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Ron Smith answers questions about plants, trees and gardens.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: My late husband had a green thumb, but I also have done OK for the past seven years. During the last year, I noticed a white mold growing on top of the soil. I've replanted, but it comes back. Recently, my daughter gave me four houseplants because her new home does not have natural light. These plants were fine until a few weeks ago. These plants also now have white mold on them. Please help because we are environmentally friendly people and love our jungle of houseplants. (e-mail reference)

A: The white mold is a saprophyte that will not harm your plants. It is the result of the humidity being too high, soil surface kept too moist, poor air circulation, too low a light condition or a combination of these factors. The mold can be removed by scraping it off or sometimes by working up the surface of the soil with a small cultivator. Using pasteurized soil also will cut down or eliminate this unsightly condition. Enjoy your jungle of houseplants and don't worry too much about this.

Q: I moved three old spruce trees to my yard about seven years ago. They did great until last year, when I noticed one of them was dropping many needles in the lower area of the tree. Now it has become worse and I feel I need to act now or possibly lose the tree. (Massachusetts)

A: There are several reasons why the needles on a spruce tree fall off. The most important thing to do is get the cause properly identified so the action taken will be effective. I suggest that you contact the University of Massachusetts Extension Urban Forestry Service at and then click on "diagnostics and soil testing" for assistance. You will be instructed on what to do about collecting a sample for an accurate diagnosis and recommendation.

Q: I bought a jade plant four years ago. It didn’t grow very fast, but once it got to a certain length, the branches just dangled over the edge of the pot because the stem wasn't strong enough to hold it up. I tied it upright to see if it would support it enough so it could get its strength back, but it didn't help. Today I touched a branch and it pulled right out along with the rest of the branches. What was I doing wrong and is it possible to save the plant? (e-mail reference)

A: I have a couple of ideas that may not save this jade plant, but certainly should keep any future ones alive. Get a plant light and direct it on the plant for 12 to 13 hours a day. This usually makes a very remarkable difference in the vigor of the plant. Most houseplants are underlit and overwatered. Get an oscillating fan with a variable speed control. At the same time the plant is receiving light energy, have the fan sweep back and forth across the plant at a low speed. This will build stronger cell walls to help hold the plant and the branches more erect. In nature, this is pretty close to what this majestic tree receives on a daily basis. We purchase these as cute houseplant cuttings and expect them to survive in our very dull indoor environment. It is a miracle that anything survives.

Q: Last winter, we moved into our new house in town. Missing all the plants from the country, I spent the summer (time and money) putting together my backyard retreat. However, rabbits have sampled many of my bushes. I have run wire caging around all the plants the rabbits have tried to eat. I’ve also tried rabbit deterrent sprays, but they didn’t work. The rabbit have sampled the new growth buds on many of my bushes and eaten almost all of a hydrangea plant. Will the bushes and hydrangea recover? The rabbits did not eat the bushes all the way to the ground. I just hate to see all the effort I put into the plants eaten up so quickly! (e-mail reference)

A: What kills the plants for certain is when they are completely girdled at the base of the stem. Most will recover from the kind of damage you are describing, especially the hydrangea. I have found two approaches that work with rabbits and voles. You can keep them off the plants by using a wire or tree wrap and ground feeding them with typical bird food. The rabbit repellents don't work for long. While they work initially, it seems that as our winter goes on, they become less effective. Perhaps the rabbits are getting more desperate, so they will eat something that tastes awful. I guess that if I was starved enough I might eat brussels sprouts!

Q: I just got some tulip bulbs for Christmas from a relative. I live in upstate New York in a rental house, so I am not quite sure what to do with them for now. If it thaws out, I might be able to plant them, but I don't want to leave them here when I move. I don't know if it is too late to plant the bulbs. Can I keep them in the refrigerator or freezer until March and then pot them? Should I pot them now and put them outside? How long will the bulbs last without planting? How would I have to store them? (e-mail reference)

A: I would suggest keeping them in the refrigerator until spring and then pot them to enjoy the blooms. Allow the foliage to die down in late spring or early fall. Take them with you, pot and all, when you move to a permanent residence.

Q: The deer ate the leaves off my climbing ivy. I am heartbroken. Will the leaves come back next spring? (New York City)

A: If it was mature ivy, it should releaf this spring. It is nothing to worry about and there isn’t much you can do about it. Look forward to a flush of new growth next spring

Q: I have a tree in my front yard that has developed a large crack running up its bark. It is in the bark only. Does this mean that the tree is dying? Do I need to get it cut down because it has such weak wood? (e-mail reference)

A: What you do depends on what else you have on your property for trees. If this is a large, mature tree (you didn't say that it was), then I would suggest taking the tree down. If it is relatively young, the tree will heal on its own without any input from you. If you have other large tree species on your property and this one will be a threat to your house or property in a few years, then remove it. The best approach is to have an International Society of Arboriculture certified arborist examine the tree for soundness and to see it there is any threat of it falling down during a windstorm. At the very least, the arborist could do some cleanup pruning to cut down on wind resistance and the possibility of branches dropping and causing damage or injury.

Q: I have taken over care of two Christmas cactus plants that have been neglected for years. They have been in large pots with good drainage and kept in a west window, but the drapes were closed all the time. Watering has kept them alive, but there is almost no growth and they have never flowered. The existing leaves are green, but shriveled. I have moved them to a south window and opened the drapes during the day. New growth has started at the ends of the existing branches and at the base of the old, brownish stems. Do I cut them back and let them start over with new growth? Will the shriveled stems fill in? I’ve had very good success with my own Christmas cactus plants. (e-mail reference)

A: I don't think it a good idea to get into the heavy pruning of these plants. I would suggest allowing the new growth to manifest itself. At some point this spring, take some cuttings and root them. If the old plants look too unsightly after you have rooted some cuttings, then dump them. However, consider that these old, wrinkled plants may be adding character to your interior environment!

Q: After doing some Web searching, I came across your site and have enjoyed reading it very much. My wife and I live in Phoenix. Thanks to my dad’s Iowa roots, I have been able to grow things that normally could not survive in our summer climate. One of those is a red hibiscus that blooms throughout the year. The only time I cover it is when we have a frost warning during our short winter months. Last year, it suffered from frost (we were not home at the time), so I had to cut it back. It took a whole year to recover from the damage, but now it needs pruning. I’ve read the advice you’ve given others on pruning pot-sized hibiscus, but what about taller hibiscus trees? (e-mail reference)

A: How I miss seeing those big, beautiful shrub- or tree-form hibiscus plants! These you want to treat as you would lilacs in Iowa. Remove one-third of the old wood back to the crown every spring to keep the plant vigorous and full. You also can pinch out the new growth to encourage the same.

Q: My amaryllis bulb shot up the bloom stem. It has no leaves, just the stem. I understand leaves help the bulb produce for the next year. I am guessing I got a dud and that it is shot after it blooms. (e-mail reference)

A: That is the way they grow, so no sad face! The flowering stem shoots up, produces the flower and the leaves follow. Given a little luck and patience, the leaves will produce enough energy to get the plant to reflower again. For details, go to to download my publication on the subject.

NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
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