Growing Onions

We offer prestarted onion plants that are grown for us from the finest seed varieties, selected for flavor, texture, and reliability. Our vigorous baby onion plants look like little scallions when they arrive. Don't worry if they seem a bit pale after being in a shipping box -- they will green up soon after they're planted.

When ordering onions, keep in mind that daylength during the growing season affects the growth of bulbing onions more than climate does. For this reason, onions are classified as long-day or short-day types. Imagine a line from San Francisco to Savannah, Georgia. Long-day onions grow best north of it; short-day onions grow best south of it. A few onion varieties are "day neutral" and will grow well everywhere.

PLANTING & HARVESTING YOUR ONIONS

UPON RECEIPT: You have received live plants (not onion sets) that should be planted as soon as possible. If you are unable to plant them right away, remove them from the box and spread them out in a cool, dry area. The roots and tops may begin to dry out, but the plants can live for approximately 3 weeks off the energy stored in the bulbs. After planting, the onions will make new roots.

PREPARING THE SOIL: Onions are best grown in a fertile and well-balanced soil. Organic gardeners should work in rich, finished compost. Spread lime if your soil is too acidic. If you use commercial fertilizer (we recommend 10-20-10), make trenches 3in deep, distribute 1/2 cup of fertilizer per 10 linear feet of row and cover with 2in of soil.

PLANTING: Set plants out approximately 1in deep and 4in apart. If you want to harvest some of the onions during the growing season as green onions, you may space them as close as 2in apart. Pull every other one before they begin to bulb, leaving those remaining to become full-size onions. Transplants can be set out 4-6 weeks before the average last frost in your area.

FERTILIZING: Onions require a lot of nitrogen. Give plants a supplemental feeding of liquid fish emulsion or other fertilizer about 3 weeks after planting; continue to fertilize every 3-4 weeks thereafter. Stop feeding once the necks start feeling soft, about 4 weeks before harvest. If you use a dry granular fertilizer, water it in well.

WATERING: Keep the soil evenly moist during the growing season. Onions require more water as the harvest approaches.

WEED CONTROL: It is important to control weeds around onion plants. Start handweeding or hoeing as soon as weeds begin to appear. Be careful not to damage the onion bulbs. Keep soil loose so onions can expand easily but do not push dirt up against the leaves because this will prevent the plants from forming bulbs. A light organic mulch helps control weeds and preserve moisture. Pull the mulch back when plants are beginning to bulb up.

DISEASES AND INSECT CONTROL: You can generally expect a disease- and insect-free crop, but onions do occasionally have problems. They are susceptible to two major diseases: blight and purple blotch. If the leaves turn pale-green then yellow, blight has probably affected the plant. Purple blotch causes purple lesions on the leaves. Heavy dew and foggy weather favor the spread of both blight and purple blotch, and when prolonged rainy spells occur in warm weather, these diseases can be very destructive. The best cure is prevention: plant in well-drained soil, run the rows in the same direction as prevailing winds, and avoid planting near windbreaks that will prevent good air circulation around the onion foliage. If conditions favoring these diseases persist, spray a fungicide labeled for use on onions, carefully following the instructions.

The most destructive insect is the onion thrips. Thrips are light brown in color and are less than 1/6" long. They feed by rasping the surface of the leaves and sucking the juices, causing deformed plants with silvery blotches. Thrips overwinter in weeds, so keeping the garden clean can help reduce the population. Combat serious infestations by using insecticidal soap or pyrethrin, again, following label instructions carefully.

If a plant bolts (sends up a flower stalk), pull it up and eat the onion right away. Bolting is caused by an unexpected dormancy period during the growing season that makes the onion think that it is time to die and therefore to reproduce. The onion is perfectly edible, but the flower stalk will penetrate the bulb and cause excessive decay during storage.

HARVESTING AND STORAGE: Once the leaves turn yellow and about half of them have fallen over, use the back of a rake to bend the remaining leaves down. This stops sap from flowing to the leaves and diverts energy into the maturing bulb. A day or so later, when the tops turn brown, pull the onions and let them dry in the sun. Lay the tops of one row over the bulbs of another to prevent sunscald. When onions are dry, clip the roots and cut back the tops to 1in. You can also braid uncut tops together and hang the onions in an airy spot. The best way to store onions is in a mesh bag or nylon stocking. Place an onion in the toe and tie a knot or put a plastic tie above the onion. Then add another onion and tie another knot, continuing in this way until the bag or stocking is full. Store in a cool dry place. When you want to eat an onion, simply clip off the bottom one with a pair of scissors or remove the plastic tie. Another way to store onions is to spread them out on a screen. Make sure they don't touch each other. As a general rule, the sweeter the onion, the higher the water content, and the shorter the shelf life, so eat the sweet varieties first.

Email Sign Up

Subscribe to enjoy gardening advice, email offers & more