May represents the transition point for gardeners in USDA Hardiness Zone 7. With the average last frost typically occurring by mid-April, this month marks the moment to safely introduce warmth-loving plants to the outdoor environment. The focus shifts entirely from frost defense to maximizing growth potential as soil temperatures begin to rise consistently. Planting now sets the stage for a productive summer harvest. May is the defined window for establishing tender crops that require a long, hot growing season.
Warm-Season Vegetables
May is the time to transplant delicate, long-season vegetables that were started indoors, giving them a head start on production. Tomatoes, peppers, and eggplant are the primary garden residents that benefit from being moved from containers into the prepared garden beds now. These plants are highly sensitive to cool temperatures and will experience stunted growth if planted earlier when nights are still chilly. Selecting determinate tomato varieties, such as ‘Better Boy,’ can be advantageous for Zone 7 gardeners, though indeterminate types like ‘Black Krim’ will also flourish when planted this month.
Beyond transplants, a wide array of vegetables should be sown directly into the garden soil during May. Direct sowing is the preferred method for crops that dislike root disturbance, offering quick germination and robust initial growth. Beans, including popular types like ‘Blue Lake’ pole beans and bush varieties, should be planted now, thriving in the increasingly warm soil. Corn, a staple summer crop, also requires a direct planting approach as it develops a deep taproot that resents being moved.
Cucurbits—squash, cucumbers, and melons—can be safely seeded outdoors this month. Summer squash varieties like zucchini, patty pan, and crookneck squash grow rapidly once established and can be continually harvested throughout the season. For winter squash and melons, direct planting in May allows them time to mature their fruit before the first expected frost in the fall. Waiting until May ensures the soil is warm enough to prevent the seeds from rotting in the ground before they can sprout.
Herbs and Annual Flower Varieties
May provides conditions for introducing heat-loving herbs and annual flowers that add flavor and color to the garden. Basil, a summer herb, should be planted as a transplant rather than seed for the quickest and most abundant yield. Its growth is hampered by temperatures below 50°F, making a mid-to-late May planting advisable.
Other culinary herbs can be established now, either from seed or small plants. Cilantro and Dill, while often direct-sown, will need some protection from the intense afternoon sun as temperatures climb to prevent premature bolting. Parsley can also be planted; while it is a slower grower, establishing it now ensures a steady supply for summer cooking.
For garden aesthetics, May is the peak season for planting annual flowers that will bloom continuously until the autumn frost. Annuals are excellent choices for either direct seeding or transplanting:
- Zinnias
- Marigolds
- Petunias
- Cosmos
These flowers attract beneficial pollinators, such as bees and butterflies, which aids in maximizing vegetable fruit set. Providing these annuals with adequate space and regular watering will result in a summer-long display of color.
Ensuring Successful Establishment
While air temperature is warm in May, the soil temperature is a more accurate measure of readiness for planting warm-season seeds. For germination of crops like beans, corn, and squash, the soil temperature should be at least 60°F, measured a few inches below the surface. Planting before this threshold is reached increases the risk of seed rot or stunted initial growth. A consistent soil reading over several days is a better indicator than following the calendar date.
Transplants, including tomatoes, peppers, and annual flowers, require a process known as hardening off before they are set out. This acclimatization involves gradually exposing indoor-grown plants to outdoor elements like direct sunlight, wind, and temperature fluctuations. The process, lasting about one to two weeks, helps to thicken cell walls and prevent transplant shock, which can otherwise slow a plant’s growth.
Once seeds and transplants are in the ground, moisture management is required to support root establishment. New transplants need deep, thorough watering immediately after planting to settle the soil around the roots and eliminate air pockets. Applying a layer of organic mulch, such as straw or shredded leaves, around the plants helps retain soil moisture and stabilize the soil temperature. Mulching also suppresses weed growth, which reduces competition for water and nutrients during the warmer months.