Gardening: Planting Onions Indoors | The Old Farmer's Almanac

Planting Onions

Photo Credit
Celeste Longacre
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                Now is the time to plant onions indoors. If you want onions that are going to keep through the winter, you need to plant a good “keeper” variety. Catalogues will generally have this information available.  I always plant them either in late February or March. This year, there are four different days which are particularly ideal in the month of March. The 11th, 12th, 20th and 21st are all spectacular. The Moon is in a water sign (the best for germination) and—because the onions grow beneath the ground—a superior time to plant them is in between the Full Moon and the New Moon. For any of you who live in a warmer climate than New England, these would also be ideal dates to plant any kind of root crop.

                I start with a rectangular plastic flat.

Placing about two to three inches of potting soil on the bottom, I add some kelp meal or greensand.

Mix it in and rake it smooth. Then I take my handy little seed tool (shown) and fill the cavity with onion seeds.

I find this tool to be quite helpful as the seeds don’t get stuck to sweaty hands and you can somewhat control the amount of seeds being sown at a time. I put quite a few on top of the soil—onions don’t seem to mind being a bit crowded at this stage in their development.

I then cover them with about ¼ inch of potting soil, water them and set them in a relatively warm spot to germinate. You have to be careful with the amount of water that you use. My flats don’t have drainage holes so I am particularly careful not to overwater them.

                It takes them a few days to germinate. The top part of the soil shouldn’t dry out completely during this stage. Once they have germinated, I put them in a sunny window. Then watch them grow!

They should be trimmed to three or four inches high as this will encourage them to build a strong root system.

               Many onions are what are called “day length sensitive.” This is what we mostly grow in the north. These onions will put all of their energy into their greens while the days are getting longer. As soon as the plants sense that the days are getting shorter, they begin to put their energy into their root (the actual onion). For this reason, never put grow lights on onions when they are inside as the extra “daytime” can confuse them.

                Once the soil warms up, onions can be planted outdoors. They don’t mind a bit of frost so they can be planted much sooner than most other crops. When it’s time, I get the bed ready and use my dibble to create a hole for the onion plant. You want to place them about four inches apart. I try to visualize a nice, big onion and give them all enough space to accomplish this feat. Each onion is its own plant so this transplanting can be a bit tedious but it is well worth the effort. In the late summer, once the onions have been sufficiently sunned, I put them in mesh bags in the pantry. I generally have onions throughout the winter and even into April or May. Happy planting!

And, just because….