March signals the transition from winter planning to active cultivation. Lengthening days and warming temperatures encourage gardeners to begin sowing seeds for a productive season. Timing is a primary concern due to the lingering threat of cold weather. Success relies on understanding the specific requirements of various plants during this variable period.
Understanding Local Climate and Timing
Before any seeds are placed in soil, a gardener must first determine the conditions of their specific locale. The average “Last Frost Date” (LFD) is the most significant piece of information, representing the approximate day after which the probability of a freeze drops to a low percentage. This date acts as the primary calendar anchor for all planting decisions, guiding when tender seedlings can safely be transplanted outside.
The USDA Hardiness Zone system classifies regions based on average minimum winter temperature, determining which perennial plants survive year-round. While useful for permanent plantings, the LFD is more relevant for annual seed starting in spring. Air may feel warm, but many seeds require a specific minimum soil temperature, often in the 40°F to 50°F range, to successfully germinate. Cold, wet soil can lead to seed rot or stalled growth, even if the daytime air is mild.
Seeds Best Started Indoors
March is the time to start seeds indoors for warm-weather crops that have a long maturation period and cannot tolerate frost. These tender vegetables need a head start to produce a harvest before autumn. Starting seeds inside allows for precise control over temperature, light, and moisture, maximizing germination rates.
Tomatoes, peppers, and eggplants are the primary candidates for a March indoor start. Peppers benefit from an early sowing, typically needing 8 to 12 weeks of indoor growth before the LFD. Tomatoes generally require 6 to 8 weeks, while eggplants need 10 to 12 weeks due to their slow initial growth. These heat-loving plants germinate best when provided with soil temperatures between 75°F and 85°F, often necessitating the use of a heat mat beneath the seed trays.
Long-season brassicas, including Brussels sprouts, cabbage, and cauliflower, can also be started indoors in March. Although cool-season crops, starting them now allows them to mature before summer heat causes them to bolt. These seedlings can handle light frost and may be transplanted outside a few weeks before the LFD. Providing strong artificial light is necessary for all indoor starts to prevent seedlings from becoming spindly and weak.
Seeds Ready for Direct Outdoor Sowing
For gardeners with workable soil that is no longer waterlogged, a variety of hardy, cool-season vegetables can be sown directly into the garden beds in March. These crops are adapted to germinate in cooler soil temperatures and can withstand light frosts down to about 32°F. Working with soil that is too wet can damage its structure, so wait until it crumbles easily when squeezed.
Peas (shelling and snap) are a classic March direct-sow, planted as soon as the soil can be managed. They thrive in cool, moist conditions and require a trellis for climbing varieties. Spinach and lettuce mixes are also suited for early planting, providing fresh greens before summer heat encourages them to bolt.
Root vegetables like radishes, beets, and carrots can also be sown directly into the soil this month. Radishes are fast-maturing, often ready for harvest in just three to four weeks, making them excellent for marking the rows of slower-germinating seeds. Carrots and beets prefer to be direct-sown because their developing taproots are sensitive to the root disturbance that comes with transplanting. Succession planting, which involves sowing small batches of these quick-maturing crops every two to three weeks, ensures a continuous harvest.
Hardy Flowers and Herbs to Start Now
The early spring sowing schedule includes hardy flowers and perennial herbs, adding beauty and functionality to the garden. Starting hardy annual flowers in March, either indoors or directly outside, provides earlier blooms.
Sweet peas are a favorite flower to sow directly in March, preferring cool soil and tolerating light frost. Since their seeds have a hard coat, nicking them or soaking them overnight improves germination. Snapdragons and calendula can be started indoors under cool conditions and moved outside before the last frost.
For herbs, perennial varieties like parsley, chives, and oregano can be started indoors this month. Parsley seeds are slow to germinate, making an early start beneficial for an extended harvest. Chives are cold-tolerant and can be sown in clumps indoors or directly outside once the soil is workable. Oregano, a hardy perennial, benefits from an early start to establish a strong root system.