Measure and mark out a grid of 18-inch squares. Use bamboo canes to mark the lines in the soil. This block arrangement is also ideal for maximizing the wind pollination of sweet corn.
Transplant one young corn plant in the corner of each square. Firm the soil around the base of each plant. Corn plants are tender, so they may have to be raised from seed under cover.
Mix the lettuce seed with fine sand and scatter thinly in between the corn plants. Rake over carefully. The lettuces will mature in 8–12 weeks and fill the gaps in between the corn plants.
Thin the lettuce seedlings to 3–4 plants per square. Sweet corn takes at least 16 weeks to produce mature cobs, but the lettuce can be harvested long before the corn casts too much shade on them.