Onions are some of the first things to go in the ground each spring. You may not know this, but onions are finely tuned creatures with a rigid hormonal profile. They are completely and utterly dependent on the sun's cycle to grow into the lovely round orbs we think of as onions. Those plump layers only grow in relationship to the lengthening days of spring. If onions are planted too late, they will never bulb out and become big and round. An onion that has been planted too late, let's say after the middle of May, will never quite size up, but will create a thick stem, and a barely bulbous orb. The engorged stem will not create rounded layers at all but rather look more like a slightly ovate leek. These are still fine to eat, but won't really be onions you can store through the winter.
We recommend that people plant onions in mid-April. When it is muddy, and cold, and you think there is no way a plant wants to go into the garden, well guess what? The onions really want to go into that cold earth. The way we grow onion plants for sale is that we seed about 80 plants into a 4 pack, and your job as the gardener is simple:
- Prepare a bed in the garden - deep, well worked, rich soil is best. I prepare my onion beds in the fall, that way they are ready for onion plants first thing in the spring.
- Gently pull the clumps of soil and roots and plants out of the 4 pack.
- Separate each plant and shake off the excess soil. The individual plants are like tiny blades of grass, but each one will grow into a big onion plant.
- Make a trench about 4 inches deep the length of your planting area. Onion rows can be about 8 inches apart, so depending on the size of your bed, you can plant up to 4 rows of onions in one bed and still reach across the bed to weed comfortably.
- Plant the individual plants in the trench, about 4 to 6 inches deep. Only a few inches of the thin green stems will be above ground. You should have about 2-3 inches between plants.
- Tamp the earth tightly around each plant.
The onions plants won't grow much at first, but they are just hanging out in the cold soil, programming themselves to grow once the soil warms up. It is these cold, long days that help make onions nice. I know, it is hard to believe that they prefer this, but they do. Southern growers, who have shorter summer days than northern growers, have entirely different onion varieties than we do. That illustrates just how much onions are day-length sensitive. A few degrees difference in latitude necessitates a whole different set of genetics.
The other things to keep in mind with onions:
- Keep them well watered. Water and day length is what makes onions big. Some straw mulch applied in late June is a good idea for keeping the moisture even and consistent.
- Keep them well weeded. Onions plants are slender and upright. They do not create any shade, therefore weeds like to grow near them, in the sunny under-story of the onion patch and because onions really don't want to compete for food, water and sunlight. They are not good at sharing.
- Keep them well fed. An application of Compost Plus in May is a good idea. It will help them get big and strong.
- Growing onions in black plastic mulch is a good option if you want to eliminate weed pressure and heat up the soil. Once onions are big, they like it hot.
- Harvest onions once the tops start to flop over. You can eat them fresh, as "green onions" or you can cure them by laying them out in a dry, airy place, away from direct sunlight. This usually happens in late July or early August. It depends on the varieties you grow and on the kind of weather we are having.
Onions are best stored in a dark, cool, airy place. A damp basement is not a good storage spot. A cold, dry, dark attic is better. Or an unheated closet, or a garage that does not get too cold. Ideal onion storing temperature is about 35F. That is pretty cold - colder than most basements.
Some onion relatives can be planted later in the season. This includes scallions, mini-purplette onions, pearl onions, and shallots. Leeks are also tolerant of a later planting, and can be planted multiple times throughout the gardening season if you would like to harvest baby leeks.
The onion varieties we grow each year:
Cipollini Gold Coin - a flat, disc like onion that stores very well in the winter. It is a strong flavored onion which mellows when cooked and is delicious caramelized, glazed, or roasted. One of our favorites for flavor.
Yellow Storage Cortland - a huge, good keeper which means that it stores well all winter. Dry the onion once harvested in a cool, airy spot, and you will be eating it until March or April of next year.
Red Storage Onion Mars - also quite big, and also a good winter keeper. Slightly milder in flavor than Cortland and can be eaten raw when sliced thinly. Red Onions develop their red interior only once they have been cured. Once harvested, coll in an airy dark spot until the tops are completely dried and can be pulled off by hand. That is the curing process for all storage onions.
Sweet Onion Walla Walla and Ailsa Craig - both are gigantic sweet onions. They do very well with lots of water and mulch. Sweet onions do not keep over the winter. They do not need to be cured, but rather get refrigerated once harvested. They are delicious roasted, grilled, or eaten raw in sandwiches.
Scallions - These can be planted in clumps of 10 or so plants. They can be planted every few weeks for a continuous harvest. If you do not want to buy scallion plants or seeds, you can eat young onion plants as scallions.
Shallots - These store very well after being cured like onions. They add a sweet and complex flavor to winter dishes, marinades, and dressings.
Mini-purplette - these are lovely purple pearl onions that are delicious in a spring braise with salad turnips and peas. They can be planted in clumps of 4 to 6 plants and can be planted multiple times throughout the season for more than one harvest. They also make great pickles. About 1" to 2" across.