Growing Onions from Seed
ALLIUM RESILIENCE ON THE HOMESTEAD
This is the time of year for starting all of the homestead's crops--some in flats, others in greenhouse pots, and some outside directly in soil. Among these starts are the storage onions that we will be eating throughout the coming year.
Sets: Our First Mistake
When we first started planting onions on the homestead, we used the most common and easiest strategy: we planted sets. Growing onions from sets has a couple advantages. Sets have a head start on the season and may reach usable size much sooner than onions grown from seed. They are also less susceptible to damage from frost, pests, and birds. That first year I bought several varieties of sets, cheerfully plunked them into the ground, and waited for the magic to happen.
While those onions did grow and were a great way to start on what was--at the time--a new gardening journey, they were not the best long-term solution for our homestead onion growing. Why? Read on.
In the first place, it is hard to know exactly how old the sets are that you are purchasing. Some of them may have lost viability, shriveled up, or begun to decay in storage. Of that first crop, there were a number that didn't come up or--if they did--that never thrived.
Secondly, onions grown from sets have a much stronger tendency to go to seed. This means that the onion will form a hard, woody stalk in the center of the bulb, using up the bulb's energy on bloom production. Bulbs that have gone to seed won't store well in the fall because the bloom stalk in the center will rot, introducing decay to the bulb.
Why are sets more prone to going to seed? Because onions are biennials. That means that the onion grows a bulb during it's first year and then either dies back or is harvested. During the overwintering period it gets chill hours--also known as vernalization--that prepare it to produce seed the following year. The sets that you purchase have usually already lived during one season, been harvested, and been dried for storage. When you replant them, they are going into their second year.
One of the biggest drawbacks of planting from sets is that they don't make good storage onions. Because the new onion is produced using material from the set, that part of the onion is already a year older than the rest. While the new material will store well (if it is a storage variety), the part of each onion that is the old material will begin to decay before the rest. On our homestead it is vital that the onions can store consistently through fall and winter and even into spring. Storage quality is top priority.
The Solution: Growing from Seed
Growing onions from seed has resolved the issues that we faced with sets. Because the onion goes from seed to bulb in the first year, the whole plant is new material. These onions are also much less likely to go to seed in their first season, because they haven't been vernalized yet. (A few still will go to seed, but those seeds should never be saved for replanting; the first-year bolting mutation is one we want to select away from.) Onions grown from the seed of a reliable storage variety are the best bet for anyone who wants to store their crop through the winter.
Initially we purchased our onion seed through Territorial Seed Company because of their reliability and wide selection. If you are intending to grow your own seed in the years ahead, it is vital to choose an open pollinated variety. (This means that the seeds from this strain will be both viable to produce new plants and will breed true to their parent type, unlike a hybrid or "F1" variety.) Open pollinated onion varieties are often hard to find, but we have found that Newburg yellow onions do well in our climate and store better than any other open pollinated variety we have tried. Since that first year, we have transitioned into growing our own onion seed each summer for the following year (read all about that process here).
We start onion seeds in March. The one disadvantage of growing onions from seed is that they get a slower start, and in climates where the growing season is short, it is important that they have developed substantial tops before day length triggers bulbing. Long-day onions like those we grow begin to shift their energy from top growth to bulb development when the daylight increases to 14-16 hours each day. In our climate, the onion seedlings need to be started early. In harsher zones that ours (6b), they would need to be started even earlier, possibly with the assistance of a grow light.
We start the onions in our growing dome from Growing Spaces, in 72-cell flats with three to five seeds in each cell. If space is limited, onion seeds can be grown in a dense block, but the cell strategy makes it easier for us to tease the roots apart without damaging them when the time comes to transplant outside. These small seeds should be planted just 1/8-1/4 inch deep, and then watered gently to settle the soil. It is important to keep the soil moist but not soggy as the seeds germinate.
The seeds will emerge like a folded-over loop, which eventually straightens into a single thin wisp for each seed. Often the seed coat will remain on the tip, like a tiny black hat at the end of the stem. These sprouts seem impossibly small at the beginning, but they will quickly begin to lengthen and thicken. One important step in growing onion seedlings is keeping them trimmed to about three inches tall. This prevents them from putting all their energy into growing upward and encourages thickness and root growth instead. Once the starts are about half the diameter of a pencil they are ready to move outside.
During the two or three weeks before the last frost date of the year, the onion starts need to be hardened off. This means that they are gradually exposed to direct sunlight and breezy outdoor temperatures by moving them outside for a few hours longer each day. This prevents them from going into shock when they are actually transplanted. (To be honest, I rarely remember to do this as thoroughly or gradually as I should. Usually I put them out for a few hours the day before transplanting.) Although they can stand some cold, onion starts are best not transplanted until frost-free weather arrives.
Transplanting the onions is the only tedious part of their entire growing season. While one of us gently teases them apart, taking care not to break the roots any more than necessary, another member of the homestead digs divots in the soil and gently places the seedlings (and their tangle of roots) in the garden. We generally plant them on diagonal, with each onion being 6-8 inches from the others. While this isn't as much space as is sometimes recommended for onions, it allows many more plants in each bed and still gives each onion enough room to grow to its full size. After transplanting is done and the soil around the seedlings is mulched, the onions don't need anything more from us but water and weeding until harvest time.
Like everything else on the homestead, growing onions has been a learning process. We have experimented with varieties, sets vs. seeds, and planting locations to find out what works best for us. By growing from seed, we have found that we are able to consistently produce high-quality onions that will keep into spring of the following year. By choosing a hard, pungent, yellow variety, we ensure that it is a good storage onion. And by saving our own seeds from the best onions of the previous year's harvest, we can guarantee that our crop is improving and becoming better adapted to our environment with each planting season.
This post may contain affiliate links that will take you to the webpages of companies we believe in and have personally used. Read more about our affiliate policies here.