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Don Kinzler, Published March 30 2012

Hortiscope: Plum tree produces many blooms, few fruit

Q: I have several questions about gardening. I have a plum tree with many blooms but very few plums. Why would this happen? Those that grow mostly are small and turn red and blue. There is a brown film or coating around the pit in midsummer.

Why would this happen? I live in zone 3, so I am wondering if it is advisable to try to grow apricots. I was told that they seldom bear fruit. I plan to plant some Carmine jewel dwarf cherry trees. Should they be planted close together or can they be 200 feet apart? They are approved for zone 2.

I had some Fort Laramie strawberries for three years. They didn’t bear a lot of fruit but spread lots of runners. Then the plants quit bearing fruit entirely. I put some Gurney’s Strawberry Food (fertilizer) on them. They are in the shade by 3 p.m.

Thank you for your help. (Sheyenne, N.D.)

A: Your plum questions relate to several possible problems. It could be an incomplete fertilization by pollinating insects. If the bees are scant in number or if the weather is not conducive to pollination, such as windy, rainy or cold, that would limit the number and size of the fruit. All plum trees will do a better job of fruit production if there is another plum species nearby.

It is not advisable to attempt growing apricots in North Dakota, unless you have the patience of Job. You can go three, four or five years without any fruit but then have a couple of years in a row with decent fruit production. However, the tree may die the year after or remain vegetative for a couple of years. Depending on winter extremes, the tree may die from exposure to extreme cold.

Your Carmine cherries can be whatever you desire. Planting them close together gets you a handsome hedge but also a greater chance for disease problems as they age.

The fact that your strawberries produced lots of runners is a possible indication that they were getting too much nitrogen or had a virus that impacted fruit quantity and quality. As a sweeping generalization, it is recommended that a planting of a particular species of strawberries in one location be looked upon as a temporary planting that will bear well but then begin declining because of a virus.

Once this is noted, I suggest tearing out the plants. If possible, locate the new patch in a different location and use fresh stock. The former planting site can be turned into an annual vegetable or flower crop. I hope this information answers your questions.

Q: My ficus tree is growing beautifully in my backyard. We cut down a tree that was growing near the ficus tree. However, after cutting the tree down, we noticed that the tree was growing into the ficus tree, so now the ficus tree has a big bald spot. There are some small branches and leaves growing in the bald area. How long will it take until the ficus is full in that bald area? (email)

A: Leaves will grow where the sun shines, especially when it comes to ficus trees in an outdoor environment. I have no idea how long it will take because I don’t know the overall condition of the tree, environment it is planted in or soil conditions. You could help regrowth along by practicing safe fertilization, which means not overdoing it. If this is something you don’t trust yourself with, then hire a certified arborist to do it properly. Some selective pruning also might help.

Q: A man just called to tell me that his caragana plants have a lot of dead areas. Can he trim them back? If so, how much and what time of the year is best? (email)

A: Anytime between now and just before new growth begins is a good time to trim the plants. In other words, whenever the spirit moves him to do it. They can be cut back to short nubs as close to the ground as possible. They will burst forth with a flurry of new growth this spring.

Q: I planted some silver maples using volunteer seedlings several years ago.

They have grown vigorously since then. However, I planted one too close to the house, but I was able to get someone to move it. After it was moved, our cats decided to sharpen their claws on the trunk. They clawed most of the way around the tree. The rather thin bark is scraped away several inches vertically. The trunk is 4 to 5 inches in diameter and protected with a chicken wire sleeve.

What can I do to keep the tree alive? (email)

A: Naughty cats. However, based on what you have told me, I don’t think the tree will have any trouble recovering on its own. The wounds should heal and leave a protective scar tissue. I would leave the chicken wire wrap on until the tree develops a corky bark in a few years. Be sure to move the chicken wire out in response to tree growth as the years pass. You might encourage it along this spring with a combination of a light nitrogen fertilizer and chelated iron.

Q: I would like to use Siberian elm trees for screening a yard. Are they prone to disease problems? Can you list some pros and cons of this tree? (Fordville, N.D.)

A: Siberian elms have very few attributes. I will give you the positives and negatives. The growth is fast but the wood is brittle. Short of planting on the moon’s surface, the tree will grow under just about any conditions found on this planet.

That the foliage will be ravished by insects is almost guaranteed. It is resistant to Dutch elm disease and phloem necrosis.

Siberian elm is rated by horticulturists and arborists as one of the worst, if not the worst, of the world’s trees. Once established, Siberian elms will begin to die but will never die completely. It is totally lacking in aesthetic value for landscaping purposes.

Siberian elms were planted by the government during the Depression of the 1930s because they become established and grow quickly to provide a makeshift shelterbelt/windbreak in the prairie states.

In my opinion, just about anything else you pick will be a better choice than Siberian elm.

Q: I just came across your website and saw that you were answering questions about hibiscus plants. I live in southern California and just bought a hibiscus.

I live in an apartment and don’t really have a place to put it to make sure it gets at least six hours of sunlight a day. I bought a 150-watt plant light that is on for nine hours a day. Some of the leaves and buds have turned yellow and fallen off. I’ve had it a little more than a week. It did have at least a dozen buds on it when I bought it.

Are the leaves and buds falling off because I repotted the plant? Is my artificial light inadequate? Have I possibly overwatered it? I’m new to plant care, but I really want this plant to do well because it has a lot of sentimental value. What do I need to do with it? (email)

A: Although a little fussy at times, hibiscus plants are extremely tough plants, so they seldom kick the bucket. I have some ideas on what may be causing your problem. Having been purchased from a facility that was providing optimal care and all the sunlight possible, it may be going through transplant shock.

The light you are providing is inadequate. Full sunlight for 12-plus hours a day is needed. Also, put your timer up to at least 14 hours per day to compensate for the lower light intensity and replace the bulb in a year.

If you repotted into a container that did not have free drainage, this could be contributing to the foliar discoloration and bud drop. If you used a potting soil that doesn’t drain well or are overwatering, it definitely will contribute to a plant’s decline.

As a generalization, plants do not like changes in their environmental settings, so this is an adjustment period for the plant.

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 ronald.smith@ndsu.edu.