For bulb-type onions, care is similar across the different varieties. Give bulbs at least six hours of sun a day at temperatures of 65-75 degrees. The more sun they have, the bigger the bulbs get. Onions also need loamy or sandy soil and about one inch of water a week. Mulch lightly to management moisture levels. Monitor the soil carefully as too much water can cause the bulbs to rot while not enough leads to splitting.

Pest and disease concerns resemble those of garlic. Be wary of thrips, aphids, onion root maggots, downy mildew and various fungal rotting. Onions are toxic to pets and other animals, so use fencing to protect the plants and critters from each other.

By starting your onion seeds indoors 6-8 weeks ahead of the last spring frost, you can enjoy an early harvest. Using a seed starting mix, create half-inch deep furrows in a tray, add four seeds per furrow and cover them lightly with soil. Keep the soil moist and place the tray where there is plenty of light and warmth. After the seedlings emerge, thin or transplant them so the remainder have 4-6 inches of spacing. Seedlings can be moved to a garden or large container when they are 2-4 inches tall.

Plant or transplant onions 1-2 weeks before the final spring frost when the soil is workable. This can be anywhere from mid-March to the end of April. Place plants 6-12 inches apart and rows 12 inches apart. You can also plant in the late summer or early fall, especially in warmer regions. Grow short-day onions in southern areas, long-day onions in northern areas and neutral onions almost anywhere.

If you want to grow onions in containers, use drainable pots or boxes at least 10 inches deep with a good potting mix. Do not plant onions near legumes, garlic, sage, chives or asparagus since they compete for nutrients.

Regular fertilization provides onions with essential nutrients. Add nitrogen-heavy fertilizer or compost when planting and again every 2-3 weeks. Fish emulsions and worm castings are good organic nitrogen sources. Side dress the fertilizer about six inches from the plants and mix it into the top 2-4 inches of soil. Test your soil before planting and periodically during the season for any deficiencies.

Bulb onions are biennial, and overwintering brings them back for a second season to grow flowers and seeds. The onions will go dormant but still need protection from the most severe conditions. Cold frames and low tunnels are excellent ways to defend against cold and wind. Raised garden beds also help maintain a good temperature range.

The only pruning necessary is to remove dead and diseased leaves as they appear. On seedlings, you can prune tangling and floppy tops so they grow upward. However, excessive pruning limits photosynthesis, which leads to smaller bulbs.

Onions can be harvested at any stage, with smaller bulbs and seedlings used like scallions. For maximum size and longer storage times, wait until the bulb skin feels like paper and at least half of the top leaves fall over. Gently dig the onion out of the soil, then cut off the roots and most of the leaves. Letting the onions dry out also helps them last longer.