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Hortiscope

Ron Smith answers reader's questions about the world of plants and animals.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: We live on a hill with the north and west side open to seasonal winds. I planted two rows of white and blue spruce and one row of green giants in those areas. We had a late spring freeze that split the trunks of the green giants. Only two trees survived. The trees looked like someone took a sharp knife and slit the trunks vertically. Should I replace the green giants with something sturdier, such as techny? I'd like that outside row to get 15 to 25 feet tall. (e-mail reference)

A: Normally I would recommend techny, but just this past week, I visited our arboretum and discovered the brandon arborvitaes that were planted about 30 years ago. I was impressed with how beautiful and majestic these plantings were! Not a speck of brown foliage on any of them. Brandon doesn’t spread as much as techny, so you need to plant the brandons closer together. You will end up with a beautiful green wall about 20 to 25 feet tall.

Q: How many dahlia bulbs would you need to grow six plants? Do you just stick the bulbs in the middle of a hole in the soil? Could you give me a few directions? (e-mail reference)

A: I'm guessing that you live somewhere in the world where spring is arriving. Dahlias should not be planted until all danger of frost has passed and the soil temperature reaches 58 to 60 degrees. Excessively wet soil may cause the tubers to rot, so if your weather has been wet and stormy, you may want to wait for a drying trend. Dig and prepare a 12-inch diameter by 12-inch deep hole. Mix a shovelfull of compost or peat moss, a handful of bone meal and a little Dolomite lime with the soil that was removed. Fill the planting hole with the soil mixture to a depth of 6 inches. Place the tuber horizontally in the bottom of the hole with the eye pointing upward. Tall varieties will need staking, so this is a good time to set an appropriate-sized stake in the ground next to the tuber (near the eye). This will prevent any damage from occurring if the stake is added after the tuber has started growing. Cover the tuber with about 2 inches of your soil mixture and water thoroughly. When the sprout begins to emerge from the soil, gradually add more soil mix until the hole is entirely filled. Once the plant attains sufficient height, secure it loosely to the stake. I recommend using a length of an old nylon stocking or old cotton undershirt to keep the cord from cutting into the plant as it grows. Add more ties until the plant is supported approximately 24 inches below the eventual top of the plant. A Dahlia in bloom is a heavy feeder, so you may want to consider using a water-soluble bloom-type fertilizer about a month before the plants begin to bloom.

Q: Would you please tell me if spider and snake plants are poisonous to my cat? I brought the plants into the house, but the cat loves eating the leaves. (e-mail reference)

A: I have three lazy, almost totally useless cats (except they do a good job of creating warm spots on your lap!) that have nibbled on my houseplants for years. The list includes spider and snake plants. Someday the cats will die, but not from eating the leaves of our plants. They throw up when they do, but that doesn't stop them. We do our best to keep the plants out of reach to protect the plants, not the cats. When we see them nibbling, they get a verbal scolding and a spritz of vinegar water. The cats eventually get the message after about a month. In a nutshell, spider and snake plants are not poisonous to your cat.

Q: We planted our garden to sunflowers this year, thinking that the birds will eat the seeds. We live in southern Alberta, where the winters are fairly mild. Can we leave the sunflowers on the stalks all winter or should we cut off the heads and place them in a protected spot so the birds have access? (e-mail reference)

A: Mild winters in Alberta? Then why do we call our winters in North Dakota severe? Anyway, you can do either. You might want to harvest a few heads to provide some for the ground-feeding birds and other critters, which I'm sure your property plays host to! Enjoy.

Q: I have a plant that had no name on it when I bought it and the store had no idea how to take care of it. It has long (8 inches) leaves that start out with a beautiful pink or mauve color. As the leaf matures, it turns green with flecks of pink. I have a problem with the ends of the leaves turning brown and then spreading to cover a lot of the leaf. I am not overwatering and I have repotted it since bringing it home. I have it in a south window, so it gets lots of light, but is slightly blocked by venetian blinds. Am I doing the right things for it? (e-mail reference)

A: It sounds like it could be a caladium because the plants come in all kinds of leaf colors. Pink is one of the colors. This is a plant that benefits from going into dry-down dormancy every year because it is tropical in origin and goes through a continuous wet to dry condition as the seasons cycle. Allow the plant to dry and leave it in the soil. In January or February, when new growth is noted, you can begin watering again to keep the tuber and soil continuously moist or you can divide the plant at that time and repot. I would suggest that after the dry-down is past, repot the plant in fresh, pasteurized potting soil that is high in organic matter because part of the problem with the burning of the edge of the foliage could be due to a salt accumulation in the soil from overfertilization or poor water quality. Keep it out of direct sunlight. Filtered or diffused light is best. Fertilize lightly as new growth is breaking in the spring, but stop fertilizing around the end of June. This plant also is sensitive to cold, so don't place it anywhere where cold drafts can reach it. The plant should be kept at a temperature no lower than 68 degrees!

Q: We extracted a northwoods red maple that we planted about 13 years ago. It was originally in a container. The tree was dying the past few years, with classic symptoms of girdled roots. Further examination proved that it had strangled itself. We want to replace the tree, but are a little shy of planting another containerized tree. Is it OK if I plant the new tree in the existing hole? I removed the stump and cleared the old roots. (Woodbury, Minn.)

A: Go for the containerized tree. However, when you make the selection, carefully knock it out of the container and make sure the roots aren’t tangled. Plant at the right depth because planting too deeply can cause root girdling. Plant it to a depth where the stem flares out to begin the root system. A younger, smaller tree will grow with more vigor than an older, larger tree because it will have more of a root system at the time of planting. Planting in the same location should not be a problem because there was no disease associated with the tree that was removed.

Q: I am so glad I found your Web site on ficus trees. I have one lyrata, one benjamina and one variegated rubber tree. The lyrata is doing fine, but I air layered it because it was getting too tall. How long will it take for the new plant to produce a good root system? What can I do for the mother plant to make new buds as soon as possible before winter? The benjamina is not doing well. The leaves are dropping on one side of the plant. It has been in the same container since I purchased it four or five months ago. My variegated rubber tree is doing OK, but the edges of the leaves are turning brown and wilting. I don’t know if this could be some form of fungus. What can I do to save my babies from dying? (e-mail reference)

A: I’m glad you read the Web site before approaching me with your questions because it makes answering a little easier. It takes six to eight weeks for roots to form on most air layers. You can check the root development by squeezing the air layer or carefully unwrapping it to see if the roots are developed enough to support the aerial portion of the plant. Once the air layer is removed, it usually results in new buds breaking beneath that point because the terminal bud was removed. Benjaminas are notorious for dropping leaves, so yours is not doing anything too unusual. They respond well to supplemental lighting, especially going into and through the winter months. I'd suggest repotting the tree into the next nominal-sized container that also has good drainage. Get a plant light and put it on a timer for 13 hours of light per day. Eventually, the tree should stabilize with a fairly uniform leaf cover if none of the stems are dead. Browning or firing of leaf edges on houseplants is usually an indication of high salts in the root system from chemically softened water, bad container drainage or overfertilization. After corrective action, the problem should disappear when subsequent new growth appears.

Q: I am having a difficult time finding Wilt Pruf other than in smaller spray bottles. Two years ago, I found it and used it in a container attached to the garden hose. Would you have a suggestion as to where to look for it? Can Wilt Pruf be over applied? I have three mature Black Hills spruce that I would rather Wilt Pruf than cover with burlap. (e-mail reference)

A: Your Black Hills spruce should not need protection this winter. They are native to the southwestern part of the state, so the trees should be able to take any weather extremes Mother Nature throws at us. In general, anti-desiccants have gotten a bad rap lately based on some studies out of the University of Minnesota and other land-grant universities. In most cases, anti-desiccants have been found to be useless in stopping transpiration because the anti-desiccants break down and disappear just two weeks after application. Some of the foliar burning that has been claimed to be caused by the use of anti-desiccants actually is the result of it not being there at all. I, along with other plant scientists, have been guilty of promoting these products for many years until someone decided to investigate why foliar burn still was taking place. If our winters ever shorten to just two weeks in duration, anti-desiccants might be something to use!

Q: I am looking for information on how to manage our birch trees. We have seven birch trees about 35 feet tall at the front of our condo block in urban Melbourne. They are important to me because they shade my third-floor windows in summer and allow the sun in during winter. Unfortunately, they have been hacked through the years by the previous residents, condo corporation and power company. I have managed to get the trees into reasonable shape and I want to keep them that way. The trees have been stressed for some years due to low rainfall. I have installed a dripper system so they get enough water. They also are planted in very poor, heavy soil. I have been fertilizing the trees. Some small branches budded and died off this spring. I cut them off and found a brown stain inside the branches. The gardener told me this was a fungus. There is evidence of fungus on the camelias in the garden, so I plan to give the whole lot a dose of Bayleton. Is this appropriate? There also are a lot of grubs in the soil. I plan to hit the grubs with a trichlorfon spray. There is no sign of borers. My worst problem is that some maniac stripped every branch and twig from two of the trees below 20 feet about five years ago. There is a gap in the trees that looks awful. Is there a way of inducing buds or grafting shoots onto these sections? (e-mail reference)

A: I'll give you my best shot based on the information you have provided. The first smart thing you did was to get a dependable water source to the root system. Be sure to check the system at least a couple of times a summer to be sure it is functioning properly. These systems can become plugged, but sometimes the problem isn’t noticed until the plant starts to wilt or die. Unfortunately, the gap the maniac created by cutting out the lower branches will stay the same. You can plant under the trees with red stem dogwoods because the trees make a very nice contrast with the white bark of the birches. What caused the death of the branch is difficult to ascertain. Your gardener may be right in that it could be a vascular disease that is just getting started. This problem usually is traced back to the root system of the trees and finding that they have been kept too wet. Be sure that is not the problem with your trees. The root system should be kept cool and moist, but not soggy or soaking. The University in Melbourne probably has a Plant Pathology Department that can run a culture test to specifically identify what, if any, pathogen is becoming active in the vascular system. Generally, systemic fungicides would have to be used to control these diseases.


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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