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Published March 11, 2011, 12:00 AM

Hortiscope: Garden crops should be rotated every year

Q: For the past two years, my squash plants have wilted and died. Also, the roots and stems become mushy. Last summer, I found what looked like grubs (white worm with a black spot on the head) on the roots. What can I do to prevent this next year?

By: Don Kinzler, INFORUM

Q: For the past two years, my squash plants have wilted and died. Also, the roots and stems become mushy. Last summer, I found what looked like grubs (white worm with a black spot on the head) on the roots. What can I do to prevent this next year? (e-mail reference)

A: First thing, rotate your squash planting sites. Planting in the same location every year will make life too easy for insects and diseases to settle in to what they do best, which is destroying host-specific crops. In other words, plant something totally unrelated to squash, such as peppers, tomatoes, beans, cabbage or corn. Keep this up every year so that you are not planting the same crop again for at least three years.

Be an unreasonable fanatic about garden hygiene. This means no litter or weeds allowed and turning the soil over early to expose any diseased plant parts or insects that may have burrowed into the soil. Finally, do all you can to optimize good drainage by adding organic matter, such as compost or sphagnum peat moss. There are many pesticides that you can use to prevent or correct insect or disease problems. However, I am loathe to recommend anything for vegetable gardening because that defeats the whole purpose behind growing one’s own vegetables, which is to have them pesticide free.

Q: I hope this finds you well and anxious for spring! What can you tell me about the portulaca houseplant? I have a client who has one, but it has problems. The plant has lost all of its leaves. (e-mail reference)

A: You bet I’m anxious for spring! What I can tell you about this plant is that it has no business being treated as a houseplant. It is a full-sun annual that needs more heat and sunlight than any house interior can provide. End of story.

Q: I have a few questions about my new lilac plant because I definitely do not have a green thumb. I am not sure what type of lilac it is. It has pink flowers. Does the care differ for each type of lilac? Do lilacs survive in clay pots? Right now, I don’t have a place to plant it outdoors. Finally, I noticed that some of the flowers on the stem have begun to shrivel. Should I remove them or wait? I appreciate all the help you can offer. (e-mail reference)

A: Lilacs growing in containers are going to become stressed after one growing season. Lilacs should be planted in their final site outdoors as soon as possible. As the flowers fade on the plant, it is a good idea to remove them with pruners to keep the plant from attempting to make seed, which is a big energy consumer. It is better to allow the plant to use that energy for growth and establishing itself in the new location.

Q: I’ve had a fichus tree for about 10 years. It has done well in the southeastern corner of my kitchen. However, I recently had my windows replaced. Since then, I’ve noticed that the bottom half of the tree has curled and dry leaves, but they are still green. Could the tree have frostbite? Will it come back? The top branches look fine. (e-mail reference)

A: Frostbite doesn’t manifest itself that way, so I suspect the plant has some sort of insect activity going on. If the symptoms were limited to just a few leaves, I’d snip them off as soon as possible and throw them away. After that, monitor the plant for any evidence of insect infestation taking place. Be especially suspicious of scale activity.

Q: I have a cyclamen question. I’ve had my cyclamen for a year and it has come through a complete cycle successfully (absolute luck on my part). At one point, I thought the plant was dead, so I was getting ready to throw it away. However, I discovered it was a bulb plant, so I decided to replant it in a new container. I kept it outside all summer and brought it inside in the fall. I put it in my sun garden window and it bloomed again. Right now, most of the blooms are gone. All you see on the plant right now are long stems and leaves that have congregated at the rim of the pot. What has caused this? The leaves are green, but the plant isn’t very attractive. Perhaps I’m not being accepting of this new look. However, I don’t think my plant is doing what other cyclamen plants do. What are your thoughts? Thanks for any help you can give me. (e-mail reference)

A: It could be that the plant is trying to enter its resting period. Begin withholding water to allow the foliage to wither and die back. Repeat what you did last summer by putting it outdoors on your patio because you had so much success doing this last year. I want you to know that cyclamen plants often are considered throwaway plants. Once they flower and the foliage begins to fade, most folks will dump the plant rather than attempt to keep it going, so congratulations on being ahead of the curve.

Q: I have been following your advice about hazelnut trees. I sent for the catalog from St. Lawrence Nursery but haven’t heard back. Are what we call filberts the same as hazelnuts? If so, can I start a hazelnut tree from the nuts we get in the mixed-nut assortment from the grocery store? How do I go about starting a tree from seed? Please advise me at your convenience. I enjoy your column. (e-mail reference)

A: Good question! We are talking about the same genus (Corylus). In the case of the hazelnut, this is the Corylus avellana that has several cultivars. Contorta is the most popular landscape novelty. Corylus americana is the American hazel or filbert and probably is what is seen in supermarkets. As to whether they will germinate, I don’t know. They may have been irradiated to prevent decay. If so, it would eliminate any chance of germinating the seeds, but it might be worth a try. The St. Lawrence Nursery catalog can be downloaded at As with most small and large companies, it is attempting to become more paperless as a way of saving money and reducing the carbon footprint.

Q: I found your website dealing with problems that occur with amaryllis plants, so I’m hoping that you can help me. This was the second year for my plant and everything was going well. It had a flower stack with four buds and I was anticipating a pleasing bloom, although it did seem to take a long time for the buds to break. However, suddenly something went wrong. I noticed that the flower stalk seemed transparent. The stem seemed to be hollow when I touched it. In other words, it was soft to the touch. A few days later, the stalk took on a brownish hue and the base of the buds started turning black. Also, I could see and feel the vascular system within the flower stalk.

A few days later, I discovered that the flower stalk had collapsed. As there was nothing I could do to salvage the flower stalk, I cut it off just below where the stalk collapsed. The leaves on the plant looked fine throughout this time. In fact, a new leaf is developing from where the flower stalk used to be. Whatever happened did not affect the entire plant because parts of it are healthy. I have not been able to find any information on the symptoms that were exhibited by my plant. I hope you can help me so I don’t have this problem again next year. (e-mail reference)

A: I have to say that I’ve never heard of this particular problem with amaryllis plants, so my answer will be confined to well-educated guesses. Let’s start by going back to the rest period. Did you allow the bulb to develop all the foliage and then begin the dry-down process in early summer by gradually withholding water? I suspect what happened is the bulb did not store enough energy or wasn’t in strong enough light to sustain the flowering cycle.

The best success stories are the ones where people have moved the bulb outdoors when in full leaf and then begin the drying process sometime around mid-July. After the leaves have completely yellowed, remove them and place the bulb in a cool, dry location until you are ready to push the blooming cycle. For most people, this takes place in October to get a flower show between the Thanksgiving and Christmas holidays.

The flowering/reproductive cycle is the energy expenditure peak for any flowering plant. Insufficient energy stores would, in my mind, compromise the plant’s flowering ability and bring the results you described. This is the best answer I can come up with for you. If anyone has a better one based on experience, I’ll gladly pass it on to you.

Q: I found your address on the NDSU Hortiscope page. I have a question about an elm tree (I think it is probably an American elm) that I want to have trimmed this spring. It is a beautiful, large elm, but I am concerned about Dutch elm disease. The tree service I am considering hiring has indicated to me that it does not sanitize its saws, which is a practice I have seen suggested on various websites to avoid the spread of Dutch elm. What is your experience on this issue and do you think that I would be putting my tree in danger by going with a tree service that does not sanitize its cutting tools? (e-mail reference)

A: Yes, in an ideal world, the saws and pruning tools should be sanitized after every use. However, it doesn’t happen in most cases. I would check with your Extension Service agent to see if there has been any reported Dutch elm disease in recent years. If not, then you can make the assumption that the tools the tree trimmers are using will not be carrying the disease to your tree. However, Dutch elm disease isn’t the only vascular disease that afflicts this beautiful tree. If your tree is healthy and displaying normal vigor, it will take most pruning operations without many problems. Healthy trees have the ability to defend against unwanted pathogens by compartmentalizing quickly where the pruning cuts have been made. Shop around for an International Society of Arboriculture-certified arborist or company and talk about your concerns. I know good companies service their pruning equipment on a regular basis with a general cleaning. Perhaps you can get the arborist to come to your place first thing in the day so that you will not be getting any residual from a previous customer. To find an ISA arborist near you, go to

Q: I never have taken care of any type of indoor or outdoor plant, so your website has been very helpful. Thank you! I received a potted, blooming mini calla lily plant for Valentine’s Day. I have repotted it into a 10-inch clay pot with a tray underneath. I watered it and gave it houseplant fertilizer after it was repotted. I live in a condominium that faces east, so I have put my calla on my balcony to get some sun. I live in Georgia, where it has been 60 to70 degrees during the day and in the 50s during the night. As soon as I repotted it, the flowers began to droop and some of the small leaves have died. I have stopped watering it for the past few days. Have I given it too much fertilizer or not enough water? I would appreciate your advice on what I should do to bring it back and how I can care for the plant properly. (e-mail reference)

A: You should have waited until the plant dried down before repotting. Not too many plants that I know of appreciate repotting or planting while they are in the flowering stage. I would suggest keeping the plant well watered for about another month. When the danger of frost is past in your part of Georgia, move it outdoors and allow it to dry down completely for about two months. I know Georgia gets plenty of rain, so I would suggest moving the plant to a rain-protected area when the threat of a storm is in the forecast. In July, move it to where it can get plenty of water again. After new growth is apparent, maintain the water regime with a garden hose if needed. During this active time of growth, you want to be giving the plant a weekly fertilization using a diluted solution. Go to for more information on the care of calla lily plants. Good luck.

Q: We have 10 very tall spruce trees in front of our house. I would like them to stop growing taller because I am afraid the wind may blow them over. What I’ve heard is that if you trim the top of a spruce tree that it will stop growing taller and grow wider. Is this true? How much does a mature spruce tree grow a year? (e-mail reference)

A: I would advise you to contact an ISA-certified arborist to have the trees inspected for safety and possible corrective pruning. I cannot answer your question about how much a spruce tree grows each year because there are many species of spruce. All have differing growth rates. Additionally, the environment influences the rate of growth where it lives. To find someone in your area of the country for help, go to and provide the requested information to locate a company or individual near you. Be sure to check credentials before allowing any major work to be carried out on your property.

Q: I was just on your website reading about Christmas cactus plants. I was very impressed with the wealth of information provided. One post talked about a Norfolk Island pine. Could you send me the propagation technique information? Thanks (e-mail reference)

A: No problem. Information is available at

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