March marks a significant turning point for gardeners, transitioning from winter planning to the first active planting of the season. The lengthening days and warming earth create an opportunity to begin sowing seeds and preparing garden beds. Careful timing and selection of plants are paramount for a successful harvest.
Determining Your Planting Timeline
Successful March planting relies not on the calendar date but on understanding your local climate factors, specifically the Last Frost Date (LFD). The LFD is the average date of the final freeze in spring, determined by historical weather data for a specific area. This date is a baseline for when it is generally safe to transplant tender seedlings outdoors, as planting too early risks damage or death from unexpected frost.
The United States Department of Agriculture (USDA) Plant Hardiness Zone Map offers a broad guide for selecting perennials that can survive the winter. However, for spring planting, the soil temperature is a more accurate indicator than the air temperature. Air temperature fluctuates rapidly, while soil warms more slowly and holds heat more consistently.
Cool-season vegetables can be sown when the soil temperature consistently reaches a minimum of 40°F to 45°F. Using a soil thermometer inserted a couple of inches deep provides the necessary data to determine if the ground is ready for direct sowing. Waiting until the soil is warm enough ensures better germination rates and prevents seeds from rotting in cold, wet soil.
Vegetables for Direct Sowing Outdoors
March is the ideal time to sow the seeds of hardy vegetables directly into the prepared garden bed. These crops are adapted to germinate in lower soil temperatures, often before the Last Frost Date has passed. Before planting, ensure the soil is workable, meaning it crumbles easily when squeezed rather than forming a wet ball, which prevents compaction.
Peas, both shelling and snap varieties, are excellent candidates for early March sowing, as their seeds can germinate when the soil temperature is around 40°F. Planting them about an inch deep and providing a trellis or support structure early on encourages vertical growth and a clean harvest later in the season. Spinach and lettuce are also highly cold-tolerant and can be sown when the soil is as cold as 35°F to 40°F.
Radishes are another fast-growing option, often ready to harvest in three to four weeks, and they germinate reliably at 40°F. Direct-sowing them in succession every couple of weeks allows for a continuous spring harvest before the summer heat causes them to bolt, or prematurely flower. Carrots can also be sown directly in March, though they may take longer to germinate in colder soil, requiring consistent moisture to sprout successfully. Kale is a brassica that also prefers cool weather and can be directly sown now for a spring harvest.
Seeds to Start Indoors
While many cold-tolerant plants go straight into the ground, March is the deadline for starting the seeds of warm-season vegetables indoors to give them a sufficient head start. These tender plants, such as tomatoes, peppers, and eggplant, have a long maturation period and are highly sensitive to frost, requiring transplanting only after the LFD has passed and the soil has warmed considerably.
Tomatoes need to be started indoors approximately six to eight weeks before the anticipated transplant date. Providing supplemental light from grow lights is necessary to prevent leggy growth, as a sunny windowsill often does not offer enough intensity during early spring. Peppers and eggplant demand an even earlier start, often needing 10 to 12 weeks of indoor growth before they are ready for the garden.
These heat-loving seeds germinate best when the soil temperature is significantly higher, ideally between 75°F and 85°F. Using a specialized heat mat beneath the seed trays is necessary to provide this consistent bottom heat, which accelerates germination and promotes strong initial root development. Herbs like basil can also be started indoors in March, as they require warm conditions and an extended growing season to thrive.
Planting Bulbs and Root Crops
March planting activities extend beyond seeds to include various non-seed materials, particularly root crops and dormant perennials. Cool-weather root vegetables can be introduced to the garden as soon as the soil is workable. Seed potatoes, for instance, can be planted out in March for an early summer harvest, typically placed in trenches or hills to allow for hilling up as the plant grows.
Onion sets and shallots are excellent for planting in early spring, as they are tolerant of cooler temperatures. These small, immature bulbs develop into full-sized bulbs over the growing season and are typically planted just below the soil surface. Bare-root perennials (plants sold dormant without soil) can also be planted in March while they are still resting.
Perennials like daylilies, hosta, and Siberian iris can be planted directly into the ground, as they tolerate the cold soil better than tender annuals. For summer-flowering bulbs, such as lilies and gladioli, March is the time to acquire and plant them to ensure blooms later in the season. Planting these materials while the soil is just beginning to warm allows them to establish a strong root system before the stress of active summer growth begins.