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.
In warm regions, tender starts–tomatoes, peppers, eggplants, squashes, and beans–can go into the garden early this month. In cool regions, be sure night temperatures are averaging 55°F or warmer before setting out tender starts–that may mean towards the end of the month or even in June. (Be sure to check out the Warm and Cool Regions Checklists below for specifics.)
Things to do in the garden during May:
- 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 tender 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 backfill. 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 to15 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.
Warm Region Vegetable Garden Checklist for May:
If the weather has settled in your region, now is the time to direct sow warm-weather vegetable seeds. Once the last frost is past, vegetable starts can go into the garden as well.
Few seeds will germinate if the soil temperature is below 45ºF (7ºC) and warm-weather crops will not thrive until the night temperatures stay consistently above 50ºF (10ºC). Follow the high and low temperatures for several days if you are unsure if the time is right to begin sowing and planting out warm-season crops.
If you do get started and temperatures unexpectedly dip, use horticultural fleece or cloches to protect summer veggies from danger.
You can minimize transplant shock if you hold off putting melons and summer and winter squash seedlings in the garden until 10 day after the date of the last expected frost. Peppers and eggplants can be transplanted into the garden two to three weeks after the last frost.
Herb starts like dill, oregano, sweet marjoram, cilantro, rosemary, sage, and thyme can be transplanted into the garden this month. Make sure the weather is settled warm before you plant out basil and lemon grass.
If you live in USDA Plant Hardiness Zones 7-11, here is a vegetable gardening checklist for May:
(In the United States, USDA Zones 10 and 9 include the Gulf Coast and parts of the South Atlantic states, the Pacific Southwest—mainly Southern California, and parts of the Desert states. Temperature lows in the coldest of these regions can drop as low as 20°F (-7°C). In Europe, parts of Spain, Italy and France and regions of countries bordering the Mediterranean Sea are in Zones 10 and 9. USDA Zone 8 includes the Mid-South, Pacific Norwest states and parts of Northern California. Zone 7 includes parts of the Northeast, Mid-Atlantic region, and eastern sections of the Northwest. Temperature lows in the coldest of these regions can drop as low as 0°F (-18°C). Much of the United Kingdom, France and parts of Spain are in Zone 8. The western regions of Germany are in Zone 7.)
Greenhouse and coldframe in warm regions:
- Sow successions of tender vegetables such as tomatoes, peppers, cucumbers, and runner beans to plant out later.
- Plant greenhouse tomato plants in large pots, or plant them in grow bags.
- Water and feed tomatoes, cucumbers, and peppers, never letting the soil dry out. Remove side-shoots from tomatoes.
- Attach slings or nets to greenhouse melons as they swell.
- Introduce biological controls to keep down pests such as greenhouse whiteflies and spider mites.
Vegetables in the garden in warm regions:
- Start sowing vegetables without protection if the soil and night time temperatures have warmed.
- Thin beets, carrots, lettuce, radishes, spinach and other half-hardy and hardy seedlings planted late last month. As crops are harvested, plant successions of early or start introducing summer crops.
- Early in the month, prepare outdoor sites for cucumbers, squashes, and tomatoes. Erect supports for runner beans, and place stakes, poles, and trellises in place for tall and climbing crops.
- Stake tomatoes and tie them gently to stakes..
- Remove cloches from broad beans, carrots, and peas.
- Mid-month sowing: sow seeds of beans, lima beans, corn, okra, squash, cucumber, cantaloupe, Chinese cabbage, and other tender vegetables and herbs after temperatures have reached the 70sF.
- Sow cucumbers in mounds enriched with plenty of well-rotted manure and compost.
- Set out transplants after mid-month: tomato, eggplant, pepper, and sweet potato.
- Set out sweet potato slips on a cloudy day. Form little mound of soil over young potato shoots to protect them from frost.
- Pinch out the tips on broad beans to encourage good pod set and to deter attack from aphids.
- Make furthers sowings of salad crops and summer spinach.
- Stop watering onions, garlic, and shallots when the foliage begins to turn yellow.
Harvest early crops in warm regions:
- Start picking broad beans when the pods are finger thick.
- Continue to cut asparagus. As the asparagus harvest ends, cut back female plants with berries.
- When peas stop producing, cut vines to ground (do not pull allowing their roots to fix nitrogen in the soil). Replace early cool-weather crops with summer crops.
Succession plantings in warm regions:
- Make successional sowings of early crops: beetroot, carrots, lettuces, and turnips. Make successive sowing of lettuce, salad crops, and summer spinach, turnips, runner beans, green beans, endive, radishes, and kohlrabi.
Late month sowing and transplants in warm regions:
- Sow sweet corn outdoors in mild areas when further frost is unlikely. Most vegetables can be sown now, so check the packets.
- Sow French and runner beans, and pole beans, long-rooted beets, sea kale, salsify, and sweet corn.
- Plant out late-summer cauliflowers and in the north Brussels sprouts. Plant out vegetable seedlings such as cabbages, cauliflowers, celery, sweet corn, tomatoes, and marrows. Plant outdoor tomatoes, and tie them gently, but firmly, to stakes to secure them.
Herbs in warm regions:
- Plant or pot up basil seedlings.
- Take cuttings of pot marjoram, rosemary, sage, and thyme.
- Divide and transplant perennial herbs.
- Divide any straggly mint and thyme plants.
- Plant or pot up basil seedlings.
Pests in warm regions:
- Watch for aphids on broad beans and root flies on cabbages, carrots and onions. Keep after weeds.
Feeding and watering in warm regions:
- Give side dressing of compost tea to half-grown plants.
- Keep all plants watered and well mulched.
Fruit trees in warm regions:
- Feed summer-fruiting plants with potassium sulfate to promote good flowering and fruit. Control weeds around bush and cane fruit.
- Thin the fruit on apples, peaches, nectarines pears, and plums when they reach marble-size. Thin heavy-cropping nectarines and peaches when fruit is ½ in (1-1.5 cm) in diameter.
- Water new plantings deeply if weather is dry. Water plentifully when fruit is swelling.
- Hang coddling moth traps on apple trees.
- Spray against apple scab, mildew, and aphids.
- Prune wood damaged by fire blight.
- Remove any shoots on wall-trained fruits that are growing directly toward or away from the wall.
- Remove the blossoms from newly planted fruit trees to direct the plants energy into the production of strong new wood.
Berries in warm regions:
- Plant new strawberries and put cloches over strawberries if you want an early corp. Harvest strawberries as they ripen. Protect strawberry fruits with straw or black plastic sheeting.
- Keep new canes of blackberries and loganberries separate from the current year’s fruiting canes. Tie new canes of blackberries and hybrid berries to a system of support wires, allowing a maximum of eight canes per plant.
- Remove weak shoots from brambles. Thin our raspberry canes. Spray raspberries against raspberry beetles. Apply the first spray as soon as the first fruit turns pink.
- Summer-prune gooseberries by cutting back side-shoots to five leaves.
- Feed blackberry and hybrid berry plants with ammonium sulfate or other high-nitrogen fertilizer. Cover berries with netting to protect them from birds.
Citrus in warm in warm regions:
- Plant citrus and tropical fruit this month. Feed citrus fruit with sulfate of ammonia; feed established trees with iron sulfate. Water citrus deeply in dry weather.
Containers in warm regions:
- Plant summer container plants when the danger of frost is past.
- Feed new transplants with liquid fertilizer and water as needed.
Cool and Cold Region Vegetable Garden Checklist for May:
In cool- and cold-winter regions, the danger of freezing weather and frost continues through May in USDA Plant Hardiness Zones 6, 5, 4, and 3. Here is a checklist of things to do in the vegetable garden in cool and cold regions during April in the Northern Hemisphere:
(USDA Zones 6, 5, 4, and 3 are the most northern and coldest winter regions of the United States the northern parts of the Rocky Mountains, northern Plains and Midwest States and the northern regions of the Northeast and into Canada. Temperature lows in the coldest of these regions can drop as low as -40°F (-40°C). Eastern Europe is largely in Zone 6 and Zone 5.)
The weather in cool northern regions can remain unsettled even in May. Remeber that both the soil and air temperatures are important when planting the kitchen garden. Few seeds will germinate if the soil temperature is below 45ºF (7ºC), and warm-weather crops are not going to thrive until the night temperatures consistently stay above 50ºF.
By the end of the month–or two to three weeks after your last frost, your kitchen garden will be able to welcome cucumbers, bush and pole beans, and tomatoes. In the meantime you can get these crops going in a greenhouse or coldframe or in the kitchen window. If you get the seedlings growing now, you’ll enjoy an earlier harvest next summer.
Strawberries can be planted now. June-bearing-type strawberries are vigorous and spread runners rapidly and should be producing in June. Everbearing-type strawberries will fruit in June and again later in the fall. If you are looking for the easiest to grow, try Alpine strawberries.
Peas. Cool-weather crops such as peas should be ready for harvest later this month or in June before the weather warms. Keep you eye on cauliflower and Brussels sprouts to get them out of the garden at their peak and before they bolt in warm weather.
Greenhouse and coldframe in cool regions:
- Open the greenhouse and coldframe for warm rain and sun; close them if the temperature drops near freezing.
- Early in the month, sow under cover half-hardy annual seeds: tomato, eggplant, pepper, and runner beans. Plant greenhouse tomato plants and cucumbers in large pots or grow bags.
- Harden off vegetable starts in the cold frame for 10 days before setting them out. By the middle of the month, you can harden off tomato plants and ready them for setting out late in month.
- Harvest asparagus and other early crops from the coldframe.
- Introduce biological controls to keep down pests such as greenhouse whiteflies and spider mites.
Vegetables early in the month in cool regions:
- As soon as the ground can be worked, add soil amendments, humus, and manure to the planting beds if these were not added in the fall. Prepare beds for planting and sowing.
- Warm up the soil in cool regions with cloches or black plastic.
- When the danger of heavy frost is past, sow or plant out cool-weather crops; harden off young plants from winter sowings of broccoli, cabbage, cauliflower, leeks, onions, lettuce, peas, and broad beans before planting out.
- Start sowing vegetables without protection if you live in mild regions. Many seeds can be sown from early spring onwards. Check seed packets as some varieties are more suitable than others for early sowing.
- Direct seed broad beans, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, kohlrabi, leeks, lettuce, onions, parsnips, peas, radishes, and spinach.
- Plant asparagus, rhubarb, and celery. Dig well-rotted manure into celery trenches.
- Prepare runner-bean trenches by digging in compost or well-rotted manure.
- Plant early potatoes and onion sets.
- Use horticultural fleece or cloches for early crops.
- Thin out overcrowded vegetable seedlings sown earlier: thin beets, carrots, lettuce, radishes, and spinach.
- Mulch after the soil has warmed and plants are several inches high.
- Put supports in place for peas.
- Turn compost pile.
Vegetable starts and transplants in cool regions:
- Protect vegetable starts from drying winds and keep them well watered.
- Shade transplants from direct sun for a week or until re-established outdoors.
- Mulch when plants are several inches high.
- Weed and water as needed.
- Watch for insects and signs of disease.
Succession planting in cool regions:
- Make a second sowing of early peas and other crops as the first harvest comes in.
- Feed lettuce and other early crops with compost.
Succession planting in cool regions:
- Plant warm-weather crops and tender herbs when the danger of frost is past and the soil has warmed up and the weather settled. Sow seeds of beans, corn, okra, squash, cucumber, cantaloupe–all tender vegetables–when the weather has warmed into the 70s. □ Set out plants of tomato, eggplant, pepper, and sweet potato.
Fruits and berries in cool regions:
- Plant fruit trees and brambles when soil workable. Paint white or wrap trunks of young trees to prevent sunscald.
- Water new plantings deeply if the weather is dry.
- Feed summer-fruiting plants with potassium sulfate to promote good flowering and fruit.
- Plant new strawberries, and place cloches over strawberries if you want an early cop. Be sure to cover strawberries if a late frost is possible.
- Plant currant bushes and raspberry canes, and water them in thoroughly. Cut the canes down to 12 inches above the ground.
- Thin brambles (blackberries, raspberries, loganberries); prune away weak shoots. Prune back the stems of newly planted and two-year-old gooseberries by about one-half. Spray gooseberries and black currants for gooseberry mildew.
- Fertilize or top-dress with compost established berries and grapes if not done last month. Feed blackberry and hybrid berry plants with ammonium sulfate. Control weeds around bush and cane fruit.
- If fruit trees are still dormant apply dormant spray to apples, pears, and plums.
- Thin the fruit on apples, pears, and plums when marble-size. Thin heavy-cropping nectarines and peaches when the fruit is ½ inch (1-1.5 cm) in diameter.
- Replace mulches removed last month.
- Prune suckers and water sprouts from trees.
- Watch for pests and signs of disease. Trap larvae on trunks of trees and destroy them.
Containers in cool regions:
- When frost danger is past, move containers outdoors again.
- Plant cool-weather and later warm-weather vegetables in containers when the danger of frost is past. Feed new plants with liquid fertilizer.