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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: Do weigela bushes need sun all day or can they be planted in a shady area? (e-mail reference)

A: They will do best in full sun, OK in dappled shade and poorly in full shade.

Q: I just received nine thuja green giants in pots. I live in northern Utah. The temperature has been between 6 and 25 degrees this week, so the ground is frozen. How should I care for my trees? (e-mail reference)

A: Fortunately these are the hardiest of arborvitaes, so their chance of survival will be better than most. You want to get the trees as hydrated as possible before moving them outside. I encourage you to completely soak the rootball as soon as possible. Then move the pots outdoors and build a small shelter around them made of potting soil and mulch. Place the pots as close to your house on the north side as possible. Once the rootball is frozen, you want to keep it that way until the spring thaw arrives. Protecting the roots like this from the extremes in low temperatures will help their survival chances.

Q: Please help us figure out what is wrong with our fiddle leaf fig. I love our tree, but it has started getting more brown spots on it and, the past few days, it has dropped a leaf a day. I noticed your responses on the Web, so I checked for scales, mites and other bugs, but do not seem to find any signs of infestation. The light conditions in our home are similar to that of the store. When we first got it, it dropped a few leaves, but we figured that was due to the stress of moving and it seemed to recover. Now we have the heat on and the air is drier than it was. However, I'm afraid to overwater it because I know these plants are sensitive. We have hard water and use a water softener, but we bring water in from outside for the plant. Since it is winter, the plant is getting less light than usual. The plant gets indirect light that is not too bright, but only for an hour or two a day (we have a lot of trees in our yard). The fig is in a room with north- and east-facing windows. Please help me save our tree. Am I not watering enough? Is it not getting enough light or does it need fertilizer? (e-mail reference)

A: This looks like salt toxicity getting started. Is the container the plant is in free draining? If not, get it out of there as soon as possible and get it into a container that allows water to drain through so you can dump the excess. Other problems that could cause the same symptoms are dry air, low light or root decay. Go to for our revised houseplant problem-solving publication. It will help you determine what the problem may be and how to solve it.

Q: I planted tulip, crocus and wildflower bulbs in two large pots. I've never done it before and now I'm confused about the next step. I planted these bulbs in October. It was a little late in the season, but our weather has been uncommonly warm. I placed the pots in an unheated garage, but it is insulated. Last week, I took a few bulbs out and they had nice roots on them. Victory! Do I now put them outside in the freezing temperatures or can I leave them in the garage where they will freeze as the temperatures continue to get colder? (e-mail reference)

A: Put them outside because these are hardy bulbs that will not be hurt. They also can respond better to the changes in weather and daylight. You accomplished what you wanted, which was to get the roots established. As the snow falls, you might want to mulch the entire planter so the temperature stays stabilized.

Q: I have a question about a cut rose I got last November that rooted in June. I planted it in a container and it has grown more than 12 inches tall. It has plenty of foliage and two buds. I live in Colorado and the cold is here. I have taken it outside in the mornings and brought it in for the night. Should I let it stay outside to let Mother Nature take its course the same as my other rose bushes or baby it this winter because it is a new plant? I appreciate any insight you might have. (Colorado)

A: My best guess is that this cut rose came from a florist who purchased it from a rose grower. The plant probably was grown in a greenhouse. Greenhouse roses are not adapted to anything other than greenhouse environments, so your new rose would make a poor candidate for surviving in the great outdoors of Colorado. That said, if you got this rose from a neighbor, then there is every chance for this plant to survive and I would encourage you to get it planted outside as soon as possible to get it acclimated to Colorado weather.

Q: I was looking for information on the Web about walnut trees and found your name. I have a walnut tree in my backyard. Although I love the shade, the tree is a real pain (walnuts, squirrels, sap and broken branches). Is there any way to treat a walnut tree so that it does not bear fruit or do I just need to bite the bullet and get rid of the tree? (e-mail reference)

A: There are fruit abortion products on the market that cause the fruit to drop when it is about the size of a pinhead. That's in a perfect world where everything does what it is supposed to do. They are so hit and miss in their effectiveness that the owner usually ends up frustrated and has the offending tree removed. You might check to see if there is any local market for the wood. If it is a decent tree with a straight trunk going up 10 to15 feet before it branches out, you might get enough for the wood to offset the cost of removing the tree.

Q: I have an 85-gallon fish tank that I would like to plant cactus in. Is this feasible? The fish tank is in the basement with no natural light. There is a fish tank light on it. Would that type of lighting work or what type of lighting do I need? How deep would I need the soil to be and how far down should I plant? Are there certain types of cactus plants that would work better for this? I have potting soil for cactus/succulents or can I use sand so that it looks like the desert? There is no drainage, so how would I address that problem? The room where the fish tank is located houses the furnace, which means it is warmer in the winter and cooler in the summer. The plan is to move the tank to a place where there is more natural light, but it’s not an option at this time. Should I wait until I am able to place the tank in a place where there is more natural light? If so, would the best spot be a north, south, east or west window? (Detroit, Mich.)

A: If you choose to grow cactus or any other houseplant in this tank, I would suggest using the potting soil mix specific for the species. In this case, the cactus/succulent mix. Since the tank has no free drainage, I would advise putting a layer of activated charcoal (about 1/2 inch thick) in the bottom to offset the accumulation of excess salts. If you want a more realistic appearance, then cover the top of the mix with just enough sand to be convincing. It is better to have deeper soil, especially since there is no free drainage. Light is an important issue. Get and use a plant light because it would be the only source of energy available to the plants for growth. Replace the bulb after one year, even if it doesn't look any duller. Get a timer and set it for 12-plus hours of light every day. If you choose to wait until there can be enough natural light, then as much unobstructed light as possible should be sought out for the placement. Usually, it is a south or west window. During the winter months, you probably will have to supplement the natural light with a plant light to keep the plants thriving.

Q: I want to plant an old-fashioned lilac bush close to my 70-year-old oak tree. We can’t seem to grow grass in the area because of the oak tree, so I’m wondering if a lilac would survive. (e-mail reference)

A: An old oak tree casts a dense shade, while a lilac needs full sunlight to grow properly and to flower. A lilac probably would grow, but not very well, especially if the shade is so dense that grass is unable to grow. Why not consider ground cover or shrubs that are tolerant to shade? Check with your local nurseries or Extension Service office to see if they have any suggestions.

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

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