University of Kentucky -- College of Agriculture -- Department of Horticulture and Landscape Architecture

LETTUCE

(Lactuca sativa)

SOIL:

• The RAFT system uses a commercial growing medium that allows the water to be wicked up through the bottom of the pot from the mat. Lettuces can be grown in small or larger containers on the RAFT system. We used bedding plant cell packs, 4" pots and larger mum pots successfully.There is no need for plowing, tilling, or soil amendments. There is no need for repeated tilling to loosen the soil to improve aeration. The soilless mix allows for good air movement even though the mix is constantly moist.
• Standard Field Practice: Lettuce will grow on a wide range of soils, but likes a rich, well drained soil, high in organic matter.

SEED: 20,000 - 30,000 per oz.

GERMINATION:

• The RAFT system allows the seed to stay constantly moist, not water logged, and not dry out during the germination process. This seemed to improve germination rates. I found that most seed germinated with earlier germination times.
• 7 - 10 days to maturity

DAYS TO MATURITY:

• The RAFT system allowed the plants to grow continuously and uninterrupted. Since the RAFT system provides constant water, most plants matured within the expected range of time. Lettuces were often harvested at the earlier maturing dates.
• 40 - 60 days to maturity.

SPACING:

• The RAFT system allows you to seed directly into the containers or transplant. Transplanting seems wise for lettuce so there is no need to thin for desired spacing (JPEG PHOTO). This results in less seed use. Individual pots of soilless mix allow plants to be spaced at any desired distance. At any time during the growing period, the pots can be re-arranged for more or less space if desired. The RAFT system is also well adapted to "square foot gardening". Plants can be place on the raft in such a way that all of the growing surface is used. Every available square foot is occupied. The RAFT system eliminates the need for walking paths in the growing area. Each plant recieves only the amount of space needed for its growth - resulting in more plants per square foot.
• Standard Field Practice: It is recommended that seeds be started in doors and transplant seedlings. Head lettuce should be planted in rows at 12" apart. Leaf lettuce can be direct seeded at 3" apart.

FERTILIZER & pH:

• The RAFT system allows a fertilizer to be placed in the water so there is a constant supply of nutrients to the plants. The fertilizer concentrations can be monitored and added when needed. Micro nutrients also can be added to the water. We maintained fertilizer levels at 80 to 100 ppm nitrogen.
• Standard Field Practice: pH 6.0 - 6.7. The plants should be fertilized with 15 - 30 lbs. 10-20-20 per acre. Phosphorus and potassium levels need to be high.

WATER:

• The RAFT system allows the plant to have a constant supply of water. However, the soilless mix is not soggy. To keep the water level at a uniform depth, a float valve can be attached to the float beds to fill from a storage tank or hooked directly to a water line.
• Standard Field Practice: The plants need to be regularly irrigated for good steady growth.

DISEASES: Bottom rot, downy mildew, gray mold, seed rot.

INSECTS: Aphids, flea beetles, grasshoppers, leafhoppers, leafminers.

WEEDS:

• The RAFT system has no need for chemical weed control because the growing medium is usually weed free.. If weeds appear in the pots, they are easily removed by hand.
• Standard Field Practice: Chemical control, mechanical cultivation, hand pulling. In the field there is a constant battle with weeds due to an infinite supply of weed seed in the ground that is constantly germinating.

More Information:

• North Carolina Cooperative Extension Service
• Ohio State University Extension Service
• University of California, Davis - Vegetable Research and Information Center
• Cornell University - Controlled Environment Agriculture - Hydroponic lettuce