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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have had my little spider plant since Earth Day. It definitely needs a new pot. I am going to get that done during my college Christmas break. What is the white stuff that forms around the edges of my pot? I water it once a week with old coffee. Any suggestions on what the white stuff is? It looks a little like Styrofoam. Thank you for your time. (email reference)

A: What you see on the outside of your pot is the salt that your water source (coffee) contains. It is harmless to the plant, but it looks unsightly. It motivates many people to get out of using clay pots and go to plastic or trash the old, salty-looking pot and get a new clay pot. One thing to keep in mind if you are going from porous clay to a nonporous plastic pot is that there is no water evaporation capability when using plastic. This means the media tends to stay moister for a longer period. Many houseplant aficionados are habitual with watering, so what didn’t cause problems with the clay container may result in overwatering when using a plastic pot.

Q: I received a hoya plant for my birthday in October. I was told that hoya plants are easy to take care of, but I'm not entirely sure how. I know it needs a lot of sunlight, so I keep it on my dining room table where the most sunlight can reach it. How often should I water it and how often do they flower? I'm looking for any advice I can get. (email reference)

A: Let’s start with what you shouldn’t do. Do not disturb the plant once the flower buds appear and don’t remove the dead flowers. Avoid repotting a hoya plant as long as possible. When you do have to repot, do it in the early spring as the days get longer. Hoya will tolerate average household warmth. However, if you can tolerate it, allow the temperature to get down to the mid-50s overnight or as close as you can to it. Water sparingly during the long weeks of winter. Anytime the plant isn’t in bloom, go ahead and mist it with distilled water that is at room temperature. Being of tropical origin, hoya plants are genetically wired to expect high humidity conditions. Fertilize only when new growth is evident.

Q: I believe I have a ficus weeping fig. Its main and strongest branch has died. To help the plant, I’ve been fertilizing, so new leaves are growing. However, the branches are not gaining strength and the weight of the growing leaves bends the branches. I tried to provide support, expecting that the branches would gain strength with time, but it continues to grow like a vine. Is this a root disease? Can something be done about this? (email reference)

A: Your ficus very likely is in a light-deficiency situation. The plant probably is not getting any movement from breezes or a fan. Unlike the human body, once a plant gets to this stage, there is little that can be done to correct the weakness with the existing branching system. Without seeing the plant, all I can do is make blanket recommendations that may work to restore the plant. Cut the ficus back to just above the lowest branch. Use a sharp hand pruner. Increase the light reaching the plant by using an artificial light that promotes and maintains plant growth. The plant should get light at least 14 hours a day. At the same time, set up an oscillating fan on low speed to run the same number of hours as the plant light. If this works, the new growth that will emerge will be thicker and stronger than what you have.

Q: I am going to transplant some eastern red cedars. I live in northeastern Missouri where the temperature is around 30. I was thinking about doing the transplanting very soon. (email reference)

A: You live in a banana belt compared with us here in North Dakota. Go for it as long as the ground is not frozen. Water them in well so that the roots will be in a protective ice cocoon when temperatures hit hard enough to freeze the water in the soil. If the soil is frozen by now, wait until the soil thaws to move the trees.

Q: Thanks so much for your website and help with understanding how to care for trees. I live in central Virginia (zone 7). About two weeks ago, I transplanted two emerald arborvitaes. The weather has been unseasonably warm (68 during the day and 50s at night). We have had a couple of freezes and are predicted to be below freezing this weekend. I think I may have waited too long to move the arborvitaes. However, with the warm weather, I went for it. I hope I was not too late. The new area where I planted the trees tends to stay moist and can be quite wet after heavy rains. The area does drain, but rarely does it dry completely except in the summer months when we experience dry periods. I noticed today that the tips of my trees are turning brown. Is that normal for this time of year or do you think it could be related to the moist soil? Could it be related to the transplanting? I understand that over or underwatering could cause this problem, so I have tried not to overwater. In your opinion, do you think it was too late to move the arborvitaes? They have been in the ground for two weeks and we are expecting freezing nights. Do you think I should use burlap to wrap the plants to protect them from the freeze? Thanks so much for any help you can give me. (email reference)

A: You did nothing wrong. Arborvitaes can be transplanted successfully in the fall. In fact, they are best planted at that time. While the soil is not frozen, arborvitaes can take in water. If the soil temperature in the root zone is at 40 degrees or higher, the roots will continue to grow and become established. Because you live in zone 7, your winters are mild. However, you should take steps to protect the trees from wind burn this first winter. This will protect the plants from the prevailing winds but not exclude sunlight or create a tight condition that would give pathogens a chance to develop. The material is coarsely woven burlap that can be purchased by the yard at most hardware or farm supply stores. When in doubt about watering, wait at least 24 hours. Better yet, wait 48 hours.

Q: I was wondering why I have hundreds of new sprouts growing under my oak tree. Under the tree is floratam St. Augustine grass that is difficult to cut because of the sprouts. The sprouts also make the yard look awful. How can I stop the new tree growth without hurting my lawn? Thank you for taking time to answer. (Tampa, Fla.)

A: Very likely these are suckers growing from the far-reaching root system. These are very difficult, if not impossible, to control. I would encourage you to contact the University of Florida Extension Service to see if someone can check to be sure what is going on. Go to to get in touch with an Extension agent in your area. If the Extension office cannot assist you, someone in the office will get you connected to a person with the university who should be able to address your concerns.

Q: I purchased a model house that came with a weeping birch that is too close to the house. I am wondering whether I can top the tree so it won’t get so tall and cause problems. (email reference)

A: You never want to top a birch! I hope this emphasis makes it absolutely clear. I have a weeping birch that is more than 26 years old. The tree is about 5 feet from the foundation of my house and the same distance from the edge of my driveway. It is 30 to 40 feet tall and absolutely beautiful. I hire an International Society of Arboriculture certified arborist to trim the tree. Trimming will lessen the branch load somewhat and get rid of anything that looks old or weak. To locate a certified arborist in your area, go to Be sure to check his or her credentials before allowing any major work on the tree.

Q: Gray squirrels are stripping large quantities of bark off a very large pin oak in my front yard. They leave the bark all around the tree. The inside of the bark appears mushroom colored and powdery. Will my tree survive? (email reference)

A: I don’t know what drives squirrels to get into damaging trees to this extent. However, your tree doesn’t sound too healthy if there is mushroom growth appearing under the pulled-off bark. It may be the squirrels are using this growth as a source of food and the bark is loosely covering these decaying areas. As long as the stripping is not all the way around the tree, there is a chance it may survive. But even if it does, your tree sounds like it needs professional attention. I would encourage you to contact a certified arborist to inspect the tree. To find one, go to Be sure to check credentials before any major work is initiated on your property.

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 email

NDSU Agriculture Communication – Dec. 14, 2011

Source: Ron Smith, (701) 231-7971, Editor: Rich Mattern, (701) 231-6136,

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