The desire to grow a sweet, juicy watermelon is a common pursuit for many Oklahoma gardeners. This warm-season crop thrives in the state’s long, hot summers, but a successful harvest begins with precise timing. Watermelons are highly sensitive to cold, making the exact date of planting the most significant factor.
Determining the Ideal Planting Date
The rule for planting watermelon is waiting until the soil is sufficiently warm. Seeds will not germinate in soil colder than 60°F, and planting in cool, damp soil often results in the seeds rotting. For optimal germination and a strong start, direct seeding should be delayed until the soil temperature consistently measures above 70°F at a depth of about one inch.
Gardeners can determine this temperature by inserting a soil thermometer into the planting bed early in the morning for several consecutive days. This measurement provides a much more reliable indicator than air temperature, which can fluctuate wildly in early spring. Planting should only occur after the average date of the last expected spring frost has passed, generally by at least two weeks. Planting too early exposes the vulnerable young seedlings to damaging cold snaps and stunted growth.
Accounting for Oklahoma’s Climate Zones
Oklahoma’s expansive geography means that a single planting date for the entire state is impractical. The state spans multiple growing zones, causing significant variation in the arrival of spring warmth. Gardeners in Southern Oklahoma, particularly those near the Red River, can often begin planting as early as late March. This region experiences earlier soil warming and earlier last frost dates.
Conversely, those in Northern Oklahoma or the Panhandle must wait longer for the soil to reach the 70°F minimum. Planting in these cooler northern zones typically begins closer to mid-April or early May. Gardeners can utilize resources such as the Oklahoma Mesonet system, which provides real-time soil temperature readings from sites across the state.
Starting Watermelon: Direct Seeding Versus Transplants
There are two primary methods for starting watermelon: direct seeding or using transplants. Direct seeding involves planting the seeds directly into the garden soil once the 70°F temperature requirement is met. This method is preferred because watermelons are highly susceptible to transplant shock, and direct sowing avoids root disturbance. The seeds germinate quickly in the warm soil, usually within ten days.
Using transplants, which are seedlings started indoors three to four weeks before moving outside, allows the gardener to move the outdoor planting date forward. This approach is often necessary for gardeners in cooler northern zones with shorter seasons or when growing seedless varieties. Transplants should be set out about two weeks after the last frost has passed, but extra care is needed. To minimize shock, the fragile root ball must remain intact, and the young plants should be protected with row covers or hot caps immediately after planting.