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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have two adult walnut trees in my yard that have green walnuts the size of golf balls. How do I know when the walnuts are ripe and ready to pick? What signs do I look for? (Franklin, N.C.)

A: They should be ripe by now or very close to it. The nut’s outer husk is dehiscent, which means the husk will split open when the fruit inside is mature. If you’ve never worked with black walnuts, be prepared to have black-stained hands for about a week or wear disposable gloves. Generally, when the local squirrel population shows an interest in the nuts also is a good barometer of when they are mature. At that point, you’d better move quickly to get any kind of a harvest!

Q: Can picking tomatoes before they are ripe lessen the chance of blossom end rot (BER) from occurring? (email reference)

A: It should, at least somewhat. The final cell formation takes place while the tomatoes are green. If BER hasn’t shown up by then, the tomato should ripen without the BER manifesting itself. By removing the tomatoes from the vine, the water pressure surges that can cause BER also are gone, so the chances of success should be increased quite a bit.

Q: The bark on my lilac tree has a green, powdery substance on it. It almost looks like a moss or mildew. Every year, the tree seems to produce fewer lilacs. I trimmed it very well this year by taking off all of the dead flower areas and any dead branches. I am worried that the tree is diseased. Is there anything I can do to treat it? (email reference)

A: This could be a combination of problems such as powdery mildew or ash/lilac borer. I encourage you to seek help locally from someone at the Extension Service. Go to to find someone in your county. The county offices often have master gardener volunteers standing by to assist in situations such as this or the agent can make a home visitation. If the problem can’t be solved with a visitation, then samples will be taken and sent to a diagnostic lab at Cornell University.

Q: I found your website while researching a tree my landscaper wants to plant in place of a dead tree he's going to take out. He wants to plant a Canadian red chokecherry. However, I am worried about planting a chokecherry tree after reading all the comments about black knot disease. Could you recommend something else that is as hardy for my area? Thank you so much in advance. (Cheyenne, Wyo.)

A: Black knot may not be such a problem in your part of the country. Check with your county office of the Extension Service to see if it is an issue. Our problem in much of North Dakota is that it was overplanted in the landscape and in shelterbelt plantings. This led to the easy spread of the disease. If you still are against selecting the Canadian red, then I’d suggest considering the spring snow crab apple cultivar. This is a beautiful, fruitless tree that is clothed in white flowers in the spring and has a nice, dense foliar cover throughout the rest of the growing season.

Q: I looked on your website and didn't see an answer to my question. My jade plant is about 12 years old and always has been very healthy. I pruned and replanted it two years ago. This summer, it was not looking healthy, so I figured that it needed to be repotted again. After I took it out of the pot, I discovered it had almost no roots and the bottom third of the pot was so wet, it was like mud. I put fresh soil in the pot, but that seemed to make it worse. After that, my 2-year- old pulled it out of the pot. When attempting to put it back in, I realized the pot had the soaked dirt again. I found part of a root buried in the dirt that must have come off the large stem. Both the buried piece and the bottom of the stem are still hard. I had not watered it and we didn't get that much rain (there is a drain hole in the pot). I am not sure what to do. The jade has a large stem, so I don't know if a smaller pot will hold it. With all the problems, I have had to make some cuttings from the soft, wilted stems. Any suggestion would be appreciated. (email reference)

A: This problem sounds like it is associated with a container that does not drain water very well. If that is the case, make a fresh diagonal cut across the bottom of the large root. Get some fresh potting soil and plant it in a pot that drains well (clay preferred). Keep the media moist but not soaked. Use an African violet soil if you can locate any in your area or a potting soil known to be high in organic matter that would have good drainage characteristics. Q: I attempted to air layer a 5-foot-tall ficus. I waited until there were enough roots and then planted it in a sandy soil mix (cactus soil mix). I use this mix because it has very good drainage properties. I kept the new tree indoors but also put it outside in direct sunlight. However, it’s shedding leaves, and the branches are drying off and becoming brittle. Is there anything I can do to save this plant? What did I do wrong? (email reference) A: You forgot one very important step. You should have put a poly tent over the cutting to keep the humidity high around the plant. This allows the limited root system to keep up with the transpiration pull being exerted by the leaves. Also, it sounds like you attempted to make an air layer on too large a part of the plant. You still may be able to save the plant if you can get the tent to cover the top of the plant and out of direct sunlight for about 10 days.

Q: I've been told that potentilla have the reputation of being a gas station plant because of its ability to sustain abuse from the vapors of cars, poor soil and lack of basic care. I've seen many of these plants live up to that reputation but look awful. However, at two locations, I’ve seen some of the most beautiful exhibits of what could be goldfinger potentilla that you'll find anywhere. One pharmacy must have close to a 100 of these plants that are in full bloom and look absolutely beautiful. There isn't a one with a flaw. At both locations, the potentillas were planted in pea gravel beds. In your opinion, what do you think they are doing to get these plants to look picture perfect even though they were planted in rocks during a very hot summer? (email reference)

A: Glad to hear that someone has planted this species and decided to take care of them for a change! It presents a good public relations image for the retailer. A couple of things could be going on. They might have brought in designer soil to facilitate good drainage and had it enriched with Osmocote (coated fertilizer). The retailers could have installed a drip irrigation system that automatically responds to soil water stress and provides adequate and consistent moisture to the root zone. Another possibility is that the potentillas are under the care of a competent landscape maintenance company that is under orders to keep the plants looking immaculate and replacing those that cannot be made to look that way. Potentillas are crowbar tough plants that thrive in our climate. They cannot be grown successfully in most parts of the eastern U.S. because of the high humidity, which causes mildew problems. As tough as our summers and winters are, these plants will survive and thrive with the right care. If you get the chance and can remember, please send me a couple of photos. I’ll use them in my talks. Thanks.

Q: Squirrels have eaten our sweet corn and chewed on our melons, squash, cucumbers and tomatoes. We’ve tried trapping, anti-animal sprays and shooting them. However, there always seem to be more of them. Do you have any ideas on how to protect future gardens? We’ve had gardens for 30 years and not had this problem. (email reference)

A: Squirrels are a problem when it comes to trying to keep garden produce. Once they discover the bounty of your garden, they get the word out. At that point, it usually turns out to be a losing battle. Exclusion fences are about the only answer. Fences are only effective if there are no tree branches hanging over the garden. What my wife and I have found that works for us is to make a source of food readily available to them on a consistent basis. She makes suet blocks using cheap peanut butter, sunflower seeds and apple bits. She hangs a block from a tree to allow for easy access. We think it is the combination of fat, peanut butter, seeds and fruit that attracts them, so they pretty much leave our garden produce alone. Visit a farm supply store and purchase some field corn still on the cob and hang it from a tree branch. They also will go after the corn. None of this is foolproof, and you have to keep changing tactics a little at a time. If any readers of this column have better or more effective solutions, I’ll pass them on.

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

For answers to general horticultural questions, go to

NDSU Agriculture Communication – Sept. 5, 2012

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