March represents a significant turning point in the gardening year, signaling the transition from winter dormancy to the primary growing season. Success in March requires strategic preparation and careful planning due to unpredictable weather. This month creates a narrow window for indoor sowing and the direct planting of cold-tolerant crops, giving them a necessary head start.
Understanding Your Planting Zone and Timing
Determining what you can safely plant in March is dependent on your local climate. Gardeners use the United States Department of Agriculture (USDA) Hardiness Zones to understand which plants can survive the average minimum winter temperatures in their area. These zones provide a framework for selecting appropriate perennial plants and timing spring activities.
The most important factor for March planting is the “Last Frost Date” (LFD), the average date the final spring temperature dip below 32°F is expected. Since the LFD is based on historical averages, a 30% chance of frost remains after the listed date. This date dictates when tender seedlings can safely be moved outdoors and when seeds should be started indoors.
For example, gardeners in warmer climates, such as USDA Zone 7, may see their LFD fall in late March or early April, while those in Zone 4 must wait until late April or early May. Additionally, local features like large bodies of water, steep elevation changes, or urbanization can create “microclimates” that slightly alter the expected frost dates for a specific neighborhood. Using the LFD to count back the required number of weeks for seed starting ensures that transplants are the correct size when outdoor conditions are finally suitable.
Seeds to Start Indoors
March is the optimal time to start seeds indoors for crops requiring a long growing season or high susceptibility to cold. Warm-weather vegetables, such as tomatoes, peppers, and eggplant, need a six-to-eight-week head start before they are ready to be transplanted after the LFD has passed. Starting these crops now allows them to develop strong root systems and mature early enough to produce fruit before the first fall frost.
Peppers, particularly, often require a longer lead time of eight to ten weeks before the last frost, making early-to-mid March the ideal sowing window. Tomatoes generally benefit from being sown six to eight weeks before the planned outdoor planting date, which keeps them from becoming leggy and weak indoors. Starting these seeds in sterile seed-starting mix and providing them with supplemental light, such as fluorescent or LED grow lights, prevents stretching and encourages sturdy growth.
Many slow-growing flowers and herbs also benefit from an indoor start in March, including petunias, snapdragons, coleus, and rosemary. Certain cool-season vegetables, such as cabbage, broccoli, and Brussels sprouts (brassicas), can also be started indoors in early March. These seedlings tolerate cooler soil and air temperatures, allowing them to be moved outdoors earlier than warm-weather crops, often in mid-to-late April.
Crops That Can Be Sown Directly Outdoors
March allows for the direct sowing of numerous cold-hardy vegetables that thrive in cool soil and withstand light frost. These crops germinate well when the soil temperature reaches at least 40–45°F, allowing for a much earlier harvest than tender summer vegetables. Direct sowing is particularly important for root vegetables, which do not transplant well because disturbing the taproot can cause malformation.
Radishes are exceptionally fast-growing and can be sown directly into the ground as soon as the soil is workable, typically maturing in just three to four weeks. Plant radish seeds about a half-inch deep and an inch apart to allow for proper root development. Similarly, carrots can be sown directly, but they require consistently moist soil to germinate successfully; sowing them a quarter-inch deep in trenches is effective.
Leafy greens are another excellent choice for March direct sowing, especially cold-tolerant varieties of spinach and lettuce. Spinach can germinate in soil as cold as 35°F and should be planted a quarter-inch deep. Cold-tolerant lettuce varieties are also sown shallowly and benefit from the cool, moist conditions of early spring.
Peas, both shelling and snap varieties, are perfect for early planting, as they prefer cool soil for germination, ideally around 40°F. Pea seeds should be planted about one inch deep and spaced two inches apart, often requiring a trellis or support structure as they grow. Gardeners can also plant onion sets or certified early potato varieties in March, provided the soil is dry enough to avoid compaction.
Preparing Garden Beds for Spring
March is the time for essential garden bed rehabilitation after winter, before any seeds or transplants are placed. The first step involves clearing away remaining winter debris, spent crops, or residual mulch. Removing this material creates a clean slate for the new growing season and helps eliminate potential overwintering sites for pests or diseases.
Check the soil’s moisture content before attempting any digging or turning. Working soil that is too wet can destroy its structure, leading to compaction which hinders drainage and root growth. A simple test is to squeeze a handful of soil; if it crumbles easily, it is ready to be worked, but if it holds its shape as a wet ball, it is too saturated.
Once the soil is dry enough, incorporating organic matter is the most effective way to improve soil health for the coming season. Adding well-rotted compost or aged manure into the top six to eight inches of the bed enhances fertility, improves moisture retention, and increases microbial activity. Gardeners should also consider testing their soil’s pH now, as a balanced pH is necessary for plants to absorb nutrients effectively. Amendments like lime or sulfur can then be applied to adjust acidity or alkalinity if needed.