Botanical name: Allium cepa
Plant type: Vegetable
Soil pH: Neutral
Onions are a cold season crop, easy to grow because of their hardiness. We recommend using onion sets, which can be planted without worry of frost damage and have a higher success rate than direct seed or transplants. Onions are a basic and essential ingredient in many meals. We will focus on other onions such as garlic in another page. This page is specifically for yellow onions.
- Onion seeds are short-lived. If planting seeds indoors, start with fresh seeds each year.
- Till in aged manure or fertilizer the fall before planting.
- Start seeds indoors about 6 weeks before transplanting. Move transplants into the garden as soon as the ground can be worked.
- Plant the transplants about three inches apart.
- Plant sets directly outdoors 4 weeks before last spring frost. Make sure temperature doesn’t go below 20 degrees F.
- Think of onions as a leaf crop, not a root crop. When planting onion sets, don’t bury them completely under the soil; if more than the bottom third of the bulb is underground, growth can be restricted. Set five inches apart.
- Practice crop rotation.
- Fertilize when bulbs begin to swell, and again when plants are one foot tall
- Generally, onions do not need consistent watering if mulch is used. If you want sweeter onions, water more.
- Onions will look healthy even if they are bone dry, be sure to water during drought conditions.
- Make sure soil is well-drained. Mulch will help retain moisture and stifle weeds.
- Cut or pull any onions that send up flower stalks.
- To control thrips—tiny insects about as fat as a sewing needle—take a dark piece of paper into the garden and knock the onion tops against it; if thrips are present, you will spot their tan-colored bodies on the paper. A couple of treatments with insecticidal soap kills them. Follow the package directions. Spray the plants twice, three days apart, and the thrips should disappear.
- Onion Maggots: Cover your emerging onion crop with a fine mesh netting. Seal it by mounding soil around the edges. The onion maggot likes to lay its eggs at the base of plants, so the netting should prevent that. You should also keep mulch away because the insects like decaying organic matter, and make sure you completely harvest your onions as the season progresses. Onion maggots are usually a problem in very rainy periods, so these precautions may be unnecessary if you have a dry season.
- When onions start to mature, the tops become yellow and begin to fall over. At that point, bend the tops down or even stomp on them to speed the final ripening process.
- Loosen the soil to encourage drying, and after a few days turn them up and let them cure on dry ground. Always handle them very carefully—the slightest bruise will encourage rot to set in.
- When tops are brown, pull the onions.
- Be sure to harvest in late summer, before cool weather. Mature onions may spoil in fall weather.
- Allow onions to dry for several weeks before you store them in a root cellar or any other storage area. Spread them out on an open screen off the ground to dry.
- Store at 40 to 50 degrees F (4 to 10 degrees C) in braids or with the stems broken off.
- Mature, dry-skinned bulbs like it cool and dry, so don't store them with apples or potatoes.
Onion varieties are classified into two categories: Long-day, best in the North, and short-day, best for the South.
- ‘Yellow Sweet Spanish’ long-day hybrid, large round shape, yellow-white.
- ‘Stuttgarter’ short-day variety sold in sets, early maturity with slightly flat shape, yellow.
Wit & Wisdom
Onion's skin very thin,
Mild winter coming in;
Onion's skin thick and rough,
Coming winter cold and rough.