March marks the beginning of the gardening season in USDA Hardiness Zone 6. This month is a period of transition where the ground begins to thaw, but the risk of freezing nights and unpredictable weather remains high. The average last spring frost date for Zone 6 typically falls between April 1st and April 21st. Successful gardening involves a dual approach: starting tender, heat-loving crops indoors to maximize the growing season and direct-sowing cold-tolerant seeds outside. This timing ensures that young plants are ready to move outdoors when the danger of a killing freeze has passed.
Starting Seeds Indoors
March is the time to start seeds indoors for crops that require a long, warm growing season. Starting seeds now ensures they develop into robust transplants rather than leggy, weak seedlings. Heat-loving plants, such as peppers, eggplant, and tomatoes, need 6 to 8 weeks of indoor growth before they can be safely moved outside.
Peppers and eggplant should be sown first, as they require a longer period to germinate and grow more slowly than tomatoes. Most seeds need a consistent soil temperature of 75°F to 85°F to germinate efficiently. Using a heat mat beneath the seed starting trays provides this necessary warmth, which is often higher than ambient room temperature.
Once seedlings emerge, they need intense light for about 14 to 16 hours per day to prevent stretching, a condition called etiolation. Fluorescent shop lights or dedicated LED grow lights should be positioned just a few inches above the plants. After germination, the heat mat can be removed, but the strong light source remains necessary until the seedlings are hardened off and transplanted.
Direct Sowing Outdoors
Direct sowing outdoors in March is reserved for cool-season crops that can germinate in cold soil and tolerate light frost. Before planting, check the soil workability; the soil should crumble easily when squeezed, indicating it is not too wet. Planting in saturated soil can lead to seed rot and compaction.
Peas are a classic March crop and can be sown as soon as the soil is workable, often around St. Patrick’s Day. They germinate well even when the soil temperature is as low as 40°F. Leafy greens, including spinach, kale, collards, and Swiss chard, are also highly cold-tolerant and thrive in the cooler temperatures of early spring.
Root vegetables like radishes, carrots, and beets can also be direct-sown in mid-to-late March. Radishes are the fastest to mature, making them excellent row markers for slower-germinating carrots. Sowing these crops in succession every two weeks ensures a continuous harvest until the weather becomes too warm, which can cause them to “bolt,” or prematurely go to seed.
Planting Bare Roots and Sets
March is the time to plant established, dormant plant material, which offers a head start over seeds. This category includes bare-root plants and sets that are already a season or two old. Onion sets, which are small, immature bulbs, should be planted deep enough so that just the tips are visible above the soil line.
Seed potatoes, which are pieces containing at least one “eye” or sprout, are traditionally planted around mid-March when the soil can be worked. Planting them early allows the plants to develop deep root systems before the summer heat arrives. Perennial vegetables, such as asparagus crowns and rhubarb roots, should also be planted now to establish themselves for future harvests.
Bare-root fruits, like strawberries, raspberries, and certain fruit trees, are best planted in early spring while they are still dormant. These established root systems allow the plants to focus their energy on developing foliage and fruit once the weather warms. This results in quicker establishment compared to planting seedlings later in the season.