March marks a significant shift in the Texas gardening calendar, transitioning from winter dormancy to the vibrant activity of spring planting. This month is the opportune moment to introduce color to beds and containers while preparing for the intense summer heat that will soon follow. Gardeners establish cool-weather flowers and lay the groundwork for tropical and heat-tolerant varieties. Successful planting in March depends on recognizing the vast differences in the state’s regional climates and their impact on frost risk.
Understanding Texas Climate Zones for Planting
Texas spans USDA Hardiness Zones 6b in the north to 10b along the coast, making local knowledge paramount for March planting success. Gardeners in North Texas and the Panhandle (Zones 6 and 7) must exercise caution, as the risk of a hard freeze remains possible throughout the month. The average last frost date in these northern regions often falls closer to the end of March or early April.
Central Texas (Zone 8), including the Hill Country, typically sees milder conditions, with the average last frost occurring around the middle of March. This allows for earlier planting of moderately cool-tolerant species. South Texas and the Gulf Coast (Zones 9 and 10) experience very mild winters, meaning the danger of frost is largely past by the beginning of March. These southern regions can begin planting warm-season favorites much sooner than their northern counterparts.
Cool-Tolerant Annuals for Early Spring Color
March is the time to plant annuals that thrive in cooler temperatures and can withstand a late dip in temperature. Available as transplants, these flowers offer immediate color that lasts until the summer heat arrives. The selection prioritizes species that perform well in fluctuating spring conditions across Texas.
Pansies (Viola wittrockiana) are a classic choice, offering a wide spectrum of colors for beds and containers. They perform best in full sun to partial shade and are extremely tolerant of late frosts, often surviving light snow or hard freezes. Pansies bloom profusely until soil temperatures consistently exceed 75°F.
Snapdragons (Antirrhinum majus) provide vertical interest with their tall, spiky flower stalks. These cool-season annuals prefer full sun exposure to produce the most blooms and handle early spring temperature swings well. Since their performance declines dramatically once summer heat sets in, March is the optimal time for their establishment.
Petunias, especially resilient varieties, can be planted in March for an early start. While less cold-hardy than pansies, their tolerance for cooler night temperatures makes them suitable for mid-to-late March planting, particularly in Central and South Texas. They require full sun to generate their best color and sprawling growth habit.
Sweet Alyssum (Lobularia maritima) is a low-growing, spreading annual covered in tiny white, pink, or purple flowers, releasing a delicate, sweet fragrance. It functions well as a border plant or container filler, preferring full sun but tolerating partial shade. Alyssum is tolerant of cool weather and, if planted early, provides ground cover until summer annuals take over.
Starting Warm-Season Favorites Indoors or From Seed
March is the ideal period for starting warm-season flowers indoors. These plants cannot tolerate frost and need a six to eight-week head start before they can be safely transplanted outdoors after the last frost date. Starting seeds indoors ensures a more robust plant ready for the long Texas growing season.
Zinnias and cosmos are popular warm-weather annuals that benefit from indoor sowing in March, especially in North and Central Texas. These seeds germinate quickly, requiring a sterile seed-starting mix and consistent moisture. A warm environment, often facilitated by a heat mat, aids quick germination, but sprouted seedlings need bright light to prevent them from becoming spindly.
A strong light source, such as fluorescent or LED grow lights placed a few inches above the seedlings, mimics necessary sunlight for healthy development. The goal is to cultivate a compact, stocky plant prepared for the transition to the garden. Seedlings must be kept moist but not saturated to prevent fungal issues like “damping off.”
This indoor process allows gardeners to select from a wider variety of specialized cultivars not available as nursery transplants later. By the time the soil temperature warms sufficiently in April or May, these young plants will have developed root systems, ready to establish quickly. This head start maximizes the bloom time for these heat-loving favorites, extending their color well into the summer.
Essential Soil Preparation and Early Care
Preparing the soil in March is paramount, especially given the heavy clay composition common in Texas. Clay soil requires amendment to improve drainage and aeration. This is achieved by incorporating a several-inch layer of organic matter, such as compost or aged manure. This ensures annuals have a loose, well-draining environment where roots can establish quickly without becoming waterlogged.
New transplants need a specific watering strategy immediately after planting to minimize shock and encourage root growth. Water the new plants deeply once they are in the ground, settling the soil around the root ball and eliminating air pockets. This initial deep soaking is more effective than frequent, shallow watering, which encourages surface roots instead of deep, resilient ones.
The first application of fertilizer should support the new growth of these annuals. A slow-release granular fertilizer, incorporated at planting time, provides a steady supply of nutrients over several weeks. Alternatively, a balanced water-soluble fertilizer can be applied a few weeks after planting once active growth begins. Applying a two- to three-inch layer of mulch around the plants helps regulate soil temperature and conserve moisture.