Beating the Heat: Southern Secrets to Summer Lettuce Success
The conventional wisdom says summer and lettuce don't mix. Scorching sun stunts growth, hinders germination, and wilts even the freshest leaves. Yet, the demand for crisp, local lettuce remains high, if not higher, during the warmer months. So, how do you defy nature's calendar? The answer lies in the strategies employed by Southern growers, who routinely coax vibrant lettuce from the soil despite relentless heat and sunshine. From the Carolinas to the deserts of Arizona, these seasoned farmers have cracked the code. As Erich Schultz of Steadfast Farm in Arizona noted in late April, enduring near-triple-digit temperatures is just part of the summer equation. Ray Tyler of Rosecreek Farms in Tennessee echoed this, recalling months where temperatures rarely dipped below the nineties. These growers don't just face heat; they grapple with it for a significant portion of the year to deliver those coveted salad greens. Their hard-won knowledge offers invaluable lessons for anyone aiming for a summer lettuce harvest.
The Variety Advantage: According to Tyler, selecting the right lettuce variety is paramount for summer production. While variety choice is crucial year-round for stress tolerance, it becomes especially critical in extreme heat. Both Schultz in the arid Southwest and Elliot Seldner in the humid Southeast rely on Salanova varieties for their summer mixes. However, Tyler's experience suggests that finding the perfect variety often involves careful experimentation tailored to local conditions. For summer planting, direct seeding often fails when soil temperatures climb above 80°F, making transplants, particularly heat-tolerant romaines like Cherokee, Batavia types like Muir, or densely planted multi-leaf varieties like Salanova, the preferred method. Yet, genetics are only part of the equation; meticulous cultivation practices are equally vital.
Germination Game Changers: Lettuce's tendency for thermal dormancy – a built-in mechanism preventing germination in unfavorable conditions – is well-known. Above 80°F, most lettuce seeds will refuse to sprout, hence the reliance on transplants. However, Southern growers have developed clever techniques to overcome this dormancy. Both Tyler and Schultz advocate for a 24-48 hour chilling period in the refrigerator before seeding trays. Tyler credits Paul and Alison Wiediger of Au Naturel Farm in Kentucky for the 48-hour cold treatment, which he says consistently yields near-perfect germination. Seldner in North Carolina opts for cool basement germination, relying on natural light and a quick transition to a propagation house once sprouting begins. Primed seed, where germination is initiated and then halted, offers another advantage, allowing seeds to germinate at warmer temperatures. However, primed seed has a shorter shelf life and should be purchased fresh annually.
Planting in the Heat: With summer soil temperatures often exceeding 85°F, cooling the soil before transplanting is essential. Schultz and Seldner water immediately after transplanting, while Tyler irrigates beforehand, emphasizing the need for wet, cool soil. Rapid transplanting followed by overhead irrigation is key for Seldner.
The Cooling Power of Misting: Frequent, short bursts of overhead misting are a common tactic to cool the plants and their surroundings, offering respite from the intense heat. Tyler even uses a timer for multiple daily and nightly misting cycles, recognizing that nighttime cooling is often insufficient in the South. Schultz in Arizona combines drip irrigation with overhead sprinklers above shade cloth to cool both the plants and the microclimate.
Shade: A Summer Essential: Shade cloth is widely used to lower temperatures. Schultz employs shaded low tunnels with open sides for airflow. While shade can sometimes lead to elongated leaves, Tyler and Seldner recommend using it primarily for the initial establishment phase after transplanting.
Early Bird Gets the Lettuce: Harvesting in the cool early morning is crucial to prevent bitterness and wilting. Tyler's crew starts as early as 5:30 or 6 am, ensuring the lettuce is chilled when harvested. He emphasizes that quality can only be preserved, not improved, so early harvesting is paramount for longevity and crispness. Schultz and other growers concur, starting their harvests earlier and using the extra time to remove any heat-stressed leaves before quickly cooling and packing the lettuce.
A Southern Opportunity: Schultz points out that many farmers avoid summer lettuce due to the added effort. However, these Southern growers view it as a valuable business opportunity. Their success in the face of intense heat proves that with the right strategies, fresh summer lettuce is achievable almost anywhere.