Composting, trimming perennials, bagworm tips offered

Bagworm nests should be removed by hand at this time of the year.

Editors note: Throughout the growing season, Mike Hogan, OSU Extension Educator for Agriculture & Natural Resources in Franklin County, will answer gardening questions submitted by Dispatch readers. Send your questions to hogan.1@osu.edu.

Q: I recently started a compost pile and I am wondering if it is advisable to add grass clippings from my lawn because we have it treated for weeds and insects several times each season.

A: That is an excellent question. Although many lawn herbicides are quickly broken down by the heat generated in a well-functioning compost pile, or bind strongly to soil particles making them safe to use around plants, some chemical residue could still be present in compost.

There is also the chance that your entire compost pile may not reach the desired temperature of 150 degrees Fahrenheit.

Most gardeners who compost desire to have an organic system and adding grass clippings from a lawn treated with synthetic chemical pesticides would not be organic.

I would seek another source of “green” materials to supply nitrogen for your compost pile. Kitchen scraps, particularly fruit and vegetable wastes, can be a good substitute for grass clippings. Or perhaps your neighbors who do not treat their lawn with synthetic chemicals need a place to recycle their lawn clippings.

Q: When is the correct time to trim perennial plants in the flower garden? I would like to get my beds cleaned up before the cold weather arrives, but some of my coneflowers and asters are still blooming.

A: Most herbaceous perennial flowers should be trimmed close to the ground when the foliage is nearly completely dried out and brown in color. Asters flower in the late summer and fall, so we would want to wait until they cease flowering in a couple of weeks (or longer depending upon how long our current warm spell lasts!).

If late-planted coneflowers or other perennials are still flowering, you should wait until the flowers fade and the foliage begins to dry out and turn brown.

You might also choose to not trim back some herbaceous perennials until late next winter or early spring, as many beneficial insects will overwinter in and around herbaceous perennials. The hollow stems of coneflower and other plants make excellent overwintering sites for several species of insects when the flower heads are removed.

Also, the seeds contained in the heads of coneflowers, Black Eyed Susan and other herbaceous perennial plants, can be an important source of winter food for birds.

Q: We have a lot of the bagworm nests hanging on arborvitae shrubs in the yard. Can we spray these insects now so that they do not hatch in the spring?

A: By this time of the year the bagworm (Thyridopteryx ephemeraeformis) caterpillars have tied off their bags with silk and have ceased feeding and causing damage for the year.

Insecticides applied at this time of the year are ineffective as it is difficult to get coverage needed to sufficiently move through the bag to make contact with the insect.

The best control at this time is to remove the bags by hand and destroy them. Do not simply drop the bags to the ground, because the eggs in the bags can still hatch next spring.

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