Can Onions Be Grown With Plastic Mulch?

Season

• Onions need cool, moist starts for adequate establishment, with hot summers for bulb formation. The Ohio State University Extension recommends starting the onion seeds or sets around last frost for your area, when temperatures hit 50 to 55 degrees F.

Site and Soil

• Choose a site and prepare the soil before you lay out the mulch, as you won't have access to the soil once the mulch is down. Find a site with full spring and summer sun, good air movement and efficient drainage. Till the top 6 inches of soil and add 3 to 4 inches of organic compost for moisture and nutrition. This amendment process warms and aerates the soil for planting. Add 5-10-10 fertilizer per manufacturer directions for quick establishment.

Plastic Mulch

• Lay the mulch out after the soil settles. Stretch sheets of plastic mulch across the site, with the edges meeting or slightly overlapping, and secure the corners with landscape staples. Cut 2-inch slits in the plastic at every 3 inches in the row, or cut one long slice for the planting row. Leave 12 to 18 inches between multiple rows.

Planting and Care

• Plant onion seeds, seedlings or sets in the sliced areas of the plastic or at every 3 inches in the row. Water the onions with 2 inches of water every week to maintain moisture. Always water plants in plastic mulch at the base to ensure the water enters into the soil. If you plant seeds, watch for germination and guide the sprouts up through the plastic. Harvest green onions early in the season and bulb onions when the plants dry and collapse.