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Hortiscope

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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I want to move my yellow peony to a sunny spot. Can I plant it in a huge pot and set the plant where it gets full sun? When should I do this? (e-mail reference)

A: Do it after a good frost has nipped it.

Q: I have a birch tree that has been in the ground for two years here in northwestern Iowa. I have noticed the leaves are turning yellow from the bottom up. I thought the tree was dry, so we have been watering it. What else could be causing this problem and is there a solution? Thank you! (e-mail reference)

A: Some guesses include extreme changes in the weather, water table rising or falling, pesticide use at the wrong time, pesticide drift or soil compaction. A final consideration that sometimes takes time to show up is the tree having been planted too deeply. The roots are slowly deprived of air, which causes early defoliation and possibly the death of the tree. If you recognize any of these as being the cause, try to get it corrected or get in touch with a certified arborist.

Q: We planted two elderberry bushes this spring (nova and York). However, I just read that the berries are not edible! We planted them so I could make jelly. Also, there was mention of preberries. Can you shed any light on this for me? (e-mail reference)

A: Green or unripe fruit is not edible. It is safest to eat the fruit and it tastes the best when the fruit is ripe and after it is touched by a light frost. The fruits contain alkaloids, which make most people sick if they eat the fruit before it is ripe. For some folks, even the ripe fruit makes them sick. As a caution, sample a small amount to see how it affects you. If there are no symptoms, then enjoy. The fruit also makes an excellent jelly. As to the two cultivars that you mention, I have information only on the York. My information says the fruit is good for jellies, pies, juice, wine and attracting birds. My poisonous text references refer to the elderberry genus as getting a "bad reputation" with poisonings and goes on to say that “cases of poisoning clearly caused by them rarely have been recorded.”

Q: I planted a paper birch in late May. I have noticed that the leaves have been turning yellow and falling off. It started in late June and is getting worse. I water the tree about once a week. I let the garden hose run very slowly for about an hour to get a deep watering. Am I doing something wrong or is this normal? (West Fargo, N.D.)

A: You are doing everything right from what you have told me. A good, weekly soaking should not cause problems. However, it may be planted too deeply. This is a very common problem. Planting a few inches too deeply in heavy soil eventually could kill a tree. Check to see if the top of the rootball is even or slightly higher than the surrounding soil and that you don't have more than a couple of inches of organic mulch over the roots.

Q: I have a spider plant my sister gave me that isn't doing well. I think it needs to be in a smaller pot because you said spider plants like to be root-bound. Should I transfer it to a smaller pot or put it in water to make the roots healthier? I've had this plant for several years. It looks horrible and has not grown an inch. (e-mail reference)

A: You must be an unbelievably patient person! Dump this stubborn miscreant of a plant and start over. Don't waste any more time, effort or money on this thing because life is too short! There are plenty of other spider plants on the market that would be prepared to give you the pleasure of seeing them grow.

Q: I was researching my dogwood problem and found your name, so I’m hoping you can help or advise me. As a child, I have fond memories of climbing in my grandparents’ white flowering dogwood trees and admiring all the flowers in the spring. After my grandparents passed away, I inherited their house and enjoyed the trees until I sold the property. After I moved, one of the first things I did was to buy two white flowering dogwood trees. I dug a hole for each tree and filled it with a mixture of enriched soil that said it had tree and shrub food in it and peat moss. Every spring around the end of March or early April, I sprinkle a granular fertilizer/fungicide that I've been told prevents fungus and makes the tree undesirable to insects. I went on vacation 10 days ago. When I returned, 50 percent of the leaves on one tree were brown and wilted. The other tree had green leaves, but they were wilted. I found out that there had been no rain at all during the 10 days I was gone, so I watered both trees and used some generic Miracle-Gro on them. The tree with the brown leaves is still looking about the same, but the other one looks better. The soil in the rest of my yard is clay. I have them planted under a large oak tree, but far enough away that they get sun about an hour or two during the day. My entire yard is on a hill. Do you have any thoughts as to why the one tree suddenly went brown? From my description, is there something I'm doing wrong or missing? Thank you! (Mansfield, Ohio)

A: The only thing you did wrong was go on vacation. Mother Nature did the rest. I doubt that the tree with the brown leaves will recover this late in the summer. Check the cambium just under the bark with your thumbnail to see if it is still green. If it is, there is a chance the tree will releaf and bloom next summer. If not, replace the tree. Whatever you do, don't overwater because that compounds the problem. Don't add more fertilizer because it is not needed. With some green foliage remaining, there is a good chance that the other tree will be OK after this episode of hot, dry weather.

Q: In late August or early September, I will have my house resided. I have four dwarf lilac bushes that I need to trim back or down completely so they can do the work. Should I prune them back or can I cut them down close to the ground in August? Will the lilacs recover?(e-mail reference)

A: If they are older lilacs, they probably would benefit from a complete cutting back to the ground. They will recover very nicely for you next spring. Don't expect any flowers, which only last for a week or so anyway, until the spring of 2010.

Q: I have a jade plant that I bought a little more than a year ago. It used to be in my office at work, but didn’t seem to be growing under the fluorescent lighting. I repotted it using an orchid medium because I knew that this plant required good drainage. I added Miracle-Gro fertilizer pellets to the medium. The plant got northeastern light for the entire day and it seemed to be very happy and healthy. About two months ago, I moved the plant to the other side of the window so that it got southeastern light for most of the day. After a couple of weeks, I noticed that the undersides of all of my new leaves were turning a dark maroon. About a month later, I noticed that all the new growth was green, except for the customary red tips. I moved the jade back to its original spot in the window. It doesn’t seem to be sick. When I repotted and added the fertilizer, did I overfed it by mixing the fertilizer into the potting medium? The plant is thoroughly watered once a week. I water it sitting under lightly running tepid water from a sprinkler head in my kitchen sink for two to three minutes. Then I make sure that the dish under the pot is dumped until the water won’t drain anymore. I’m curious as to what caused the change in color during a month’s worth of growth. Should I use liquid fertilizer rather than the pellets? Since the new growth seems to be fine, should I bother with making any changes to the routine I’ve established? I just pruned it to give it better shape, so most of the maroon leaves are being rooted. The color does not seem to be fading from the undersides of the leaves, so I don’t think it’s sunburn. Could it be a genetic glitch? (e-mail reference)

A: Jade is prone to forming periclinal chimeras, which this just might be. If it doesn't stay with the rooted plant, then it is just the plant expressing the red pigmentation that usually is masked in mature leaves by the chlorophyll. You don't have anything to worry about. At least your thumb is green! Continue to do whatever you have been doing.

Q: I have a question about a phal orchid. I know that you claim not to be an expert, but I’m sure you know more than I do! I purchased a beautiful pink phal orchid about three years ago. It was blooming and held the blooms for about a month after purchase. When they died off, I followed the directions on the tag by cutting back the spike. The plant sat for about a year on the center island of my kitchen. It grew leaves and air roots, but no flowers. Realizing the plant wasn’t getting enough light, I moved it to an east-facing window. The plant also seemed to be harboring gnats in the sphagnum moss, so I repotted it. That was a good thing because the majority of the root system was rotted! I removed all of the dead roots and repotted it in an orchid medium. I have monitored the plant for the last year. It seems to be happy and growing air roots and leaves like crazy, but it will not flower. I provide it with Miracle-Gro pellet fertilizer for houseplants. It gets a soaking once a week. Should I be feeding it something other than the Miracle-Gro? Should it be pot-bound? Any advice you can give would be greatly appreciated. (e-mail reference)

A: If you are willing to accept less than expert advice on orchid culture, here goes! My one reference on orchids says to encourage a dip in night temperature by 10 to 15 degrees from the daytime temperature during the summer and fall months and keeping it cool (65 degrees) during the winter months. As to being pot-bound, I know it works for most other plants, but I cannot say with orchids. Plants often fail to flower because of low light duration or intensity. You might try adding a grow light to help induce flowering. Keep it on a 12-hour day to see if it helps.

Q: I have a Christmas cactus that has been living with me for 15 years. It bloomed every year to such extent that I would invite all my friends over to look at its beauty. Recently, it started to lose its branches at the base. I don't know what to do to save the plant. (e-mail reference)

A: I don't know what causes this to happen with this species of plant after so many years of carefree growing and flowering. If there is such a thing as old age with these plants, that would be my only guess. If disease, insect and environmental problems have been ruled out, then reflect on what might have taken place within the past six to12 months as far as any environmental changes, such as air quality, new construction, water quality changes, more shade or higher temperatures. Not all may be lost because these plants easily are propagated through cuttings. The cuttings will have the exact same aesthetic qualities as the original.

Q: I have a hoya plant my mother gave me more than 15 years ago. My sister was given one at the same time. Her plant has bloomed, but mine has not. I get lots of leaves and vines. I keep it in a northeast window that gets lots of light, but no direct sunlight. I did transplant it at the beginning of August. I am not sure what I am doing wrong. Any help would be greatly appreciated. (e-mail reference)

A: This can be a challenging species to get to bloom. Don't overwater the plant. Stress it slightly with reduced watering. This is an art, not a science, so I would suggest that you contact your sister to find out what she does in this respect. Bright light and low fertility is good. Having the plant pot-bound is good and so are cooler temperatures.

Q: What is a good schedule to follow for the care of a Christmas cactus? I've heard that it should be put in a closet in January and February. I’ve also heard that it should not be watered for six weeks after blooming. (e-mail reference)

A: In general, watering and too low a light intensity leads to failure. Next to a poinsettia, this is a commonly given holiday plant. The care and culture of a Christmas cactus just about parallels that of a poinsettia. Pruning your Christmas cactus after blooming will encourage the plant to branch out. Remove a few sections of each stem by pinching them off with your fingers or cutting with a sharp knife. These sections can be rooted in moist vermiculite to propagate new plants. Christmas cactus will bloom if given long, uninterrupted dark periods of eight to 10 or more hours each day. Begin the dark treatments in mid-October to have plants in full bloom by the holidays. Christmas cactus also will bloom if they are subjected to cool temperatures of 50 to 55 degrees at night. Plants will be ready for the holidays if the cool treatments are started by early November. While light and water are important to this species, it should not be overdone. Water when the top part of the soil is dry to the touch and dump out the perked water within 20 minutes of watering. Bright, indirect light will intensify blooming. Direct sunlight may cause foliar burn. Keep in mind that a Christmas cactus is a subcanopy, tropical forest species. Hope this helps!

Q: My bougainvilleas have leaf curl. It is always there, but the plants bloom. Why is this and how can I get rid of it? (e-mail reference)

A: I don't know. It could be from moisture stress or herbicide drift. I would suggest finding a local horticulturist or master gardener for assistance.

Q: How do you start sweet potato slips at home? (e-mail reference)

A: It is a little late to do so now. However, if you have some sweet potatoes growing, take one or as many of the stems as you want. Lay them on the ground and cover with sand over a 4- to 6- inch area of the stem with node. It should root in a couple of weeks or so. It will depend on soil temperature and how moist you can keep the area. As growth shows, cover the base with more sand. This encourages adventitious roots to form on the stem. When well-rooted (a judgment call), dig out and transplant.

Q: I am writing about the care of a hibiscus tree that I bought from a local nursery two years ago. It was a small tree and full of blooms. I set it on my back deck and it flowered all summer. Before the weather got cold (frost), I brought in into the house and placed it in a sunny window. I watered it very little, so it went dormant and lost some leaves. About four months later (late December), it bloomed a couple of flowers. When the weather was warm enough, I put it back on the deck and enjoyed a second season of gorgeous flowers. Just before a frost hit, I brought it in and treated it the same as the previous year. It reacted the same way and remained in the house until early June, when it produced one flower. Around that time, I tried to put it back out on the deck. We were having a heat wave, so in 20 minutes it became very stressed and wilted. I immediately brought it back into the house. I tried again to put it out three weeks later, but the same thing happened. Since the beginning of July, it has remained in my house near the window, but it is now very leggy, overgrown, losing leaves and hasn’t produced any flowers. There is very little new growth. To complicate matters, it now has spent a month in cooler temperatures (70 degrees) because of the air conditioning in the house. Can I move the tree outdoors again? Should I put it outside for short periods at a time or should I just bring it out now? Should I give the plant a good trim and transplant it into a larger pot? I live in New Jersey. (e-mail reference)

A: Since the plant has not been repotted or trimmed in the two years you have had it, it definitely needs both. Why not leave the plant outdoors all winter? Is it that tender? The winters in your state are mild enough that it (assuming it is a hibiscus syriacus) easily can tolerate temperatures of 5 to 10 degrees below zero. The weakness of the plant is due to you not allowing it to go through its normal seasonal changes that it is genetically hardwired to do. Throw all of the above out if you have purchased a Chinese hibiscus (H. rosa-sinensis). This extremely tender plant can’t tolerate exposure to cold at all. Moves from the indoors to the outdoors is a shock to the plant, so it should be done gradually. Place the plant in canopied shade or along the north side of a house or garage to allow acclimation to take place.

Q: I want to create a privacy screen between my home and the neighbors. I have looked at Thuja and it seems to be the tree for me. It grows fast and provides good coverage. My concern is being able to prune the trees into a nice shape and keep them from growing into my neighbor’s driveway. The spot where I want to plant them is a few feet from the driveway. Will it be possible for me to plant there? How close can these trees be planted from each other? (West Fargo, N.D.)

A: It all depends on the species/cultivar you select. Brandon, emerald and techny (mission) are good selections that will not spread excessively as they mature. You can plant them 3 to 5 feet apart, but it depends on how fast you want to form a solid barrier or screen.

Q: We have had our cotoneaster hedge for almost 50 years. It’s beautiful! We sprayed (as usual) this spring for insects and again in early summer because we sometimes have had spider infestations. About three weeks ago, we noticed places where the hedge was turning brown. We found a white, powdery-looking substance on the plants. Assuming it could be a disease, we sprayed with a systemic spray used for several different diseases. It is looking worse! I checked out the Web looking for answers, but have had no luck identifying our problem. Last spring, we debated cutting the hedge back to get some new growth. We now have resorted to cutting it back to about 18 inches and then spraying again. However, we don't know if we need to spray for insects or diseases. (e-mail reference)

A: Your cotoneaster has a bad infestation of scale insects. The only way these insects effectively can be controlled is by using a systemic insecticide called Bayer Advanced Tree and Shrub Insecticide. You still might want to cut it back next spring before new growth emerges. Cut it right to the ground and the systemic you apply at this time will be taken up into the new growth as it emerges.


NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161, ronald.smith@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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