You are here: Home Columns Hortiscope Hortiscope
Document Actions


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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I would like to plant a tree next to a brick patio to provide privacy, plus some shade and a windbreak. I am concerned about roots eventually spreading and breaking up my patio. Do you have any recommendation for trees that might be best to plant? The trees will get full sun and the soil is mostly clay. Thank you and I enjoy your column. (Bismarck, N.D.)

A: Brick patios are porous. That means air and water will seep through, so the roots from most trees will find their way under the patio and cause some surface lifting. You can install a barrier between the patio and the tree you intend to plant. I would suggest a Ginala maple. I’ve had one in my backyard next to my patio for more than 20 years. It provides perfect dappled shade to our patio in the late afternoon.

Q: We have two mock orange bushes that are located in different parts of our yard. For the last few years, the large majority of their leaves have been eaten by what looks like a gray caterpillar that is about 1 inch long. Can you suggest what we can do to get rid of this pest? (Charlotte, N.C.)

A: Use a systemic insecticide, such as Ortho Max Insect Tree and Shrub Control, with the active ingredient Imidacloprid. Follow the label directions and you will get seasonlong control.

Q: Two years ago, I planted a cottonless cottonwood about 30 feet from my septic system's leach field. I read somewhere that cottonwood roots will not invade my biodiffuser leach field system and that the roots will help absorb some of the effluent from the septic system. The tree is growing fast, so I am concerned the roots will invade the leach field and cause problems. Is 30 feet too close to the leach field? (e-mail reference)

A: I never have heard of a biodiffuser, but if this is what the company says and gives a guarantee, then you shouldn't have anything to worry about. Poplars grow quickly, so given any kind of encouragement from leach field effluent, the tree will take off like Jack's Beanstalk. Poplar roots will expand as far as 30 feet or more.

Q: We planted 15 tower poplar trees along our property for privacy. Two of the trees died, but we replaced them. However, the center leader of six other trees died four to six weeks after planting last year. The nursery told us that if we cut back the dead center leader, the tree will develop a new leader and will continue to grow properly. Is this correct or should we have all six trees replaced? Thank you for your advice. (Strathclair, Canada)

A: There is some truth to what the nursery told you. The trees will develop new leaders, but may not develop according to your wishes. The tower poplar is a hybrid noted for rapid, narrow growth. What likely will happen with the dead center leaders removed is that the trees will be bushier. If that satisfies your needs, then nothing is lost. If not, then you should get them replaced.

Q: We bought a pear tree that we want to plant near an ash tree that we plan to cut down in a couple of years. How close can we plant the new tree to the old? (Jamestown, N.D.)

A: Plant it outside the direct shade of the ash. Otherwise, it will be a weak and spindly tree. Pear trees require full sun.

Q: What is a safe bug killer to use on my newly planted mock orange bush? The pests are little black bugs. (e-mail reference)

A: The safest is Insecticidal Soap, which is available at just about any garden store outlet.

Q: We have a 15-year-old plum tree with purple leaves. Two years ago, we had some 2-inch plums, but haven't had any since. The bark around the trunk looks like it’s coming apart and there's some green mold stuff on the tree. I wanted to put tree tape around it so the bark would stay on. There also is one big branch in the middle of the tree that hasn’t produced leaves for a couple of years. I appreciate any suggestions. (e-mail reference)

A: This sounds like the tree may be having problems with borer activity. If the tree is worth trying to save, cut the dead branch out and dispose of it. Get a systemic insecticide, such as Ortho Max Tree and Shrub Insect Control, and apply it according to the directions. You will not be able to eat the fruit for this year, but this will eliminate this very destructive insect for a full growing season.

Q: Is there anything I can do about the dying out at the bottom of my arborvitae trees? They are beautiful, full trees, so I would hate for them to have growth only on the top. Thanks so much. (northwestern New Jersey).

A: The biggest nemesis for arborvitae is deer predation. Deer will graze to their height right down to the trunk of the trees, which then gives the trees a naked lower look. If you do any trimming, make sure you taper the growth to be narrower at the top. This follows the natural form of most arborvitae. Never cut all of the green leaf tissue off because it will be bare forever. There are plenty of stately arborvitaes with attractive, dense foliage covering the entire architectural form of the plant. If you do not have deer in your community causing grazing damage or your trees are not shaded by larger trees, you should have nothing to worry about.

Q: I replanted a spider plant from a shady outdoor location. The plant went from very sandy soil to a pot with some sand and garden potting soil. The plant is doing well in an office without any sunlight, but it gets plenty of fluorescent light. However, I’ve noticed that the new leaves it produces don't have bright white highlights. The new leaves have light green highlights. The new and old leaves are very different. What affects the colors of the leaves? Is it soil, light or watering? (e-mail reference)

A: Leaf variegation is influenced mostly by light intensity. When in full sunlight, the variegation can express itself easily and the plant is able to carry on sufficient photosynthesis. The variegation actually masks the chloroplasts in the leaf. Keep in mind that full sunlight on a cloudless day can have intensity greater than 10,000 foot-candles. The best fluorescent lighting in an office will provide 200 to 300 foot-candles, depending on their age. This big reduction in light intensity causes the green tissue to migrate to the surface with the new leaves that are formed in the lower-light environment. If you could examine the leaf cells with a microscope, you would find the cells formed in the full sunlight packed densely with relatively thick cell walls. The lower-light intensity cells would be larger and have thinner cell walls. Plants do their best to survive a changed environment. Keep in mind that Mother Nature did not create houseplants. Thanks for the good question!

Q: I need some advice on what to be aware of and how to grow African violets, Easter lilies and petunias. (Hawley, Minn.)

A: African violets are weeds in their native environment. As a houseplant, it will thrive with a little benign neglect. Allow it to dry down a little between watering. Give it as much bright but indirect light as possible. In the winter, place it on a tray of pebbles with water to maintain high humidity. Water with tepid water, but keep it off the leaves. Leaves will grow new plantlets if cut off and laid on a sterile or pasteurized media with a slit in the main leaf vein. Easter lilies are as tough as crowbars. Plant them outdoors with an east exposure if possible. If not, then just about anywhere will do. Water and forget them. Petunias are heavy feeders and like to be kept moist but not soggy and in full sun. Deer relish them, so watch out for that. As a bargain, get the wave series of petunias. One plant will cover a 4-foot by 4-foot area in one growing season with the proper care. Fertilize once a month with something such as Miracle-Gro and remove them once they have been nipped by frost in the fall.

Q: I have had my braided ficus tree for about a year. As soon as I got it, it lost almost all of its leaves. I thought this was normal due to the stress on the plant from moving. The leaves are growing back on one of the four main branches. I cut the other three branches down to where they were living because the entire top had died. There are little bugs flying out of the pot (gnats I think) and these gross, crawly, white larva things in the soil, which are much more prominent when the soil is wet. I'm wondering what the best course of action is. Should I repot my tree and try to get all of the bugs off? (e-mail reference)

A: The white larva probably is feeding on the finer roots of the tree. With the weather warming up, I suggest moving the plant outdoors and then doing a major repotting using pasteurized potting soil. Clean out the pot with a 10 percent bleach solution (one part bleach to nine parts water). As long as the upper part of your plant isn't infested with insects, such as scale, aphids or spider mites, you have a good chance of this plant recovering.

Q: I have a kilmarnock willow tree that is growing fine. This spring, I have branches coming out from the main trunk around 6 inches from the bottom. However, the leaves aren’t the same as the rest of the tree. The leaves are about 6 inches long and dark green. (e-mail reference)

A: The rootstock is sending up shoots. If not removed and sprayed with Sucker Stopper RTU, it will take over the tree you purchased (the scion wood or budwood that was grafted onto this rootstock). Try to avoid injuring the trunk of the tree because this encourages suckering from the roots to take place.

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

NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
Prairie Fare: Prairie Fare: De-stress with Gardening  (2019-05-23)  According to researchers, gardening can be beneficial for mental, physical and social health.  FULL STORY
Use of Releases
The news media and others may use these news releases in their entirety. If the articles are edited, the sources and NDSU must be given credit.

Powered by Plone, the Open Source Content Management System