How to Grow Onions at Home: Onion Growing Guide

Onions should be planted in cool weather conditions. If you live in a frigid climate, plant onions as soon as the ground is workable (when the soil can be smoothed), which may be your late Spring months. In milder climates, onions can be planted as late as the fall, withstand a winter growing season, and be ready for an early Spring harvest.

Planting onion seeds can take more time, so germinate your seeds indoors first to get the process going:

• Prepare. Fill a planting tray or other appropriate container with moist soil and dig furrows half an inch deep for your seedlings. Cover lightly with soil and keep the temperature warm, around 60 to 70 degrees Fahrenheit.
• Transplant. When your onion seedlings germinate (anywhere from a few days to a few weeks), they are ready for transplanting into your garden. Dig holes about two inches deep and four to five inches apart for your onion transplants, in rows that are 12 to 18 inches apart.
• Companion plant. Cabbage, tomatoes, leeks, and carrots all make good companions for your onion crop. Keep helpful plants nearby to bring in beneficial insects and other organic defenses.
• Add mulch. Laying mulch or other organic matter between your onion rows can help smother weeds and retain some moisture for your soil (lessening the amount of watering you need to do).

You can plant onion seeds or plant onion sets. Onion sets are small onion bulbs that can be planted and grown into full-sized bulbs after a few months. If planting onion sets, you can bury them one inch under the soil in your vegetable garden, two to six inches apart. Don’t compact the soil around the onions, just loosely cover the onion bulb.

Onion plants are simple crops that require little maintenance. To properly care for your onions:

• Fertilize them. Onions require a bit of nitrogen, so fertilizing with a nitrogen fertilizer or compost every few weeks can help the bulbs grow nice and big.
• Let them breathe. As the onions form bulbs, they will emerge above the soil—don’t try to re-cover them. Loose soil means a drier environment, which is good for your onions’ development (and can help prevent maggots, which prefer moist soil). Your soil (or garden bed) should have good drainage capabilities as well.
• Water them. Give your onions about an inch of water per week (and for sweeter onions, a bit more). However, if you choose to lay mulch between your onion rows, you will not need to water as much.
• Give them sun. Onions should get full sun. Keep your onions from shading to ensure they get direct sunlight.
• Check them for pests. Even though onions are great companion plants to ward off pests, they are still susceptible to their own. Thrips and onion maggots are two insect pests that plague onion crops—thrips feed on the leaves of onions (which can be damaging for onions that use more of its top part, like green onions/scallions), and can be sprayed with insecticide. When onion maggot eggs are laid, the larvae dig through the onion root, destroying your crop. A mesh netting over your growing crops can help prevent egg laying at the base. You can also use parasitic nematodes to deal with onion maggots. You can also use dill, ginger, or ground cayenne or chili powder to use as a repellent against the females, which will keep them from laying eggs.

The ideal time to harvest mature onions is late summer, before the weather turns cool (they can grow in colder conditions, but once mature they’re prone to spoiling). Onion tops will turn yellow and fall over when they approach their final ripening stage.

When harvesting onions, look for brown onion tops crowning their heads through the soil—you can pull these directly from the ground. Store onions in a cool, dark, dry place. Onions that have sprouted flower stalks are already mature, and should be pulled right away and used immediately.

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