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Hortiscope

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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: We have potted petunias that are turning yellow, so we would appreciate your thoughts as to what to do. The plants get full sun on the south side of our house. They are watered daily and fertilized on a routine basis. Any ideas? (Fargo, N.D.)

A: My first guess is that they are being overwatered. This is easy to do, especially if the containers are not free draining and the soil is heavy. About all you can do is back off on the watering. Water the plants when the soil is dry down to the first knuckle of your index finger.

Q: I have problems with tomato blight, so my tomato crop is a total loss. Now I have brown spots on most of the leaves on my beets. Could this be blight or some type of bug infestation? Will the beets still be good to eat fresh, freeze or use for pickling? Also, is the blight situation this year going to cause a problem for next year's growing season? Thanks for any information you can send my way. (Bismarck, N.D.)

A: This could be either a leaf miner infestation or fungal spots showing up. The best thing you can do this year is to remove the affected foliage as the spots appear. For next year, don't manure the soil, practice crop rotation and clean up all the garden litter this fall. Turn the soil over before it freezes this fall.

Q: I am redoing some landscaping and would like to move some bulbs. I have tulips, daffodils, lilies and irises. If I dig these up now, how long will they last before I need to replant them? How should I store them until I am ready? (e-mail reference)

A: All the bulbs can be dug up and stored for a few weeks before planting. Don't wash the bulbs! Just knock off most of the soil. Keep the bulbs out of direct sun, cover with mulch or store in a cool basement until ready to plant. Replant only healthy stock.

Q: My established hostas are fine, but the ones I planted this spring have tiny holes on the leaves. What is eating them and what can I do about it? (e-mail reference)

A: Very likely your problem is slugs. There are several materials on the market that will take care of slugs. It is almost never fatal to these plants because slugs and hostas evolved together. You also can get some beer and pour it into a shallow pie tin. Set the pie tin into the soil to attract the slugs. They will fall in and drown.

Q: I’ve had my fishhook cactus now for almost 10 years. We brought it outside for the summer sun. All of a sudden, some of the tops of the cactus plant started to turn a brownish-red color and are turning white in some places. Could you possibly help me in finding out what is going on and how I might be able to save my cactus? I would greatly appreciate it. (e-mail reference)

A: I don't think you have anything to worry about. The cactus is reacting to being put in full sunlight after a winter of darkness. Like humans who react to their first full day in the sun by getting sunburned, the same thing happens to plants. I predict that if you moved it into a semishady spot, such as under a tree, it will recover from this shock with no harm being done to the plant.

Q: I saw a schefflera actinophylla (umbrella tree) at my doctor’s office. I’m planning to grow one because I want a large plant in my front window. However, I read this plant can grow to more than 20 feet tall. Can I keep this plant trimmed so it will not grow into the ceiling? (e-mail reference)

A: You certainly can limit the height of this plant. You can do it by selective and careful pruning or limiting the size of the container. Enjoy!

Q: I found your Web site and picked up some valuable information. Thank you. I have a question specific to moving to a new home. The water in our new home is really hard. The previous owners put in a good water-softening system and an under-the-sink reverse osmosis system. I know I can't water my plants with soft water, but what about the RO water? Can I use this water and add additional fertilizer? Can you recommend a good fertilizer to use with an RO system? I don't have many houseplants, but those I do have are ones I treasure and don't want to lose them. (Casa Grande, Ariz.)

A: You are right on the mark with the RO water. It probably is set at about 10 parts per million of dissolved salts, which is about as pure as you can get it without going distilled. This is the best water to use for houseplants because you will not be getting any confounding elements, such as salts, that would be tying up your fertilization attempts. Keep in mind that fertilization is effective when plants are growing actively, which is roughly between March and October. During the rest of the year, fertilization is not recommended. Which is the best houseplant fertilizer for you to use? This will depend on the types of plants being grown, cultural conditions and your schedule. In general, foliage houseplants appreciate fertilizers high in nitrogen, while flowering plants respond best to those with higher phosphorus. There are plenty of specialty houseplant fertilizers out there, so make sure you examine the labels. Often the difference is more in the packaging than in the amounts or proportions of nutrients supplied. Frequently, houseplant lovers amass quite a collection of different plant species. Sometimes plants have specific fertility requirements, but usually an all-purpose, balanced fertilizer can be applied to all the plants. For example, a balanced fertilizer is one in which the three numbers on the package are equivalent or just about equal, such as a 20-20-20 or a 10-8-7. Houseplants are overfertilized unintentionally by their owners because they think that if the label calls for an application every two weeks, then weekly applications would be better. If the plants are not in freely draining containers, the salts will tend to accumulate with the result being partial root death and browning along the edges of the foliage. Should this ever happen to you, use your RO water to flush the excess salts out after repotting in a container that drains well.

Q: I’m having a problem with my tiger and day lilies. I divided many of them last year. Both the transplanted and stable plants are small and losing leaves. It’s surprising because they are always hardy and started the season looking great. A couple of things have changed this year. First, we added an irrigation system that uses lake water. We also put down a weed barrier around the lilies. Could the soil be too moist? Could we have a pest problem? The rest of our plants seem fine. (Missouri)

A: Take up the weed barrier and back off on the watering. They don't need as much water as most people give them!

Q: I left my umbrella plant out in the rain. Now the leaves have drooped and it looks like it's dying. Should I cut it back? If so, from what point? (e-mail reference)

A: It should recover from a summer shower without any problems. Let it be unless the roots are standing in water. If so, pour it off or get the roots free from being immersed in water.

Q: I’ve tried growing pumpkins for the first time this year. Of the three that I planted, one survived, but it is growing very well. I've never watered or fertilized, so I’m impressed. It’s taken up an extraordinary amount of space sprawling endlessly into my backyard, which I don't mind because it is less to mow. However, I only have one large green pumpkin. There are yellow flowers everywhere, but only one pumpkin. Is this normal? Should I pick the pumpkin to stimulate more to grow? If I pick it, will it turn orange if I leave it out in the sun? (e-mail reference)

A: If you want it to turn orange, let it stay on the vine. Pumpkins picked green will rot that same color. It could be the flowers you are seeing are males and that the only female flower is the one that produced the pumpkin. If by chance you get more pumpkins setting up this late in the season, I would remove them right away and let the plant put its energy into the one pumpkin because it is too late for any fruit to mature.

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 ronald.smith@ndsu.edu.


NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161, ronald.smith@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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