March represents the transition from winter planning to active cultivation and the start of the main growing season for many regions. This month offers a dual opportunity: a final chance to start long-season crops indoors and the first opportunity to sow hardy vegetables directly into the garden soil. Successfully navigating March planting depends on understanding your local climate’s limitations, particularly the risk of a late frost and the current soil temperature. Timing these initial plantings precisely maximizes the harvest window and ensures vegetables develop under optimal conditions.
Identifying Your Frost Date and Soil Readiness
Planting success in March is tied to a gardener’s geographical location and the timing of the Last Expected Frost Date (LEFD). The LEFD is an estimated date, derived from historical weather data, after which the probability of a temperature drop to 32°F (0°C) significantly decreases, signaling the safe period for tender plants. The specific LEFD is the practical metric used to schedule both indoor seed starting and outdoor transplanting.
Even with a late March or early April LEFD, planting decisions must consider the soil itself, which warms up much slower than the air. Cold soil inhibits the germination of many seeds, even if the air temperature feels pleasant. While some cold-hardy seeds can germinate in soil temperatures as low as 40°F (4°C), most warm-season crops require soil temperatures to be consistently above 60°F (16°C) for successful growth. The soil must be thawed and workable, not frozen or waterlogged, before any direct sowing can begin.
Vegetables Best Started Indoors in March
Starting seeds indoors in March is necessary for heat-loving crops that require a long growing season. These plants are highly susceptible to cold and frost damage, so they must remain indoors until the LEFD has passed. The goal is to grow a robust seedling that is approximately six to eight weeks old when the outdoor environment becomes safe for transplanting.
Tomatoes, peppers, and eggplants are key candidates for indoor March sowing, as they benefit significantly from this extended period of controlled growth. Peppers and eggplants have a slower germination and growth rate. Providing a seedling heat mat for these crops is beneficial, as it can raise the soil temperature to the optimal 75–90°F (24–32°C) range, which accelerates germination.
Other vegetables and herbs that benefit from an early March indoor start include basil, which is extremely sensitive to cold, and slow-growing brassicas like cauliflower and broccoli. These seedlings need strong light exposure—ideally from a dedicated grow light—for at least twelve to sixteen hours a day to prevent them from becoming tall and weak.
Hardy Crops for Direct Sowing Outdoors
March is the time to directly sow cold-tolerant, hardy vegetables into the garden, provided the soil is no longer frozen or excessively wet. These cool-season crops are adapted to thrive in lower soil temperatures, often germinating well when the soil is just slightly above 40°F (4°C), and they can withstand a light spring frost. Planting them early allows them to mature before the summer heat causes them to “bolt,” or prematurely go to seed.
Vegetables to sow directly in March include leafy greens such as spinach, kale, and lettuce. Spinach is notably cold-hardy and can germinate once soil temperatures exceed 40°F (4°C). Root vegetables are another excellent choice for March, including radishes, carrots, and beets, all benefiting from an early start.
Radishes are often the first harvest of the season, as they mature quickly, sometimes in as little as three weeks. Peas, both snap and shell varieties, should be sown directly into the soil as soon as it can be worked, roughly four to six weeks before the LEFD, as they prefer the cooler temperatures of early spring. For continuous production of fast-growing crops like lettuce and radishes, gardeners should use succession planting, sowing small batches of seeds every two to three weeks until the weather becomes too warm.