May is the month when the vegetable garden begins to look more and more like the summer garden. By the end of May, the threat of late frosts should diminish and tender crops can begin to go into the garden without worry. Crops started indoors should be hardened off before they are planted.
During May you can:
• Continue succession sowings of hardy vegetables.
• Sow tender vegetables.
• Set out tender vegetables started indoors.
• Sow or set out tender herbs after the last frost.
• Water as necessary.
• Take steps to keep pests out of the garden.
Prepare to plant eggplant, melons, squash, and zucchini. Early in May prepare the planting spots for tende eggplant, squashes, melons, and zucchini. Dig holes 12 inches square, 12 inches deep, and 3 feet apart. Add a forkful of well-rotted compost or manure to the bottom of the hole and then refill the hole. Draw soil from the surrounding area to form a mound over each hole. At the end of the month, sow three seeds on each mound. When the seedlings come up, clip away the two weakest and leave the strong seedling to grow on. If you are planting starts, set one on each mound in early June.
Prepare and plant pole and runner beans. Early in the month prepare to plant pole and runner beans. Dig a trench 18 inches wide and 12 inches deep. Add several inches of well-rotted compost or manure to the trench and back-fill. In the second half of the month, sow bean seeds. Set them 3 inches deep and 9 to 12 inches apart in two rows 12 to 15 inches apart. At sowing time, set bean poles in place alongside each side of the bean row. Set poles at an angle and tie opposing poles together near their tops. You can strengthen the poles with horizontal struts. Alternatively, sow the seed alongside 6 foot canes erected in the form of a wigwam and tied together near their tops.
Prepare to plant tomatoes. Early in the month, prepare planting spots for tomatoes. Dig holes 12 inches square, 12 inches deep, and 2 to 3 feet apart. (Space holes 2 feet apart for determinate tomatoes; 3 feet or more apart for indeterminate tomatoes.) Add a forkful of well-rotted compost or manure to the bottom of the hole and then refill the hole. Draw soil from the surrounding area to form a mound over each hole. Tomatoes starts can be safely set in the garden when nighttime temperatures average 55°F, toward the end of this month or early in June. Tomatoes planted earlier should be protected from cold nights.
Harden off starts. Spring cabbages, carrots, lettuce, and broad beans growing under cloches of plastic tunnels can be hardened off now. This process of gradual exposure to outdoor temperatures can be carried out over three weeks, so that the plants harden-off gradually. Lift covers a few inches each day, increasing the gap by an inch or two at intervals over four or five days.
Beets. About the middle of the month, sow seeds of long-rooted beets–Cylindra and Rodina are two–which grow well in warmer months. Sow seed 1 inch apart and cover with ¼ inch of compost. Later, thin plants to 3 inches apart. Keep soil evenly moist to produce tender roots.
Brussels sprouts. In cool-summer northern regions, set out Brussels sprouts starts this month for summer-to-fall harvest. (In warm-winter regions, wait to plant Brussels sprouts in late summer and fall.) Set plant 1 ½ to 2 feet apart. Keep plants growing vigorously by keeping the soil evenly moist.
Carrots. Sow main crop carrots in May. Carrots grow best in light, sandy, stone-free soil. The varieties Imperator or Gold Pak–which grow roots to 9 inches long–are good choices in light soil. In shallow, rocky, or clay soil, plant the varieties Chantenay or Nantes with roots that grow 6 or 7 inches long. Sow successive crops at three-week intervals.
Cauliflower. Cauliflower grows best where temperature don’t get too hot (above 75°F) or too cold (down to the low 30s°F–light frost will not hurt cauliflowers). Growing temperatures in the mid-60s°F are optimal. Set out cauliflower starts sown indoors last month when both the soil and air temperature is at least 50°F. Plant cauliflower starts 24 inches apart in rows 24 inches apart. Place a bottomless paper cup around each plant to protect the plants from cutworms.
Sweet corn. Sow sweet corn when all danger of frost is past. Sow seeds any time average temperatures are expected to stay within a range of 40°F at night to a high of 85°F during the day. Prepare the planting area in advance by working in an inch of well-rotted manure. Sow seed 1½ inch deep in groups of three, at intervals of 18 inches apart. Thin to the strongest plant a couple of weeks after the seedlings emerge. Sow corn in a number of short rows arranged in a rectangular block. Block sowing will facilitate pollination; corn is pollinated by wind-borne pollen, which cannot travel far.
Cucumbers. Start cucumbers indoors about three weeks before night temperatures will average 55°F. Seedlings can not go into the garden until all danger of frost is past. Prepare the growing site advance: dig holes 12 inches square, 12 inches deep, and 3 to 4 feet apart for trailing plants, 12 inches apart for climbing plants. Add 3 to 4 inches of well-rotted compost or manure to the bottom of the hole and then refill the hole. Draw soil from the surrounding area to form a mound about 4 inches high. Plant out cucumber starts when the weather has sufficiently warmed.
Potatoes. Potatoes planted last month should be protected from late frosts. Set floating row covers of spun poly over potato plants when night temperatures are predicted to dip.
Salad crops. Make further sowings of salad crops–lettuces and spinach–to maintain a continuous cut-and-come-again harvest. Continue to sow lettuce and spinach ever two weeks until about eight weeks before maximum daytime temperatures are expected to average about 80°F. Where summer temperatures do not average 80°, continue successive sowings until about six weeks before the first frost is expected.
New Zealand Spinach. Sow heat-tolerant New Zealand spinach when danger of frost has past. This crop is a summer substitute for spinach in warm-summer regions. New Zealand spinach is tolerant of sandy, salty soil. It loves sun and doesn’t like shade. Mature plants spread 1 to 2 feet.
Herbs. Make further sowings of chervil, dill, fennel, hyssop and parsley and thin out seedlings to 3 inches apart.
• Basil seedlings can be set out late this month when the danger of frost has passed. Set seedlings about 15 inches apart and water well in the early stages until the plants are established. Sow basil seed 1 inch deep garden beds that have warmed or directly into the cold frame.
• Cuttings. Take cuttings 3 to 4 inches long of pot marjoram, rosemary, sage, and thyme from last year’s growth. Strip the lower leaves from the cutting, and with a sharp knife cut straight across the stem below a joint. Set the cuttings into a sand-filled pot or into open, sandy soil. If the weather is cold or windy, give cloche protection.
• Division. Mint and thyme which has overgrown pots or have become straggly in the garden can be divided or rooted now. The tiny roots at each joint on the runners will set new roots if buried in fine soil.
Pest control. Pests become active in May. Begin scouting the garden for pests and take appropriate action. Aphids will reappear this month. Knock them off plants with a stream of water. Protect tender shoots from cutworms with paper collars around newly set seedlings. Control slugs and snails by placing sandpaper collars around seedlings. Place loosely rolled wet newspaper “traps” around the garden to collect snails, slugs, and earwigs during the day; these pests seek a cool, moist place to hide during the day.
Watering. Watering new sowings and seedlings is very important. A check to growth can be disastrous to crops grown from seed. Normal growth depends upon an even supply of water. Check the garden daily to make sure the soil stays evenly moist. Put your finger in the soil, if it comes away just moist, the watering is good. If your finger comes away from the soil dry, water.