Grow-How:
Succeeding with Alliums
We get more excited about starting alliums from seed than any other garden crop. They are a bright green beacon of spring that tell of winter's demise—which, by late February, is the only story we want to hear.
Seeds for this plant family—which includes onions, scallions, leeks, chives, garlic chives, and many other lesser known specimens—are among the earliest that can be started indoors. Onions transplant most successfully and yield the biggest bulbs and shanks when started from February 1st through March 15th in the Northeast (though I've had great harvests from mid-March sowings and acceptable harvests from late-March to early-April direct sowings). Leeks, scallions, chives, and garlic chives are more forgiving as to start time, and scallions in particular are best grown in succession with several sowings in spring and throughout the summer.
TIPS FOR SUCCESS
Thinking about starting onions, scallions, leeks, and chives? Here are a few growing tips to help you succeed with these essential vegetables and herbs!
- Onions do best when they are started very early indoors. In most northern zones, now is a great time, but anytime from now until mid-March works well, in our experience. (We've had good luck direct sowing our New York Early variety, in early April, as it's a moderately-sized bulb and a quick grower.)
- Chives, Garlic Chives, Leeks, and Scallions (Allium fistulosum types) are not particularly day-length sensitive and can be grown, harvested, and enjoyed at any time within the growing season as long as sufficient days remain before hard freeze. Starting now is great! But so is starting in March or April.
- Onions, however, are day-length sensitive. They will begin bulbing when sun conditions trigger the process, no matter at what stage of growth the plants find themselves. Typically this is when the day length begins to shorten just after reaching its maximum, so usually in July. Bulbing typically completes by early- to mid-August, making onions one of the first storage crops to come out of the garden. Large plants will form large bulbs, and small plants will form small bulbs, all at about the same time. This is why an early start is so useful; there's no way around the timeline set by the sun.
- All allium seeds germinate best when sown in room-temperature conditions. Heat mats will speed up the germination but typically will result in a lower germination rate. At 65-75 degrees Fahrenheit (18-23 C) they will emerge most abundantly after 5-10 days.
- All of our onions are "long-day" onions, meaning they mature best in northern zones. Imagine a line between Washington DC and San Francisco. If you're near this line or above it, long-day onions will work just fine for you.
- Pro tip for leeks: the deeper you bury them at transplant time, the more blanched white stem you end up with. They will require careful cleaning after harvest, but you'll get the most usable stalk this way.
- Did you know that Evergreen Scallions are hardy through the winter? For best eating in the second year, harvest them soon after spring regrowth begins, before the stems hollow and move toward flowering.
SEED SOWING
Starting allium seeds is easy. Fill a flat or deep wide tray (the deeper the better) with compost-amended potting soil. Then make and firm down quarter- to half-inch furrows the length of the tray that are about 2" apart. Sow the seeds heavily in these furrows, about 6 per inch. An alternate method for onions and scallions is to fill six-packs with amended potting soil, moisten, and then create a quarter-inch-deep dibble in the center of each cell. Drop 6-8 onion seeds or 12-15 scallion seeds into each dibble and then cover them with potting mix. (The advantage of this latter method is that transplanting is a breeze—just thin the cells to 3-5 plants each and pull and transplant the whole plug. Space them about 12" apart in the bed and they will happily grow to full size in an easy-to-weed-around clump.)
Place your trays somewhere where they'll have plenty of air to breathe and get abundant light (if using artificial light, set to no more than 12 hours per day). If you have a small fan, you can even hook it up near your trays. This will help combat any extra moisture, and it will also encourage your seedlings to develop sturdy bases which will help them when they enter the real world of the garden bed. Onions are especially sensitive to damping off, so the more air flow, the better.
TRANSPLANTING
The traditional advice for alliums is to allow them to grow until they are pencil-thick before transplanting them. However, even with a mid-February start date it is hard to achieve this by transplant time, which is about 4 weeks before the last frost (mid-April here in upstate New York). I think that shooting for seedlings that are between one-eighth and one-quarter of an inch in diameter is a more realistic goal. These size seedlings are easy to achieve, transplant great, and start growing within a day or two of transplanting. They produce big onions, thick leeks, and fast scallions. The thin, spindly seedlings are not worthless—they will usually catch. But they often waste days or weeks looking practically lifeless before resuming growth. Tip: for really thick seedlings, start your seeds in a tray that is very deep, around 6-8". Some growers use a window box for this purpose.