Not only do homegrown onions taste better than store-bought varieties, but they’re also super easy to grow. You’ll discover a wide array of yellow, red, or white varieties that you can start from seeds, sets, or transplants. If you’ve been considering a vegetable garden, growing onions is a great way to get started, no matter how green your thumb is.
There are all shapes and sizes of onions or alliums:
Your location heavily influences what type of onion will grow best for you. Choose from three types: short-day, long-day, and day-neutral. Short-day varieties, like Texas Super Sweet, need about a half-day’s worth of daylight to bulb. They grow best in USDA zone 7 or warmer. Long-day varieties, such as Red Zeppelin, thrive in areas with long summer days, in zone 6 or colder. This includes southern Canada and the northern United States. Day-neutral varieties like Superstar are more suited for zones 5 and 6.
This vegetable needs both cool and warm weather to grow. Cool weather helps the onion produce their tops, the green leaves that push up through the soil from the bulb. Warmer temperatures produce the bulbs, which grow underground. Optimal temperatures for growth are between 55 and 75 degrees. In areas with mild winters, you can plant some varieties in the fall or winter. Frost and cold temperatures can damage young onion stalks and slow down bulb production. If the bulb freezes, it will rot after it thaws. Use mulch to protect plants in colder regions.
If you’re seeking a wider choice of onion varieties, your best bet is to start plants from seeds. Start indoors for best results, about four to six weeks before the last frost. In colder regions, some gardeners use grow lights to give their seeds a light boost. If the outdoor temperatures are at least 40 degrees, plant the seeds directly into the soil, in holes 1/4 to 1/2-inch deep. You should see seedlings sprouting in about a week to 10 days. Onions need room to breathe, so thin out the seedlings. Replant into two-inch deep holes, in rows 12 to 18 inches apart.
Some people prefer to start their onion crops using sets, which are immature onions that growers pulled from the soil and stored. They are widely available at gardening centers and through online seed companies and nurseries, but there are fewer varieties to choose from. Avoid using the larger onion sets. The bigger the onion set, the sooner it stops growing and goes to flower. You’ll get larger, better-tasting onions by planting smaller sets.
The right amount of water makes the difference between high yields and poor ones. Water-starved onion plants produce overly pungent bulbs, but overwatering encourages disease, pests, and rot. Watering once or twice per week works well. Try using the "knuckle rule" to determine whether your onions need water. Stick your finger into the soil surrounding the plants. If you detect no moisture up to the first knuckle, the onions need water.
Onions need nitrogen, so use a fertilizer or compost every few weeks to encourage large, healthy bulbs. Experts recommend ammonium sulfate in alkaline soils or a calcium nitrate fertilizer for acidic soils. Stop fertilizing onions once the ground starts to crack and the onions are emerging from the soil. That means the bulbing process is in full swing.
Dry bulb onions take between 100 and 175 days to reach maturity. Harvest your onions once the green tops of the plant have fallen over. The veggies are at their peak flavor when harvested early in the day. Pull the onion from the ground, then clip the roots. Cut the tops to approximately one inch. Store in a cool, dry, place, or wrap each onion individually in foil and store in the refrigerator.
Silvery leaves or leaves with white streaks or blotches are a sign of onion thrips, tiny insects that appear during warm or dry conditions. Another major issue for onion plants is pink root, a fungus that attacks and turns the plant’s roots pink, red, or yellow, reducing yields. Flowering onion stalks prevent bulb growth and are usually from temperature fluctuations or planting at the wrong time.
Once the bulbs peek out from beneath the soil, don’t cover them with more dirt. Dry, loose ground around the emerging onion bulb is good for its development. It also deters maggots that live in moist soil. Additionally, planting the right companion plants around your onions attracts helpful insects and boosts the plants’ organic defenses. Cabbage, kale, Brussels sprouts, tomatoes, leeks, and carrots make excellent buddy plants.