Onions are one of the easiest things to grow in your garden. From large onions to shallots and scallions, we have all the information you need for a bumper crop. Easy to grow and cool loving these are one of the first plants to go into the garden.
This article was first written for and published on Earth, Food and Fire.
Growing Onions From Sets
You can grow onions from both seeds or from onion sets. Onion sets are onions that were grown then picked prematurely to be sold as starting bulbs the next season.
Large onions like white, yellow, red as well as Sweet and Spanish onions are grown from sets. Because they mature much faster than onions grown from seeds they are a great choice.
You can find these in grocery stores, garden centers and greenhouses in late winter to early spring. Be sure to buy them early, once the stores are sold out they usually will not receive any more until next season. Choose sets that have bulbs about ½ inch in diameter.
Growing Onions From Seed
If starting onions from seed, start them indoors around 6 weeks before you plan to transplant them into the garden. Using small trays start your seeds in potting soil. Set them in a warm spot or use a heating mat made for starting seeds. Seeds love warmth and moisture, cover the tray with a lid to help speed up germination.
When watering be gentle so not to disturb the seeds, bottom watering is a good idea. Alternately using a spray bottle will work for watering seeds and young seedlings. Once the seeds have spouted remove the lid from the tray.
Sprouted onions can be placed under fluorescent light or in a sunny window. After the chance of frost has past they can be moved outdoors and be transplanted into the garden.
Growing From Purchased Seedlings
If you are short on time, you can purchase onion seedlings from your local greenhouse and garden center. Water them well when you get them home. Plant them soon after bringing them home for best results.
When Do I Plant Onions?
Onions are a cool weather crop so you can plant them quite early in the season. Wait until after the last frost of the season to plant when the ground can be worked. If the temperature does drop they can tolerate temperatures to just below zero.
Onions grow their tops in cool weather and form bulbs when the weather warms.
Where Do I Plant Onions?
Select a location where they will get full sun. It is a good idea to plant them in the front part of the garden so things that grow taller and fuller will not shade the onions.
Work the soil well adding amendments like peat moss and compost. Because the plants grow into bulbs, loose well draining soil is important. Place the bulbs with the pointed end up. The round part on the bulb is the root. Cover lightly with soil.
Onions are considered heavy feeders so adding compost before and during the growing season will encourage good bulb growth.
When planting onion sets, plant them between 2 and 6 inches apart no more than 1 inch deep. When planting transplants into the garden, space plants 4 to 5 inches apart in rows 12 to 18 inches apart.
Caring For Onion Plants
Because they love nitrogen, fertilize every second week with a weak solution of fertilizer high in nitrogen. The most common fertilizer we see is a balanced 20 – 20 – 20. Select one where the first number is a just a tiny bit higher than the other numbers. The first number is representative of the nitrogen content in the fertilizer.
Stop fertilizing once the bulbs start emerging above the soil line. Be sure to allow the onions to remain above the surface, do not cover with soil. If you practice mulching in your gardens now is the time to apply mulch. This helps maintain soil moisture and retains weeds.
It is said that the more you water, the sweeter the onion!
Be sure to water during dry periods. The onions may look fine but the soil may be dry.
Weed your onion rows regularly so they do not have to compete with weeds for nutrients. Onion roots grow just under the surface of the soil, take care when weeding close to plants. You do not want to disturb the roots, hand weeding is recommended.
If you find the odd onion that has sent up a flower harvest that one first for fresh eating.
When onions are maturing the greens start to yellow. Once this begins completely bend the stems of all the onions. This forces them to finish ripening. Feel free to lightly loosen the soil around the bulbs to encourage drying.
Once the tops are brown harvest the onions. Gently brush off any remaining soil. Trim the tops down to an inch above the bulb. Some people will braid onions, similar to braided garlic, if braiding the onions do not trim the tops.
If the weather permits, allow the onions to dry on the soil for a few days. If rain or cold weather is in the forecast, place the onions on screens or cardboard in a location that will keep them from getting wet and cold.
A garage or garden shed should work well. Allow the onions to dry for a few weeks.
Be gentle with the onions to prevent bruising. Bruising can create rot to start on onions.
Onions are stored best at cooler temperatures, some place dark and dry is best.
Loose onions can be stored in mesh bags or nylons that have been cut. You can check with your local produce department for large mesh bags, some store will keep them for customers if asked to. Braided onions should be hung someplace dry and cool.
Never store onions with potatoes. The gas emitted from the onions will cause to potatoes ripen quickly and spout.
Other Onions You Can Grow
Bunching onions, also called scallions or green onions can be grown from seeds or sets. Plant onion seed as soon as the soil can be worked in the spring. Sow and cover seed with ½ inch of soil and keep moist.
Seeds can be started indoors at the same time you start the large onion seeds. They can be set in the garden about 1- 1½ inches apart. To plant onions sets, simply press sets into the soil about 2 inches apart.
Green onions are best picked when they are young and tender. Dig or pull them when the tops reach between 6-8 inches tall and the bulbs have begun to swell. You can harvest scallions throughout the growing season. Store in the fridge.
Shallots are usually grown from sets or bulbs and they are planted like garlic cloves. With similar growth, shallots multiply in the ground like garlic but are considered an onion. Shallots have a mild, subtle onion flavor and are small tear drop shaped bulbs.
To plant shallots, separate each bulb and plant just below the soil surface, 4 – 6 inches apart with the pointed end up. Unlike garlic, which forms a larger bulb, shallots spread out into clusters and should be spaced further apart than garlic.
Harvest is similar to that of onions. Bulbs are ready for harvest when the tops yellow, wither and fall over. Allow the harvested bulbs to dry for a month.
If properly dried and stored, your onions should be good for at least 6 months.