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Ron Smith answers questions about the world of plants, trees and gardens.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have some rhubarb plants with leaves that are turning brown and have holes in them. (e-mail reference)

A: It sounds like the rhubarb is being kept too wet or the plants are in a poor drainage situation. The holes in the leaves probably are being caused by slugs.

Q: I have a huge spruce tree that was planted in the 1950s, but has been severely damaged by spider mites. I was told by a local arborist that he could release some predatory mites on the tree to kill the mites. Should I invest in doing something like this or should I have it removed? If I stand under the tree, all I see are brown branches with no needles. The only healthy needles are on the tips of the branches. Will any part of this tree turn green again? (e-mail reference)

A: Spider mites may be just part of the problem, so I advise against investing in the predatory mite control. The brown branches will remain that way. The tree is very old, and in that environment, multiple problems are bound to arise. You would be better off removing the tree and replanting something for the next generation.

Q: I have three different species of trees I use for a windbreak. The three species are ponderosa pine, green ash and common lilac. I'm looking for a herbicide to kill broadleaf weeds between the rows. What would you recommend? (e-mail reference)

A: You might be able to use Plateau. Go to for a listing of possible choices based on your particular conditions. This information was developed by Richard Zollinger, a weed specialist at NDSU. The information was updated for 2008.

Q: I have a flowering crab that I believe may be suffering from apple scab. I know that we need to clean up all the leaves after they fall from the branches, but I was wondering if it is bad to leave mulch under the tree. We like to do that because we live in such a dry climate. However, could doing that be contributing to our problem? This spring was unusually wet, so I was wondering if that is the cause of our problem. (e-mail reference)

A: Wet springs usually equal apple scab fungus on susceptible cultivars. Yours may be one of those. Leaf cleanup is a big first step. The mulch under the tree should not have an impact on the scab organism. Next spring, spray the tree with lime-sulfur just before the leaves and blossoms open up to help prevent a recurrence.

Q: We have a large pussy willow in our backyard. I noticed some sap running down the branches last spring. Today, I noticed there are bald areas on each branch just a few inches from the tips. There are some leaves on the tips. I also have noticed black patches on some leaves and what looks like a kind of grey mite or larvae on the lower branches. What can I do about this problem? Also, the leaves are much smaller than usual for this time of year. (e-mail reference)

A: Sounds like borer activity is getting started. I'd suggest getting some Bayer Advanced Tree and Shrub Insecticide. Be sure to follow the directions on the label. This material has worked well.

Q: We just moved to a new house, so I brought my iris bulbs to transplant into a new bed. Right now the bulbs are in a planter. Should I wait to put them in the ground or go ahead and plant them? Also, what type of sun conditions do they need? (e-mail reference)

A: If they have finished blooming, go ahead and plant them. The more sun, the better the bloom will be.

Q: I am wondering who I would talk to about our sod. A builder put down 10 truckloads of sand, but that only leaves about 2 inches for black dirt. I know that isn't enough for the sod, so I was wondering how much black dirt the builder needs to put down so the grass will grow as it should. (e-mail reference)

A: It is possible to grow sod on just 2 inches of topsoil, but it would require very tight management and extensive input of resources to do so. A depth of 4 to 6 inches is much better and easily will support Kentucky bluegrass or a mixture of such with perennial rye and creeping red fescue.

Q: I was at a local retail store and noticed that some spider plant babies had fallen off the mother plants. I picked them all up and asked if I could have them because I knew they would be thrown away. They told me it was OK for me to take them. I brought them home, put them into water for about a month and then planted them in potting soil. They are doing great and looking very healthy. I know it is time to put them into bigger pots. What sized pots should I put them in? Should I leave together the six to seven babies that are in each pot? Any help would be greatly appreciated because I am very attached to these plants. I feel like their mother. (e-mail reference)

A: By now, they have tangled their roots together, so it would be difficult to separate the plants at this point and have them survive. I would suggest moving them into the next nominally sized pot. Let them stay there until they start producing some offspring on their own. When it appears that the conjoined plants are pushing out of the container, you will have a couple of choices to make. You could split them in half or quarters with a sharp knife and put them back in the same sized pots or move them up to a larger pot. Eventually, there will be a physical limitation as to how large you want these plants to become. They gain weight as they continue to get older and larger.

Q: We have large holes in our string bean leaves. What could be doing this? We put some Garden Guard on them, but would like to hear what you recommend. (e-mail reference)

A: If there is no visible evidence of munching critters, they probably have moved on or predators took care of them. Bean beetles and caterpillars are candidates. As long as the plants have recovered, I wouldn't worry too much about this, but continue to monitor your garden on a daily basis.

Q: I have two apple trees. On some of the branches, there is something that looks like a brown scab. If you pinch it, it crumbles in your hand. Also, the leaves are turning yellow and have black spots. Can you tell me what this is? (e-mail reference)

A: A diagnosis is difficult with the little bit of information you provided, so this is an educated guess. Your problem could be scale insects and apple scab. Scale insects can be controlled with a light horticultural oil. The scab can be controlled using a Bordeaux mixture or Funginex fungicides. It would be better if you went to a local garden center or found a master gardener in your community who could assist you with more accurate advice than I can.

Q: We have an abundance of mushrooms in our lawn. How do we get rid of them? (e-mail reference)

A: Mushrooms show up when the soil is moist for extended periods of time and an abundance of decaying organic matter, such as rotting tree roots, construction wood or excess thatch, exists. There is no chemical control. If you are watering your lawn, back off. You can pick the mushrooms and throw them away. If you or your spouse are golfers, use them to practice your golf swing. Just keep children from eating them.

Q: I've noticed some round spots in my front lawn this year. The biggest spot is about the size of a soccer ball. The grass in these areas is darker in color, with thin, but dense, leaves. These areas feel very firm and hard. Is this anything to worry about? If so, what should I do? I have a very nice, well-kept lawn. I'd hate to see anything spoil it. (e-mail reference)

A: This sounds like one of the forms of fairy ring fungus. You may want to rent a core aerator and go over the entire lawn. Do this sometime after Aug. 15, but before Sept. 15. When done, fertilize and apply a wetting agent to the raised or hardened areas. Water heavily after that. If you don't have an automatic irrigation system or a decent movable one, then wait until a good rain is in the forecast and complete these tasks just before the weather opens up.

Q: I read your column in the Aberdeen Green Sheet each week. I hope you can help us. Our zucchini plants looked healthy, but now they are drying up. When my husband pulled one out, the roots looked like something was eating on them. Can you tell us what to do? We don't want to lose our other plants. (e-mail reference)

A: This could be grubs feeding on the roots. Try to find evidence of their activity in the soil before applying an insecticide. They shouldn't be hard to find. Assuming it is grubs, apply some granular Sevin insecticide around the remaining plants and water in. Thanks for being a faithful reader.

Q: I know some folks who are having problems with plum trees suckering. Is suckering common with red diamond cherry plum trees? I just planted two of these trees in my backyard. I am not wild about the thought of having to worry about new trees coming up or having a root system that is that aggressive. Is there a way to prevent this from happening? Also, the tag on the trees when I bought them says to use a compass cherry as a pollinator. I’ve not seen that variety in the few places I’ve looked. Can another variety pollinate my plum trees? How long before I can expect the trees to bear fruit? (Moorhead, Minn.)

A: I don't know the suckering potential of this cultivar. It is something that breeders have to eliminate or minimize due to many complaints. If the tag stated that a compass cherry should be the pollinator, I don't think anything else would be too successful. Generally, it takes three to five years to get decent fruit production.

Q: My father planted two royal red maples in our front lawn about 18 years ago. He is positive they are royal reds and they do have the characteristics. Both trees have been red through the summer, even though we have been told they are sometimes green during the summer months. This year, both trees are green and only the new shoots are red. I've been searching endlessly to try to figure out if there is something wrong with the trees. I came across your e-mail address, so I hope you can help me with a response. The trees seem to be in decent shape. The trunks and branches are all fine and we have no new pests this summer. The trees are watered and fertilized on a regular basis. My father treats them like a part of the family. In addition, this green is not a bright, healthy green. It is a sickly green. It's very strange. Thank you for your time. (e-mail reference)

A: This is normal, so stop worrying about it. The chlorophyll is winning out in the war of expression over the red pigment. It is not uncommon for this to occur in trees with leaves colored something other than green.

Q: I am new to planting gardens. I just bought two crepe myrtle trees and I am wondering what type of dirt should go in the hole once I dig it. Would Miracle-Gro work? (e-mail reference)

A: If you haven't planted them, backfill with the soil you removed to dig the hole. They don't need any special soil.

Q: We moved two maples and an ash tree to different locations on our property last spring. We moved them because they were losing space and sun in a tree row. We are concerned about them making the winter. Is there anything we need to do? For now, they look good. We water the trees a lot. We also would like to know how long we need to keep them supported. Any help you can give us would be greatly appreciated. (e-mail reference)

A: Stop trying to straighten them out. Let the wind move them and don't water any more than once every seven to 10 days or the trees will be delayed in hardening off for the winter. In a year or two when they are established, you can do some corrective pruning to improve their overall form.

Q: The honeycrisp apple tree in my backyard never blossoms in the spring. It is 3 years old. Some of the bark has been damaged by deer that live in our suburban Minneapolis neighborhood, but otherwise the tree looks healthy. I seem to recall that the tree had blossoms on it when I planted it, but never has had any since. (e-mail reference)

A: It will get around to blooming and bearing fruit, but I’m assuming there are crabapples or other apple trees in the neighborhood. It often takes three to five years for a tree to bear fruit after it has been planted. Don't get carried away with high-nitrogen fertilizers (the ones used for lawns) or else it will continue to remain vegetative and not go into the reproductive stage of growth.

NDSU Agriculture Communication

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