Owens Corning

National Gardening Association Are You Ready for Strawberries?

by Larry Roche

As we dream of a patch of strawberries, bright green and brimming with fruit, weeds are probably the last item on our list of things to think about before planting day. But weeds are actually one of the biggest problems in growing these easiest of all common fruits. Strawberries are perennial, so you should get about five years out of a healthy strawberry bed. But if you don't take care at planting time, you could be lucky to get even one good crop.

The essence of the weed problem with strawberries is that they are low-profile plants. They need ample soil moisture and lots of sunlight to produce large crops with a high sugar content, but they are poor competitors. With fifty to ninety percent of its roots in the top six inches of soil, the strawberry plant is easily crowded out by both annual and perennial weeds.

Beacuse it's the nature of the strawberry plants to sprawl by means of runners, forming a bed or wide row of plants, the weed problem gets more difficult to deal with the months pass. First-line weed-control methods -- hoeing and cultivating -- can be very damaging to strawberry roots once roots and runners start to spread, which can be midway through the first season. That's why it's crucial to have a plan for your weed problems before you plant. Fortunately, there are many ways to deal with those weeds -- some old, some new --to deal with strawberry weeds.

What About Mulch

It's standard practice to grow strawberries on mulched ground. The mulch thwarts annual weeds and keeps the fruit clean and dry. But if the soil harbors perennial weeds, ordinary mulching won't be enough -- these weeds will thrive in mulch once they've sprouted.

If your bed-to-be is weedy, or land not recently cultivated, the traditional way to prepare the ground is thorouqh digging. Turning the soil over with a shovel, fork, or rototiller kills many weeds by chopping them up and burying them. However, some perennial weeds -- quackgrass, for example -- resprout readily from chopped pieces, so pick out as many root pieces of these weeds as possible. One digging probably will not do the job on perennial weeds. Wait a couple of weeks for any weeds that survived the first digging to sprout, then dig again and remove them.

Strawberries thrive in rich soil, so take advantage of all this digging to incorporate compost, leaves, or other organic materials into the ground. Once you've cleared the ground of perennial weed roots, mulch will effectively smother annual weed seedlings, so you could be ready to plant strawberries now.

Plan Way Ahead

The further ahead you start, the more you can clean weeds from the strawberry bed. If you are opening new ground, the ideal approach would be to cultivate the soil for a full year before planting strawberries. Use the space for annual vegetables or flowers planted in rows along which you can easily keep weeds in check with cultivation or mulch. If you don't have time to tend vegetables or flowers in the new ground, you could plant a cover crop, which is a plant grown not for harvest, but for soil improvement, enriching the soil with organic matter. Choose a cover crop that produces dense growth quickly and it will do your weeding for you by shading the ground. Certain cover crops also release natural chemicals that inhibit weed seed germination. Leguminous cover crops also add nitrogen to the soil but most of them aren't dense enough to smother weeds effectively.

Bring on the Marigolds!

Marvin Pritts, a small-fruits specialist at Cornell University, has recently been evaluating cover crops specifically for strawberries. One that he is particularly excited about is French marigolds, broadcast at the rate of 0.2 ounce per 100 square feet, then raked in. Besides shading the ground, the marigolds are especially thirsty plants, drinking up lots of soil water and doing to the weeds what the weeds would do to the strawberries. Marigolds also suppress nematodes, a problem in some areas.

Marigolds do not survive cold weather, so in early fall, Dr. Pritts killed them off (by mowing) and planted a cover crop of rye grain (not ryegrass, which is used for lawns). The rye not only shades out cool weather weeds, but also leaves a residue in the soil that suppresses weed growth.

Strawberry need to be planted in early spring. The traditional way to kill a rye cover crop is to till it into the soil. But because you should never till sodden ground and must wait for the soil to dry, this method often means waiting until it's too late for strawberries. Tilling also brings up buried weed seeds, present in all soils and just waiting to be awakened by light and air.

After You Plant

Once you have thoroughly weeded -- by traditional or "modern" methods -- you are ready to plant strawberries. But don't turn your back on them after they are safely in the ground. Whether you cultivate with a hoe or rototiller, keep in mind those shallow strawberry roots. Cultivate every couple of weeks, just skimming the surface of the soil, and mulch as soon as possible.

The strawberry plants will soon strew daughter plants around the garden (the word "straw" in strawberry may have come from the word "strew.") If you want the daughter plants to take root and grow, cultivation will soon be impossible, and so it's time to mulch. The traditional mulch for strawberries is straw (another possible origin for the word "strawberry"), but beware of importing weed seeds. Other good organic mulches include pine needles, shredded leaves or excelsior. Black plastic also suppresses weeds too but does prevents runners from rooting. Moreover, it does not add organic matter to the soil or keep it cool in summer, and ultimately presents a disposal problem.

A few weeds will eventually start poking through mulched ground. This is the time to get down on your hands and knees. In a small plot, nothing beats the intimacy and thoroughness of hand-pulling each weed.

In spite of your best efforts, weeds probably will eventually make their way into your strawberry bed. In fact, strawberry plants often become one of their own worst weeds, as daughter plants incessantly pop up too thickly, or where they are unwanted. Usually in about five years, a bed becomes overcrowded, as well as unproductive and diseased. So to hedge against that day, a year or two before putting your old bed to rest, start a new strawberry bed somewhere -- weed free, of course!

A Living Mulch

A few years ago in Ohio, strawberry researcher Craig Chandler (knowing that head is hard on strawbs) found that summer shade decreased growth of strawberry plants, but had no ill effect on fruiting the following year. Putting this information to use, Marvin Pritts, small-fruits specialist at Cornell University, has successfully suppressed weed growth in productive strawberry beds by broadcasting seeds of a cover crop (sudan grass) right after the plants finish fruiting for that season. The sudan grass suppressed weeds in the open ground between rows of strawberries, without reducing yields of berries the following year!

Sudan grass, a vigorous, warm-weather annual proved to be a nearly ideal cover crop. Sudan can grow very tall, so was mowed when it was about eighteen inches high, down to just above the strawberry plants. Then allowed to regrow. That amount of growth did not affect strawberry production, but did shade out many weeds. Sudan is killed by frost so presents no problem the following spring when the strawberries need as much light as possible. Sudan also suppresses nematodes. Pritts found that other cover crops didn't work so well as living mulches. Oats did not grow enough bulk, and marigolds were too competitive for water.

Crops That Stop Weeds

Cover crops need at least 60 growing days in the ground to do enough good to be worth planting. In fall, they'll need even a little more time, especially in the northern half of the country where daylight hours shorten dramatically. Cut and till (or compost) all covers when the first flowers appear, if not earlier. This keeps them from going to seed and becoming weeds themselves. Here are some of the best cover crops, for both hot and cold weather.

SPRING AND FALL

Annual Rye Grain (Secale cereale). Germinates and grows quickly in cool soil down to 45 degrees F.

Oats (Avena sativa). Grows quickly, then winterkills (zone 6 and north), making a good mulch.

Winter Wheat (Triticum sp.). The most cold hardy of the grain covers.

SUMMER

Buckwheat (Fagopyrum esculentum). Fast growing and the best for smothering weeds.

Marigolds (Tagetes sp.). Low growing and kills nematodes. Seed may be expensive and slow to establish, however.

Soybeans (Glycine max). Fast growing and a good nitrogen source. Sow thickly -- seed is cheap and readily available.

Sudan Grass (Sorghum sudanense). Heat tolerant and drought resistant. Prevent self-sowing by mowing.

Larry Roche gardens on an acre in New York's Hudson Valley. He has grown strawberries for more than 15 years, along with a rich assortment of grapes, berries and tree fruit.

Copyright NGA

Reprinted with permission HouseNet, Inc.

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