As indicators that plants need more water. Sandy soils drain faster and may need deep daily water, while clay soils retain moisture longer and can go 2 to 3 days between waterings. This decreases the temperature by at least 10 degrees and will help retain soil moisture and protect plants from extreme heat. Plant corn next to cooler season plants like lettuce or spinach. Use vining plants to help cover more soil area as they insulate the ground by releasing moisture into the air.