Weeds absorb soil nutrients and reduce the potential plant size. Using plastic mulch, while growing onions, is an effective method for weed reduction. Ideally, onions grow best in raised gardening beds. Planting onions under mulch is a little tricky, but not impossible. Better soil moisture retention, fewer weeds and healthier plants are benefits to using plastic mulch with this garden vegetable.
Prepare a raised gardening bed in late August to early September. Till the gardening area. Add coarse organic compost, sand and peat to the raised soil mixture to provide adequate nutrients and promote drainage.
Cover the area for 72 hours, allowing the soil to settle and nutrients to disperse.
Lift the covering off the raised gardening bed. Cover with a 2-inch layer of plastic mulch.
Separate the mulch to form small, open pockets for planting the onion bulbs.
Dig a 2-inch deep hole in each pocket with a bulb digger. Place one onion bulb in each hole. Cover with 1 inch of organic potting soil.
Soak the raised onion gardening bed with water. The ground should be saturated with water, but without standing puddles.
Unroll chicken wire over the raised onion gardening bed. Make certain all the plastic mulch pockets, with planted onion bulbs, are covered. Cut the excess chicken wire from the roll. Secure to the ground with gardening stakes. Raise the height of chicken wire as the onion tops grow.
Remove chicken wire after onion tops are 8 to 12 inches tall. The wiring protects shoots from wildlife consumption.