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Don Kinzler, Published July 22 2011

Pesticide use may have affected hibiscus

Q: I have a beautiful tropical hibiscus plant growing outside. Recently, I noticed the edges of the blossoms are curled inward. Any ideas why this is happening and what I can do? (Missouri)

A: Anyone using pesticides in the immediate area on very hot days? It doesn’t take much to get the reaction you describe. I assume you are good at maintaining an even moisture regime in the soil without keeping it saturated.


Q: I’ve had a double begonia for three years. This year, the leaves are growing heavily, but there are no flowers. What do I do? (email reference)

A: This sounds like it could be insect or mite damage or a virus that was transmitted by an insect that fed on the plant. In either case, there isn’t much that can be done except to take a leaf, root it, and see if a normal plant will develop. If so, then it was just the unfortunate victim of nonlethal insect activity. If it is a virus, then dump the mother plant or simply enjoy the unique character this affliction has produced.


Q: My cucumbers grew like wildfire this year and the leaves are huge. They were planted around Mother’s Day. There are flowers everywhere, but no cucumbers.

What could be the problem? (email reference)

A: Life is too good for your cucumbers. The problem could be too much nitrogen.

I’m willing to bet the few flowers are frustrated male flowers. They have ample pollen but no female flowers to pollinate. Check the flowers carefully. If there are any female flowers, there should be a very small ovary at the base (slight swelling). If you find female flowers, remove a male flower and use the male to pollinate the female flowers. It could be that your cucumbers are lacking any pollinating insect activity.


Q: Two weeks ago, a landscaping service planted a purple clematis vine on my light post. It was blooming beautifully, and I do see new buds. However, some of the leaves are drying out. Is this normal for this time of year? Do I leave the spent flowers alone or remove them? Should I remove or cut off the dead leaves that are on the vine? I’d appreciate your advice because I spent a small fortune on the plant and don’t want to lose it. Also, when and how should I prune the plant? Thank you so much for any help you can give me. (Annapolis, Md.)

A: The secret to clematis success is a cool, moist root zone and morning sun. If your plant does not get any shade during the very hot afternoon part of the day, it could be the problem. Some people find the seed of the clematis as attractive as the flower itself and simply leave them alone. However, it depends on what variety was planted. There are more than 200 species and cultivars of clematis, with each one requiring slightly different care. I’d get back to your landscaper for advise on when and how much to prune.


Q: I’m thinking about planting a crimson king maple in my backyard. I really like the color of the leaves. We have a large field under cultivation across the street to the west. We are subject to very strong winds periodically and have been surprised at times that our Marshall seedless ash, which is about 20 years old, hasn’t been ripped right out of the ground. I’ve been reading that the root system of the crimson king is shallow, but I’m not sure how shallow. Several years ago, our neighbor’s mature ponderosa pine did blow over. I would hate to have this happen to my tree in 10 years. (Alliance, Neb.)

A: I’m afraid that you are wishing for a little too much if you expect a crimson king maple to establish successfully in Nebraska. Like North Dakota, Nebraska is a land of extremes in weather that this poor tree cannot tolerate. If the wind doesn’t shred the leaves to confetti, the heat will cook it to death. It is your call, but I wouldn’t invest my money, wishes and hopes with this beautiful tree unless you see a crimson king thriving in your area under the same environmental conditions.


Q: I think I made a terrible mistake last spring when I sprayed my apple trees and grapes with a Bordeaux mixture. One of my apple trees is dead, and the rest have little and deformed leaves. There is no new growth. Also, my grape is not looking very good. It has little green leaves that are misshaped. Some of my clematis plants that got some mixture sprayed on them are not blooming. They have many buds, but they are misshaped and never open. My Bordeaux mixture obviously was too strong. Will my trees and grape vine survive and grow normally next year? Is there anything I can do to help them recover? Any advice would be appreciated. (email reference)

A: It sounds like your mixture deviated somewhat from the 10-10-100 standard, which ended up toasting everything you sprayed. There is a good chance most of the plants will recover, especially with our rainy conditions this year. Copper is a trace element needed only in very low parts per million. If the dose becomes too concentrated, it can be toxic. All you can do is wait to see what happens. Try to keep the plants from becoming water stressed during the hot and dryer months of July and August.


Q: I have tomato plants that won’t blossom. They form buds, but they curl and don’t form a blossom. I have some in hanging planters that are doing great. Any suggestions? (email reference)

A: Obviously, something is different between the two planting sites. Blossom drop on tomatoes could be caused by a number of factors. It could be fluctuating temperatures from one extreme to another or being too hot from reflective heat.

You may be allowing the soil to get too dry before watering. You may have too much nitrogen, which often is a problem when gardeners use a lawn fertilizer on tomato plants. The problem could be incomplete or absolutely no pollination.

Your plants may have other stresses such as insect or disease damage.


Q: About a year ago, I received an African violet from a friend. It has done wonderfully until the past week. The leaves are green but drooping. Until a week ago, the leaves would go out parallel to the table. We had the plant in a southeastern-facing window, so it would have direct sunshine for the morning and early afternoon. Any thoughts about the problem? (email reference)

A: Something has changed that you are not aware of, such as the composition or temperature of the water, drainage characteristics of the pot or water splash on the leaves or crown, that is causing rot to get established. It also could be the impact of central air conditioning. A plant often can be resurrected by repotting it in a clean container. Be sure to use African violet potting soil.


Q: I have a large hackberry tree in my backyard that is approximately 80 years old. The tips of many of the branches are bare and have been for the past couple of seasons. I’m concerned that I may lose the tree. Do you have any advice? (email reference)

A: This is something to be concerned about. You need to find a certified arborist to determine the cause and possible treatment to save the tree. Go to http://goo.gl/90Nyj to find someone in your community. Be sure to check credentials and insurance before allowing any major work to be carried out on your property.


Q: I hope you have the time to answer my question. Yesterday, the landscaper mowed down our blueberry plants because they were hidden in the weeds. Will the plants grow again or do we need to buy new plants? (email reference)

A: In all likelihood, they will grow back. If they were healthy when they were mowed, chances are they will send up new growth. If you don’t see any evidence of new growth breaking in about six weeks, then replant.


Q: I have a rose bush that has lost almost all of its leaves. Should I cut it back? I believe I should pick up all the leaves that have dropped to the ground and treat the plant with something, but I’m not sure what I should use. (email reference)

A: Give the plant a hard pruning to about 6-inch stubs and pick up every leaf.

Give it a shot of liquid fertilizer, such as Miracle-Gro, and get an all-purpose rose fungicide at a local garden center. Begin applying the fungicide as soon as new growth appears and apply again every 10 to 12 days. Begin this regime next spring when new growth begins and avoid water splash as much as possible when watering.


Q: What is the simplest and best way to preserve strawberry plants for the winter? We live in Ohio. Should we trim them back or let them grow? Should we cover them up with anything? We are trying to grow a few for personal use. Thank you so much for answering my questions. (email reference)

A: The easiest and surest way to get them through a winter is to mow them back and collect the mowings once they have stopped bearing fruit. After the last hard frost in late October or early November, cover them with a geotextile cloth (frost blanket) to help them survive the vagaries of winter weather. After you witness the first blossom opening, remove the cover to allow the pollinating insects to do their work. Go to http://goo.gl/bWlI7 for more basic information on strawberry culture.


To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or email ronald.smith@ndsu.edu.