In the garden, broccoli (Brassica oleracea) and lettuce ( Lactuca sativa) can be fast friends. Both plants enjoy cooler temperatures and both will bolt, or produce flowers, when things warm up. Broccoli and lettuce also have similar soil requirements. Lettuce does best in soil with a pH between 6.2 and 6.8, a range agreeable to broccoli, which thrives in soil with a pH between 6.0 and 7.5, according to Cornell University. Both like a fertile soil that drains well.
Pick a spot for your lettuce and broccoli plants. Both perform best in full sun, but can tolerate part shade. A week or two before planting, work a few shovelfuls of compost into the soil, using the shovel to loosen the soil.
Plant lettuce seeds outdoors as you can work the soil in late winter or early spring. Wait until the soil temperature is at least 40 degrees, or about three weeks before the last frost. Plant the seeds about an inch apart and no more than 1/8 inch deep. If you plant in rows, space the rows at least 12 inches apart. If you're growing loose-leaf lettuce, you can scatter the seeds over a wide area. Once the seedlings are a few inches high, remove extra plants so that each lettuce plant is about 6 inches from its neighbors. Cut the plants at the soil line, using garden scissors. You can eat the plants you remove.
Plant broccoli seeds outdoors at the same time you plant lettuce, when the soil temperature is at least 40 degrees. Space the seeds 3 inches apart and plant them 1 inch deep. When the seedlings are 4 inches high, remove extra plants so that the broccoli plants are 12 to 20 inches apart. The farther apart your broccoli plants are, the larger the head of broccoli will be. Use garden scissors to snip the extra plants off at the soil.
Both lettuce and broccoli have shallow roots and need a ready supply of moisture in the top inches of soil as they grow. Water the soil thoroughly after planting the seeds to help encourage germination. You might want to use a gentle misting spray when you water, to avoid washing away the lettuce seeds.
You can plant broccoli and lettuce together again in summer for a fall crop. Sow the seeds for broccoli outdoors no earlier than 100 days before the first expected frost in your area. Broccoli bolts readily in hot weather and tolerates frost, so plan your planting time accordingly. Lettuce doesn't need as much time to mature as broccoli, so you can start it later in the summer. The seeds won't germinate if the soil temperature is above 85 degrees.