Preparing a Weed Free Onion Patch

Keeping your onion beds weed free is important as weeds compete with onions for nutrients. Below are some tips for preparing your beds in advance to keep you onion patch weed free.

Preparing Your Beds in Advance

Annual weeds respond to a wide range of environmental factors that stimulate germination such as light, water, oxygen, and nitrogen. If beds are prepared in advance, they should be shallowly worked (to a depth of 2″, or approximately 5 cm) immediately before planting to kill emerging and established seedlings.

If you prepare your beds far enough in advance to kill several generations of weeds, it will greatly reduce weed pressure during the growing season, upping your chances of keeping a weed free onion patch. After each new crop of weeds emerges, shallowly work the soil to destroy the newly emerging weeds. Cultivation is always more effective in dry soil conditions. In moist soil conditions, weeds are more likely to re-root and continue growing.

Burning Weeds

Another option for creating a sterile bed for planting onions is by burning the weeds. Flaming should target broadleaf weeds; grasses, with their basal growing points, are less susceptible. Ideally, flaming should be performed just before planting your onion transplants or the crop emergence of other vegetables if planted from seed. If the ground is cracking and the new seedling is starting to emerge it can be killed by the flame. This method can be used in moist soil conditions.

Using Mulch to Prevent Weeds

Both plastic and organic mulches help modify soil temperature, conserve moisture, and provide weed control. Managing weeds in the wheel tracks or paths between plastic-mulched beds remains a challenge, however. Use a heavy application of mulch hay between the beds, aiming for a depth of at least 1″ (~2.5 cm) of compressed mulch.

to provide season-long weed control. The mulch must maintain this thickness, overlapping the plastic, to avoid weed problems on this edge. While costly, both for the mulch and the labor, it benefits soil quality and reduces weeding requirements. 

Living mulches are another option for the areas between plastic mulched beds, but compared to straw, hay, or leaves, the living mulch will compete with the crop for water and nutrients, and provide an environment more favorable for perennial weeds to proliferate. If living mulches are used, consider strategies to manage the competition. For example, drip irrigation and band application of fertilizers can be used to deliver water and nutrients to the crop; frequent mowing can manage resource uptake by the living mulch. So, weed early, weed often, and use all means available to keep weeds from competing with your onions.