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

By Ron Smith, Horticulturist NDSU Extension Service

Q: I want to plant emerald green arborvitae a few feet from my pool. Will the root system spread under my pool from this distance? How far out do the roots spread? We are going to buy five or six trees. (Pittsburgh, Pa.)

A: The arborvitae probably will, but that shouldn’t be a problem for the pool. I’ve never seen or heard where roots from arborvitae were a problem for sidewalks, pools or foundations.

Q: I’ve been reading your information on red sunset maples. I am very concerned about a red sunset maple that we purchased and planted in our front yard a few weeks ago. The leaves looked wilted on delivery (from a reputable garden center), but I’m afraid that we’ve also overwatered it. My dad suggested that we pull the mulch back to speed the drying of the soil. Even if we’ve overwatered up until now, can it still survive? Any other advice? Thanks for any help you can provide. (email reference)

A: The tree probably was delivered unwrapped and driven along a highway at 50-plus mph on a sunny, warm day, which caused the wilting. Your dad’s advice is right on. Pull the mulch back to allow the soil to dry somewhat, then water only when the soil feels dry, then give it a good soaking. Basically, a soaking like this should be done once or twice a week at most. The foliage probably will continue to appear wilted no matter how much water you apply. I would give the nursery that delivered the wilted tree a call and scold it for this action. I know you paid close to a king’s ransom for this tree to be delivered and planted. It is a shame to lose it due to some thoughtless delivery people. Only time will tell if it will recover.

Q: We are experiencing worms of some kind eating our oak tree from under the bark. I would like to know how to fight them off. I live in northern Georgia. (email reference)

A: This problem should be addressed soon to bring the problem under control. I suggest that you contact the Extension Service county agent where you live. Go to to find the contact. The agent can look at your situation or send samples to the University of Georgia diagnostic lab. Generally, when caught early, pests like these can be brought under control with little or no harm to your tree.

Q: We have a Norfolk pine in a pot that has many shoots. It looks like a forest is starting to grow in the pot. We would like to know what we can do with it. Can we take some of the smaller trees out and transplant them? Should we cut some of them off so they don’t get too thick? Two of the trees are about 5 feet tall. If we take one out to give the other more room, I think we will have a bare area. If so, will that fill in with time? (email reference)

A: Norfolk pines are among the most sensitive at being disturbed when used as houseplants. I was surprised when you told me that some are 5 feet tall. I’m afraid that, at this late date in their age, the roots have intermingled and grafted together. I would encourage you to leave things alone because I’m afraid that any action on your part might end up causing regrets.

Q: I have a treasured autumn blaze maple tree that developed a split in the bark almost the entire length of the trunk. The bark continues to open and curl inwards. The nearby nursery said nothing should be done to it. I am concerned about infestations or a fungal disease. Do you have any recommendations? I would appreciate any help. (email reference)

A: This is sunscald that I hope will heal through time. The nursery is correct in what it told you. Trees have the ability to heal most wounds on their own quite efficiently without our help. In fact, research has shown that our help actually slows or inhibits normal healing. With the tree canopy filling and the tree maturing during the upcoming years, this no longer will be a problem. With the arrival of fall and the tree defoliates, I would encourage you to wrap the trunk from the base to the first branch with Kraft paper, plastic tubing or a whitewash covering prior to the onset of winter. Be sure to remove it the following spring before leaf opening takes place. Do this every year until the trunk develops a corky character.

Q: I have two common purple lilacs planted between two Mount Baker lilacs. Two are 2 years old and the other two are 4 years old. I planted them because I wanted something tall and thick to block the lights on the road beside our house. They are next to a low area that drains water from the neighborhood to the road. They have grown steadily and have bloomed each year. This spring, they were covered with buds and looked very healthy. Then the buds shriveled and the leaves started to dry, curl and turn brown. We had a great deal of rain this spring and sometimes water stood around the lilacs for days. The water has gone down, but the soil is still damp. There are no holes, sawdust or other visible damage. The area is sunny most of the day. We have a clay soil, but I replaced half the soil with something to improve drainage when I planted the lilacs. I think it was called Clay Buster. They did have some mildew on the leaves late last year, but I didn’t think it was a bad case, so I didn’t do anything about it. I assume that the excess water killed the lilacs. Is that right? Did the mildew weaken them? I’m wondering what to do next. One thought is to build a raised bed and plant new lilacs in it so that the water doesn’t collect on top of the soil. Will that work or would wet soil lower down kill them in wet years? If this will work, how high should the top of the raised bed be and how wide? Space is a bit of a problem because I can’t interfere with the drainage area. Another thought is to get plants that can stand extra water in the spring. Is there a type of lilac that doesn’t mind a wet spring? If not, is there another flowering shrub that will get thick and tall and can tolerate a wet spring? Thanks for any advice you can give me. (email reference)

A: The only plant that might approach being something to consider would be pussy willow shrubs. However, many folks consider them too weedy looking to be of any ornamental value except when the branches are cut and brought indoors in the early spring. Raised bed gardening is gaining in popularity because of the wetter springs and water lingering longer and longer in the root zone. Get some stone or other construction material that will allow water to seep through the sides and the base. I would recommend going up 6 inches at the very least, with 12 inches being better. Use a commercially available soil mix that will provide the percolation of water for the lilacs to survive. We haven’t dried out in the Fargo-Moorhead area, so everything is being delayed as far as planting goes. Is there such a thing as ornamental rice?

Q: I have silver maple trees in my yard. I am trying to find out how to tell if the tree is a male or a female before it gets to the age that it produces helicopter seeds. Do you know how to tell the difference? (email reference)

A: There is no way to know. Many will have both sexes on the same plant. Yours must be quite juvenile in age because maple trees usually start flowering early in life.

Q: Fertilizer and its function continue to puzzle me. Every other article I read and every other so- called garden professional I listen to has different opinions about what functions nitrogen, phosphorus and potassium play in plant life. I just need to know about this subject and feel confident that the advice I'm sharing about each of these elements is accurate. Can you direct me to some publication you have that I may have missed that I could use to get a better grip on this subject? A couple of weeks ago, I got back the results of a soil test that the NDSU lab did for me on one of the flowerbeds at the library. One of their recommendations was to add nitrogen to the soil. One of the directors couldn't understand what nitrogen had to do with the soil problem. I'm just amazed when I walk through garden centers and listen to what the employees are telling their customers. I just walk away shaking my head. (email reference)

A: Let’s concentrate on the big three of plant elements: nitrogen (N), phosphorus (P) and potassium (K). Nitrogen and phosphorus are taken into the plant in soluble forms and synthesized into compounds, while potassium remains in the ionic form as K-plus. Most of the soil nitrogen is a component of organic matter and unavailable to plants. Only about 2 percent is available to plants in a growing season. This availability involves a process called mineralization. The atmosphere containing about 78 percent nitrogen and plants that are legumes have the ability to fix this nitrogen. Alfalfa is an example of a plant with this characteristic. When the customer is told the nitrogen level is too low, it is based on the available nitrogen, which generally is something less than a pound of nitrate N per 1,000 square feet. What nitrogen does for the plant is to stimulate new vegetative growth. In some crops, such as turfgrass, vegetative growth is desired over flowering or fruit production. Too much nitrogen will cause soft, succulent and fast growth, while not enough N will cause stunted, hard growth. In the old days, fertilizer was granular in form and had three nutrient salts mixed in. I got my start in horticulture by hauling 80 pound bags of 5-10-5 to people’s cars to use everywhere on their property. Gradually, it was realized that fertilizers for lawns would need more N and less of the other elements, so it was boosted until we now have it at typical ranges of 24 to 28 percent for lawn formulations. In the past, the N was readily soluble and available for plant growth, with a high burn potential if not watered in immediately. Today, high-quality fertilizers will be coated with sulfur, which adds another essential element and is designated as “SCU” on the bag. Some are poly coated and have the designation of “PCU” on the bag. The U stands for urea nitrogen. Nitrogen is available to plants in urea, nitrate and ammonium forms, the latter of which is immediately available. To put this small thesis to an end on N, the bag of fertilizer should have the nitrogen listed as fast release, which are ammonia Cal and nitrate. They sometimes are referred to as WSN (Water Soluble N) and WIN (Water Insoluble N), which includes long-chain methyl urea forms. In most instances (except very sandy soils), phosphorus is not a limiting factor for plant growth. It can be limited to plants at either pH extremes, which are very acid or very alkaline soil. When the pH gets below 6, it is tied up by aluminum. If it is above 7.5, it is fixed or tied up by calcium. In either case, it is not a stone wall, but a sliding scale. The higher the pH (say 8.5), the more it is tied up. When a soil test calls for the addition of phosphorus, it should be understood that it is relatively immobile in the soil. For vegetable and flower gardeners, it should be worked into the soil prior to planting. For lawns, it should follow a core aeration to get it into the root zone. The presence of P in the soil stimulates seedling development and root formation and hastens maturity. As stated earlier, K remains in the ionic form within the plant and is involved in plant health. It helps increase resistance to stress brought on by the environment (too cold or hot), disease resistance and wear tolerance. In typical winter fertilizers, you will find the K being higher than in the typical spring-applied materials. Excess K is not a problem normally because it has the ability to consume more than needed without detrimental effects. All of this is just the very tip of the iceberg on plant nutrients. Many courses dealing with plant nutrition and the proper utilization of fertilizer formulations is an ongoing process of research at universities and companies around the country. Soil test lab results are standard responses. If a particular element is too low for most plant growth, it will be recommended to increase it through the addition of fertilizer. If a particular crop, such as asparagus or lettuce, is known, then specific nutrient levels of say, phosphorus, can be suggested. If the soil test comes back fairly balanced among the big three and the soluble salts are low, plus the pH is not distorted too much, then obviously something else is wrong with the soil or crop. The next step would be to have a pathologist look at what is being grown and what the symptoms are.

Q: I would like to move four elephant ear hosta plants from the side of my yard to the back. Someone told me not to move the plants until fall. Is this true? (email reference)

A: Hosta is a tough species. However, moving them now in full leaf will set them back significantly. You are better to wait until the fall after a good frost or two has nipped the foliage and stopped growth for the season.

Q: For what period is ground sterilizer effective? Our Fair Board is attempting to do some landscaping around a new multipurpose building. Ground sterilizer was sprayed last year on an area that was to be a graveled parking lot. However, after a year of looking at traffic patterns, it would be better to move the parking lot and plant grass and have a garden on the area that was sprayed. There are weeds growing on the area that was sprayed. (email reference)

A: I have witnessed where soil sterilizer has been 100 percent effective where it was applied for at least five years. There are all kinds available, with some having a greater longevity than others have. Many times the affected soil is removed and new soil brought in. The fact that weeds are growing where the application was made certainly is encouraging. If they are broadleaf weeds and not grassy types, such as quack or barnyard, then perhaps the active ingredient in the sterilizer for monocots is active. If so, corn might not be able to make it.

Q: Do you have a method to kill grass that grows up through ground cover plants, such as phlox? (email reference)

A: Look for a selective grass killer on the retail market that has sethoxydim as the active ingredient. There are several products on the market, such as Vantage and Poast. Be sure to check the label carefully before applying because many weed killer products on the market have a combination of herbicides in a formulation that will kill both broadleaf weeds and grasses. You want something that is for grasses only. Even then, test it in a limited area first to see if there is any impact on your ground cover before applying it on the entire area.

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 – June 1, 2011

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