It’s easy to grow lettuce in container gardens, says Kim Martin, manager of Tiger Garden, the student-run floral shop on the University of Missouri campus.
Martin said four lettuce or spinach plants in a 10-inch container provide enough greens for two people to have a
large salad weekly.
Choose a pot with good drainage, she said. Do not put rocks in the bottom of the pot, as this may cause water to pool above the rocks and cause root damage. “A plant sitting in water is one of the fastest ways to kill a plant,” she said. “You want your water to be able to escape and flow free.”
Use a good soilless potting mix. Do not use soil, as it compacts around the root of the plant and may contain root-damaging bacteria. Soil also does not drain well.
Fill the pot halfway with a soilless medium containing perlite. Do not pack the soil. Mix crystals of a silica-based wetting agent with water and place a thin layer of this on top of the medium. This holds the water and keeps the plants moist. “One of the biggest downfalls of container plants is that they don’t get enough water,” Martin said. Fill the pot with medium within an inch of the top of the container.
Choose four plants for a 10-inch pot. She recommends red leaf lettuce, buttercrunch lettuce, arugula and spinach. Spinach works best by itself but also pairs with arugula. Lettuce grows more quickly than spinach and can take over the container. Because arugula and buttercrunch lettuce are tall, plant them toward the center of the pot. They pair well together.
Loosen the plants by squeezing the plastic cell of the planter pack from the bottom. Do not fluff the delicate roots. “The soilless media in your container is loose and airy, and roots will go out and explore on their own,” Martin said.
Make a hole in the center of the pot and three holes around the edge. If you are using a rectangular or square pot, place plants at least 6 inches apart. Put the plants in and gently add medium just to the soil line of the plant. Put two teaspoons of slow-release fertilizer over the top of the medium, keeping it away from the plant. Keep the medium moist.
When harvesting lettuce, pinch off leaves near the base from the outer edges of the plant. Leave the inner leaves to grow.
When choosing plants, ask the garden center if the plants have been “hardened.” This is a gradual exposure of the plants to outside temperatures and sun. If the plants have not been hardened, gradually expose them to the outside for a week.
Frost kills lettuce and spinach, so bring plants inside if there is a danger of frost.
Cared-for plants should produce lettuce until mid-June, when flowers, called bolts, and seeds appear and the leaves become bitter-tasting.