Weed-Blocking Flowers


Moss phlox, lady's mantle, and catmint are more than just pretty perennials. They certainly are beautiful in the flower border, but when researchers at Cornell University studied perennial plants to see which suppress weeds while maintaining their good looks, these three, along with four others, turned out to be the seven samurai of weed control. Plant them in your beds, and they vanquish pesky plant invaders.

If you had to name plants that give weeds no room to move in, you'd probably come up with low-growing groundcovers such as pachysandra, vinca, and bugle. But with the exception of moss phlox and thyme, the winning weed-smotherers we are talking about here are all taller than 8 inches, and some grow to 2 feet tall.

They share two traits that make them great weed-thwarters: All are fast spreaders, and they have dense leaf cover--which prevents sunlight from reaching germinating weed seeds. The Cornell seven either blocked weeds right from the start or needed just light weeding in spring until their foliage filled out.

The perennials tolerate weather extremes that would stress most plants: drenching rains and sporadically soggy soil, as well as periods of drought. And they're low-maintenance, to boot. To keep weeds from getting established in your flowerbeds, plant one of these top performers.
No Weeding Required

'Emerald Blue' moss phlox (Phlox subulata) provides good spring and summer coverage, although it thins out a bit by fall. A native evergreen, moss phlox displays gorgeous lavender-blue blossoms during April and May.

'Thriller' lady's mantle (Alchemilla mollis) grows a dense canopy of broad, scalloped leaves and attractive pale yellow flowers that are present for several months, from late spring to early fall. It adapts well to a variety of conditions.

'Walker's Low' catmint (Nepeta x faassenii), voted the Perennial Plant Association's 2007 Perennial Plant of the Year, sports rapidly growing foliage that provides dense cover by late spring, and it puts on a continuous show of light blue flowers from late June to mid-September.

'Golden Fleece' dwarf goldenrod (Solidago sphacelata) is exceptionally stress-tolerant. It has dark green foliage and bright yellow flowers throughout the summer and into early fall. Native to North America, dwarf goldenrod brings even more color to your garden, because it attracts butterflies.
Some Weeding Required

'Albiflorus' creeping thyme (Thymus praecox) is a vigorous spreader, forming a compact mat at ground level that thickens again in early fall after flowering. Noted particularly for its pleasant fragrance, its evergreen foliage, and its carpet of tiny blooms in late spring and early summer, creeping thyme is also a good choice for dry conditions.

'Herman's Pride' false lamium (Lamiastrum galeobdolon) quickly forms a dense canopy, particularly in its second year, spreading by stolons (stems that grow along the ground, sprouting roots and new shoots at each node). It maintains its pleasant mottled yellow-green foliage throughout the growing season and shows pale yellow flowers from late spring through midsummer.

'Majestic' lilyturf (Liriope) produces widening clumps of dark, evergreen, grasslike foliage, emerging in late spring. In July and August, it shoots out prolific spikes of tiny violet-blue flowers, followed by a flush of shiny blue-black berry clusters.
Planting for Weed Control

When planting groundcovers to suppress weeds, the strategy of "the more, the merrier" holds true, say the Cornell specialists on weed-suppressive groundcovers. You'll need more plants, sited closer together, than if you were simply using them for decoration. For full soil coverage, set plants in the ground on 9- or 12-inch centers.

One thing to consider: These groundcovers are so effective because they're aggressive species that outcompete weeds (and potentially other ornamental plants) vying for the same space. They won't necessarily take over your garden, but before planting any of them, check with your state's invasive-plant council or with the Nature Conservancy chapter in your region, just to be sure that your newfound problem solvers won't cause problems of their own.

For growing information on the Seven Samurai groundcovers mentioned here, visit OrganicGardening.com.

PHOTO (COLOR): Win the weed war: Perennials that keep weeds from germinating include 'Herman's Pride' false lamium (far left): 'Walker's Low' catmint (left), and 'Emerald Blue' moss phlox (below).


By Seth Palmer

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