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Hortiscope

Ron Smith answers questions about flowers, trees, gardens and shrubs.

By Ron Smith, Horticulturist

NDSU Extension Service

Readers: A correction to a previous column. When pruning a Miss Kim lilac, it should be done in the spring AFTER it blooms. Thanks to reader Tony G.!

Q: I have a very large Thanksgiving cactus plant in a tall pot. The blooms go lower than the bottom of the pot and the plant takes up the whole pot. I would like to split it in half or quarters. What is the safest way to do this? (e-mail reference)

A: It can be split into quarters, thirds or halves, but do so after it has completed flowering, which should be sometime in March or April. I would encourage you to take some cuttings from the plant to root before doing the dividing in case there is some sort of disaster. That probably won't happen, but it is best to cover all possibilities.

Q: I had a gentleman come in this morning and ask if he can use vermiculite in his garden soil and how much he should use. (Carrington, N.D.)

A: Vermiculite use is questionable in garden soil because of the potential asbestos it may contain. I have worked with it in the past because I was naive to the presence of this carcinogen. However, I'm still alive and healthy. Since asbestos was discovered to be a carcinogen, huge efforts have been launched to minimize human exposure to it, especially the asbestos that was used for insulation. At the time (late 1970s), vermiculite contained about 4 percent to 5 percent asbestos. The material that was used for insulation had up to 80 percent asbestos. With most of the industrial asbestos now taken out of the environment, the Environmental Protection Agency redirected its focus to the lesser concentrations, such as vermiculite. The EPA determined that the amount of asbestos in vermiculite will not pose a potential risk to casual users. However, to further avoid exposure to any potential airborne asbestos, the EPA came up with several recommendations. Use vermiculite only in outdoor situations and keep it damp when distributing or working with it to minimize dust particles becoming airborne. Avoid bringing vermiculite indoors on clothing. Use a premixed potting soil because it has a lower vermiculite content and usually is moist. This should minimize the generation of vermiculite dust. Try to use other garden soil conditioning products, such as peat moss, compost, weathered sawdust or bark. All of that said, it is up to the user to determine if the risk outweighs the benefit of using vermiculite. For me the risk outweighs the benefit because there are so many other available products that lack any human health hazard that can be used.

Q: The leaves on my three houseplants keep turning yellow. It's not that they are overwatered because I only give them 2 cups every two weeks. I put a tablespoon of Miracle-Gro in the water. The water I use is spring water I buy at a grocery store. What is the best soil to use for houseplants? (West Fargo, N.D.)

A: The problem could be drainage. If the containers are not freely draining, the water could be sitting in the base of the potting soil and causing anaerobic conditions. If that isn't the case, then it could be that the light the plants are receiving is insufficient. If that is the case, you need to move them to a location where the plants can get better light or get a plant light that you can put on a timer so the plants get 12-plus hours of light. As for the soil, any media that is designated for use as a houseplant soil is acceptable. You could use soil that is designated for use with African violets. This type of soil usually is high in organic matter. One other thing to note is that houseplants do not need fertilizer. Fertilizer only is needed if the plants are actively growing, which yours are not. Save the fertilizer until spring as new growth begins.

Q: I am experiencing new tree growth below my established malus prairie fire. Will these volunteer trees be an exact copy of the mother tree or will they be another type of apple tree? I am assuming these trees come from the fallen fruit because I have dug up one of the volunteer trees and found it is not connected to the mature tree. (e-mail reference)

A: Thanks for the good question! The seedlings and suckers from your mature tree will not be the same type of prairie fire. Seedlings reflect the genetic makeup of the tree, but can vary all over the place. The suckers from the root system will be identical to the root stock the prairie fire is grafted to. If you want to venture into experimental horticulture, collect some of these seedlings and plant them in an innocuous spot on your property to see how they turn out. If you like the trees, keep them. If not, remove them.

Q: I have a schefflera tree that is having some problems. Its leaves become very sticky. I have used insecticides for scale and spider mites. The plant is then OK for a little while, but then the problem returns. Should I repot it or prune it down to 3- or 4-inch branches? It does have some new growth on it. It sits by a kitchen window that faces south and west, so it gets plenty of light. Any suggestions on how to take care of this problem? (e-mail reference)

A: Whatever this insect or mite is, it is surviving your best attempts to get this taken care of. I would suggest that you prune it back heavily. Repot the tree using fresh potting soil and a new pot. Dip the entire plant into an insecticidal or miticidal soap solution. If this doesn't take care of the problem, dump the plant.

Q: I have a goldfish plant and would like to know the proper way to propagate it. (e-mail reference)

A: The success of rooting cuttings from this plant depends on a few things. Take cuttings after the plant has finished flowering. Use a rooting hormone to aid in root initiation. Use temperature- controlled bottom heat. This is available at most garden center stores. Without it, the rooting will be greatly delayed, which may cause rotting problems. Be sure to use a pasteurized or sterile media for rooting.

Q: We hope you can help us figure out what’s wrong with our honey crisp apples. We have a tree that was planted about 15 years ago. It did not bear fruit for quite a few years. However, since it started, we have enjoyed these wonderful, crisp, juicy apples. In 2008, some of the apples weren’t as good. Some had brown spots inside and tasted bitter. In 2009, we had many apples on the tree, but many did not get very big. This may have happened because of our cool growing season. Many of the apples were bumpy and sort of mottled on the outside and had brown spots on the inside. What do you think has happened to our honey crisp? This tree is in our backyard next to a haralred apple tree that bore beautifully this year. (Bismarck, N.D.)

A: This sounds like an apple maggot problem got started on your tree. The high density of apples you had on the tree made it worse. Remove any apples that are on the tree. When the snow disappears next spring, pick up and remove any fallen fruit that is on the ground. Spray an insecticide that contains carbaryl (Sevin) at petal drop and again every 10 days or so going into July. You also want to hang a fake apple trap or two. The trap is covered with a sticky substance that will act as a monitoring device to see what insects are coming into the tree’s canopy. The apple maggot is a small fly that is identified easily. If any significant numbers start showing up on the false fruit, resume spraying. The Sevin also acts somewhat as a fruit thinner, so you should have fewer but better fruit. I would hang a couple of the false apple traps on your haralred to make sure that this pest doesn't also decide to raise a family in this tree!

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 e-mail ronald.smith@ndsu.edu.


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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