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Ron Smith answers reader's questions about the world of plants, trees and gardens.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I was hoping you could tell me exactly how to pinch back or prune my impatiens. I have them in flower boxes. They are gorgeous, but I am noticing that some are starting to get a little leggy. How do I pinch them back and still keep my flower boxes looking somewhat full? Thank you for any help you can offer. (Virginia Beach, Va.)

A: A thumb and forefinger nail will do the trick nicely. You also could use pinking shears. In either case, be selective so that you are getting new growth stimulated and not denuding the planting with an all-at-once shearing.

Q: Our lilacs are more than 40 years old, but some are dying and we don't know why. Is it old age? There is a white fungus on some of them. I now have half a cord of dead branches that I trimmed off. What can I do to save them? (e-mail reference)

A: Cut back the oldest canes all the way to the base of the plants. While some canes will die back, I don't think I have ever seen lilacs completely dead. Lilacs can be badly damaged by borers, cankers or mildew, but not completely killed. You might want to cut down every other plant at the base with a chain saw to stimulate regrowth. You need to do that before the leaves come out this spring. If they have opened up where you live, do the selective pruning with heavy loppers and get to the major cutting back early next spring.

Q: I have six arcadia junipers that turned brown this winter. They were on the south side of the house that gets lots of shade in the summer, but full sun in the winter. They looked great for about 12 years and I kept them trimmed so they looked nice. I’m very disappointed that they all died. Do you have any suggestions for a similar replacement? Is arcadia considered a good choice or are there other varieties out there now that are better and look nicer? I looked at one nursery and saw buffalo and Skandia junipers that seemed similar in size. (e-mail reference)

A: Be sure your junipers really are dead. Look for green cambium under the bark of the branches. If they are dead, go for the buffalo juniper. It is hardier, darker green and does a better job of retaining winter color.

Q: I have a weeping willow tree in my yard. On the north side of the tree, the branches are blooming and growing, but on the south side, the branches look dead. What would cause this? Can I save the tree? (e-mail reference)

A: Most likely the south-side branches or branch has been killed by a stem canker. The tree could live on like this for many more years, but it would not look very attractive. It also would provide a good nest for insects and disease organisms to develop that could spread to other woody plants on your property. I would suggest removing the tree.

Q: Can I prune and cut back bushes in my yard now before they grow leaves? (e-mail reference)

A: You are correct. Go for it as soon as possible.

Q: We have eight techny arborvitaes in the backyard that we planted two years ago. Now that it is finally spring in Minnesota, I went to do some yard work and saw that the trees were a bit brown in the middle, but green on the outside. I trimmed off the dried branches in the middle. Is this normal for techny arborvitaes? (e-mail reference)

A: Yes it is, so don't worry about it. Enjoy spring finally arriving!

Q: I have a female apple tree that had four leaders coming off the bottom of the tree. I took out two leaders, but nicked one that I did not want to cut. What should I do to help it heal? (e-mail reference)

A: Leave it alone. The tree will do a fine job of healing itself. For your information, there is no female or male apple tree. Apple trees have a complete flower, which means they have both male and female parts.

Q: Last fall, a porcupine chewed most of the bark off my two burr oak trees. About a third of the bark is left. I immediately watered them and put white plastic pipe around the trunk of both trees. Is there a possibility they will survive or should I replace them? (e-mail reference)

A: With one-third of the bark remaining, there is a chance the trees may survive. I'd suggest giving them a chance.

Q: I have just read your detailed information about crabapple trees. I wonder if you could help my tree. It has developed a cankerlike growth at the base. On top of the growth is a white, sticky, powderlike substance. It looks like a fungus to me. Any thought on what I should do or where I could go to find an answer? (e-mail reference)

A: What you described is common on older trees. It indicates that some internal decay is taking place. While there is nothing you can do about it, you also need not worry about it, either, at least on a crabapple tree. The tree could produce leaves, flowers and fruit for another 10 or more years.

Q: My mom gave me a Christmas cactus last week. In the last few days, I've noticed little, black bugs flying around the base of the plant and crawling in the dirt. I also found a millipede crawling on the side of the pot. Today I got rid of the top quarter inch of dirt and found more millipedes. I began noticing because one of the buds fell off my plant and some of the stems are beginning to wilt. The leaves at the base also are beginning to dry. Are these pests causing the problems? Will they harm my small spider plant? What is the best way to get rid of them without harming the plant? I know my mom broke the original plant apart and replanted it in three separate pots. One of the pots is the one she gave me. She told me the roots were rotting, but the plant was better. (e-mail reference)

A: It sounds like the soil your mom used was not pasteurized or sterilized. That is why you have the creeping characters you are getting acquainted with in an unwelcome way! If you can, get some potting soil that is labeled for African violets. Check the bag to see if it has been pasteurized or sterilized. Knock the plant out of the container and dump the soil in your garden or scatter over the lawn. Nature will play host to the pests in an appropriate way. Soak the container in hot, soapy water for about 10 minutes. Rinse the pot well and repot the plant. The plant should come around with the improved media.

Q: We have a mature crepe myrtle in a garden bed with good, but not extraordinary, sun. Every year since we bought this home it has bloomed beautifully. Last fall, we ripped out a lot of privet that was behind the crepe myrtle to make room for a fence. The privet was beyond the crepe myrtle drip line. Spring has arrived, but the crepe myrtle is not leafing out! The cambium layer is green on the branches we can reach. We had intended to trim (reduce the tree height) this year, but now we don't know if we have a dead, dormant or tired tree that has taken an extended holiday and will come back later. We did have a rather lengthy drought in our area. (South Spring, Md.)

A: Sometimes plants go into a shock or setback following construction or physical activity that may disturb their established ecosystem. I would say that if the plant doesn't leaf out by Mother's Day in your area, it is unlikely that it will. When plants get to a certain age, the root system becomes quite extensive. Even though the privet was outside the drip line, the two root systems may have become intertwined. When you took out the privet, you may have damaged the feeder roots of the crepe myrtle.

Q: I saw your Web site, but didn't see an answer to my question. I have a garden of tulips in my front yard. Almost every year when the tulips are about to open or have just opened, I wake up to find all of the blooms have been lopped off. Some look like they have been half eaten and the rest are still whole. Each and every stem is left without blooms. I noticed that my neighbor’s tulips look untouched. Even my neighbor two doors down who never looks after his garden has tulips in full bloom. Is this some kind of animal or bird doing this? This has been happening for about four years. Why my garden? Do I have a nasty neighbor I don't know about? (e-mail reference)

A: The Case of the Toppled Tulips. It could be a neighbor, but I doubt it. If people are going to be nasty, they think on a higher level than simply destroying tulip flowers. It could be a combination of bunnies and voles (field mice) that are eating some blooms and destroying others. Bunnies are the most likely critters to suspect. Why they pick on you and no one else is beyond me. In the future, spray the tulips with pepper spray as the flower buds begin making a showing. Reapply if you get a rain or snow cover that may dilute the heat from the pepper spray.

Q: I have a peace lily that was given to me when my stepfather passed away. I keep it in my office in a self-watering pot. It has been healthy, but it seems to have taken a bad turn the past few weeks. It had three blooms that had brown spots even before opening up. Several of the stems also have light brown splotches on them. However, the stems in the center of the plant are tall and have a nice color. A friend looked at the blooms we removed and said he thought it might be some kind of blight. However, I have no idea how to treat that. Any help you can provide would be welcome. (e-mail reference)

A: It sounds like it possibly could be a micronutrient deficiency that is showing up. Try to locate a houseplant fertilizer that contains iron and magnesium. Apply it every other watering or about every two weeks to see if it changes the condition of the plant. Also, check to be sure the watering device is not overdoing it. The soil should be damp, but not soggy.

Q: We have an old birch tree that split all the way up during the winter. The split is about one-half inch deep. What should we do? Also, we have clump birches that seem to suffer greatly every year. They weep and do not leaf out all the way to the top. They were transplanted two years ago. (e-mail reference)

A: The old birch can pretty much take care of itself through natural healing. Just leave it alone. As for the clump birches, they probably are responding to losing most of their roots during the transplanting process. They also could be infested with bronze birch borer. I suggest you contact a local International Society of Arboriculture certified arborist to determine what corrective action can be taken.

Q: Do you know the life expectancy of a lilac bush? We have several bushes that are very tall and have tons of suckers, but don’t bloom very much. (e-mail reference)

A: Who knows? They could be 40 or 50 years old. It depends on a ton of variables that are too complex to pontificate about in an e-mail. They are tough, dependable plants!

Q: It is my understanding that hibiscus and rose of Sharon are related. I am curious to learn if one can graft the hibiscus to the rose or if there is some way to propagate the hibiscus to be tolerant of the weather conditions in the Philadelphia suburban area. I have a series of hedges made up of rose of Sharon (never really liked it until I learned it was a member of the hibiscus family). I have friends in Bermuda who have beautiful hedges made up of hibiscus, so that is why I’m curious. (e-mail reference)

A: In Bermuda and Key West, the hibiscus rosa-sinensis or the Chinese hibiscus are beautiful. In Philadelphia, the hibiscus syriacus have the potential to be beautiful with cultivar selections such as Aphrodite, Diana and Minerva. There also are at least two dozen more selections you could make. You probably just got the species, which is nothing to write home about. Intergeneric grafting would work, but the plant would die back to the root every winter. If it was something that worked, I assure you that path would have been traveled a long ago.

Q: I am trying to do a little research on how to care for calla lilies. I received one at my niece’s funeral. As you can imagine, this plant is very important to me. My niece died at birth and I was given this plant to take home from her. The lily is in a small pot right now and will have to remain in a pot because I live in an apartment. I need to know the best way to care for this precious flower. I have some Miracle-Gro organic potting soil that I was told would be good to use. Do I need to get a bigger pot for it and how often does it need to be watered? I also read that they like morning sunlight and shade in the afternoon. I hope that you can help me or point me in the right direction. Thank you for taking the time to read this e-mail. Any helpful advice you can give will be gratefully appreciated. (e-mail reference)

A: This plant's natural habitat is in the swampy regions of South Africa. In order to be successful with calla, allow it to dry down for about six to eight weeks after it is finished blooming. This somewhat apes the cycle of the plant’s natural habitat. At the end of that period, repot the plant in the next larger sized pot. Begin watering again to keep the plant moist. The plant will do best in full sunlight or a semishady location.

Q: We planted two white gumpo azaleas last fall. We live in Chicago, which I believe is in zone 5. It’s now spring in Chicago and most of the azaleas are starting to bloom. I’ve noticed that my azaleas are mostly bare. The brown, barky stems are showing and no new growth has occurred. They look dead! They do have a small portion of green leaves toward the bottom, but 90 percent of the plants are leafless. I suspect rabbits might have been eating them during the winter months. How can I test to see if the azaleas are dead? Is there a chance they will come back? My mother suggested snipping a piece of the barky stem off to see if it’s green inside. (Chicago, Ill.)

A: You mom is right about the stem being alive if it is green inside. However, this species of azalea usually is not cold hardy enough to be dependable in your part of the country. You probably will get some growth coming from the crown of the plant where it was protected against the weather extremes, but there will be no blooms.

Q: I have a cane-stemmed begonia that was a gift from a friend. She started it from a cutting when she pruned her own plant. It blooms several times a year and grows like crazy. I have started three separate plants from the cuttings. I have one cutting right now in a jar of water until it grows enough roots to plant it. My problem is that the plant itself is blooming, but the leaves are rather pale and sickly looking. I might not have noticed this, but it’s obvious when compared with the cutting in the jar of water. Am I not watering the plant enough or does it need some plant food? Since it’s blooming, it seems like it must be happy. The plant and cutting are located in the same corner of my kitchen. (e-mail reference)

A: Give it a shot of fertilizer about once a month when you are watering it to keep the color up. Flowering can be an expression of joy or desperation on the part of the plant. In your case, it sounds like a desperate message is going out for nutrients.

NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
Prairie Fare: Prairie Fare: De-stress with Gardening  (2019-05-23)  According to researchers, gardening can be beneficial for mental, physical and social health.  FULL STORY
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