Organic Weed Control in the Summer Garden

5 June 2014, written by Barbara Pleasant

My man Roger is a wonderful weeder, though I must occasionally rein him in lest he take up the weeding tools and do more harm than good. Such a situation arose this week, just before he attacked the few weeds still lurking in the peas. "Don't weed the peas, they're already starting to bloom," I called from the other side of the garden. His hands flew into the air as if he'd been stung by a bee. A few weeks ago he accidentally weeded out the lettuce seedlings growing among the onions, which is enough humiliation for one season.

Later I explained the problem. Every crop has a "critical period" for weed competition, which is usually 6 to 8 weeks after sowing or transplanting. Weeds that are allowed to compete with young plants during this time will reduce yields, but weeds that are allowed to grow after the critical period has passed cause no harm provided they are not allowed to produce seed. Another factor in the organic weed control equation is the crop's sensitivity to root disturbance. A violent weeding session can set back peas and beans so much that they never recover, so almost-mature legumes are safest in the company of a few weeds. Cucumber family crops are easily damaged by late-season weeding, too. Even slight mangling of the vines can cause cucumbers, melons, squash or pumpkins to stop ripening properly.

Growing Green Canopies

Fortunately, vigorous vining cucurbits are capable of forming a dense canopy of green that shades out weeds. Sweet potatoes also provide their own organic weed control as the stems form a dense green ground cover. These talents can be used strategically in the summer garden when you locate canopy-forming crops near areas that would otherwise require constant monitoring for weeds. For example, when I harvest my garlic in a few weeks, I will replace it with winter squash (the seedlings are already growing in containers). The squash will form a weed-suppressing canopy in its bed and the adjoining row, which is occupied by sweet corn. Both crops will benefit in terms of reduced weed competition and the retention of soil moisture from the green canopy provided by the squash.

I like to use leafy greens to smother weeds, too, especially when growing onions, carrots, and other veggies that seem to go weedy overnight. Leaf lettuce sown between rows of onions or carrots shade out weeds and can be pulled before the preferred crop needs more space. From midsummer to fall, mustard greens will grow into a great green mulch that will choke out all but the nastiest weeds, and reduces soil-borne diseases if you chop it up and turn it under.

Using Short Term Nurse Crops

Frequently there are short gaps in summer when one crop has finished, but it's not quite time to plant cool-season crops for fall. This is a great opportunity to use buckwheat or beans as "nurse crops" that will keep the soil busy and provide organic weed control until the space is needed. Then, you can pull out the nurse crop by the handful to make openings for seedlings of broccoli, bulb fennel or whatever.

Once the seedlings start growing, the remaining nurse crop plants can be pulled up and placed on the soil surface as mulch.

Working with little plots of nurse crops is fun, and much more enjoyable than watching your fall carrot bed go weedy before the first seed is sown.

Essential vegetable garden weeding tools

The Best Weeding Tools

I've written before on the importance of sharpening garden tools, and a sharp edge is absolutely crucial for taking down weeds that have gained a foothold in the garden. I also believe in precision weeding tools built for reaching into tight spaces, of which a current favourite is the long-handled Cobrahead weeder, which has eliminated a lot of bending and stooping. For hand-to-hand combat with well-rooted weeds, however, a razor-sharp Japanese Nejiri scraper simply has no competition. Once you've learned to use one, it can cut your weeding time in half.

To keep weeds from coming back, it's best to cover the soil's surface with a light-blocking mulch, which will also help keep the root zone cool and moist. Especially in summer, I like to double-mulch with newspapers (or brown packing paper) spread over the soil's surface, which is then covered with grass clippings, old leaves, aged sawdust or wood chips, or another biodegradable mulch. A paper base layer will enhance the organic weed control you get from any mulch, as it is doing now for me, covered with weathered sawdust, in our pretty and peaceful pea patch.

By Barbara Pleasant