May marks the transition in the gardening calendar, moving beyond the last threat of freezing temperatures to a period of reliable warmth. This shift signals gardeners to begin establishing the majority of their summer vegetable production. Accumulated solar energy has warmed both the air and soil, allowing heat-loving plants to thrive and produce a high-volume harvest.
Understanding Your Regional Planting Window
Successful May planting relies less on the calendar date and more on two specific measurements: the average last frost date and the soil temperature. The last frost date is an estimate, often falling around mid-May, but a late cold snap can still occur, making local forecast monitoring essential. Planting tender vegetables before this date risks damage or death.
The temperature of the soil is arguably the more important factor, especially for warm-season crops. Cold soil significantly hinders root growth, often causing seeds to rot or transplants to remain stunted, a condition known as “sulk.” Use a soil thermometer to measure the temperature at a depth of about four inches, ensuring it consistently reads at least 60°F before setting out any warm-weather transplants.
Planting the Warm-Weather Heavy Hitters
May is the traditional time to plant the garden’s heavy-hitting, heat-loving crops, which include members of the Solanaceae and Cucurbitaceae families. Tomatoes (Solanum lycopersicum), peppers (Capsicum annuum), and eggplant (Solanum melongena) are typically set out as transplants, as their long maturity windows require an early start. These plants demand soil temperatures that are consistently above 65°F to initiate robust root development and growth.
For cucurbits, which include summer squash, zucchini, cucumbers, and melons, direct sowing into the ground is often preferred once the soil reaches 70°F. Planting these seeds too early in cold, wet soil can lead to poor germination and susceptibility to rot. If using plant starts for any of these crops, they must be “hardened off” by gradually exposing them to outdoor conditions over a week or two before planting. This process minimizes transplant shock by toughening the plant cell walls against the wind and sun.
Quick Yields and Succession Planting
While the heavy hitters are establishing themselves, May is an excellent time to maximize garden space by planting quick-yielding crops that can be harvested in just a few weeks. These vegetables are generally direct-sown from seed and have a short window from planting to plate. Radishes, for example, can be ready in as little as 25 to 30 days, providing an immediate harvest while slower crops mature.
Bush beans are another rapid producer that thrive when the soil is warm enough, offering a harvest in just over a month. Carrots, beets, and Swiss chard are also ideal candidates for direct seeding in May due to their relatively short maturity periods. These quick-maturing vegetables are perfect for succession planting, a technique that involves sowing small batches every few weeks rather than planting the entire supply at once.
Continuous planting ensures a steady, manageable supply of fresh produce throughout the season, preventing a single, overwhelming harvest. Once a patch of fast-maturing crops like radishes or early lettuce is harvested, the space can be immediately replanted with another crop, such as bush beans. This strategy maximizes the use of available square footage, ensuring continuous productivity while slower crops like tomatoes and peppers are still developing their first fruits.