Crown vetch isn't the best ground-cover choice

Question: I have a large area on my property that needs to be sprayed several times a year with an herbicide to keep the weeds under control. There is grass abutting the area. Could I use crown vetch as a ground cover to keep the weeds under control, or would it spread into the grass areas• I know that crown vetch grows and spreads quickly, but I'm afraid it will invade areas where I don't want it.

Answer: Your fears are more than reasonable, and I'm glad you asked before you planted. Crown vetch (Coronilla varia) is, indeed, a rapid grower, but not necessarily in a good way, especially in a garden situation. It was introduced to the United States in the 1950s as an erosion-control plant on roadsides and banks. Its tenacious roots and ability to adapt to, and thrive in, a wide variety of soil conditions are what make crown vetch perfectly suited to PennDOT "gardens." The plant is dangerous in true garden situations, because it spreads by underground stems and seeds, making it very, very difficult to control. Crown vetch has overtaken many meadows and pastures in Pennsylvania and is displacing some beautiful native wildflower species. It is not a plant I would recommend for your property.

That being said, let me offer you some more suitable options for your area. First and foremost, if you choose to leave the area unplanted, mulch it well. Three or four inches of good-quality shredded-bark mulch, spread every year or two over the entire area, will significantly reduce the number of weeds growing there. If you do find it necessary to turn to herbicides for weed control (although hand-picking the few that emerge from the mulch is an even better idea), reach for an organic product based on clove oil (available online at here and here ), and use it when the plants are young for best control.

If you prefer to plant the area, choose your varieties carefully. I'll assume that the area is in full-sun (because that's what crown vetch prefers) with reasonably decent soil. Prepare the site first by adding a few inches of compost, or another organic matter, then tilling the soil to a depth of 6 to 8 inches. If you prefer to plant something by sowing seeds rather than planting transplants, I would go with a mix of low-growing perennials started easily from seed. Roman chamomile ( Anthemis nobilis ), creeping thyme ( Thymus serpyllum ), yarrow ( Achillea sp. ) and candytuft ( Iberis umbellata ) are good choices. You also could sow the area in a biennial crimson clover ( Trifolium pretense ) or a perennial white Dutch clover. Be warned, though, that anything you plant in the area might wind up spreading into the grass (although not nearly with the doggedness of crown vetch).