Irrigation
Lettuce, spinach, and other leafy vegetables require frequent irrigations for optimal quality. As many as eight to ten irrigations and 10-12 inches of water per acre may be necessary depending on seasonal variation, variety, and planting date. Soil type does not affect the amount of total water needed but dictates the water application frequency. Lighter soils need more frequent water applications but less water applied per application.
If available, use drip irrigation to improve marketable yield and performance and reduce irrigation inefficiencies associated with other methods. Since leafy green vegetables have shallow root systems, drip is often a more efficient way to irrigate. Most of the leafy green vegetables are extremely sensitive to water stress. Critical times when irrigation can aid productivity are during crop establishment (seeding or transplanting), rapid leaf sizing, and right up until harvest. Different irrigation methods are commonly used to irrigate leafy green vegetables, each with different management considerations. Historically, furrow irrigation was common. Furrow irrigation results in large fluctuations in soil moisture, nutrient leaching, and low water use efficiency. Sprinkler irrigation is slightly better than furrow, but not as good as drip.
Plastic mulches conserve water and reduce weeds. Use white-on-black plastic mulch (white on one side and; black on the other) for growing transplanted lettuce and other leafy green vegetables. White-up helps keep the soil temperature several degrees cooler, which can reduce bolting in high temperatures. Black-up may have a place for very early or late season crops and for use in high tunnels in winter when extra heat can help with growth.