Spinach Handbook

Spinach Production
This handbook is directed toward the production of 5 ounce (150 grams) spinach plants. The crop used in our experiments was Spinacia oleracea L., cv. Nordic and cv. Tyee. Other cultivars were not evaluated.

The production of the spinach crop is separated into two growing areas. Seeds are started in a germination area where they germinate and grow for 8 days. On Day 8 the plants are transported to the greenhouse and transplanted in to the Nutrient Film Technology (NFT) troughs where they are grown until harvest on Day 33.

Spinach seeds contain inhibitors, which may result in erratic uneven germination. Some seed germinate very quickly, after being placed in an environment favorable for germination; others are delayed for various periods of time. In nature this increases the probability of survival and reproduction of at least some of the seed stock. However, this characteristic is not consistent with the CEA goal of producing a crop with consistent size and maturity on a predictable schedule.

Consistency of spinach seed germination can be improved by "priming" the seed. Priming enables the seed to break dormancy by absorbing some moisture, while simultaneously inhibitions are removed.

Each lot of seed may react somewhat differently to various priming protocols and in a commercial application each lot of seed should be evaluated with several variations on the priming method. We obtained the most consistent germination results from the following treatment.

The seed was soaked in 1% sodium hypochlorite (NaOCl) for ten minutes (disease prevention), followed by soaking in polyethyleneglycol (PEG 8000, 30%) for 72 hours. The PEG was agitated vigorously with an air defuser. After a final rinse with NaOCl solution, the seeds were dried with a small fan for 5 hours. Between each treatment the seeds were rinsed with RO water. After the last rinse the seeds were dried with a small fan for 5 hours.

Day 0 - Sowing

Rock wool cubes and plugs provided the best results of the materials tested in our trials. However, the rockwool provided less aeration than we feel was desirable. As a result the search of better aerated media continues.

Seeds were sown in rockwool slabs containing 200 seeds each. Holes (11/64 inch diameter) were drilled through each cell to allow easy penetration of roots. A single primed seed was placed in the hole in each cell. This can be done with an automated seeding machine.

After seeding, the rock wool medium should be thoroughly moisted with RO water and placed in the ebb and flow benches in the germination area. In order to improve aeration a rather unique irrigation and fertilizer configuration is used. The rockwool slabs were placed in a growth room on a layer of landscape fabric positioned on top of a layer of capillary mat fabric. The landscape fabric inhibits roots from penetrating into the capillary mat fabric; this minimizes root damage at transplant. Both layers of fabric are supported by a platform elevated 4 inches (10 cm.) above the surface of nutrient solution in the ebb and flow bench. At the edges of the platform, the capillary fabric hangs into the nutrient solution (note photograph below). The nutrient solution is continuously recirculated between the ebb and flow bench and the nutrient solution holding tank. In addition to the capillary mat as a source of water and nutrients, the rock wool slabs are manually top watered each day the plants remain in the germination area.

Spinach in rock wool seeding cubes after being placed on ebb and flow bench

For the first 24 hours, RO water is used for irrigation instead of the nutrient solution. This reduces osmotic pressure of the solution and allows the seed to imbibe additional moisture. The rock wool cubes are top-watered with RO water during the first 24 hour period.

The plants remain in darkness for the initial 24 hours. Thereafter, the light level is maintained at 250 micromol m^-2s^-1 with a photoperiod of 12 hours. The temperature is set at 20 ^o C (68 ^o F). The seed trays are covered with plastic humidity covers for the first 48 hours to ensure high relative humidity and prevent desiccation.

Remove humidity covers from spinach seedlings on Day 2

Day 1 - Environmental Adjustment
A concentrated nutrient solution is added to the sub-irrigation water 24 hours after sowing. The EC of the diluted nutrient solution is adjusted to 1.2 milliSiemens/cm. The pH of the solution is adjusted to 5.8. The solution is continuously recirculated between the ebb and flow tray and the holding tank. The plants are top watered with nutrient solution each day.

The temperature is set to 25^o C (77^o F) during the day and at 20^o C (68^o F) at night. The light intensity is held at 250 umol m^-2d^-1 (fluorescent - FCW) with a photoperiod of 12 hours. These environmental factors are maintained for the remainder of the stay in the germination area (8 days).

Day 2 - Decreasing Humidity
The humidity covers in place on Days 0 and 1 are removed on Day 2.

At this time, the seed has germinated and the radical started to penetrate into the medium. High humidity levels during the first two days of germination are to ensure the seed does not become desiccated.

Day 3 - Removing Double Seedlings
Any double seedlings should be removed from the plugs on Days 3 or 4 to ensure a uniform crop. Also, germination percentage should be calculated to monitor seed quality and proper germination conditions at this stage. It is critical to have consistent environmental conditions and, thus, consistent plant growth during this stage.

Day 7 - Seedling Selection
Plants are visually selected for production on Day 7, when the majority of seedlings exhibit 0.5 - 1.0 cm of their first true leaves. Seedlings which have unacceptable growth are discarded. Expect to discard 20-30% of the seedlings Any seedlings with good growth at this time will be acceptable at the time of transplanting. Seedling selection is a vital process for the uniformity of the crop.

Day 8 - Transplanting
On Day 8, the seedlings are transported to the greenhouse and transplanted. Just prior to transplanting, the seedlings are thoroughly sub-irrigated once more in order to prevent desiccation during transfer.