Lettuce grows best during cool weather. Head types are particularly sensitive to warm weather and rarely grow well when the temperature gets higher than 75°F. Some types of lettuce grow satisfactorily at lower, warmer elevations in Hawaii, but even for those varieties, growth is generally better during cooler seasons. When the temperature is too high for the variety, lettuce plants will have symptoms including leaf tip-burn, early bolting (flowering), and bitterness, and head types will also have loose heads. The term “greens” is often used to refer to a number of leafy vegetables which belong to several unrelated plant families. Common greens that could be produced in a greenhouse include spinach, turnip greens, collards and mustard greens. Speciality greens, such as arugula, sorrel, chicory, and Asian greens, also show potential.
When to Plant?
- The minimum soil temperature should be 50°.
- Leafy greens grow best at 55°‐60°; colder weather will merely slow growth.
- Plant early spring through early summer; late summer for fall harvest.
- Hot weather causes greens to bolt or set seed which can cause leaves to become coarse and bitter. Look for slow‐bolt or long‐standing varieties.
How to Plant?
- Direct sow: remove all weeds, amend the soil if needed, level bed, sprinkle lightly with seed,
cover seeds with ¼” soil; thin plants to avoid overcrowding. - Transplants: choose vigorous plants, soak them well in pots to ensure they are thoroughly watered, loosen
roots, plant in the ground or container.
How to Harvest?
- Snip the entire plant at ground level.
- Pinch off lower leaves allowing the plant to continue to produce more leaves.
- Best to harvest in the early morning before leaves begin to wilt.
Cultural Considerations
- Greens are adaptable to various soil types.
- Can be heavy feeders; apply ammonium sulfate at planting time and again in 3‐4 weeks.
- Vegetables require approximately 1” of water per week; water greens frequently.
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