Gardening in Missouri presents a unique challenge because the state’s climate is highly varied, stretching across a significant range of latitudes and elevations. This variation means the ideal planting time can shift by several weeks depending on whether you are in the northern plains or the southern lowlands. Successfully timing your garden requires understanding these regional climate differences and using historical weather data to plan for spring and fall. The goal is to start seeds and transplants at the optimal moment, maximizing the growing season while avoiding damaging cold or intense summer heat.
Understanding Missouri’s Planting Calendar Foundation
The most important factor for determining when to plant outdoors is the Average Last Frost Date (ALFD) for your specific location, which represents the point after which there is a historically low probability of temperatures dropping below 32°F.
For instance, the southeastern lowlands, often called the Bootheel, may see their average last frost as early as the first week of April. Conversely, gardeners in the higher elevations of the Ozark Plateau or the far northern counties typically must wait until the last week of April for the danger of frost to pass. This regional difference dictates that a gardener in Sikeston can begin planting several weeks sooner than one near Kirksville.
The USDA Hardiness Zones, which classify regions based on average minimum winter temperatures, range from roughly Zone 5b in the north to Zone 7a in the southern tip. While these zones dictate which perennial plants are suitable for your garden, the ALFD remains the foundation for calculating the precise timing for both cool- and warm-season crops.
Spring Planting: Timing Cool vs. Warm Season Crops
The spring planting season is divided into two distinct windows based on a crop’s tolerance for cold temperatures. Cool-season crops can withstand a light frost and thrive in the mild temperatures of early spring. These include vegetables such as peas, spinach, lettuce, radishes, and root vegetables like carrots.
These hardy crops can be planted outdoors four to six weeks before your local Average Last Frost Date. Cool-season crops generally tolerate temperatures down to about 27°F to 29°F, though any temperature below 25°F is likely to cause significant injury.
Warm-season crops require both warm air and warm soil. Plants like tomatoes, peppers, squash, and beans should not be moved outdoors until all danger of frost is gone. Planting these crops too early, even if a late frost is avoided, can stunt their growth for the entire season.
The soil temperature is a more accurate measure than the air temperature for these sensitive plants. For direct seeding of beans and squash, the soil temperature should be consistently at least 55°F to 60°F, measured at a two-inch depth. For setting out transplants of tomatoes and peppers, it is safer to wait until the soil reaches a consistent 60°F or higher. In Central Missouri, this safe period for warm-season planting typically arrives in late April to early May, ensuring the plants establish themselves before the intense heat of summer arrives.
Extending the Harvest: Planning for Fall Gardening
Fall gardening focuses on a second planting of cool-season crops, strategically timed to mature before the first killing frost of autumn. This secondary season allows gardeners to maximize their yield and enjoy a harvest well into the cooler months. The key to successful fall planting is calculating the necessary planting date by counting backward from the average first fall frost date.
Missouri’s average first frost date generally ranges from the second week of October in the northern regions to the first week of November in the Bootheel. To determine the correct planting time, you must take the number of days a crop needs to reach maturity and add an extra two weeks. This two-week buffer accounts for the slower growth that occurs as days shorten and temperatures begin to drop in late summer.
For many fall crops, such as kale, fall broccoli, and late cabbage, this calculation means planting seeds or setting out transplants during the heat of July or early August. It is necessary to ensure the plants are mature before the season-ending frost. Providing afternoon shade and consistent moisture during the establishment phase helps these cool-season crops survive the summer and thrive in the approaching cooler temperatures.