually non-active until they reach an environment that suits their development. That is apparently what has happened in your situation. Good luck - keep up the fight!

Q: The house I bought was devoid of trees so I purchased a hybrid live oak three years ago and had the nursery plant it in my backyard. It is now about 13 feet tall and I'm afraid it may be too close to the house at 16 feet away. Another problem is that I also purchased a red oak several months later and it is now 18 feet tall and 20 feet from the house. Are the trees and/or our concrete foundation in danger if we keep the trees? I wish the nursery had given me some kind of warning. (E-mail reference)

A: You have nothing to worry about. If your concrete foundation has no leaks, then the roots are not going to be a problem. If it does, then the roots will only exacerbate the existing problem. These are beautiful trees that have root systems that go way beyond their canopy spread as they mature. Most of the "feeder" roots are within the top 9-12 inches of soil, competing for air, water, and nutrients with annual flowers and vegetables, as well as the turfgrass root system. With intelligent pruning, you will be able to enjoy these beautiful trees for as long as you live.

Q: I recently got a spider plant for my birthday. It has many stems growing out of it. Lots of babies too. It was vibrant with color. I had a friend water my plants while I was out of town for a week. I came back and now my spider plant's leaves are brown and it looks bad. But the babies are still green, and there are still some stalks that have not turned orange or dark brown. It is sitting in my front room window. Is there anything I can do to get my spider beautiful again? Please help -- this is my first plant and I don't want to lose it. (E-mail reference)

A: It may be the direct sunlight the plant is getting that is causing the problem. I find it difficult to believe that a friend could kill off one of the toughest houseplants ever with just a week of improper care, whatever that may be. I would suggest patience, and not to water it any more than once a week to every 10 days. I have my spider plants outside under the canopy of an Amur maple tree in the hanging pot it grows in, and have been doing this for the last 15 or more years! In hot weather, we water it about every other day. Try cutting out the affected plant parts and seeing what happens to the rest of the plant. You may get a surge of new, fresh growth.

Q: We purchased a house last fall and in the yard is an enormous cottonwood tree. The house was built here in Minnesota in 1902 and we assume it was already here. We were waiting for the cotton buds to consume our yard, but they never did. I am wondering if that is any sign of an unhealthy tree, or if it could just be non seeding. Did that variety exist so long ago? Should we be concerned about the tree? (E-mail reference)

A: Good questions. Yes, you are one of the blessed to have a cottonless cottonwood tree. And yes, you should be concerned about any tree that age, especially if its collapse could harm property or limb. A checkout by a local certified arborist would let you know of the soundness of the tree.

Q: I have noticed some shrubs in commercial areas in the Twin Cities area that look like miniature lilac bushes. The blossoms seem to be the same and the fragrance is heavenly but they grow low to the ground . Could this possibly be a small breed of lilac? I would love to know just what they are. I have a lilac hedge (full size) and they are tall and spindly, producing only a few blossoms each year. I would like to know when and how to trim these back to about 5 feet high in hopes they would start to bush out. Maximum height now is about 7 - 8 feet. (Minneapolis, Minn.)

A: Yes, there are miniature lilacs, and they are becoming more popular with homeowners each year. The 'Palibin' cultivar gets 4 feet tall and 5 feet wide, 'Tinkerbelle' gets 5 feet x 5 feet, 'Miss Kim' 6 x 6 feet, and the Littleleaf Lilac (S. microphylla) gets just 4 feet x 4 feet. Cut your oldest canes down to ground level every year, no more than a third of the total canes, and remove the seed heads as soon after flowering as possible. All of this should help increase the size of your blooms.

Q: We have an old shrub rose in our yard, which I think may be a Harison's Yellow. It blooms in the early summer and has beautiful sunshine yellow flowers. Ordinarily this is a healthy plant, but this year almost all of the leaves and buds have dried up. The ailment worked its way up from the bottom of the canes to the tips so that the only green left on the plant is on a few branch tips. I did not see any insects on it and have not been able to identify the problem from my gardening books. We have heavy clay soil and the rose ordinarily does fine with very little supplemental watering. Do you know what would cause this problem, if the rose will recover, and if there are preventative measures that should be taken? (Fergus Falls, Minn.)

A: Sounds like it could be stem canker or root rot. Check for canker on the stems first, as that is my strongest suspicion. It might just need a good cutting back to healthy tissue, some water and fertilizer, and it will be OK. Otherwise, if it is root rot, it is a goner.

Q: Is there a reason for variegated plantings changing to nonvariegated over a period of three or four years? Are the nonvariegated more competitive? (Jamestown, N.D.)

A: Most of the variegated plants are sports or somatic mutations, having nothing to do with the sexual process of breeding. Consequently, the variegation that we see in most plants are only "skin deep" and are sometimes overcome by the basic character of the plant, reverting back to the original form. Sometimes, if the new growth shows non-variegation, it can be pruned out and the variegated growth will remain. A lot depends on the vigor of the plant, along with the planting site, care and the growing season.

Q: Any tips for control of cactus in a grass environment? The area of concern is a cemetery, There is more cactus than could practically be hand spot-sprayed with Tordon. Is there a product to use that will not kill out all the grass, since the whole area must be sprayed? The only publications I can find are ones that recommend either Picloram or a 2,4-D diesel fuel mix, which would be quite tough on the grass. (Hettinger, N.D.)

A: Trimec has been known to take out unwanted cacti, when mixed with a wetting agent. It isn't toxic to lawn grasses when label directions are followed.

Q: How do I fight existing tomato and potato blight? What can I do to prevent it? (Breckenridge, M.N.)

A: If it is just getting started, carefully pick off the infected leaves and dispose of them. Then, try to keep the water from splashing onto the foliage when watering. This can be accomplished with a soaker hose, drip irrigation, and/or generous mulch around the plants. If it is widespread, then fungicides need be applied. There are plenty of "garden" fungicides for you to select from at the local nursery or garden supply store. Finally, select those cultivars that are resistant to the diseases, and try to rotate the plantings with something that is not in the same family as the potato and tomato for about three years.

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