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Growing Onions From Seed

Onions have become one of my favorite things to grow. They are a staple ingredient in most of our favorite recipes, so we eat (and buy!) them a lot. They store well, so we can continue to enjoy produce from our garden long after the growing season is over. They have done well in the past few rainy summers we have had, so they are a small triumph amid the rest of my drowned, soggy garden. Plus, they are one of the first seeds we start in the spring, so they are always linked with the excitement of springtime in my mind!

While many folks choose to buy onion sets (dried tiny onions) or starts (started green plants), they are actually very easy to grow from seed. Growing onions from seed is much cheaper than buying started plants, so they are more economical if you are growing a lot of them. Onions started from seed will also make a bigger and nicer onion than one grown from a set. Of course, they do take time, so if you'd like to start onions from seed you should start now!

You can buy plain seed or pelleted onion seed, which is a personal preference. I like to use the pelleted seeds, because they are easier to space in the starting tray and don't need to be thinned later. My favorite variety is Patterson from Johnny's Seeds, a nice long-day yellow onion that stores very well and is available in both pelleted and non-pelleted varieties. If you live at a vastly different latitude than we do in New York, look for varieties that match the day-length requirements of your area. Onion bulbs will grow in response to day length in the summer, so northern latitudes should plant long-day onions while southern latitudes should plant short-day onions.

Start your seeds in late February to mid-March, about 6-8 weeks before you plan to transplant them. Last year I started my onions fairly early on February 27th, but they were actually a bit larger than I'd like at planting, so this year I am starting them a few weeks later. I use a 1" deep seed starting tray, but any container that is at least 1" deep should do. Fill the tray 3/4 of the way full with a good seed starting mix or potting soil. Sprinkle or place your seeds about 1/2" apart. Top with a thin layer of potting mix, then water. The trays that I use don't have drainage holes - if yours are the same, take care to not over-water.

As soon as your onion plants have 3-4 leaves, they are ready to transplant. Onions are cold hardy and can be transplanted a couple of weeks before your last frost date, with larger plants able to stand colder temperatures than smaller plants. I usually wait until my plants are a little thinner than the width of a pencil - partially to make them easier to handle and partially because spring is busy and tasks get away from me! If your onion starts get too unruly while waiting to be transplanted, you can trim the leaves to 5" long to keep them under control. New leaves will sprout from the center, so this won't hurt the plant.

Onions like fertile, rich soil and need a lot of organic matter to reach their full size. We plant them in permanent garden beds top-dressed with 1-2" of compost. To transplant, use a dowel to punch a 1.5" hole into the prepared soil, or use a trowel to open a slot in the soil by sticking the trowel blade into the ground and gently levering an opening. Gently separate an onion start from the bunch, drop it into the slot, and gently press the soil back around it. Plant onions 4" apart in rows 12" apart. Water your onions immediately after planting.

Water your onions regularly and watch for weed growth - small onion plants grow slowly and are easily overwhelmed by large weeds which compete for light, space, and nutrients. Also, don't be alarmed if the first leaves of your transplants fall over or turn yellow and die - this is normal! New green leaves should sprout from the center of the plant, so if you see those, you're okay.

Onions are ready to harvest when the bulbs are fully grown and the tops fall over, usually around late August here in New York. Onions need to be cured to form the protective papery outer layer and to store well. Pull your onions and put them in a dry, sunny place until the leaves are dry and paper has formed, about 1 week. Move them out of the sun into a dry location for storage. We usually leave them on a table in our greenhouse for the first week, then braid the onions together and hang them in the house to continue curing. Any time you need an onion, just clip one off the braid!

What other "kitchen staples" are you planning on growing this year?

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