March marks a significant turning point for California gardeners, bridging the dormant cool season and the explosive growth of summer. This month requires a dual focus: a final push to plant crops that thrive in spring’s mild weather and early preparation for heat-loving favorites. Gardeners must pivot their attention from frost protection to maximizing the remaining cool days before the inevitable rise in temperatures. March is an active period of transition, demanding decisions about which seeds to sow directly outdoors and which tender starts need indoor warmth. Successfully navigating this month ensures both a final spring harvest and a bountiful summer yield.
Understanding California’s Microclimates
California’s sheer size and varied topography mean gardening advice must be tailored to specific local conditions. The state is a patchwork of distinct microclimates influenced by the Pacific Ocean, mountain ranges, and expansive valleys. Gardeners should consult specialized zone maps, such as those provided by the Sunset system or the USDA, which account for winter lows and summer heat patterns.
Coastal areas, buffered by maritime influence, typically experience a prolonged cool season and may still be planting cool-weather crops well into March. Conversely, inland areas like the Central Valley see temperatures rise much faster, compelling gardeners to shift focus to warm-season crops sooner. Mountain regions, facing later last-frost dates, often use March primarily for indoor seed-starting and garden preparation. This regional variation makes a soil thermometer an invaluable tool, as soil temperature is a more reliable indicator for planting than the calendar date.
March Planting: Last Chance for Cool-Season Staples
March represents the final window for planting many cool-season vegetables before rising daytime temperatures cause them to “bolt,” or prematurely flower and turn bitter. Direct-sowing root vegetables like carrots, beets, and radishes should be a priority now, as they prefer to grow undisturbed and their quality declines once the weather warms significantly. Radishes, which mature quickly, are particularly suited to succession planting this month, offering a rapid final harvest.
Leafy greens such as spinach, lettuce, and Swiss chard can still be planted, but gardeners in warmer, inland zones should choose heat-tolerant varieties to extend the harvest period. Peas (shelling and snap varieties) must be planted early in the month to ensure a full pod set before the heat inhibits flowering. Brassicas like cabbage, broccoli, and cauliflower transplants should also be set out now, especially in cooler coastal zones. Selecting varieties with shorter days to maturity increases the likelihood of a successful harvest before May’s heat arrives.
March Planting: Starting Warm-Season Favorites
The primary warm-season task in March is starting the most tender summer crops indoors to gain a critical head start. Tomatoes, peppers, and eggplants require a long growing season and should be sown indoors six to eight weeks before the last expected frost date. These seeds germinate best when provided with consistent warmth, ideally using a heat mat to maintain soil temperatures around 70 to 85 degrees Fahrenheit.
Gardeners in the warmest, most protected areas, particularly in Southern California, may be able to direct-sow early warm-season crops toward the end of the month. However, most of California should resist transplanting until soil temperatures consistently reach at least 60 degrees Fahrenheit (65 to 70 degrees is ideal for tomatoes). Waiting until the soil is sufficiently warm prevents the seedlings from becoming stunted, a condition known as “cold-shocking,” which can delay maturity and reduce overall yield.
The process of hardening off—gradually exposing indoor-started seedlings to outdoor conditions for 7 to 10 days—must be completed before transplanting. Direct-sowing of summer squash, zucchini, and corn can be attempted in warmer zones late in March, but only if the soil has warmed sufficiently, as these seeds will rot in cold, wet ground. For gardeners in cooler regions, starting these less-sensitive warm crops indoors in peat or newspaper pots is recommended, as it minimizes root disturbance when transplanting in April or May.
Herbs and Flowers for Spring Color
March is an opportune time to establish a wide variety of herbs and flowers, providing both culinary ingredients and garden aesthetics. Hardy, cool-tolerant herbs can be planted directly into the garden or containers. These include:
- Parsley
- Chives
- Cilantro
- Dill
- Oregano
- Thyme
Cilantro should be planted now to benefit from the cool weather before it quickly bolts in the summer heat.
Tender, heat-loving herbs such as basil should be started indoors from seed this month to ensure strong transplants are ready when summer temperatures arrive. For immediate spring color, cool-season annual flowers like petunia, calendula, and viola can be planted from starts. Direct-sowing annual flower seeds, such as California poppies, cosmos, and zinnias, can also be done now for color later in the spring and early summer.
Perennial herbs and flowers, such as lavender, rosemary, and coreopsis, can be planted from small starts this month, allowing their root systems to establish before the stress of summer heat. Planting flowers that attract beneficial insects, such as feverfew and yarrow, is also recommended as pest pressure increases.