May represents the start of the growing season in USDA Hardiness Zone 6, which covers areas experiencing average minimum winter temperatures between -10°F and 0°F. This month marks the transition when gardeners can finally move from cultivating cool-season crops to introducing the majority of heat-loving plants. The shift in temperature allows for the safe planting of tender annuals, herbs, and warm-season vegetables that cannot tolerate the cold of early spring. With the threat of a hard freeze largely past, May is the time for getting the garden established for the summer harvest.
Warm-Season Vegetable Planting
May is the prime window for transplanting and direct-sowing the vegetables that require summer heat to thrive. Tender plants like tomatoes, peppers, and eggplant should be transplanted outdoors from their nursery pots after the estimated final frost date. These nightshade family members require both warm air and soil temperatures, with soil ideally above 60°F, to prevent shock and encourage vigorous growth. Waiting until mid-to-late May for these transplants ensures a higher rate of survival and better overall yields.
Other highly sensitive crops, such as basil and sweet potato slips, also benefit from waiting until the end of the month for outdoor planting. Direct-sowing seeds of crops that do not transplant well should also happen now, once the soil has consistently warmed. This includes vine crops like cucumbers, melons, and all types of squash, along with corn and beans.
Bush beans and pole beans are typically direct-sown in May because disturbing their root systems can stunt their growth. Corn also prefers to be seeded directly into the garden, and planting can be done in succession every two weeks through early summer to ensure a continuous harvest. For gardeners seeking quick harvests, fast-growing crops like radishes and lettuce can still be sown early in the month, as they thrive in the mild May temperatures before the severe summer heat arrives.
Annual Flowers and Herb Transplants
Beyond the vegetable garden, May is the ideal time to introduce a wide variety of annual flowers for season-long color. Annuals complete their life cycle in a single growing season and provide continuous blooms until the first frost of autumn. Popular sun-loving options that are typically purchased as transplants include petunias, marigolds, zinnias, and impatiens, which can be safely moved into garden beds or containers now.
Shade-tolerant annuals, such as begonias and coleus, are also ready for planting in May, providing vibrant foliage and color in less sunny areas. Many annual flowers, like cosmos and sunflowers, can also be easily direct-sown into the soil, offering a cost-effective way to fill large spaces with blooms. Planting these flowers now allows them to establish strong root systems before the high temperatures of July and August arrive.
Herbs that are not cold-tolerant, like basil, must be treated as annuals in Zone 6 and should be transplanted outdoors in May. Other common culinary herbs, such as dill and parsley, can be transplanted or directly seeded, ensuring a supply of fresh aromatics for cooking. While many perennial herbs like thyme, oregano, and chives are already established and actively growing, May is a good time to add new perennial starts to the garden.
Soil Preparation and Late Frost Considerations
The success of May planting depends heavily on monitoring both the air and soil conditions. Historically, the average last spring frost in Zone 6 falls between early April and early May, though a late frost can sometimes occur around the second week of May. Gardeners must remain vigilant for unexpected temperature drops below 32°F, which can severely damage or kill tender transplants.
A more reliable indicator than the calendar is the actual soil temperature, which should be measured before planting warm-season crops. Most heat-loving vegetables require the soil to be at least 60°F for optimal root growth and nutrient uptake. For extremely warm-weather crops like melons, a soil temperature closer to 70°F is preferred for proper germination and development.
In preparation for planting, the soil should be amended with organic materials to improve structure and fertility. Incorporating a generous layer of compost into the garden beds provides a slow-release source of nutrients and enhances water retention. If a late frost is predicted after planting, new transplants can be protected overnight using simple methods like covering them with floating row covers, cloches, or even overturned buckets to trap ground heat.