USDA Hardiness Zone 7’s average last frost date generally falls between mid-April and late April. This month is characterized by the soil beginning to thaw and day length extending noticeably, which triggers the earliest opportunities for planting. Gardeners can begin preparing the ground and starting seeds indoors, leveraging the increasing light and moderate temperatures. The activities undertaken now determine the timing and success of both the early spring harvest and the later summer bounty.
Direct Sowing Cold-Tolerant Crops
March is the ideal time to directly sow seeds for crops that germinate best in cool soil temperatures, often requiring only light working of the topsoil. Utilizing raised beds or low tunnels can be advantageous, as these methods help the soil warm up several degrees faster than traditional in-ground rows. Soil temperatures hovering around 40°F to 50°F are suitable for many cold-hardy varieties to begin their growth cycle.
Leafy greens such as spinach and kale can be planted now, thriving in the early spring conditions before the heat of summer causes them to bolt. Many popular lettuce mixes, particularly those labeled as ‘spring mix,’ are also good candidates for March planting and can be harvested using the cut-and-come-again method. These crops tolerate light frosts after they have established their first true leaves.
Root vegetables are another important category for direct sowing this month, beginning with quick-maturing radishes, which can be ready for harvest in as little as four weeks. Beets and carrots should also be planted, focusing on varieties that mature quickly to maximize the harvest window before warmer weather arrives. When planting peas, both shelling and snap varieties, it is beneficial to treat the seeds with a legume inoculant to enhance nitrogen fixation in the soil.
March is the final opportunity to plant alliums like onion sets and garlic cloves. Onion sets, which are small, immature bulbs, establish quickly and mature faster than those grown from seed. These cold-tolerant plants have a high frost tolerance and will utilize the moist, cool soil conditions to develop strong root systems.
Starting Warm-Weather Crops Indoors
While many crops can handle the March cold, heat-loving plants require a significant head start indoors to be ready for transplanting after the last frost. Solanaceous crops, including tomatoes, peppers, and eggplants, should be started from seed six to eight weeks before the estimated mid-April frost date. These seeds require consistent warmth, often achieved using seedling heat mats, to reach their optimal germination temperature of 75°F to 85°F.
Successful indoor starting depends on providing adequate light intensity immediately upon germination to prevent seedlings from becoming tall and spindly. A south-facing window is often insufficient, necessitating the use of supplemental grow lights suspended just a few inches above the growing plants. The warm soil environment mimics the conditions these tropical plants need to develop strong initial root systems and sturdy stems.
Cucurbits, such as melons, cucumbers, and squash, also benefit from an indoor start, though they should be planted slightly later in late March or early April. Starting them too early can result in oversized, root-bound seedlings that suffer transplant shock. Utilizing biodegradable pots for these varieties is often preferred, as it minimizes root disturbance when they are eventually moved outdoors.
Ornamental and Herb Plantings
March is also an active time for introducing non-food plants into the Zone 7 garden, enhancing both aesthetic appeal and culinary options. Hardy annuals, including pansies, snapdragons, and violas, can be planted now and will provide color through the cooler spring temperatures. These flowers can withstand light freezes and are generally unaffected by the occasional dips below freezing.
Gardeners can also begin planting or tending to perennial additions, such as bare-root roses, which should be soaked and planted before they break dormancy. Established perennials that have become overgrown or crowded can be divided this month, taking advantage of the cool, moist soil to help the separated sections re-establish their root systems quickly. This practice rejuvenates the parent plant and increases the overall stock.
Hardy herbs are another excellent choice for March planting, as many are highly tolerant of cold conditions. Parsley and cilantro seeds can be sown directly into the garden for an early harvest, as their leaves are frost-tolerant. Perennial herbs, including chives and oregano, can be divided and transplanted now, ensuring a steady supply throughout the growing season.
Protecting Early Plantings from Late Frost
Despite the warming trend, late frosts remain a significant risk in Zone 7 throughout March and into early April, necessitating preparation to safeguard early plantings. Utilizing floating row covers is one of the most effective methods, as the lightweight fabric traps heat radiated from the soil while still allowing light and water penetration. These covers can be draped over hoops or directly onto the plants, providing several degrees of protection.
Cold frames, which are essentially bottomless boxes with clear lids, offer a more robust barrier against freezing temperatures and cold winds. Simple cloches, made from repurposed materials like plastic milk jugs or bell jars, can be placed over individual seedlings to create a miniature greenhouse effect. It is important to remove the covers or open the cold frame during warm, sunny days to prevent overheating.
Another technique involves using thermal mass to regulate temperature fluctuations, such as placing water-filled plastic jugs near vulnerable plants. Water has a high specific heat capacity, meaning it absorbs heat during the day and slowly releases that warmth throughout the night. Gardeners should consistently monitor local weather forecasts, as knowing when a hard freeze is predicted allows for timely deployment of these protective measures.