Alliums for March: transplant bulb onions, harvest garlic scallions, ramps, minimize onion bolting

Flats of March-sown leek seedlings in our coldframe in early April.
Photo Pam Dawling

Allium Planting in March

  • Divide and replant Egyptian onions and perennial leeks, during March or April
  • Sow leeks in flats, coldframes, or raised beds. See below
  • Transplant fall-sown bulb onions early in the month. see Alliums for November and February. More info below
  • Transplant cipollini seedlings. Cipollini, also known as pearl or boiling onions, are varieties of short day onions sown in spring, planted at high density, which form small bulbs and mature in a couple of months.
  • Plant shallots Jan-Feb.
  • Plant softneck garlic cloves or bulbs for garlic scallions. See Alliums for February
Garlic scallions ready for harvest.
Photo Wren Vile

Allium Harvests in March

  • Start harvesting garlic scallions (3/10 to 4/30 in central Virginia). See below for more details
  • Harvest hoophouse scallions (our 10/20 sowing Feb 20- mid-Mar and our 11/18 sowing from mid-March.)
  • Harvest leaves of Egyptian onions & perennial leeks, Sept- April
  • Harvest winter leeks Dec- March. See Alliums for January and Alliums for November
  • Harvest ramps, sustainably for one month, from when tree buds appear (late March or early April in the Appalachians). Ramps are a spring ephemeral of deciduous forests. By late May, the leaves die back and a flower stem emerges. Wild ramps are being over-harvested, and it is important to make sure that not all these wild culinary delights vanish and they are still able to find their way onto plates in a sustainable fashion. See
Harvested ramps.
Photo Small Farm Central

Alliums to Eat from Storage in March

  • Eat softneck garlic from storage once all the hardneck has been used (softneck stores longer)
  • Eat bulb onions from storage, including bulbils from Egyptian onions if you stored those.

Alliums to Weed in March

All overwintered alliums will need weeding in March and once a month after that until harvest. Mulched crops can be weeded during wet weather, if necessary, and the pulled weeds can be discarded on top of the mulch, where they stand a much better chance of dying then weeds discarded on bare soil! It is helpful to have a list of tasks that can be done when the soil is wet, in case of a wet spring (or any season really). Perennial crops and annuals with mulch are the main jobs for this list (along with tool repair and sharpening).

Newly planted alliums in bare soil will benefit from hoeing during dry weather before the weeds get very big at all. Hoe every 1-4 weeks as needed until harvest. Because of their vertical tubular or strap-like leaves, alliums do not compete well with broadleaf weeds and can easily become stunted in high weeds. We learned the hard way one year when our leek beds grew very big weeds. Even though we did pull the weeds, the leeks never grew very big. As well as the competition for light, we think our huge weeds pulled too many nutrients from the soil. After that, we acknowledged the wisdom of growing fewer leeks and taking care of them better, rather than over-extending ourselves.

A fine bed of onions in spring.
Photo Kathryn Simmons

Special Allium Topics for March: Sowing leeks, transplanting onions, harvesting garlic scallions, onion bolting factors

Sowing leeks

Calculate how many leeks of each variety you want to harvest, add a margin. Each of our 90 ft (27.5 m) raised beds takes 4 rows of leeks, with plants 6″ (15 cm) apart. That’s 720 plants per bed. We sow in 24″ (60 cm) long flats, aiming for 3 seeds per inch (<1 cm apart). With 6 rows per flat, we need 1.67 flats/bed with no extras. We’ll call that 2 flats per bed.

We don’t need heat to start the leek seedlings, only time, so we put the flats directly into the coldframe. The minimum temperature for leek germination is 35F (), the optimum 65-85F () and they take 8-16 days just to germinate, even at the ideal temperature. Alliums are so slow! I always allow at least 10 days.

Leeks take 10-12 weeks to grow to transplant size. We sow ours March 21 for June 1 transplanting, which is only 10 weeks. When we grew them in a raised bed, it took 12 weeks. We like Lincoln and King Richard for leeks to eat in October and November and Tadorna for over-wintering, to eat December-February.

Transplanting onions

Transplant fall-sown onions as early in spring as possible, and those sown after New Year once they have at least three leaves (four or five is better). The final bulb size is affected by the size of the transplant as well as the maturity date of that variety. The ideal transplant is slightly slimmer than a pencil, but bigger than a pencil lead. Onion seedlings are slow-growing: even in spring they can take ten weeks to reach a size suitable for transplanting. Overly large transplants are more likely to bolt. If seedlings are becoming thicker than a pencil before you can set them out, undercut two inches (5 cm) below the surface to reduce the growth rate. Or use them as scallions.

Some books recommend trimming the tops at transplanting time, but I used to avoid this because I believed it reduces the yield. I forced myself to test out this idea one year, and found I got the same yield from trimmed and untrimmed onions. Trimmed ones are easier to plant. Transplant 4″ (10 cm) apart for single seedlings or 12″ (30 cm) for clumps of three or four (not more than four). Set plants with the base (stem plate) 1/2″–1″ (1.3–2.5 cm) below the soil surface. Some books recommend as deep as two inches (5 cm). Don’t plant too shallowly. Give plenty of water to the young transplants: keep the top 3″–4″ (8–10 cm) of the soil damp for the first few weeks to prevent the stem plate from drying out.

Onion bed in late April.
Photo Kathryn Simmons

Harvesting garlic scallions

With a last frost date of 20–30 April, we harvest garlic scallions from early March until May, if our supply lasts out, and we don’t need the space for something else. Harvesting is simple, although depending on your soil, you may need to loosen the plants with a fork rather than just pulling. Trim the roots, rinse, bundle, set in a small bucket with a little water, and you’re done!

Some people cut the greens at 10″ (25 cm) tall and bunch them, allowing cuts to be made every two or three weeks. We tried this, but prefer to simply lift the whole plant once it reaches about 7″–8″ (18–20 cm). The leaves keep in better condition if still attached to the clove. Scallions can be sold in small bunches of three to six depending on size. If you do have more than you can sell in the spring, you could chop and dry them, or make pesto for sale later in the year.

Onion bolting factors

Onions are cool-season plants. They have three distinct phases of growthvegetative, bulbing and blooming (bolting), and the switch from one phase to the next is triggered by environmental factors. It does not work to plant onions at a random date in the year without taking account of these environmental factors. Success depends on understanding what this crop needs during each of the three phases. To get a full understanding of the three phases and the factors that cause plants to switch to the next phase, see the Bulb Onions chapter of my book, Sustainable Market Farming.

 

The first stage is vegetative growth (production of roots and leaves). To grow large onion bulbs it is important to produce large healthy plants before the vegetative stage gives way to the bulbing stage. If plants are small when bulbing starts, only small bulbs are possible. Cool, but not cold, weather and adequate irrigation encourage heavy leaf growth.

It’s important to grow varieties that are suitable for the latitude of your farm. The further north you are, the more hours of daylight you have in summer. Onion varieties are often described as “northern/long day” or “southern/short day.” The names refer to the relative day length needed before the plant will start to make a bulb. The dividing lines between short day (south of 35°N) and long day (north of 38°N) varieties leave a gap where neither type is ideal. There are also “intermediate day” types and a few genuinely “day neutral” varieties.

Bulbing is initiated when the daylight length reaches the number of hours critical for that variety. (Actually it is the length of darkness that is important, although varieties are normally classified by day length.) Temperature and light intensity also determine when vegetative growth stops and bulbing starts. It takes a daily average temperature of 60°F (15.5°C), or even 70°F (21°C), to trigger bulbing (depending on the variety).

The rate of bulbing is more rapid with high light intensity and increased temperature. The optimum temperature for rapid bulb development is 75°F–85°F (24°C–29°C). Long day onions are bred to start bulbing at 14–16 hours of daylight. In cooler northern regions, the day length trigger may be reached before the temperature trigger. In these places, bulbing is delayed until warmer weather. Onions then bulb during the summer and are harvested in the fall.

Further south, the temperature trigger is reached before the day length trigger, so bulbing starts as soon as the days are long enough, and finishes early in the summer. South of their ideal growing region, long day onions don’t start bulbing until triggered by daylength near the summer solstice, and the bulbs are exposed to hot conditions as they mature. Soils dry out fast under hot conditions, and if water supply is insufficient, growth will be stunted.

Short day onions start to bulb at 10–12 hours of daylight, provided the temperatures are warm enough. In the South, below 35° N, they are sown in September or October, grown through the winter, and are harvested in May. If short day onions are grown too far north (where they cannot be overwintered and must be started in spring) they will bulb before much leaf growth has occurred. Only small bulbs can result from this. Here at 38° N bulbing initiation for short day onions gets delayed beyond the day length trigger, until temperatures are higher than 60°F–70°F (15.5°C–21°C), which is early April. It’s a waste of time to sow short day onions here in spring, as they have an impossibly brief time (January to early April) to grow a decent-sized plant before bulbing starts.

One way to deal with this is to start short-day onion seedlings in the late fall/early winter, let them make some vegetative growth, and keep them alive indoors over the winter, to continue growth in the spring. Further north or inland, it gets harder to keep onion plants alive through the winter. Onion seedling can survive at 20°F (–7°C), but not under colder conditions. We have tried overwintering onions outdoors, but even with rowcover, our losses were too high.

The third growth stage is flowering (bolting). Onions are a biennial plant, which means that they normally grow leaves and produce a bulb in the first year. Then they go dormant when they experience an extended period of cooling temperatures, such as winter. When temperatures rise, they start growing again, and send up more leaves, followed by a thick central flower stem. After being exposed to cold temperatures, smaller seedlings with a diameter less than pencil thickness (⅜” or 1 cm) and fewer than six leaves will resume growth and not usually bolt (bloom). The trigger for the transition from bulbing to bolting is temperatures below 50°F (10°C) for 3–4 weeks, after the plants have six leaves or more. This can happen after an unexpected cold period in spring. Bolting is to be avoided because the flower stems are tough and inedible, and the bulbs start to disappear to feed the growing flower stems. Bolted onions will not dry down to have tight necks and so will not store.

If you can sow onions in the fall and plant the seedlings out in the early spring, you will get more vegetative growth and therefore the chance of bigger bulbs. The temperature-and-size trigger limits how early in the fall seeds can be sown; if the seedlings have made lower stems larger than a pencil in diameter when winter closes in, the plants are likely to bloom in the spring rather than forming big bulbs.

Starting seedlings in a hoophouse in early November works well for us. The plants are protected from very cold temperatures and can be easily seen and cared for. They grow faster in the hoophouse than outdoors, so we can start them later. Outdoor sowings tend to suffer some winter killing and varying degrees of mold. The colder the temperatures the plants experience, the more likely it is for the larger ones to bolt before growing large bulbs. Hence a more moderate microclimate, such as a hoophouse, reduces the rate of bolting. In colder zones, a slightly heated greenhouse might work better for overwintering.

 

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