Garden Mastery Tips
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March 2007 |
Seeding Hardy Vegetables in March
What do the seeds of cool-season vegetables require in order to germinate and prosper (and make the gardener happy)?
- Soil that crumbles easily. Pick up a handful, squeeze it tightly into a ball, and then poke at it. If the "ball" fails to crumble, your soil is simply too wet. You risk permanent damage to the tilth of your soil if you insist on working it.
- The correct fertility, planting depth, soil pH, and temperature ranges (air and soil). See OSU's Vegetable Gardening in Oregon .
- Pre-soaking or even pre-germination, when advised.
- Protection, when appropriate, from slugs, insects, birds, voles, rabbits, cats, dogs and other pests, and, of course, weather. Floating row covers are often all you need, although they may not be adequate protection from voles, who have been known to play late-night "onion set" soccer under them.
Much advice on when to plant is given in terms of the last expected spring frost, a date that can vary widely here in Clark County. Let us say that most of us don't need to worry too much about frost after May 1st. In that case, we can seed most cool-season vegetables after mid-March, which would be six weeks before our last expected frost. If you or a neighboring gardener have kept good records over a number of years, you can use your data to figure the last frost date more accurately, and adjust accordingly.
Old-timers might watch to see when the maple trees start leafing out – then it's probably warm enough to start planting. To be conservative, plant only small amounts of your seed, shallower than usual, and don't firm the soil over the seeds.
So, which seeds should we consider planting directly into the garden during March? (This list does not necessarily contain every vegetable seed which might be planted during March. Also, please be aware that the focus is those vegetables which are best sown directly into the garden, not those which do best if started indoors or in a cold frame.)
ARUGULA (ROCKET, RUCOLA, ROQUETTE) is an easy-to-grow early spring green which will germinate in the wettest, coldest spring soil, at soil temperatures as low as 40° F. Sow every few weeks in loose, well-composted soil. If flowers develop, pinch them off to prolong plant growth. Use a floating row cover to prevent flea beetle damage.
BEETS, which appreciate slightly alkaline soil, can be sown 2 – 4 weeks before the last expected frost, and successive sowings made 3 weeks apart after that.
BOK CHOI (PAC CHOI) AND OTHER CHINESE MUSTARDS may bolt when seedlings are exposed to prolonged temperatures below 55° F. Strategies for preventing bolting of early sowings include using "bolt-resistant" varieties, or treating bok choy as a cut-and-come-again seedling crop. If plants do bolt, harvest the flower stalks before the flowers open and use them in a stir-fry or salad. Optimum soil temperature range for germination is 50° - 75° F.
BROCCOLI RAAB (SPRING RAAB, RAPINE, RAPA), a member of the mustard family selected for its shoots and flowers, is direct seeded for a quick crop of small florets with the few small leaves that surround the sprout. It doesn't hold long, so harvest before it bolts to seed.
CARROTS may be sown 2 – 3 weeks before the last predicted frost, or when the daily average soil temperature is about 55° F, and every 3 weeks through July.
CELTUCE germinates at soil temperatures as low as 45° F.
CHARD, which germinates at soil temperatures of 45° – 75° F, may be sown 2 – 4 weeks before the last expected frost. PERPETUAL SWISS CHARD, sometimes called PERPETUAL SPINACH, is grown in the same fashion as Swiss Chard.
CHINESE CABBAGE grows best in the shortening days of fall. If you choose to try it as a spring crop, wait for soil temperatures to be above 50° F.
CORN SALAD (FELDSALAT, LAMB'S LETTUCE, MÂCHE, NUSSLI) is a cold-hardy salad green with a mild, nutty flavor. Because it is able to withstand frost, it is a favorite for fall planting. With appropriate protection or in mild climates, it can be harvested during the winter; and, in any case, it will provide late winter/early spring greens when little else of that nature is available. For spring sowing, select a variety such as "Mache Large Seeded Dutch", from Nichols Garden Nursery ; "Piedmont" from The Cook's Garden ; or "Vit" from Johnny's Selected Seeds - these tolerate the heat of summer better than the varieties bred to stand the cold of winter. Germination may take up to two weeks. Protect seedlings from slugs, rabbits, and deer. At the three-leaf stage, thin seedlings to 6 inches apart, using thinnings in a salad. Corn salad, which is edible at any stage, can be treated as a cut-and-come-again crop. Young tender plants (which look like tiny Bibb or butter lettuce plants) may be used whole. Cut the rosette-like heads 1 inch above the ground - the plant will resprout (more slowly in warm weather than in cool).
FAVA BEANS germinate in soil temperatures as low as 40° F and grow well in air temperatures ranging from 45° - 70° F. Try the "Windsor" type for a spring planting.
KALE, which is tastiest after a hard frost, is best planted mid- to late summer. If planted in spring, it will germinate at soil temperatures as low as 40° F.
KOHLRABI can be sown directly in the garden 2 – 6 weeks before your last expected frost, at soil temperatures ranging from 50° – 75° F.
LETTUCE requires a minimum soil temperature of 40° F. If you plan to harvest entire plants (instead of just the outer leaves) of leaf lettuce, seed at two-week intervals, starting, as some "old-timers" will tell you, "when the apple trees begin to bloom."
ONIONS should ideally be direct-seeded in mid-April in western Washington and Oregon, but if your soil seems ready, try some in the latter part of March. The optimum soil temperature range is 48° – 90° F.
PARSNIP culture is similar to that of beets. Direct seed at soil temperatures in the 50° – 70° F range. Parsnips don't transplant well.
PEAS are definitely at the top of the list of seeds to plant as early as possible.
POTATOES grow best when soil temperatures are in the 55° F to 70° F range. At the Ronniger's Seed and Potato Company (also known as Irish – Eyes Garden City Seeds) website, read How to Grow Potatoes , for some expert guidance.
RADICCHIO will germinate at 40° F, but several successive nights with temperatures below 50° F could cause seedlings to bolt, so growing transplants indoors may be advisable. Otherwise, treat like heading lettuce (romaine or iceberg), but don't expect the radicchio to mature quite as fast as the lettuce.
RADISHES may germinate at 40° F, but their ideal soil temperature range for germination is 50° - 65°. Interplant these fast-growers with slower-growing vegetables or plan to replace them with something else when you have harvested them. Make sowings every 10 to 14 days from 6 to 8 weeks before the last expected frost until daytime temperatures are expected to average 80° F or above.
SALAD GREENS, in general, are good candidates for early spring sowing.
SHALLOT bulbs, for a good crop, are best planted in the fall, but they may be planted in very early spring. The Ronniger's Seed and Potato Company (also known as Irish – Eyes Garden City Seeds) website offers good information in their Grower's Guide, Growing Shallots .
SPINACH does best in well-aerated, well-limed, fertile soil that is well-drained but moisture retentive. Spinach will germinate in soils as cold as 35° F, so begin sowing it as early as 8 weeks before the last frost, making successive sowings every few weeks. As the days lengthen, it will "bolt" and you will be able to replace it with another vegetable. For directions on accessing the OSU publication Grow Your Own Lettuce, Spinach, and Swiss Chard (EC 1268), see the end of this article.
TURNIPS are often better tasting and more productive if planted midsummer (about two months before your first fall frost). If you are going to plant turnips in the spring, direct seed them 3 weeks before the last expected spring frost. If the greens interest you more than the roots, look for varieties selected and bred specifically for greens production.
Below are links to Oregon State University (OSU) and Washington State University (WSU) Extension publications on growing some of the above vegetables.