Most gardeners start out growing onions from sets or the little onions transplants. Sets are little dry dormant bulbs and transplants are usually the size of a pencil and like green onions. Sets are easy to grow and a great way to start, but if you want more bang for you garden, more variety, turn to seeds. Growing from seed lets me pick varieties to suit my own needs or whims. Colors range from dashing purple to pure white. Shapes and sizes to boot. Long cylinder shapes like ‘Italian Torpedo’ to my favorite the flat yellow ‘Cippolini’ onion. I feel like onions grown from seed out perform better than those grown from sets (bulbs). They are less prone to disease, store better and they bulb up faster. However, if I only had the choice between sets and transplants, I would always pick transplants.
You may find on your seed packets a description that says “Long Day” or “Short Day”. What does this mean and does it really matter? This means there are two different types of onions. Onion varieties differ in the length of daylight and the temperature required to make a bulb. short-day types are ideal for the South, where they grow through cool southern fall and winter months. They’re triggered to bulb by the 12 hours of sunlight that come with the return warm, early summer weather. Long-day onions are best grown in the North, where the summer daylight period is longer. These onions require at 14 hours of light to bulb up. The plant grows foliage in cool spring weather, then forms bulbs during warm summer weather, triggered by the long days. If short-day onions are grown in the North, they will bulb to early, then languish and never get to a good size. On the other hand, if long-day onions are grown in the South, they’ll produce lots of leaves, but no respectable bulbs. If your onion varieties have not produced outstanding bulbs you may have been planting the wrong type of onions for your area. I plant ‘long-day’ onions, but sometimes can’t resist some of the varieties of the ‘short-day onions. They end up with much smaller bulbs, but then again I don’t always want a big onion, where-as a 1/4 cup of chopped fresh onion is perfect. In the long run an onion will still taste like an onion.
Just when you thought that there was nothing to plant in December along came the onion seeds ready to be put into flats. If you live in very cold areas, wait until January or even February. I sow seeds in to flats or even 4″ pots for fewer onions seeds. Fill flats with soiless potting soil, sprinkle onion seeds and then cover with 1/4″ of the soil. I grow mine in the greenhouse, but you can start them in your warm house as long as you have a south window or sunroom with plenty of light. Water your newly planted seeds by a sprinkle or from the bottom up to ensure all the soil is moist. Cover with plastic. Regular kitchen plastic wrap will work fine. If you are growing in a greenhouse you can skip this step. When covering with plastic the need to water is slim if at all. Onions germinate in about a week. Once their string-like tips poke through the soil, remove the plastic. I feed the seedlings a very weak (1/4 strength) solution of water-soluble fertilizer every time I water. Onions seedling shouldn’t dry out, but they also shouldn’t be soggy. With anything to much of a good thing isn’t always good!
Once the little guys leaves have reached 7-8 inches, it’s time to plant outside. For me that is around mid-February time. Carefully overturn the flat to expose the seedlings’ roots. Handling the plants by the leaves, I gently tug to separate the roots of individual plants. Cut back the leaves to 4 inches to keep the plant from being too top-heavy and to give more nutrients to the roots instead of the leaves. Onions prefer a fertile, loose loam soil amended with well-rotted compost made with animal manure, a well-balanced fertilizer and I add greensand as I will explain later. Plant the seedlings 1/2 inch deep 4-6 inches apart. 6 inches for larger bulbing onions and 4 inches for smaller varieties. I like to plant around the perimeter of my garden beds as to not take up much room and the onions will deter some insects. Keep onions well weeded so they don’t have to compete with water, nutrients and light. Water and nutrients are an important part of growing onions. The soil surface should be evenly moist. If it’s too dry and plants are grown under stress, the bulbs will be smaller and have a stronger flavor. To help keep moisture in, mulch, but keep away from the bulbs to avoid disease and rot. Onions are heavy feeders, so besides the initial feeding at planting time, they love a dose of fertilizer when the bulbs begin to swell. I use a well-balanced fertilizer and greensand. Greensand is an excellent organic source of potassium and without it the onions necks will thicken and the bulbs won’t store well. Every time I have skipped adding greensand I end up with thick necks and hallow bulb centers.
At full maturity, the plant go dormant. The inner leaves stop producing blades, and the hollow-centered neck weakens, causing the tops to bend over. It is so important to let the plants go dormant before harvesting, or they won’t store well. As the onions start to mature, ease up on water and fertilizer to encourage dormancy. I am sure you have heard to bend the tops over before maturity. Don’t do it! By doing this you are inviting disease. Breaking the tops will allow water to enter the bulb and cause rot in addition. However if you have a flower head forming you can bend that over. Usually an onion that have formed a flower head will be inferior. I just use those right away even if the tops are green. Another thing that you probably have been told is to remove the dirt away from the bulb to increase the size……Well, It’s a good idea to do this, but it is more for aiding in the drying process. By keeping the soil away from the bulb will help dry the papery skins for better storage. Do this only about a week before harvest. I have grown great big onions, (two pounders) and never pulled away the dirt until the last week before harvest.
Time to Harvest! When most of the onions tops have toppled over and started to brown and the bulbs have developed skins, pull the bulbs and place them in a warm, dry, airy location out of direct sun and out of contact with moist soil. Curing onions in hot summer sun will burn, bleach and soften the outside tissue and allow disease to enter. This is especially true for large sweet onions, which have the greatest water content. Spreading onions out on a screen and drying them on a porch or in a garage works well. Onions take up to three weeks to cure before they’re ready for storing. Once onions have dried adequately, cut the foliage back to 1 to 2 inches from the top of the bulb or braid them as you would garlic. So pretty! Store the crop in a cool, dry location and remember that good air circulation is a must. Onions can be stored in the traditional onion bag or in a shallow box. Separating them with newspaper keeps them even longer. You can also use a skinny net with knots between each onion bulb and hang it up for optimum storage.
This new growing season give planting onions from seed a whorl! You will find they are far better than those named red, white and yellow onions you find at the local grocery store. Onions have names too!