University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article


Dr. Leonard Perry, Extension Professor
University of Vermont

Three questions many ask us in Extension this month include how to establish a wildflower garden, how to get rid of Japanese knotweed and poison ivy, and the best method to overwinter geraniums and coleus indoors.

The common misconception is that you can just scatter wildflower seeds anywhere, as nature does, and end up with the same effect.  The difference is that nature uses millions more seeds than you can afford!  So you must prepare a fine seedbed, as you would for seeding a lawn.

Make sure all weeds are removed, a process that may take a year or two.  Chemical herbicides may be used, but residual ones (ones that last in the soil) may also harm your subsequent wildflowers.  You may cover smaller areas with black plastic for a year.  Repeated tilling, with cover crops, may also be used. Then sow seeds on this fine bed, into which an organic slow-release fertilizer has been incorporated.

Make sure you use a mix containing primarily native species.  Otherwise, you may just end up with pretty annual flowers, native to California for instance.  Keep seeds well-watered regularly until they germinate.  You may need to keep the area weeded, as weed seeds blow in or germinate, at least for the first year or two until your desirable plants are established.

Poison Ivy and Japanese knotweed are very vigorous weeds  Eradication requires persistence says Margaret Hagen from the University of New Hampshire Cooperative Extension.  She suggests repeated mowing over several years to deplete stored root reserves of food, eventually killing the plants.  This means three or more cuttings in a season.  Just make sure, if cutting or weed trimming, not to get sap or plant parts of poison ivy on you.

Grubbing or digging out the roots may help, but missed ones can sprout and regrow.  An alternative to digging, once the tops are removed, is to cover the area with heavy black plastic.  Anchor it with rocks or metal pins, and leave in place for a year.  Herbicides also may be used.  Check with your local full service garden center on recommended ones, and be sure and follow all label precautions and directions.

If you plan to bring coleus or geraniums indoors for winter, Dr. Lois Berg Stack from the University of Maine Cooperative Extension recommends digging plants in late August before nights get too cool.  Pot, water, and leave outside in shade for a week to acclimate, then bring them indoors.  Make sure an bring in healthy plants, and ones without insect pests.

Place them in south or southwest windows for the brightest light possible.  In low winter light, geraniums may stop flowering and coleus may lose their colors.  In spring, cut back the plants and allow them to develop strong new growth outside in full light.  Just make sure to protect from cold and frosts such as by bringing back inside.

An alternative to overwintering whole plants is to root stem cuttings in late August, pot, and keep indoors.  When new growth develops, pinch it back to encourage branching.

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