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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 large silver maple tree in my front yard close to a sidewalk. It has raised my sidewalk about 4 inches, so I will have to replace the sidewalk. I also have had problems with tree roots blocking my sewer discharge line. I would like to kill the tree as soon as I can and remove it. What is the best and easiest way to do this? (e-mail reference)

A: I regret telling you how to kill an established silver maple tree. Hire an International Society of Arboriculture certified arborist to cut the tree down and grind the stump and visible roots. This will get the job done cleanly and neatly without needing to use toxic materials.

Q: I have a black thumb when it comes to plants, but I have had some success with a rope hoya. It was doing well for three years. However, all of a sudden, two strands of the plant have shriveled leaves. The others look great. Last year, I forgot to water it one week, so all the leaves shriveled. I watered it and left it in the bathroom when I showered. The leaves came back fine. This time, nothing is bringing those two strands back. I don't overwater the plant. Any suggestions would be very helpful. (e-mail reference)

A: If a steamy bathroom from showering cannot bring these strands back, then they are dead. I would suggest cutting those strands back to keep any pathogens from getting started in the remaining living portions of the plant. Hoya is one plant that will tolerate dry indoor winter conditions. However, there is a difference between tolerance and thriving. If I had to, I could tolerate brussels sprouts if there were nothing else in the world to eat, but I would thrive on a well-balanced diet of fruits, veggies and whole grains. The same applies to your hoya or any other houseplant other than a desert cactus. They can get by with winter's dry interior air but would thrive with a visit to the bathroom when you shower. It doesn't have to happen every time, just occasionally. All houseplants need to have their watering schedule adjusted during the winter and get their light duration and intensity increased. Supplement the light coming in with an artificial light on a timer set for 14 hours. Do it through March.

Q: What are the perfect months to trim a spruce or pine tree? (e-mail reference)

A: Spring is the best time if I need to give a season to your question. Spruce trees need very little, if any, pruning. However, you may cut the new shoots to half their length throughout the tree to shape and retard growth. Make sure it is done with a hand pruner, not hedge shears. Use the same technique on pine trees unless you are grooming them to be full Christmas trees. In that case, a machete is used by commercial growers. On either evergreen species, if an entire branch is removed, it will not grow back. This is sometimes practiced on spruce trees as they get older to allow for better air circulation and to cut down on snow drifts. On either species, remove any secondary growth to keep it from competing with the main trunk. Reach in or up and cut it out where it originates.

Q: I have just discovered my jade plant is covered in what I think are brown scales. Can you please tell me how I can get rid of them? I seem to recall they are hard to control. Hope you have an easy fix! (e-mail reference)

A: It could be scale or edema from overwatering. Do a test by scraping some off with your fingernail to see if there is any sign of an insect. If not, then it is just a corky lesion that has developed. Think of it as freckles on the foliage. The reason I’m a little suspicious is that scale usually attach themselves on the stems. If on the foliage, they would be on the underside of the leaf. However, Mother Nature abounds with exceptions to the expected. Another reason for my suspicion is the plant looks too healthy to support that heavy of an infestation of scale. If this does turn out to be scale, then you would need to find a systemic insecticide for houseplants at a local retail outlet. Apply it according to label directions. You have way too many to swab off with alcohol or with a topical application of any insecticide.

Q: I found your information on Christmas cactus care while I was looking for information on whether or not to pinch or remove dead flowers from my cactus. I read all the information, but I didn’t find an answer to my questions. Can you tell me whether I should remove these wilted or dead flowers or should I let them drop off? (e-mail reference)

A: Allowing the spent flowers to remain will not hurt anything except the attractive looks of the plant. If you choose to remove them, do so carefully so you do not damage the plant.

Q: I came across your Web page while searching for information on the best time to plant tulips. I read through the information but didn't see my question answered, so I thought I would ask to make sure I do the right thing. Due to my job, I am a regular visitor to the Netherlands. This time, I decided to grab a bag of 60 tulip bulbs at the Amsterdam airport. I’m thinking I can give some to people as a Christmas present. I live in northern California, where most people who I will give them to also live. I saw from the questions asked that it was best to plant them in September. Unfortunately, I just got back from the Netherlands two weeks ago, so it is too late. I also plan to give my sister some bulbs. She lives in Tennessee. I saw people do a couple of different things when planting the bulbs. Some planted now and all was OK. I also noticed some people store the tulip bulbs in the fridge or a cool place. Thank you very much in advance for your suggestions. (e-mail reference)

A: Sounds like a nice job to have. If the ground is not covered with snow or isn’t frozen, go ahead and plant them now. The bulbs will need to go through a normal chilling process unless the bag of bulbs states that they are ready to bloom without any prechilling needed. Depending on where your sister lives in Tennessee, she might have to give them a refrigeration treatment for 60 to 90 days before setting them out. The temperatures may not get low enough to get the bulbs to rebloom. Also, the temperature in Tennessee gets too hot too quickly. This wastes the foliage without the rebuilding of carbohydrates stored in the withered bulb. Tulip and other cool-season bulbs are used often as flowering annuals in the deep part of the South, where the temperatures get too hot and the winters don't get cool enough for dependable reblooming. When I lived in Georgia, people would plant bulbs in the late fall, allow them to bloom and dig them up for disposal every spring once the flowers were spent.

Q: I have a question about a small lilac bush. Can I transplant it now or do I need to wait until spring? I would like to get it done if it will not hurt the bush. Our ground is not frozen. Thank you so much. (e-mail reference)

A: If the soil is not frozen, you can transplant it now if needed. It also could be transplanted in the spring once the ground thaws. Generally, spring shrub transplanting is a more successful operation because the plant is moving into the growing season with warmer temperatures and increasing moisture.

Q: We have a spider plant we kept outside during the summer. After we brought it inside, the tips started to turn brown. We water it once every two weeks and give it plant food once a month. We have had healthy babies, but we don’t understand why the tips are turning brown. We live in northern New Jersey, if that makes a difference. What can we do to stop this from happening to the plant? Any input would be appreciated. (e-mail reference)

A: Allow me to direct you to my website at for information on houseplants. Your problem comes from either too much salt in the water or from continuous fertilization that has built up in the root area. It also could be the fluoride in your water source. If it really drives you crazy, I would suggest backing off on the fertilization schedule and water with distilled water for a few weeks to see if you get new growth without the dead leaf tips. The plant also might benefit from repotting if it has been some time since you did that.

Q: I have some goldfinger potentilla and pink beauty potentilla shrubs. Grass is growing around the shrubs, but I cannot get between the branches to remove the grass. Can I spray the grass with Ortho Weed and Grass Killer or will it kill the shrubs? (e-mail reference)

A: If the word “weed” is on the label, I would advise against using it. Read the label to see if it is safe for use on woody plants. I’m betting it is not because one of the active ingredients is for broadleaf control. Look for a product that is labeled strictly for grassy weed control. Apply it next year because our winter weather is going to occupy our concerns for the next four to five months!

Q: My high school biology class is doing a planting project. I have chosen to plant a pale purple coneflower. I'm doing a planting calendar and report about the plant. However, the information I can't seem to find is how often it should be watered and how much I should use. I also have found conflicting opinions about how long the cold-stratification process should last before planting. I am hoping you can help me with this. (e-mail reference)

A: Glad to assist whenever I can. I have to admit to not knowing of any particular length of cold treatment. I have had success with either sowing them in the fall and allowing Mother Nature to do all the work or simply stratifying them for 90 days at refrigerator crisper temperatures (40 degrees). This is considered a default low temperature treatment when there is no clear research on the subject. What I have found is that the seed usually is low in viability (less than 50 percent). If one wants to grow them outdoors for beauty or research purposes, allow Mother Nature to do most the work because she can get them to germinate better than I can indoors. This probably hasn’t helped much, but this is the way I have worked with this very beautiful perennial in the past.

Q: I have two dieffenbachia plants in my home from a plant at the office. Last weekend, my husband and I changed the soil because it was too wet and had flying bugs. The bugs were travelling through my house and were very annoying. Since the roots were so wet for so long, I decided not to give the plants water until I returned home the following weekend. When I did return, the leaves were droopy and look as if they will wilt away. I took the plants out of the soil and placed them in a tall bucket with enough water to cover the roots. Did I do the right thing and will my plants come back? I take care of all the plants at my job and they are growing beautifully. By the way, I live in Pennsylvania, so the climate is very cold. Do you think this could be the problem also? (e-mail reference)

A: It sounds as if you had the plants in sealed containers instead of freely draining pots. You did the right thing in replacing the soil. The mistake you made was not watering in the freshly replanted dieffenbachia. This always needs to be done with a fresh repotting to get the soil particles into intimate contact with the roots. The fact that this did not take place allowed the roots to be exposed to more air than needed, which caused dehydration and wilting. If the plants are going to recover should be apparent in about 24 hours. If the plant is still wilted after an overnight soaking, then all is probably lost. You mention Pennsylvania and cold weather. I assume you are keeping the plants at room temperature in your house and not placing them outdoors this late in the fall. Being cold outside would have little to no bearing on a plant kept indoors unless the temperatures were allowed to get too low. Go to for answers to many houseplant questions.

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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