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   Ask the Plant and Pest Professor!


Ask the Plant and Pest Professor!

Question #1: I have many hydrangea bushes of various ages. They all bloomed nicely last year, but this year there are just a few blooms on the sides of the plant. Do I need to trim them yearly to get them to bloom well the following year? I have both the pink and blue blooms since I have rich acidic and some alkaline soil.
Answer #1: Even though the mophead, or bigleaf, hydrangeas you describe prefer partial shade, flower production is dependent on sunlight. If the shrubs are located in the shade of other trees and the canopy of shade has increased substantially, the number of flowers that bloom will diminish. Hydrangeas are very sensitive to drought. Yours may have suffered some root dieback last year which is manifesting itself now. Also, a harsh winter will lead to dieback of many stems.
       Pruning hydrangeas is a tricky proposition. Hydrangeas must be pruned immediately after flowering, because they quickly begin forming the buds for the next spring's flowers. If you pruned in late summer, fall, winter or this spring, you removed this year's flower buds. Pruning is not necessary for good flower production.
       A last possibility: too much nitrogen fertilizer can result in fewer flowers. Typically, a shovel or two of well-rotted compost, spread around the root zone each spring, is all that is needed.
Question #2: Help! This has occurred now for a second year and I don't know what to do. I just let my dogs outside and I looked at my garden. Now, even through my nylons, I must have 5 welts (just like mosquito bites) but I never saw anything that might cause them to occur. I was outside for maybe ten minutes. This occurs only on one side of the garden.
Answer #2: Your leg bites could be caused by fleas, which can infest some areas of a yard inhabited by dogs. Fleas prefer protected, moist environments away from direct sunlight. They are tiny, black insects, which jump quickly and might not be felt. Spot treat with a pesticide recommended by your veterinarian. If you eliminate fleas as the culprit, mosquitoes are the best bet. The Asian Tiger Mosquito, a recent invader of our area, is extremely pesky. It feeds during the day (unlike its native nocturnal cousins), is more aggressive, and may carry the West Nile virus.
       Cover up with light-colored clothing when in the yard and spray exposed skin with a repellent containing "deet." Tour your landscape periodically and eliminate any standing water. Pay particular notice to drain pipes, saucers under flower pots, bird baths, etc. Have your rain gutters cleaned periodically and be sure they drain properly. Call us for a handy checklist.
       Tiger mosquitoes range only about a football field's length from where they hatch. If you are being bitten, so are your neighbors. By cooperating as a community to eliminate breeding places, you all can rid yourselves of Tiger mosquitoes.
Question #3: Why can't I get bell peppers to grow? All my other fruits and veggies grow fine.
Answer #3: Bell peppers like it warm and will be stunted and slowed during cool periods (Do not set out transplants until soil is thoroughly warmed and be sure the transplants are six to eight weeks old sturdy so that they get off to a good start). On the other hand, they also don't like it too hot and dry! In the summer, production will often slow or stop entirely. If your garden gets very hot and dry, spray the plants with water to cool them down during heat waves. Next year, you may want to plant the peppers where they get some afternoon shade.
       In addition to fertilizing with a starter solution when planting, side-dress with 1/4 lb of 10-10-10 (or something similar) per ten foot row after first fruit set. To get proper a fruit set you need a block of pepper plants to crosspollinate (at least four to six). And, as always, encourage your pollinating insects to help out.
Question #4: What is the best way to deal with Japanese beetles? I have tried the traps at the far end of my property. I am using an organic citric acid spray that seems to kill the beetles on contact but has no residual benefits. I hate to spray with a systemic insecticide, but I love my roses and hollyhocks.
Answer #4: It's a problem. The traps attract more beetles than are originally in a yard, not only to the trip but along the flight pattern, so we don't recommend them. This is supposed to be a year with low numbers of Japanese beetles, because last year's drought made the soil so hard it was difficult for them to lay eggs. If you are seeing large numbers, do you by any chance irrigate your lawn? Irrigated lawns will attract beetles at egg-laying time because the soil is moist and soft.
       As for spraying, it is not a good idea to spray beetles on any plant in bloom as the pollinators may be killed (Honeybees are rare enough already because of a recent disease). We need all the pollinators we can get.
       Usually Japanese beetles favor one or two plants in the yard, such as roses or raspberries. Because they are concentrated in one place, handpicking can be effective. Every day or so simply knock them off into a container of soapy water held underneath. They will bail out naturally when disturbed. Plants tolerate some foliage damage. Do not expect to rid your entire yard of beetles. If they are defoliating a large plant that defies handpicking and spraying is the only recourse, neem, permethrin, or imidacloprid are all possibilities (Systemic pesticides are no magic bullet, because they will not be absorbed into the flower itself). Spray late in the day when pollinators are not active. A strategy for shrub roses: After the first flush of bloom, which occurs before the beetles emerge, cut back the spent blossoms and a bit of branch tips. This will delay the next flush of blooms until the beetles have stopped feeding for the year.
Question #5: My Lemon Fluff perennial has finished blooming. The old flower stalks are still green. They are large and block the view of other flowering plants. Can I cut the stalks back? What is the best time and by how much?
Answer #5: There is a lemon fluff knapweed and also a lemon fluff daylily. In either case, you can cut the flower stalk back as far as you like, leaving the foliage intact, after the plant finishes flowering.

”Ask the Plant and Pest Professor” is compiled from questions sent to the website of the Home and Garden Information Center (HGIC), part of Maryland Cooperative Extension, an educational outreach of the University of Maryland. To ask a home gardening or pest control question and find other help, go to Or phone HGIC at 1-800-342-2507, Monday through Friday, 8 a.m. to 1 p.m. (Readers please note that funding for this program is endangered; consider communicating to your state legislator that you believe it should be continued.)

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This story was published on August 15, 2003.
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