The desire to start work on a lawn immediately as the weather turns mild in March is common for many homeowners. However, the success of planting grass seed depends almost entirely on the specific type of grass being planted and the sustained temperature of the soil beneath the surface. For most regions, March is a highly conditional time for planting, with the outcome depending on when the soil truly begins to warm.
Why Timing Hinges on Soil Temperature
The success of grass seed germination is governed by soil temperature, not the warmer air temperatures that often arrive in March. Soil acts as an insulator, retaining the cold from winter long after the air above it has warmed up significantly. This means the ground can still be too cold to trigger the biological processes necessary for a seed to sprout.
Cool-season grasses, such as Kentucky bluegrass, perennial ryegrass, and fescue, require a soil temperature consistently within the 50°F to 65°F range for optimal germination. If seeds are planted when the soil is below 50°F, they remain dormant, exposed to the elements and vulnerable to fungal diseases or consumption by birds. Planting too early risks the seeds rotting in cold, moist soil.
Warm-season grasses, like Bermuda or Zoysia, have an even higher thermal requirement, needing the soil to be consistently in the 65°F to 70°F range before they will sprout. In most regions, the soil temperature does not reach this threshold until late spring or early summer, making March planting for warm-season grasses premature. Using an inexpensive soil thermometer, measured at a depth of about two inches, is the most accurate way to determine the best time to plant.
Regional Differences in March Planting
The viability of March planting shifts depending on the region and the type of grass that thrives there. In Northern states and the upper transition zone, where cool-season grasses are the standard, March is typically too early for reliable results. The soil in these areas often remains below the 50°F minimum for germination until mid-April or later.
For homeowners in the warm-season grass regions of the deep South and Southwest, March planting is frequently viable. Warm-season varieties like Bermudagrass can be planted from late March through the summer months, capitalizing on the long growing season. The Southeast, for example, often sees soil temperatures reach the required 65°F to 70°F range by late March to mid-May.
Planting in March in northern climates is sometimes attempted using dormant seeding, where seeds are spread while the ground is still frozen. The goal is for the seed to remain dormant and germinate immediately when the soil temperature becomes favorable in the spring. However, this method carries an increased risk of seed wash-out from melting snow or early spring rains, making it less reliable than waiting for the correct soil temperature.
Essential Soil Preparation for Early Seeding
Proper soil preparation is essential for success when planting in March. Grasses prefer a relatively neutral pH between 6.5 and 7, which allows for optimal nutrient absorption.
Key Preparation Steps
- Get a professional soil test to determine the existing pH level and nutrient deficiencies.
- Aeration is beneficial for early spring planting, as it relieves soil compaction caused by winter snow and moisture.
- After aeration, a light raking helps ensure good seed-to-soil contact, which is necessary for germination.
- Apply a starter fertilizer at the time of seeding, as these products contain higher levels of phosphorus beneficial for strong root development.
- Avoid applying pre-emergent weed control products, as these herbicides prevent all seeds, including the new grass seed, from germinating.
Comparing Spring vs. Fall Planting Success
While March planting can work, especially for warm-season grasses, fall is the superior time for seeding cool-season varieties. The period from late August through early October offers the optimal blend of warm soil, which encourages fast germination, and cooler air temperatures, which reduce stress on young seedlings. This timing allows the newly established grass to develop a deep root system before winter.
Spring planting, even when timed correctly, forces new grass to face two immediate challenges: intense competition from weeds like crabgrass and the stress of summer heat. Spring-planted grass has only a few months to establish roots before facing the scorching temperatures and potential drought conditions of July and August. This early stress can lead to patchy growth or failure, often requiring more water and attention to survive the season.
Fall seeding avoids these issues by allowing the grass to establish itself during a season of natural decline for weeds. The reliable rainfall and moderate temperatures of autumn create a nurturing environment, giving the grass six to eight months of steady growth before it needs to withstand summer conditions. For most lawns in cool-season regions, planting in the fall maximizes the likelihood of achieving a dense, resilient turf.