March is a transitional month for gardening across Tennessee, marking the shift from winter dormancy toward spring activity. Success depends on recognizing the state’s varied climate zones and understanding the risks of unpredictable weather. Gardeners must use March to initiate both cool-season outdoor planting and the indoor preparation of heat-loving summer crops. This strategic approach ensures a continuous harvest by maximizing the short spring growing window before the intense summer heat arrives.
Understanding Tennessee’s March Climate and Soil Preparation
Tennessee spans multiple USDA Plant Hardiness Zones, ranging from the cooler 6a in the high eastern elevations to the milder 8a in parts of West Tennessee. The average last spring frost date is a critical calculation, generally occurring from late March in the warmest western areas to early May in the higher eastern mountains. Because of this variability, March planting involves a calculated risk, as a late frost can easily damage or kill tender young plants.
Before any direct seeding begins, the soil must be workable, meaning it should not be saturated with moisture or frozen solid. Squeezing a handful of soil should result in a loose ball that easily crumbles when poked, indicating the proper moisture level. Working with overly wet soil destroys its structure, leading to compaction that hinders root growth.
Cool-season crops generally require a soil temperature of at least 45°F, with 50°F being optimal for many seeds like peas and asparagus. Gardeners should use a soil thermometer to confirm the ground is consistently warming rather than relying solely on the air temperature. Incorporating a layer of compost now provides necessary organic matter and improves soil tilth.
Hardy Vegetables for Direct Outdoor Sowing
March is the ideal time to direct-sow seeds for vegetables that thrive in cool soil and can tolerate light frosts. These cool-season crops mature quickly, allowing for a harvest before the summer heat causes them to bolt or turn bitter. Focus on quick-turnaround root vegetables to maximize the early spring bounty.
Radishes can be planted early and mature in as little as three to four weeks, making them perfect for succession planting throughout March and April. Carrots, beets, and turnips should also be sown directly into the prepared garden soil, as these root crops do not transplant well. Planting these in succession every two weeks extends the harvest window.
Leafy greens, including spinach, kale, collard greens, and leaf lettuce, are highly frost-tolerant and can be direct-seeded now. Spinach and kale are particularly resilient, often surviving unexpected dips below freezing. Peas, both shelling and snap varieties, should also be planted as early as possible in March to ensure they complete their life cycle before the high temperatures of June.
Transplants of cole crops, such as cabbage, broccoli, and cauliflower, can be set out in the garden during March. Gardeners should be prepared to use floating row covers. These lightweight fabric barriers protect them from both insect pressure and sudden cold snaps, mitigating the risk associated with Tennessee’s variable early spring weather.
Seeds to Start Indoors for Summer Transplant
While the outdoors is ready for cool-season crops, March is the deadline for starting seeds indoors for the warm-season vegetables that require a long growing period. These crops cannot tolerate any frost, so starting them inside ensures they are mature enough to produce quickly once transplanted after the final frost date. The goal is to produce robust, stocky seedlings that are eight to ten weeks old by the time the weather is reliably warm, which is typically late April or early May in most of Tennessee.
Tomatoes, the most popular summer crop, should be started now, as they need significant time to develop strong root systems before moving outside. Both peppers and eggplants require even more time and warmth for germination and early growth, making a March indoor start necessary. These seedlings benefit from heat mats, which maintain soil temperatures in the ideal 75°F to 85°F range for quick germination.
Supplemental lighting, such as fluorescent or LED grow lights, must be positioned closely above the seedlings to prevent them from stretching toward the light. Stretched, weak seedlings, known as “leggy” plants, are poorly equipped to handle the transition to the garden. Warm-season herbs like basil, oregano, and thyme should also be seeded indoors during March.
Establishing Perennial and Ornamental Foundations
March offers the best window for establishing long-term plantings while the plants are still dormant. Bare-root stock, which includes fruit trees, cane berries like blackberries and raspberries, and asparagus crowns, should be planted now. Planting these while dormant minimizes transplant shock and allows the root system to establish itself in cool, moist soil before it has to support leaf growth.
Asparagus, a long-lived perennial vegetable, is best planted from one-year-old crowns in mid-March, placed in trenches that will be gradually filled in as the spears emerge. Planting dormant blueberry bushes and cane berries in early spring gives them a full season to develop strong feeder roots. These foundation plantings will provide harvests for many years.
For immediate color, cool-season annual flowers like pansies, violas, and snapdragons can be planted directly into the ground or containers. These ornamentals are tolerant of cold temperatures and will provide vibrant color during the weeks leading up to the last frost. Perennial herbs such as chives and oregano can also be transplanted or divided now.