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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: Would you know if a tree lilac has an extensive, aggressive root system like the common lilac? I am thinking of planting a tree lilac to provide shade for some plants. (email reference)

A: Tree lilacs are beautiful plants that have an extensive root system. However, you can plant herbaceous plants under it successfully with no negative consequences to the lilac or planted material.

Q: Last year, I had a white snow fountain and dogwood tree transplanted after the trees bloomed and were trimmed. The white snow fountain had overgrown its home. It was given shock transplant treatment and watered very well. However, it lost all of its leaves shortly after moving. The dogwood was given the same treatment and also lost its leaves. This year, both trees are not showing any signs of life. Are they dead? Is there any hope to save them? (email reference)

A: You are obviously not from our frozen northern climate. That being the case, I encourage you to contact your local Extension agent. Go to to find the Extension office nearest you. The Extension agent can answer your questions or hook you up with a horticulturist or arborist who can.

Q: I have seen your website on tree advice and gather from your comments on poplar trees that you don't like them very much. I have an 80-acre poplar plantation that was planted in 2005. I’m also becoming disillusioned with them because the weed and disease problems are driving me nuts. The trees are planted on a 2.5-meter square grid, so it is possible to cultivate between the rows. However, in many areas, canopy closure has not occurred, so the weeds just continue to thrive. Is the poplar tree book you refer to on your website still available? (email reference)

A: “A Guide to Insect, Disease and Animal Pests of Poplars” is from the U.S. Department of Agriculture. You might be able to order it through your library or the land-grant university in your state. I have one copy for reference, so I don’t want to give it up. If you have a problem locating a copy, contact your state or national Forest Service. Even though the publication was produced 20 years ago, it still is extremely good with detailed, color photos and descriptions to aid in nailing down problems.

Q: We are buying a house with cottonwood trees growing along the edge of the property. We want to remove the trees. Our tree person wants to dig out the stumps after taking down the trees and then fill in the holes with topsoil so that we can put up a fence. Will this kill most of the root system? (email reference)

A: The “tree guy” is going to cut down the trees and dig out the stumps? I would assume you mean that he will remove the stumps by grinding them to sawdust. If you can, get him to go well into the major roots that come up to the stump. Doing this will remove more food from the roots that remain and will lessen the probability of sprouting roots. Sprouts that do come up can be treated with a broadleaf herbicide to finish them off.

Q: My boyfriend just bought me strawberry and mint plants a couple of weeks ago. I've followed all the instructions and they are blooming. However, I have two questions. Are terra-cotta pots good for growing mint and strawberries? We hate to use plastic containers because they aren’t biodegradable, so we thought terra-cotta would be better. Also, how often do I need to replant my mint and strawberry plants in fresh soil? (Austin, Texas)

A: Mint and strawberry plants need to be summered outdoors for the best, most continuous results. The terra-cotta pots are fine for growing plants. If you have no way to get them outdoors, then at least get some grow lights to provide the plants with extra light energy for healthy growth. Repotting should be done when the plants start to crowd the pots. Use fresh potting soil. Good luck and have fun.

Q: I'm having a hard time deciding on what to use for hedges in our backyard. Many people are telling me to put up a fence because it's easier. However, I would like to have greenery and privacy. I live in northern New Jersey. The backyard is surrounded by large trees, so there's lots of shade from the middle of the yard back to the property edge. I have standard soil but do have some clay when you dig down. There are old, out-of-control and dying arborvitaes that line both sides of the yard. I do have a 40-foot section of newer arborvitaes that are doing fine. Looking out my back window, picture two lines of hedges 100 feet long on each side of the yard. The hedges would run north to south. Is there any bush or hedge that you might recommend for these circumstances? (email reference)

A: Based on your description and location, I would suggest Canadian hemlock for what you want. There should be other good choices available at the local garden centers this spring.

Q: I received tulip bulbs as a gift for Christmas. I planted them in large patio pots. In late February, they began to blossom beautifully. However, my dog ate the red flowers (probably thought they were apples) and most of the green leaves. I believe the bulbs are still in the soil. Any chance they will come back next spring? (email reference)

A: Good thing for the dog that the plants were not daffodils or you’d be making funeral arrangements for the dog. There is no chance they will come back to any worthwhile degree next year, so forget it. This fall, plant some tulips outdoors for springtime enjoyment.

Q: We bought a house along the gulf in southern Texas that included a large ficus tree. About a month and a half ago, we had an ice storm, which is very rare around here. The tree lost all of its leaves during the storm. After a month and a half, there are no signs of life. Am I going to have to cut this tree down or should I give it more time? (email reference)

A: It all depends on how long the ice hung around. If it lingered, the tree is probably dead. If the ice disappeared quickly, then it is suffering from physical damage that may not be permanent. I would wait at least another month to see what will happen. If nothing is showing by then, I would declare it dead and replace it.

Q: Can I plant two trees together? A friend gave us two trees that my wife would like to have intertwine. My plan is to plant the two trees in a pot until the roots get thicker and then transplant them outside. Would this be possible? (email reference)

A: It should work. I’ve seen it happen naturally with many species, so I don’t know why it wouldn’t work for what you have in mind. Good luck!

Q: I saw your column and have a question that I hope makes sense. I ordered three hybrid poplar trees. The trees came with what appears to be the old trunk of the tree with roots coming from it. It is cut off above a sprout that was left. So, I have a sprout connected to what used to be the trunk, which is now cut off. I was told to plant the tree to the root collar and leave the rest above ground. If I do that, the main trunk will be about 5 inches above ground and the sprout will be at an angle. Is that sprout going to become the main trunk of the tree? Do I need to tie the sprout to the main trunk so that it grafts with it? I just don't understand how it all works. Can I just cut off the sprout and let it root itself? What is the best way to handle this? (email reference)

A: If I understand your questions correctly, you are describing a grafted tree. The stump that you refer to is the rootstock and the sprout is the scion wood that will become the visible tree as it grows. Do not cut anything off at this time or at planting. You were given proper planting instructions, so follow them and don’t worry about the stub sticking up. Give the tree a year or two to become established. If the stub still annoys you, carefully cut it back to where the scion wood growth is emerging. Good luck and enjoy the rapid growth of these trees.

Q: We bought a home that has a mature walnut tree, but I’m not sure if it is a black or English walnut. In any case, the base of the tree is buried 3 to 5 feet below the level of the ground around it. We have been told to clear a circle around the tree to a depth of 5 feet so that it can grow properly. What do you think? (Salt Lake City, Utah)

A: I believe you had better follow that advice as soon as possible. Go deeply enough until the trunk of the tree’s flare at the base is obvious. That is the crown where the roots originate.

Q: I live in zone 4. I am wondering if ruby slipper oak leaf hydrangeas that are rated for zone 5 through 8 will survive our winters. The ruby slippers were just released by the National Arboretum. They would be planted on the south side of my home that gets full sun. During the winter, the plants would be covered with snow. I also would use Styrofoam cones to cover them. If not feasible, do you know of another hydrangea that would survive our winters? Thanks for any information you may have and for all your great knowledge that you give out each week. (Ellendale, N.D.)

A: It might survive the winter if you do what you described. The hardiest hydrangea that I know of is the Annabelle, which is grown throughout the state. It doesn’t need much coaxing and will grow on the north or south side of the house and produce an abundance of white flowers. I would encourage you in that direction to avoid any risk of loss because of a brutally cold and low-snow winter.

Q: I received a clipping of a red twig dogwood. I put the clipping in a vase filled with water. How long should I keep the clipping in water before I plant it in potting soil? I live in Michigan, so there still is snow on the ground. Right now, the clipping has leaves and little flowering buds. (email reference)

A: I hate to disappoint you, but this stem probably is not going to root for you if it hasn’t by now. The flower and leaf production you describe comes from the stored energy in the branch. Usually, dogwoods are propagated by taking cuttings in the fall that are cut into 6- to 8-inch lengths. The cuttings should be dipped in a rooting hormone and stuck in a rooting media. Plant the cuttings outside when the danger of frost is past.

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 – April 6, 2011

Source:Ron Smith, (701) 231-7123,
Editor:Rich Mattern, (701) 231-6136,
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