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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: Our two ninebark shrubs have been eaten to the ground this spring by rabbits (we think). Can they be saved? (email reference)

A: They very likely will recover on their own. Get some rabbit repellent, such as Liquid Fence, Plantskydd or a similar product, and spray the stubs and around the area. You also would be wise to put a chicken wire fence around the area to give the plants a chance to get re-established.

Q: The red maple in my front lawn seems to be pulling itself out of the ground. The ground around the trunk is heaved almost 12 inches. This 15-year-old tree always has looked healthy, but the leaves are very tiny and never turn red in the fall. Also, my lawn looks terrible this spring. The lawn has brown patches around the tree’s drip line and starling holes over the same area. I read somewhere that starlings make a half-inch diameter hole by pushing their beaks into the ground to feed on white grubs. Can you advise me on what this problem is and the solution? What type of care or maintenance does this type of tree require? (Gatineau, Quebec)

A: Starlings mine the soil for grubs that are feeding at the upper root zone of newly developing roots. These would be large grubs that make a tasty meal for the foraging birds. As to your tree lifting out of the soil, I don’t have a good answer for you. I would encourage you to locate an International Society of Arboriculture (ISA) certified arborist in your area to make a determination. Subsidence could be the problem, but that can only be determined with an onsite visit. Go to to find certified arborists in your area. Check his or her credentials and ask for references before allowing any major work to be carried out.

Q: Attached are three pictures of a silver maple in our backyard. I estimate it was planted around the time the house was built (1938). There are some new dead branches at the top of the tree. Is this a sign that the tree is on the decline? I love the tree and it adds such character to our home. Any recommendations on how to take care of this tree? (Billings, Mont.)

A: Judging from the size of the tree and other silver maples I've seen that are the same size as prewar housing, I'd say you are approximately correct on the age of the tree. With proper care, it can continue to live for many more years with grace and beauty. I would strongly suggest making contact with an ISA certified arborist to do some selective pruning. Also, ask for age documentation of the tree. This can be done with an increment borer that will pull a pencil-sized plug out of the center of the tree. With the plug, an annual ring count can be made to establish the age of the tree. It also serves as a safety check to see if any internal decay has taken place. If there is some decay, it can be determined to what extent the tree may pose a hazard in your yard. Be sure to check credentials and ask for references before allowing work to be carried out on this tree.

Q: Would it be OK to move my 20-year-old snowball bush (quite large) to another place? If so, any tips on replanting? (email reference)

A: This is not the time of year to do it, especially a bush this large. You’d be better off waiting to move it this fall or early next spring, which are times when the bush is dormant. Disturbing the roots at this time of year while the plant is fully leafed out will cause the bush to wilt and make recovery very difficult.

Q: The leaves on my irises are big and beautiful, so they seem to be healthy, but I don't think they flowered last year. The plants do not have buds this year. They are located in a very sunny spot. Please advise. (New Jersey)

A: You likely have them planted too deeply. Go to to get cultural instructions.

Q: A little more than two years ago, we bought a house with a cutleaf weeping birch in the front yard. The house and the tree reside near Cliff, N.M., which is on the western front of the Gila Wilderness just above the Upper Gila River corridor. They are at about 5,400 feet in elevation and on the northeastern side of a ridge top. Needless to say, it seems this weeping birch is a bit out of its typical region. The soil composition is a mix of midslope decomposed granite and limestone. There are some areas with caliche clay. The area around the tree has improved soils. The previous owner dug a 6-foot hole and filled it with amended soil when he planted it. The tree is about 20 to 25 feet tall. It gets full sun in the summer (house/yard built on a solstice line). About a 20-foot perimeter around the tree is planted with a variety of heavy ground-cover plants, and I’ve mulched the area directly under the tree. When we bought the house, the top of the tree looked like it was dying. The previous owner stated that he never watered anything. I identified the tree and began watering the tree using a drip tree soaker. I also scouted for any evidence of borer activity. The bark looks in great shape. The tree is so far out of its typical range that I think borer activity won’t be much of an issue. This spring, I watched the tree turn green with the hope that the top of the tree would recover. So far, I’ve only seen a slight improvement. There are a few green leaves on top but not full and lush like the rest of the tree. It puts out huge, healthy-looking catkins and looks in good shape. This is such a beautiful tree that I’d hate to see it die. However, I’m at a loss as to what else to do for it. Would it take more than one season of adequate watering to show a full recovery? Could the root system have reached the poorer- quality soils below the initial hole? I would be more than happy to send a photo of it if it would help paint the picture. Any thoughts, suggestions or advice you might provide would be greatly appreciated. (email reference)

A: With the exception of not watering the tree, the previous owner knew what he was doing to get this tree established and growing. This tree is without a doubt outside its natural range by a long shot. With everything the previous owner did, a microclimate was created that allowed the tree to survive and thrive. The dead part of the tree you described is a typical bronze birch borer (BBB) start pattern and should be addressed as soon as possible. Get in touch with an ISA certified arborist to have the dead part of the tree properly pruned and inspected for evidence of borer activity. If found, the tree should be treated with a systemic insecticide that has the active ingredient imidacloprid (Merit) to keep successive generations from becoming established. It could be some boring insect other than the BBB, which this treatment also will take care of.

Q: I have a Canada cherry that has black knot. What is the best way to control it? (Ellendale, N.D.)

A: Cut it down and dispose of it. I know that is not the answer you were anticipating, but that is the usual conclusion of repeated attempts to control the spread of this plague on Canada cherry trees. If you want to hope that your tree is an exception to the rule, here’s what you can try. Carefully cut the infected branch off back to a lateral branch and destroy it. Begin a spraying program using lime sulfur while the tree is dormant. During the growing season, spray the tree with a Bordeaux mixture or Captan. By being extremely vigilant in your pursuit of controlling this disease, you may be able to rank yourself in the column of exceptional individuals who gained control over black knot without destroying their tree.

Q: We have a client who is looking for a good shrub or bush (hedge) to plant between his yard and his neighbor’s. The hedge row would be about 150 feet in length. It would run east and west and have very little light blockage from other trees. He is looking for something that will grow fast, be attractive and provide a privacy barrier between the two yards. The soil is a good loamy type and has good drainage. Any suggestions would be greatly appreciated. (Carrington, N.D.)

A: A number of good selections exist. Possibilities are common lilac, biburnum, meadowlark forsythia, red twigged dogwood and arctic willow. I’ve used some of them for the same purpose.

Q: We have six evergreens in a row that are about 40 feet tall. They are very old now, so they are getting thinner and thinner. We put in evergreen spikes every spring and fall, but the spikes don’t seem to be helping. Do you have any other ideas on how we can get them to grow thicker and not die? Is it possible they are not getting enough water because they are in a row? (Toronto, Canada)

A: It is too bad that you have wasted time, money and hope by investing in fertilizer spikes because they have little to no value. I’ve written at least a few dozen times in recent years about what a waste of money they are. However, the message just doesn’t reach everybody. Save your money from this day forward. It is difficult to advise you when there is such a distance between us. I’d suggest that you contact an ISA certified arborist in your area. Go to to locate an arborist nearest you. An ISA certified arborist is more than a dues-paying member. The arborist must pass standardized testing and maintain the education through workshops and courses. Members also are required to promote ethical business practices. An onsite evaluation by someone with these qualifications would be the best option for you to consider.

Q: I have several arctic willows in my yard. I am quite concerned with the leafing-out process this spring with two of the older willows. A few of the branches have a full set of leaves, but many do not have any leaves. I broke off a wispy branch and found definite green under the thin bark. Should I be patient or start planning a removal project? (Cooperstown, N.D.)

A: It is ironic what problems are showing up this spring considering the mild winter we’ve just had! It seems that the lack of adequate snow cover has caused a lot of this irregular growth response or even the demise of plants that have been on the site for more than 10 years. I’d suggest waiting until Memorial Day weekend to see if these nongrowing branches decide to join the crowd and open their buds for you. If not, then they have lost the opportunity to contribute to the beauty of the shrub and should be removed without remorse.

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 – May 23, 2012

Source:Ron Smith, (701) 231-7971,
Editor:Rich Mattern, (701) 231-6136,
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