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Hortiscope

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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I received a cactus plant that is dying. The plant tries to put out leaves, but they wither and die. This has been going on for almost two years. Today, I saw a little red spider on it. My other noncactus plants do not seem to be infected. Can I get rid of whatever is keeping it from growing? Do I need to get rid of the plant and start with a new one? (e-mail reference)

A: There is never just “one” spider mite. The fact that you saw one is a very good indication that the plant is infested with this microscopic pest. If the plant has been struggling for the past two years, you are better off getting rid of this one and starting over with a fresh, bug-free plant.

Q: I noticed a commercial lawn maintenance service putting down a granular-type fertilizer, so I confronted him to see what he was doing. He told me he was applying straight sulfur into the soil. We are well into October, so I asked him what value the soil would gain from this application. He said the sulfur will assist the soil in holding moisture and improve the health of the root system. What are your thoughts on this subject? (e-mail reference)

A: I wonder who made up that line you were given. Did he cite any research? I couldn't find any when I scanned the turfgrass information file at Michigan State University. However, sulfur is a versatile element. It helps improve the physical structure of certain soils by allowing the soil to hold more water. If the soil is alkaline, sulfur reduces the pH value to a neutral or acid level, but only temporarily at best. This process liberates other elements already present in the soil, such as phosphorus, potassium, calcium and magnesium. How do plants get sulfur? Through direct absorption from the air, the decomposition of organic sulfur into the available sulfate form in the soil, water that contains sulfur and from fertilizer and chemical materials that contain sulfur. Nature provides a cycle for conversion of sulfur into the various useable forms needed by plants. Basically, sulfur occurs naturally as a solid, crystalline form and as gasses, such as hydrogen sulfide and sulfur dioxide. These gasses are carried into the soil by water or absorbed directly into the plant. In the soil, natural inorganic sulfur is converted (oxidized) to sulfurous acid, which combines with some of the soil mineral elements to form sulfides of calcium, magnesium, sodium and potassium. These sulfides then are oxidized further into sulfates, such as sulfuric acid. Although considered a secondary nutrient, research shows that in intensely managed turfgrass ecosystems, such as golf courses and high-visibility athletic fields, the sulfur needs by the plant parallel that of nitrogen. What do I think of what you were told was being done? Sorry, but I don't believe the story one bit. What was likely being applied was sulfur-coated urea. Because of the coating, the sulfur slowly will become available during the remaining warm days and early next spring as the soil temperature warms up. Will it help hold moisture? That is very doubtful. Will it help improve the root system of the grass? Yes, as far as that element is needed by the plant, should there be a sulfur deficiency in the soil.

Q: You wrote that people should put a Reemay blanket over their strawberries in the fall. Where can I buy a Reemay blanket? No one seems to know what it is. (e-mail reference)

A: Reemay is the commercial name for a frost blanket. You can find it at http://www.typarlandscape.com/ls_blanket.html. Otherwise, just look for frost blankets in most garden center retail outlets to get something that will do the job.

Q: You mentioned something on your website about using Miracle-Gro instead of fertilizer stakes. Can you tell me why stakes shouldn't be used? I have 17 arborvitae plants that were given fertilizer stakes about a year ago. Is this damaging to them? I noticed the inside of the plants are turning brown. However, my lawn service person says this is normal three years after planting them. My husband waters the arborvitae a little bit every other day with a hose. Is this too little or too much? Also, we have a Colorado blue spruce that is doing well three years after planting. I put fertilizer stakes all around it because it's a big pine. Should I discontinue using stakes? Should I put mulch around the pines for the winter? They are across the dividing line with our neighbor. We live near Chicago, so the weather gets pretty cold in the winter. Thanks so much for your input on this. (e-mail reference)

A: Most evergreens don't need fertilizing. Are you sure you are placing the stakes where the feeder roots are? What do you think the impact on those delicate feeder roots would be when a stake full of concentrated fertilizer finds its way to them? Finally, fertilizer stakes are a rip-off nutrientwise. Chances are they stimulated the grass where you inserted them or created a burn spot from excessive salts. In other words, don't waste your time or money. You should not be watering the arborvitaes every other day. Deeply water them to encourage deep root development. Water them once or twice a week for the first year to get them established and then back off to a couple of times a month during any extended hot period without adequate rainfall. Your lawn service informed you correctly that you will have an annual shedding of older foliage at this time of year or in the spring. It is nothing to worry about. If your evergreens have been planted for three years, there is no need to mulch around the trees at this time except for aesthetic reasons. Next spring, to help conserve moisture in the root zone, you can add about 3 inches of mulch.

Q: I was delighted to find your information about African violets. I have a problem with fungus gnats in all my houseplants. I plan to get a pyrethrin spray for them. Is it safe for my African violets? (e-mail reference)

A: The fungus gnats will be controlled with repeat applications of pyrethrin-based insecticides. Repeat applications are needed because of the very short residual these products have, so what you miss the first time, you can catch the second or third time. Use the pump bottle form and not the pressurized container. The pressurized container will cause frostbite on the delicate African violet foliage. You also might want to revisit your watering schedule. Fungus gnats show up on houseplants that are overwatered or the soil is kept too moist. This is especially true in high organic soil, such as that used in African violet culture.

Q: I bought 100 arborvitaes to border my property. Most are growing well and have good color. I dug a trench when I planted. In one area, I have what looks like a clay type of soil. The plants in that area are not doing as well as the others. I was going to change the soil, but I was told there was no need to do that. I’m sorry I did not go with my gut feeling. Anything I can do short of digging up the trees in that area? Also, I used urea to fertilize. One last question. How close does a canopy from a tree have to be to cause a negative effect on my plants? The tree is 20 feet above my plants. The tree does not block any sun. (e-mail reference)

A: You can alter your cultural practices where you know the soil is heavy clay. In that area, reduce your watering frequency and duration. If the plants don’t respond favorably, then you have no choice but to replant. Urea should not be necessary for the successful establishment of these trees. Urea is used more for turfgrass fertilization where a high nitrogen level will be most useful to the grass. As long as the adjacent tree does not shade the evergreens, there shouldn't be a negative impact.

Q: I have had my umbrella plant for about two years. This summer it grew out about seven to 13 new umbrellas. My problem is there is a big root under the dirt. I don't want to push the dirt away to see exactly what it is, but is that a sign of more growth coming? I have not lost any leaves to date. It is getting indirect sunlight and the state I am living in is getting a little cooler. (Michigan)

A: It sounds like you lived somewhere else where you could leave this plant out all year long. Not so in Michigan! Get the plant indoors as soon as possible and give it indirect light and moderate watering and fertilize when new growth is evident. Don't worry about the new root that is developing.

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 ronald.smith@ndsu.edu.


NDSU Agriculture Communication

Source:Ron Smith, (701) 231-7123, ronald.smith@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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