March marks the transition from winter dormancy to spring growth in USDA Hardiness Zone 7b, a period characterized by unpredictable weather swings. Gardeners in this zone must balance the desire for an early start with the risk of late frosts. By focusing on appropriate timing and specific varieties, you can maximize the growing season and ensure a bountiful harvest.
Essential Groundwork and Timing for Zone 7b
March is six to eight weeks before the average last frost date for Zone 7b, which falls around mid-April. While the air temperature may feel pleasant, the soil remains quite cool, often below the \(40^{\circ}\text{F}\) required for most warm-season seed germination. Successful gardening now depends on respecting this difference between ambient conditions and soil temperature.
The primary task is preparing the garden bed, starting with ensuring the soil is workable. Workable soil crumbles easily and does not compress into a muddy ball when squeezed. Working saturated soil destroys its structure, leading to compaction that impedes root growth and drainage. Once the soil is ready, lightly amend beds with a layer of well-aged compost or other organic matter to improve aeration and nutrient availability.
Gardeners should also begin “hardening off” any cool-season seedlings started indoors in late winter. This involves gradually exposing young plants to outdoor conditions—including direct sunlight, wind, and cooler temperatures—over seven to ten days. This acclimates the plants’ cell structure, preventing transplant shock when they are permanently moved into the garden.
Starting Seeds Indoors
March is the time to initiate the growth of long-season, heat-loving crops that require a significant head start before the weather stabilizes in late spring. These tender varieties cannot tolerate cold soil or late frost events common in Zone 7b. Starting them now ensures they develop into sturdy, mature transplants ready for the garden after the final frost has passed.
Tomatoes should be sown indoors early in the month. They require a consistent temperature of around \(75^{\circ}\text{F}\) for germination, often achieved using a heat mat placed beneath the seed trays. Once sprouted, seedlings need 14 to 16 hours of strong, direct light daily, usually provided by a dedicated grow light system to prevent the plants from becoming leggy.
Peppers and eggplant should also be sown alongside tomatoes in March. Both are sensitive to cold and will suffer stunted growth if their roots encounter soil temperatures below \(55^{\circ}\text{F}\). Certain warm-weather herbs, such as sweet basil, should also be started now to produce substantial plants by the time outdoor planting is possible in May. These seedlings will need to be gradually stepped up into larger containers as they grow before their final move outdoors.
Cool-Weather Vegetables for Direct Sowing
A wide range of cool-weather crops can be sown directly into the garden soil in March, as their seeds germinate in cooler conditions, often as low as \(40^{\circ}\text{F}\). These hardy vegetables thrive in the mild temperatures of early spring and require two months to mature before the intense heat of summer causes them to bolt. Direct sowing is beneficial for root crops, which do not transplant well due to their long taproots.
Peas should be planted about one inch deep and two inches apart along a trellis or support structure. As legumes, they fix atmospheric nitrogen in the soil, which benefits subsequent plantings in the same area. For continuous harvests, practice succession planting by sowing small batches of quick-maturing crops every two to three weeks.
Root crops like carrots, radishes, and beets can also be direct-sown now, but they require careful attention to depth and spacing. Radishes should be planted shallowly, about a half-inch deep, and thinned to two inches apart. Carrots require a similar shallow planting depth but need to be thinned to a final spacing of three to four inches.
Hardy leafy greens, including spinach, kale, and collards, will flourish when sown in March, offering a spring harvest. Spinach seed can be planted a half-inch deep and spaced about three inches apart, while kale and collards benefit from a wider spacing of six inches. While these crops withstand light frost, gardeners should keep row covers handy to protect young seedlings from any prolonged, hard freezes that may occur.
Early Spring Ornamentals and Herbs
Beyond the vegetable garden, March offers opportunities to enhance the ornamental landscape and establish perennial herbs. This period is suitable for transplanting or dividing many perennials that have just emerged from winter dormancy. Perennials like hostas, daylilies, and garden phlox benefit from division now, allowing them to re-establish their roots before the heat of summer arrives.
Bare-root stock, including roses, asparagus crowns, and berry bushes, should be planted this month while they are still dormant. Planting dormant stock allows the roots to grow in the cool, moist soil before the plant expends energy on leaf and stem growth. This establishes a strong foundation for the coming season.
Hardy, cool-season herbs such as cilantro, parsley, and dill can be direct-sown into the garden bed. They perform best when planted in cool soil and provide a harvest before rising temperatures cause them to flower prematurely. Cold-tolerant annuals, such as pansies and violas, can also be planted to provide immediate color in containers or flower beds, as they readily handle late winter temperature fluctuations.