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When to Plant Onion Sets?
When to Plant Onion Sets?. Onions can be grown from seed, seedling transplants or sets. During the first year, when grown from seed or transplanted seedlings, onion plants concentrate on foliate top growth and developing a bulb. An onion set is a small bulb that has been harvested from a seed plant or transplanted seedling the first year, before it...
Onions can be grown from seed, seedling transplants or sets. During the first year, when grown from seed or transplanted seedlings, onion plants concentrate on foliate top growth and developing a bulb. An onion set is a small bulb that has been harvested from a seed plant or transplanted seedling the first year, before it reaches maturity. Onion sets are stored in a dormant state over the winter to be planted the following spring.
Earliest Garden
Plant onion sets in early spring as soon as the soil thaws and dries out enough to be worked. Onions tolerate light frost. Plant onion sets in cool soil when the soil temperature reaches 48 degrees Fahrenheit. In the U.S., late February or early March is the time to plant onion sets in the Deep South, March in the mid-zones, and about mid-April in northern zones.
Raised Beds
The soil in raised beds warms up and dries out earlier than ground soil. You can plant onion sets earlier if you are growing them in a raised bed, but keep protective mulch handy in case of a dip in temperatures. Onions have shallow roots, so keep the raised bed moist. To raise early salad onions from sets, plant early sets 4 to 6 inches deep. The planting depth determines the length of the white part of the sprout.
Selecting Sets
Onion sets are dormant, so you can purchase them as soon as they are available in your garden center and keep them until your garden is ready. When purchasing onion sets, look for firm, solid bulbs. Prepackaged bulbs will probably contain a variety of bulb sizes. If you buy sets from a bulk bin, you can select the size you want. Look for marble-sized bulbs that have not begun to sprout. Large onion sets typically split into two halves and send up flower stalks early instead of developing larger bulbs.
Photoperiodic
Onion plants are photoperiodic, or sensitive to day length. Onion varieties are sometimes categorized as long-day or short-day. Long-day onion varieties have active top growth until the day length reaches about 14 to 16 hours, and then the plants are triggered to develop bulbs. Short-day onion varieties have a day length trigger point of about 10 to 12 hours. Remember that each layer of onion in the mature bulb is the base of one leaf of top growth. The earlier you plant onion sets, the more leaves will grow, so larger bulbs will develop by harvest time.
