Lawns to Love

Lawn weeds have something to say about the soil.

By Paul Tukey

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Weeds in the lawn tell a tale of the soil

The secret to gardening success is in the soil, and that applies to growing healthy lawns, too. When it comes to nurturing turf organically, the basic principle of feeding the earthworms and soil microbes still applies. And when you do your job well, you’re rewarded with green grass.

You may also find, however, that plenty of robust weeds dot the turf. Garden wisdom says that most weeds are messengers, their type revealing something about the soil below. In other words, if the lawn features more weeds than grass, it’s because they are what the soil is predisposed to grow. You can kill the messengers any number of ways, but the weeds will keep coming back until you change the underlying problem.

If the lawn is studded with lots of plantain, thistle, or quack grass, the soil is probably compacted. Excess clover, trefoil, or wood sorrel indicates a lack of nitrogen. Several weeds point to acidic soil, including violets, knotweed, and hawkweed. The dandelion, at once the most hated and nutritious weed of all, is a bio-accumulator with a deep taproot that draws calcium to the surface.

Identifying the weeds that dominate the lawn is key to winning the lawn game. If the lawn’s topsoil has plenty of calcium, dandelions are less likely to take root there. Ten pounds of high-calcium limestone, gypsum, or wood ash per 1,000 square feet can often make up for a calcium deficiency. Likewise, aerating the soil to reduce compaction will begin to eliminate plantain. Adding a high-nitrogen organic fertilizer from fish, corn, feather, or blood meal will reduce clover (if you feel you must).

Watching these weeds will, in time, create a seasonlong blueprint for success. No matter where you live, organic lawn care—unlike synthetic-chemical lawn care, which relies on a rote four-step program—can be adapted to specific conditions relative to the soil, the microclimate, and the nooks and crannies of your yard.

The same commonsense approach applies everywhere. In spring, let the lawn grow at least 3 to 4 inches tall so that the grass shades the surface of the soil. (Lawns of bermudagrass and seashore paspalum, which are low-growing by nature, are exceptions to this rule.) Taller grass prevents weed seeds that need sunlight, such as crabgrass, from germinating. In summer, keep the lawn as tall as possible so the soil doesn’t dry out and the grass outcompetes weeds.

Tall grass in summer will also reduce the need to water. If you must irrigate, make sure the water penetrates several inches into the soil so the grass roots learn to grow deep—then don’t water again for a week or more. The appearance of a lot of weeds in summer may mean you’re watering too frequently.

If weeds are still a problem when fall arrives, take note of what’s growing and consider a soil test. Autumn is the best time to overseed the lawn and apply soil amendments and fertilizers so the grass will be optimized for the following year.

Winter is typically a quiet season for the lawn. As long as the ground isn’t frozen, however, weeds can still be pulled or spot-sprayed with natural products such as horticultural vinegar. And even though it is winter, lawns shouldn’t be treated like pavement to be carelessly driven upon. Vehicles compact soil, and plowing snow onto the lawn can deposit driveway salt in the wrong place—which means you’ll probably get more weeds come spring.

You might have noticed that more and more companies are selling products to eliminate weeds organically. Weed killers made from naturally occurring iron or sodium hold great promise for instant and environmentally safe control. In the long run, though, you’ll still need to look below for the best answer. The secret, as always, is in the soil.

Originally publishined in Organic Gardening Magazine, June/July 2013.

Photos: Thistle and Knotweed: Nigel Cattlin/Alamy; all others: Rob Cardillo Photography

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