March is the month to start growing vegetables in ernest. Seed starting can begin outdoors in mild regions and indoors in cold regions. There are still six to eight weeks, maybe even ten weeks, before warm-season plants can go into the garden in most cool- and cold-winter regions, but now, or soon, is the time to start seed-sowing indoors.
Seed start warm-season crops indoors. By the middle of the month, tomatoes, peppers, cucumbers, eggplants, squashes, cantaloupes, and watermelons can be started in flats indoors. These warm-season crops can be sown in flats nearly filled with pre-moistened potting mix. Level the soil then gently sprinkle seed on top. Sow one flat for each vegetable. Press the seed into the soil surface with a piece of flat wood to make good contact then add a layer of soil on top–three times the diameter of the seed. Next, slip the flat into a plastic bag and tie it off. Set the flats in a warm spot out of direct sunlight until the seeds sprout. Be sure to label each flat.
When seeds sprout, remove the plastic “greenhouses” and place the flats where they will stay warm, but not hot, and where they will get full sun during the day, a greenhouse, hothouse, or south-facing window is best. Use fluorescent lights where sun is not available. Use room temperature water to keep the soil moist, but not wet. After seeds have been sprouted three weeks water seedlings with a diluted mix of fish emulsion or compost tea once a week.
Seedlings will likely need potting up once or twice before they go into the garden. Don’t allow seedlings to get leggy or spindly before potting them up.
Outdoor seed sowing. Cool-weather crops can be sown or set in the garden as soon as the soil is workable in early spring. If you pick up a ball of soil in your hand and the lump crumbles apart when you open your fist, the soil is workable–not too wet or too cold. If the lump is shiny or sticky, wait for the garden to dry out.
Vegetable crops for sowing or setting out in the garden in March:
Brussels sprouts. Sow seeds for main crop Brussels sprouts and set out hardened-off plants. Sow seed ½ inch deep and 6 inches apart. Hardened off Brussels sprouts starts will be in garden centers this month. Set starts into planting beds turned and amended with aged compost. Brussels sprouts that have been over-wintered in cold frames can be set in the garden now.
Parsnips. Sow parsnips this month, early in warmer regions, later in cold regions. Add aged manure or compost to the planting bed in advance of sowing and turn the bed. Broadcast a blend of 2 parts bone-meal and 1 part sulphate of potash at 3 ounces per square yards. Sow seed ½ inch deep and 15 inches apart, later thin seedling to 6 inches apart. Harvest will come next winter.
Kohlrabi. Sow kohlrabi in warm regions. Sow seed ½ inch deep in rows 12 to 15 inches apart. Do not plant kohlrabi where club root disease has been a problem in the past.
Potatoes. Plant early potatoes in mild regions starting the middle of the month. Hold off planting if the soil is very wet. Set seed potatoes in trenches 12 inches wide and 9 inches deep. Place 2 to 3 inches of aged compost or aged steer manure at the bottom of the trench. Set tubers 12 to 14 inches apart then draw up and cover them with a ridge of soil
Onions. Set onion bulbs this month in well-drained soil. Set bulbs 9 inches apart in rows 12 inches apart. Set bulb tips just above soil level. Onions grow best in beds that were amended with aged manure in the fall.
Salad onions, radishes, and lettuce. Salad crops can go into sheltered beds in warming regions. Sow these seeds ½ inch deep in drills 12 inches apart. Take time sowing evenly so that you don’t have to spend a lot of time thinning seedlings later.
Cabbages. Sow seed of late summer cabbages in a sheltered bed. Sow cabbage seed 6 inches apart and ½ inch deep.
Peas. Continue sowing early, round-seeded peas this month. Sow seed 2 inches deep and 2 inches apart in rows set 9 inches apart. If you plant in drills, sprinkle bone meal at the bottom of each drill.
Leeks. Sow seed of leeks in rich soil this month. Sow seed ½ inch deep. Leeks grow best in well-worked soil amended with aged compost.
Spinach. Sow summer spinach for harvest in May and June. Sow seed 1 inch deep in rows 9 inches apart. Sow seed 1½ inches apart and later thin seedlings to 6 inches apart.
Carrots. Sow carrots under cloches or plastic tunnels. Sow seed ½ inch deep in rows 9 inches apart.
Shallots. Complete shallot planting this month. Set shallot bulbs in well-drained soil. Set bulbs 6 inches apart in rows 10 inches apart. Set the bulb tips just above soil level.
Asparagus. Set asparagus roots 15 inches apart. Spread the roots out fanlike and place the crowns 3 inches below soil level. Do not harvest asparagus the first year and only sparingly the second year. Dress asparagus beds in advance of planting with aged manure and a 3-inch topping of planting mix or topsoil.
Jerusalem artichokes. Set sunchoke tubers in holes 12 inches square and 12 inches deep. Add aged compost or manure to the hole before planting tubers. Space plants 18 inches apart.
Tomatoes. Tomatoes for transplanting in the garden in May can be started from seed this month in a cold frame or greenhouse that does not drop below 65°F day or night. Tomato seed germinates best at 75°F to 85°F. When seedlings get their first set of true leaves they should be potted up to 4 inch containers.
Herbs. Prepare herb beds as soon as the soil can be worked. Herb beds should be finely rolled and raked; even small clods should be broken up. Sowing can start when the soil has warmed. Sow chervil, chives, dill, marjoram, parsley, and sorrel this month. Sow seed in drills 1 inch deep and rows 8 inches apart. Sow just enough for cookery seasoning, a pinch or two. For drying and storing herbs, sow more.
Old clumps of bergamot, sorrel and chives can be separated, new plants taken from the parent plants and re-planted.
Basil can be sown in a greenhouse or coldframe that does not dip below 55°F.