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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have mature lilac bushes along the side of my home. What I want to do is take these bushes and spread them around my entire yard to be used as a privacy fence. What would be the best way to go about doing this without killing them and making sure they grow as thick as possible? (email reference)

A: Leave them alone because they will spread and make a nice, dense privacy screen. Depending on your intentions, lilacs are famous or notorious for spreading through sucker growth. In a normal spacing arrangement of 8 to 10 feet apart, this would be evident within a couple of years after planting. There would be shoots coming up from the spreading root systems that knit together and eventually form a wall of greenery that provides excellent, attractive summer privacy. If the spacing is too far apart to do this within your mental time frame, then make additional purchases and interplant them to speed up the desired effect.

Q: After looking on the Web, it appears that you are the Midwest rhubarb expert! If you have time, I'd love some help with my questions. When we bought our house three years ago, my husband accidentally mowed over a patch of rhubarb. It died and I forgot all about it until it came back with a flourish this year. After it started getting large, I cut a few stalks and chopped them up into smaller pieces for rhubarb pie. I didn't have time to make the pie right away, so I let it sit in the fridge for four or five days. Tonight, I made two different recipes for rhubarb pie. For some reason, both turned out horrible. The rhubarb is very woody and completely inedible. Any thoughts on what I might have done wrong? Maybe it isn't really rhubarb. Although it was mostly green, there was definitely rhubarb red at the bottom of the stalks and it looks exactly like other rhubarb. Although I followed directions, could it be that the rhubarb was undercooked? Could it be a bad rhubarb plant? Is it too late in the season to pick more rhubarb? Did I let it sit in the fridge too long before cooking? Could it be that I am a horrible cook? This isn't usually true, but I'm feeling discouraged. Any thoughts you can give would be wonderful. (email reference)

A: Interesting. I find it difficult to believe that your hubby mowed over some rhubarb plants in the first place. The fact that it was mowed down three years ago and just this spring it re-emerged is equally amazing. It could be burdock weed that you assume is rhubarb. Don’t laugh, it sometimes is confused by the unwary because it has the same basic form and growth habit during the first year (rosette stage) of growth. However, the leaves on rhubarb plants are hairless, while burdock leaves are covered with hair. As for cooking it, that is outside my expertise, so I’ve sent this email to my colleague, Julie Garden-Robinson, who is our resident nutritionist. I’m sure she will provide you with some recipes for using rhubarb. No, it isn’t too late to be harvesting rhubarb. My wife is in the process of making some delicious strawberry-rhubarb pie as I write this response. I can’t wait to get home and have an oven-warm piece of pie. Julie Garden-Robinson’s response: Interestingly, I just wrote a column about rhubarb that you can read at Everything you would ever want to know about rhubarb is in the rhubarb compendium found at Even if you harvested a weed, you might want to find a generous neighbor with some rhubarb to share so you can try out these recipes. Have fun!

Q: We just moved to a new home in West Newbury, Md. There are a number of old cedar and evergreen trees on the property. The trees have been growing out of control for a long time and many of the branches on the lower section of both types of trees are dead. There are bare branches with no needles. Also, the trees are crowding each other, so the growth is stunted where the trees have grown into each other. Should I thin out some of the branches where I want to encourage growth? If I cut away the dead branches at the bottom third of the trees, will new branches grow? (email reference)

A: The answer to both questions is no. You should get in touch with a local landscaping/maintenance firm to make an onsite recommendation. Contact the Maryland Nursery and Landscape Association at Someone in your area will be able to help you much better than I can from North Dakota. Good luck.

Q: We are looking for a large, fast-growing tree as a centerpiece in our backyard. Is a tulip poplar a wise choice for our area? (Barnesville, Minn.)

A: The term tulip poplar is misleading because it is not a poplar species. It is botanically known as Liriodendron tulipifera. I have not seen any outside of the Twin Cities area. It is listed as being marginally hardy in zone 4, which would put it at great risk for survival in Barnesville. I would encourage you to select one of the lindens that are available on the market. They establish easily, grow quickly, produce dense shade, need little pruning and generally are pest-free. For other ideas, go to Look through the color photos and descriptions to give you a better perspective of what you may want. After doing that, feel free to get back to me if you have more questions.

Q: We just planted bare-root lilacs from the Soil Conservation Service. I have green ash trees that were destroyed by deer. I am worried that the lilacs will suffer the same fate. Can I use corrugated drain hose to protect them? I see white tubes at hardware stores but I have tons of black hose from my sump pump that I don’t need. I am wondering if the black plastic will block sunlight more than white plastic. Also, can I prune the ash trees into something or will they look like a mess forever? Thanks for the help. (email reference)

A: The ash trees can be shaped to look halfway decent, so go for it. However, follow the adage of “think twice and prune once” before going whole-hog with pruning shears or saws. Once removed, pruned off branches cannot be replaced. While a branch ought to be pruned, it doesn’t need to be removed right away. Never take off any more than about 25 percent of the branching system of a tree in any one growing season. The black corrugated pipe you are considering probably is not a good idea. Total exclusion of light and temperature buildup would weaken and eventually destroy the vigor of the new plantings. There are plenty of deer repellants you can use if the timing and persistence of applications are employed. Plantskydd and Hinder are just a couple of good ones on the market. Get it put on early in the season and repeat as directed on the label.

Q: Four years ago, we planted a small weeping birch and have enjoyed watching it grow. This year, it has started taking on real bark and looks marvelous. How do we groom it? The branches on the lower trunk of the tree probably need to be cut off because they are so close to the ground. We are hesitating to do that because we don’t want to stunt the tree’s growth. Can you tell us how to proceed? Your advice is valuable and we read your column weekly. (New Rockford, N.D.)

A: Thank you for the very nice compliment. Birch trees, especially the weeping ones, need very little pruning. When they do, it is usually for the reason you just stated. Prune the lower branches you want to remove with either a bypass hand pruner (scissorslike cutting action) or a small pruning saw. Be careful not to prune back into the trunk of the tree. Go just up to the small creases you see where the stem connects to the tree trunk. No need to apply tree wound dressing because the tree will heal better without it. My wife and I totally adore the weeping birch we have in the front of our home. It has been there for more than 25 years and really graces our little house beautifully. It also provides ample shade. Try to keep the tree from becoming stressed by compaction and drought. We planted ours in a landscape bed and surrounded it with strawberry plants. The strawberry plants have long since been replaced with hosta, lady's mantle, heuchera, ferns and black snakeroot. About five years ago, I hired a certified arborist to selectively prune this beautiful tree because I’m too old to do it myself. He made careful cuts to take out any dead wood of consequence. He also inspected it for possible bronze birch borer activity. I have him do this every spring after the tree has leafed out to minimize excessive sap flow. If borers are detected, as they were about four years ago, I have the tree treated with a systemic insecticide. Glad to know there is another person who loves these beautiful trees.

Q: Summer greetings to you. I am hoping you may have some insight as to what is going on with our tomato plants. We planted roma, celebrity, brandywine and early girl tomatoes. They have been in the ground for four weeks. We noticed the leaves on many of the plants are curling into cocoon-shaped balls. There are no discernible disease spots or insect damages. What are we doing wrong? We've not had this problem in previous years. We are hoping you can advise us on how to remedy the problem, or is it too late? (Hawley, Minn.)

A: What you are describing is referred to as tomato leaf curl. Some researchers say it is a purely physiological disorder brought on by wet, cool and flip-flop weather. Others speculate that this is caused by a virus if the leaves that are affected eventually turn yellow and die. Another blames the sweet potato white fly for causing this problem. Strange as it may seem, sweet potatoes don’t need to be present to have this pest attacking tomato plants. Essentially, this is an annual reaction of the tomato plants grown in our region of the country. I can’t remember a recent spring that has been kind to our garden plants because of too much rain, wind, cold, a shot or two of hot days and then back to the cycle of cold, wet and windy. The tomato plants will bear the fruit we want and in the quantities that are characteristic of the tomato cultivar. Vegetable researchers attach a “no apparent effect on production” in their analysis of this phenomenon. In essence, don’t worry about it because there is nothing that can be done about it.

Q: I have a number of black willows located on an easement in my backyard. They are beautiful trees, but I had to cut some down because the roots kept popping up in my grass. At first, I thought they were weeds. However, a lawn professional told me that they are part of the root system. My problem is that the roots still are popping up. They are not as bad as they were, but I am afraid that the roots eventually will cause harm to my foundation and the piping into the house. I do not have a septic system. What is the best way to kill off these roots? If the tree is dead, how big will the roots get? How far below the surface do these roots go? I was thinking of digging a trench in front of the tree lines to severe the root systems. Will that work for me? How can roots grow without a tree? Any suggestions would be appreciated. (Minnesota)

A: Rest easy because your foundation and piping system are safe from harm. Have your lawn care operator treat them as broadleaf weeds or you can do it yourself. The roots eventually will die from starvation unless you allow the suckers to continue growing. The roots are working off stored carbohydrates that the trees delivered through the process of photosynthesis. Remove that photosynthetic source and they will die. Enjoy your home without worrying about this problem.

Q: I came across your website when trying to research a problem that my parents are having with their grape plants. They have had established plants for many years. This year, many plants appeared to have died. When they broke off a stem of one of the plants, it appeared hollowed out, and a number of beetles came out of the stem. My dad says the beetles were red, but my mom says they were black. The bugs are approximately 1/2 inch long and 1/8 inch wide. They asked the Extension agent, but he had no answers. They would like to try to save the rest of the plants if possible. They live in northeastern Colorado and don't have access to the Internet. Do you have any ideas what these bugs are? They don't appear to be black vine beetles because they seem to feed on the stems and not on the foliage. I would appreciate any thoughts you might have as to what they are and how to treat the plants. (email reference)

A: This sounds like the grape cane borer. It is a pest that doesn’t confine its feeding activity to just grape canes. The adult is a small beetle that is dark brown to black. They bore into the canes to feed on the internal part of the cane. This causes the cane to collapse and wilt the foliage. The juvenile stage is equally destructive. The small maggots copy the parents’ feeding habit by working on the internal parts of the cane. Pesticide use is not recommended. Instead, practice good sanitation by keeping the vines pruned and the areas clean of any dead or dying vine parts. Survey the area around the vine plantings to detect any evidence of this pest carrying out any feeding activity on surrounding woody plants and fruit tree plantings. You can use systemic insecticides on plants not used for human consumption. Cleaning up any old woodpiles also is a good step in helping to limit the activity of this pest.

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

NDSU Agriculture Communication – June 30, 2011

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