Lettuce is a cool-season crop, and successful cultivation depends on avoiding temperature extremes that trigger bolting. For gardeners in Kansas, the state’s highly variable climate presents a specific challenge, as the transition from cold spring temperatures to intense summer heat can happen quickly. Precise timing is the most important factor to ensure a full harvest before the plants turn bitter and form a seed stalk. Understanding the local frost dates and the plant’s temperature tolerance is the direct path to maximizing the yield of fresh, crisp greens.
Timing the Spring Planting Window
The primary window for planting lettuce in Kansas revolves around the last expected spring frost, which typically falls between mid-to-late April for most of the state. Starting seeds indoors provides a significant advantage, allowing plants to be well-established before they face the rapidly warming conditions of late spring. Seeds should be sown indoors about four to six weeks before this average last frost date, generally beginning in late February to early March.
These indoor-started seedlings can be transplanted outside as soon as the soil is workable, often in late March, since lettuce seedlings are tolerant of light frosts. Planting transplants early gives the lettuce a head start, enabling it to reach maturity during the ideal 60°F to 65°F temperature range. The alternative is direct sowing outdoors, which can begin as soon as the soil thaws and is dry enough to work without compacting.
For direct sowing, planting should occur in succession every two weeks, starting in late March, to ensure a continuous supply rather than a single massive harvest. This allows the plants to mature quickly during the favorable cool season before the hot days of June arrive. Because lettuce is shallow-rooted, maintaining consistent soil moisture is crucial for good germination and rapid growth.
This early spring window is the most reliable time for the largest and most successful harvest of all lettuce types, including heat-sensitive varieties like crisphead.
Extending the Harvest Through Summer Heat
The main obstacle for Kansas lettuce growers is the phenomenon known as bolting, where the plant rapidly grows a tall stalk and produces bitter leaves. Bolting is primarily triggered when the average daytime temperatures consistently rise above 75°F to 80°F, coupled with warmer nighttime temperatures above 60°F. Once bolting begins, the plant’s energy shifts from leaf production to seed production, making the leaves unpalatable.
To push the harvest into early summer, growers should employ succession planting, continuing to sow small batches of seeds every two to three weeks until the high-temperature threshold is reached. This strategy ensures that new, younger plants are continually maturing before the heat forces the older plants to bolt. However, planting succession batches should stop once the forecast indicates that temperatures will remain consistently above 80°F, typically around late May to early June in Kansas.
Selecting heat-tolerant varieties is necessary for summer extension, as these types are slower to bolt than traditional head lettuces. Romaine varieties, such as ‘Parris Island Cos’ or ‘Little Gem,’ and loose-leaf types like ‘Black-Seeded Simpson’ or ‘Salad Bowl,’ resist bitterness longer. Providing afternoon shade (using a 30% to 40% shade cloth) physically lowers the leaf surface temperature, delaying bolting and prolonging the harvest by several weeks.
Planning the Fall Planting
The fall planting window offers a second, highly rewarding opportunity to grow lettuce, as the cooling temperatures can result in a sweeter, more tender final product. The timing for this second season is determined by counting backward from the average first frost date, which generally occurs in Kansas between mid-to-late October. Lettuce seeds need approximately 6 to 8 weeks to reach a harvestable size, depending on the variety selected.
Therefore, seeds should be planted in the garden between late August and early September to allow the plants to mature before the first killing frost. Planting too late means the lettuce will not size up adequately, while planting too early can cause germination failure or bolting due to late-summer heat. Lettuce seed germination can be inhibited when soil temperatures exceed 80°F, which is a common issue in August.
To manage high soil temperatures, start seeds indoors during August and transplant the seedlings outside once temperatures moderate in September. Alternatively, keeping the soil cool and consistently moist during germination can encourage successful direct sowing. This late-season growth benefits from decreasing light and temperature, signaling the plant to focus on producing sweet, leafy greens.