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Ron Smith answers reader's questions about the world of plants and gardening.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: Several of my bearded irises have rotting leaves and some have bore holes. Is there something topical I can apply to cure the problem? (e-mail reference)

A: Once the borers get into the iris rhizomes, all you can do is dig them out and throw away the affected plants. Dust the rest with Sevin insecticide and replant.

Q: Please help! We have a wonderful, healthy 50-year-old maple tree in our backyard, but it is being attacked by grey squirrels. The squirrels are eating the bark right off the branches! It is amazing how they can take such great swaths, but worrisome. I've read that branches actually can be killed off by this. Our options seem to be guns, slingshots, hoses, hiring a teenager to live in the tree or taking valium and watching nature do her always fascinating work. Any advice? Thanks in advance for your help. (e-mail reference)

A: You could try timed fireworks, an action-sensitive sprinkler to startle them, a scare owl, balloons or other birds of prey.

Q: My wife and I just got a small, purple plum tree. Her grandmother had it growing in her yard. Our grandmother passed away, so we decided to bring the plum tree to our house. The roots are long, so I want to cut them back some and replant. Is this OK? I was going to plant it today, but my shovel broke. We put it in a bucket of water until I get home from work tomorrow. Please help us because neither of us has a green thumb. (e-mail reference)

A: The more of a root system you can leave on a tree, the better the chance for it to establish successfully.

Q: I was reading through your Web site about how to kill dandelions. However, something needs to replace that space when the dandelions are killed. Will the surrounding grass naturally fill in that space or would it be best to spread some grass seed to prevent new weed competition? If so, when would be the best time to spread the seed after applying the dandelion spray? (e-mail reference)

A: A herbicide treatment followed by a fertilizer application would thicken the grass to fill in the spot. Kentucky bluegrass, which makes up 90 percent of the northern turf lawns, is a rhizomatous grass that fills in bare spots when given a little encouragement by fertilizing, watering and high mowing (2.5 to 3 inches). The dandelions will be out-competed under those conditions!

Q: Are there any pre-emergent liquid herbicides for quackgrass? Please let me know because I heard you are the turf expert. If you know of any good books on North Dakota turf care, I would appreciate it. (e-mail reference)

A: Sorry, there is no selective herbicide to control quackgrass in lawn grass. For a quick version of how to establish a lawn, go to For more detailed information, go to

Q: We have a fig tree in our living room. During the years, the leaves have become quite dusty. I began the task of taking a damp cloth and wiping each leaf individually. Cleaning the leaves this way will take quite some time. Do you have any helpful hints on how to clean the leaves? (e-mail reference)

A: If it is moveable, take it into the shower and rinse it with tepid water. Otherwise, I know of no shortcut to cleaning the leaves other than one at a time. Hire a young teen to do the job for a couple of dollars.

Q: Someone at a nursery told me there is a deer repellent formula on the NDSU Extension Service Web site. It is made with habanera peppers and mixed in a blender. Can you please direct me to where I may find this concoction? We live in the country and have been using Plantskyd. It works, but it's expensive. (e-mail reference)

A: Here is the concoction lifted right from the Web site. Red cayenne, jalapeno or habanera fresh peppers can be used in the preparation, but be careful if you use habanera because the capsaicin concentration is high enough to cause serious damage to the preparer! Jalapenos should be hot enough to keep the bunnies away. The quickest way to come up with a concoction is to take three fresh peppers and run them through a food processor with enough water added to create a liquid. Pour the liquid through a cheesecloth mesh into a glass quart jar. Add about 2 tablespoons of olive or other vegetable oil, a squirt of Elmer's glue and a drop or two of liquid dishwashing detergent. Use one part of the concentration to 10 parts water. Shake well just before application. This should discourage the bunnies without hurting them. If not, then make the concentration stronger (30 percent) or use the cayenne peppers for extra heat. Be sure to reapply after new growth appears or after a good rain. Deer will be controlled with this as well.

Q: When is the best time to trim our lilacs so we don't affect their flowering next year? (e-mail reference)

A: Right after they finish flowering this year!

Q: I have a tree over my garden. Will this affect my cucumbers, tomatoes and zucchini as far as the garden having too much shade? Also, with all this rain we've been getting, is there anything I can do to make sure my plants thrive? (e-mail reference)

A: The shade and roots from an adjacent tree definitely can affect the performance of the vegetable garden. You can have problems with disease, root rot, spindly growth, low fruit set and size. The plants will thrive if you can thin out the tree canopy that is shading your garden. There is no better "thriver" for vegetables than pure sunshine!

Q: My sister has a beautiful, white eastern viburnum that came from our mom. We would like to start a new plant. Can you tell me how? We live on Long Island, N.Y., and have pretty cold winters, yet not too extreme most of the time. (e-mail reference)

A: Try softwood cuttings dipped in a rooting hormone and stuck in a sand/peat moss mixture. Keep it moist, misted and in the shade.

Q: I was at your Web site checking out the questions, but I didn't see an answer to mine. I bought a little jade plant about two or three years ago. It is happy and healthy. However, it is still the same height. The roots have not taken over the pot, so I know it shouldn't be due to that. If I pinch off the top section to promote growth in the bottom section, the part I pinched off will grow back fairly quickly, but it isn't getting any bigger. What is the deal? (e-mail reference)

A: I don't know. Could it be a dwarf jade? Surely, in the time you have had it, some size increase should have taken place, so that is my best guess.

Q: I live in central Pennsylvania and have a thundercloud plum tree. The tree was planted two years ago and flowered wonderfully last year. Last summer I noticed some of the branches did not have leaves on them, so I cut them off. I occasionally fertilized the tree last summer with a basic 10-20-20 mix. I also know that the tree was hit hard by Japanese beetles before I noticed and started spraying. This year, the tree barely flowered and the top 1 to 2 feet of every branch did not grow leaves. Is there anything I should do or look for to explain why no leaves are growing on the top of the tree? Thanks for any help you can give me. (e-mail reference)

A: The possible explanation based on what you have told me could be that the tree was planted too deeply. The top of the rootball should be even with the surrounding soil, not deeper. Many folks plant trees too deeply, with the thought that doing so will keep the tree from being blown over. This effectively disrupts the air/moisture balance in the root system, causing the dieback in the canopy of the tree that you described.

Q: I have a large iris bed of 90 percent white and 10 percent lavender sprinkled among the white irises. I want to replant all the lavender in a group. If I wait until August, I won't be able to identify the lavender plants. What are the drawbacks to replanting now while I can see the color? (e-mail reference)

A: Moving them now will not kill them, but will keep them from blooming next year. I would suggest marking the leaves with a "W" or "L" now and moving them late in the summer or early fall.

Q: I just got back from British Columbia and noticed their extensive use of Bellis/English daisies. It's a neat flower because it is nice, compact and has perfectly round blossoms. I'm assuming I can add this to the long list of flowers we can't grow here, but thought I would confirm this with you. As always, thanks for your advice. (e-mail reference)

A: These beauties would be considered half-hardy perennials in our area, but may move up to fully hardy if global warming continues in our favor! You can at least enjoy them as annuals by planting them in a cool, semishady, moist site. If they come back the following year, you've got double the benefits for your dollars! British Columbia is an unfair environment to make comparisons with because it is considered the Florida or California of Canada, but without all the stifling heat and humidity.

Q: I have the type of pear tree that does not bear fruit, but is supposed to have white blossoms in the spring. My trees never have blossomed. Any idea why? (e-mail reference)

A: The tree is not flowering for one or a combination of reasons. It is being too generously fertilized, which encourages vegetative growth, but no reproductive growth. The tree is a subcanopy tree, in part or totally, where insufficient light exists for flowering to occur. Temperatures during the winter or more likely, coming into the early spring weeks, fluctuate to the extent that the flower buds lose their cold hardiness and then are killed by a sudden drop in temperature. What you have may not be a flowering tree.

Q: I have a hydrangea snowball shrub. I am wondering how to start another one. I've heard that if it is a flowering plant, it will not root. Is this true or do I need to start from a rooted piece? (e-mail reference)

A: Hydrangeas are among the easier plants to root. Take a cutting from a branch of the hydrangea shrub about 5 to 6 inches long. The cutting will work best if taken from a branch that did not flower this year. Remove the lower leaves of the bottom two leaf nodes. Cut the largest leaves down to about half their size. Dip the cuttings in rooting hormone (this is entirely optional) and insert into a damp vermiculite or sterile medium. Water the pot well and allow draining. Make sure the soil is moist, but not soggy. Cover the cuttings and pot with plastic. Try to keep the plastic from touching the leaves by adding stakes.

Q: If we remove our oak tree and stump, will the suckers that are all over our yard remain or will they die? (e-mail reference)

A: It depends. If you continually mow them off, they eventually will die. Left alone, some could develop into trees again, depending on environmental factors. They easily can be controlled with regular applications of a broadleaf herbicide that contains dicamba.

Q: We have two Beverly Hills apple trees. They have been doing fine up until last year. At that time, the apples began falling from the trees, leaving little, if any, fruit. The same thing has started this year. We got lots of blossoms and young apples, only to have the young apples fall. Do you have any ideas? (Carlsbad, Calif.)

A: Some apple drop is normal in mid spring to stabilize the energy demands of fruit production. This balance can be disrupted by improper pruning or a gradual decline in vigor of the tree. It also could be tied to the lack of adequate pollination. The honeybee population in the U.S. has declined tremendously in recent years, so the lack of their activity could be a major contribution to premature apple drop. Another cause is the use of the carbaryl insecticide Sevin to control insects as the flowers mature.

Q: I have three birch trees in my backyard that were planted two years ago. Two of them are thriving, but the third is brown and bare at the base of the tree. My neighbor has a raspberry patch located next to this tree on the other side of our fence. Every week I have to pick raspberry weeds that have grown over to my side of the fence. Is the raspberry patch overgrowth cutting off the growth of my birch tree? The other unusual thing that happened to the birch tree is that during the first year of growth, a bunny family nested in the tree during the winter and ate some of the low growth. Could the tree be suffering as a consequence of the bunnies? (Winnipeg, Manitoba)

A: The raspberry suckers will be a recurring problem, but unless you let them take over, they will not harm the growth of your trees. As for the bunny damage, it definitely could be a factor. If the base of the tree was girdled with their feeding and nibbling, that would do it in.

NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
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