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

SPINACH

Spinacia oleracea

CULTURE: Spinach is a cool season plant grown in the spring and fall in Kentucky. Warm, long days will cause the plant to flower and produce seed. The plant can withstand frost and temperatures as low as 20 degrees F. Sow every 10 days for a continuous supply. This plant is rich in vitamins and minerals.

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. Spinach 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: The plant likes a fertile, well drained soil with organic matter.

SEED: 1,500 - 4,000 per/oz.

GERMINATION:

The RAFT system allows the spinach 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.
Standard Field Practice: 6 - 16 days. Cool, moist soil improves germination.

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. "Leafy" vegetables showed signs of maturing at the earlier maturing dates.
40 - 45 days to maturity

SPACING:

The RAFT system allows you to seed directly into the containers or transplant. There is no need to thin for desired spacing. 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 placed 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: Sow seeds in rows 1/2" deep, 1" apart. Thin to 3" apart in the row.

FERTILIZER & pH:

The RAFT system allows 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 - 6.8. Spinach is very sensitive to acid soils. 100 lbs. of 10-10-10 per acre is recommended. It is a heavy feeder of Nitrogen and Boron.

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 an adequate supply of water but not a water logged soil.

DISEASES: Damping-off, downy mildew, leaf spots, virus complex

INSECTS: Aphids, flea beetles, 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:

Cooperative Extension Service --- University of Kentucky