Onions and leeks are an essential part of a veggie garden. To get the biggest bulbs, there are two steps: selecting the correct type for your location, and deciding whether to plant transplants, sets, or seeds. Get ready for your best onion harvest yet!
The Long and Short Of It
The most important step in successfully growing onions is choosing a variety with the correct day length for your garden. Before you consider any other pros and cons of specific varieties, you’ll need to know which type of onion grows best in your area. This is based on sunlight and temperature. Leeks are not sunlight dependent, and can be grown in most zones.
Long-day onions need at least 14 hours of summer sunlight to bulb up, prefer cooler temperatures, and thus are suited for northern regions. These are usually planted in the spring and form a bulb over the summer. If planted in the south, they won’t get enough sunlight to form a good size bulb.
Short-day onions need 12 hours of sunlight to bulb up, and are best suited to the temperatures of southern regions. They are usually planted in the fall to over-winter. Bulb growth is triggered in the spring as the days lengthen, for a late spring or early summer harvest. If planted in the north, they will begin to bulb up early but stop short of reaching full size.
Intermediate-day onions, also called day-neutral onions, can be grown in almost any zone, but will not do well in south Florida or south Texas. They form bulbs at 12 to 14 hours of daylight. They can be planted like long-day or short-day onions, depending on how mild your winters are.
For a map and more information on onion day lengths, read this post and watch our video.
Growing from Transplants
All transplants are intermediate-day varieties. Both onions and leeks are available as transplants. Transplants are harvested a few days before delivery, and should be planted right away.
Planting these in the fall will provide a harvest the next summer. Transplants give you an extra few months of growing time before you plant them, because they were planted from seed earlier in the same year. This can help you get an earlier harvest and larger plants.
Growing from Sets
All onion sets are long-day varieties. Leeks are not available as sets. Sets are immature bulbs that are grown under controlled conditions to keep them small by the time they go dormant in fall. Then they are harvested for sale. They can be stored in a cool place until conditions are right for planting.
Sets can be planted in the fall or spring for harvest in the summer. Like transplants, they give you a few extra months of growing time. However, they can be difficult to bulb up and have a tendency to bolt, and so are often better grown as scallions than as full bulb onions.
Growing from Seeds
Onion seeds are available for short-, intermediate- and long-day varieties. Planting by seed gives you many more choices for selecting your favorite color, shape and flavor. Leeks are also available as seeds.
Plant onion seeds in the spring, either indoors before the last frost to transplant, or outdoors as soon as soil is workable. Harvest in the fall, or the following year if growing as a biennial for seed saving.
Onions grown from seed are less prone to disease, and tend to store longer after harvest. However, they can be more difficult to grow than the other methods, and take several months longer to mature.
With a little planning, you can be harvesting big onions and delicious leeks in no time!