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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have a question about my Christmas cactus plant. If I put the plant in a coat closet, is it OK if I open the door twice a day to get my coat or does it need total darkness for 13 hours a day? Also, I have a new orange tree that has done well outdoors this summer. What low temperature can it tolerate? I have an unheated sunroom facing west that will stay warm for another few months. Otherwise, I will have to bring it indoors and put it in a spot where it will not get as much light. When is the best time to prune it? A couple of branches on the plant are a bit long and look a little out of place. (Milwaukee, Wis.)

A: As ridiculous as it might sound, those brief openings of the closet door may be just enough to set back flowering. It does when a night watchman comes into the greenhouse to check the temperature with a flashlight. The plants in the immediate area around the thermometer are delayed in their flowering progression when compared with those in the rest of the greenhouse. Modern greenhouse operations now have temperatures and other functions automatically controlled and recorded by a computer system. Your orange tree can tolerate temporary dips into the low 40s or so. However, tolerance and thriving are two different situations. Don’t expose it to these temperatures any longer than necessary. You are better off bringing it indoors and giving it 14 hours under a plant light that is set by a timer. You can prune the unwanted branches anytime the spirit moves you.

Q: I live in rural northwestern Illinois. I planted two hard maples trees. One was planted seven years ago and the other five years ago. Both were planted in the fall and had full orange and gold colors at the time. Since that time, the trees have done very well. However, neither tree has ever displayed the bright colors that were on the trees when planted. Both trees remain full of green foliage until a hard frost. The leaves then turn brown and drop off. Is there anything I can do to encourage the typical fall maple color? (email reference)

A: You probably have the trees planted in locations where all the conditions are perfect for growth, such as adequate and balanced nutrients, water, good aeration, and no insect, disease or environmental stresses. If any of these factors are within your power to control, I’d suggest backing off on at least a couple of them, such as withholding water or fertilizer. If that doesn’t work, mildly stressing the trees by severing their root systems out by the canopy edges with a straightedge spade in several locations will do the job.

Q: I purchased my first gloxinia plant this summer at a nursery. It looked like way too much plant in a small pot, so I repotted it. It is now October and our days are a little chilly. However, the plant is huge and very healthy. The leaves are as big as the palm of my hand. I brought it inside yesterday because of the cold weather. It has sat on an outside wall where it got sun and shade all summer, but it never bloomed. I’m guessing that it didn’t bloom because I replanted it in a large pot. Am I correct, or what caused it not to bloom? Also, now that it is inside, what course of action should I take? Should I water it the same or less? (email reference)

A: Gloxinias are more likely to flower when they are a little pot-bound. With a little time, it should get around to blooming for you. The blooming should last six to eight weeks under the right conditions. Hang in there.

Q: A homeowner cut down a couple of mugho pines with a chainsaw. She tried cutting out the roots but couldn’t get them all. She’s wondering if a commercial stump remover (she didn’t specify which one) possibly would injure a juniper that is about 5 feet from the roots of the pine. (email reference)

A: There might be some intermingling of the roots. Expect some damage if that is the case. However, the roots of the mugho pines should not be a problem. She won’t be able to get every root, but those remaining should rot away slowly.

Q: Your advice is not to put gravel in the bottom of a pot. Is this all pots or only nondraining types? I've always used broken terracotta or stones in the bottom to facilitate drainage and keep the dirt from flowing out the bottom. (email reference)

A: A stone or piece of crockery over the hole in the bottom is all that is needed. Undisputed research supports a homogenous medium supporting good, continuous drainage. A medium that is interrupted with a layer of media of different particle sizes acts as a “choker layer” that is used in many golf course greens to hold the water back. This will keep the water in the root area to saturate that zone before allowing any water to pass through. This is known as a “perched water table.” Since overwatering is one of the two biggest causes of houseplant death, it is believed that the major cause is this drainage layer, which commonly is recommended in potted houseplants. The top of the soil dries while the area just below this layer remains moist or wet. This creates anaerobic or near anaerobic conditions. Meanwhile, the homeowner sees dry soil and adds more water, which compounds the problem. I hope this helps you understand this recommendation.

Q: I have a problem with some green ash trees in my yard. I have four trees. Three of them are ash trees. The trees are about 15 years old and large, but dying. I called our city forester but he had no idea what was causing our trees to die. Each year, there are fewer and fewer leaves. They appear to be fading from the inside out as far as the foliage. The top of one tree is dead and all of the trees have many branches with no leaves. There are many ash trees around our neighborhood, so I am concerned that there is a disease that could spread. Would you have any thoughts on what is happening to our trees? We also have an evergreen on the opposite side of our yard. I just noticed the other day that the needles are turning brown on the inside of the tree. (Bismarck, N.D.)

A: The needles turning brown on the inside of the evergreen is completely normal for this time of year, so don’t worry about that. Based on your description, it is difficult to determine just what is killing your ash trees. It could be an infestation of the lilac/ash borer or it could be verticillium wilt. Only a lab culture can make a determination. Look closely at the bark and branches to see if you can see any exit holes. The forester should have seen them if they were there, so this is only a guess. The holes are smaller than the lead in a pencil. If that is the case, you are probably better off having the tree removed.

Q: I saw your question and answer page for cottonwood trees, so I hope you can help me with my concerns. We took over the management of a 40-year-old apartment complex. The original developer had planted cottonwood trees next to the parking lot. The trees are so big now that the roots are growing under the parking lot and cracking the asphalt. However, removing the trees is an undesirable option for us. Is there anything we can do to manage the root structure to remediate the damage to the asphalt and prevent further damage? (email reference)

A: You can, but it might compromise the stability of the tree if too many roots are removed. There is a product known as Biobarrier ( that will keep the roots from penetrating any further in the soil. The installation usually is done by licensed contractors. You should get in touch with someone who will do the installation for you. You also should have a certified arborist do a balanced tree pruning so the trees are not top heavy and prone to falling over after the roots are removed and confined to a limited space.

Q: Can you tell me if putting coffee grounds on houseplants is good? One problem that we have is small bugs on our plants. We don’t know if coffee grounds will kill the bugs. (email reference)

A: Using coffee grounds is absolutely a good thing. The grounds will not harm the plants and it will become organic matter eventually. I would encourage attempting to work it lightly into the surface for better integration into the soil below. I do this all the time to our houseplants in the office and in our landscape. Coffee grounds also provide some small nutrient value.

Q: I planted 19 white spruce trees three weeks ago. They were out of the ground less than 24 hours before being replanted. I installed a drip irrigation system that is at the outer edge of the roots. The trees are starting to yellow in the center. Is this from the stress of the transplant? Is there something I should be doing? (email reference)

A: You are seeing normal needle desiccation for this time of year. While the trees are called evergreens, they are not forever green. The oldest needles drop off every year. In some species, the needles will stay on the tree for two, three or four years. Needle drop also can vary from year to year, depending on the stresses the plants are subjected to, such as excessively high temperatures, drought, windy conditions and flooding. Your trees are perfectly normal, but don’t start overwatering.

Q: I am having trouble growing grass. The people who tested my soil say the fertility level of my lawn is good, so there is no reason to apply fertilizer at this time. I do have a very high soluble salt content in the soil. Fixing a soluble salt problem is very difficult because the salt needs to be leached out of the soil. In late summer, most of my yard turns red and, in some spots, nothing grows. What is the best grass seed to use on soil that has a very high soluble salt content? The pH is 7.9. (email reference)

A: Very high soluble salt soil will pose a problem, even if you use salt-tolerant grasses. The most tolerant grass for northern climates is Fults alkali grass. It is not a beauty queen for looks, but it does the job. If this doesn’t take hold, then there is no other grass to recommend. Tall fescue also is a salt-tolerant grass, but not as much as the alkali grass. You could start by attempting to grow one of the many cultivars of tall fescue. If that doesn’t work, then opt for the Fults. If it is as bad as you say, then I’d just go for the most salt-tolerant alkali grass. In the western part of the state, Fults often is used where the salt levels are too high.

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

NDSU Agriculture Communication – Oct. 26, 2011

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