The gardener's biggest problem is usually not bugs, plant diseases or weather. It's weeds. And the best time to deal with weeds is early, while they're still small. It's important not to give them enough time to develop seeds, which will make your future weed problems worse than ever. For example, one shepherdspurse plant produces 38,500 seeds in a single growing season, while a single redroot pigweed can produce 117,400 seeds.
In a large garden, or a small one where weeds have gained a foothold, you may have to resort to mechanical cultivation to control weeds. Rotary hoes, wheel hoes and powered garden tillers do a good job between rows, but hand tools or hand pulling are often necessary close to crops.
The first green carpet of annual weed seedlings usually appears in late May or June. Attack these weeds while they're still in the seedling stage, scraping them off at the soil level. If you do this on a hot, sunny day, the sun will kill the damaged weeds for you.
It's important to scrape weeds away rather than chop them off. Chopping or working the soil brings additional weed seeds to the surface where they will germinate.
To halt a weed takeover, you may even need to use your lawn mower. Close mowing between the rows on a hot sunny day sets weeds back and may even kill them. It will at least give you time for some hand weeding and an application of mulch to regain control.
The longer weeds are allowed to grow and the bigger they get, the more time and effort it takes to get rid of them. As they get larger, hoeing becomes difficult and most will have to be removed by hand pulling.
Do this on a hot, sunny day after rain or irrigation has softened the soil. Weeds are easier to pull when the soil is moist and you'll be more successful at getting the roots. Plus there's less chance of disturbing desirable plants in the process.
As with hoeing, pulled weeds will be killed by the sun if allowed to remain on the soil on a hot, sunny day. If pulled on a cool day, in the evening, or before rain weeds allowed to remain on the soil may reroot; so remove them from the garden.
Mulch is a very helpful tool in the vegetable garden to slow the germination of weed seeds and conserve soil moisture. This means you will have to water less frequently.
Common organic mulches commonly used in the vegetable garden include compost, old hay, straw, leaves, shredded or whole newspapers and grass clippings. But be aware that straw, hay and lawn clippings can contain large numbers of weed seeds so choose your mulch carefully.
When using coarse materials, like straw, hay or grass clippings, apply a 3- to 4-inch layer of mulch.
Using any organic mulch, such as shredded leaves, bark, sawdust, pine needles and ground corncobs, may tie up soil nitrogen as the materials decompose. If plants appear yellow or are growing slowly they may benefit from an additional fertilizer application.
Sidedress plants in the vegetable garden by sprinkling granular fertilizer down the side of each row, then lightly raking it into the soil. Apply 1-2 pounds of 5-10-10 per 100 feet of row when corn is 12-18 inches tall or the first tomato fruits have set.
Once the current weeds are controlled, apply a pre-emergent herbicide to kill additional weed seeds as they germinate, which they will continue to do throughout the summer. Only use this method, however, if you do not plan to seed any additional vegetables in your garden since pre-emergent herbicides will kill your germinating vegetables, too.
Products labeled for use in the vegetable garden include trifluralin (Preen Garden Weed Preventer) and corn gluten meal (Preen Vegetable Garden Organic Weed Preventer). Trifluralin provides approximately nine weeks of control, while corn gluten meal provides 4-6 weeks of control. For the best results, apply the product to weed-free areas and top with mulch. Then water the product into the soil.
Chemical weed control of existing weeds in a vegetable garden is risky. The chances of damage from drifting spray or movement of chemicals through the soil often outweigh the potential benefits.