HYDROPONIC SPINACH PRODUCTION. Hydroponic systems. The preferred system is NFT. [Nutrient [Nutrient film technique]. But there are also varieties of media bed and part part media systems systems that produc produce e excellent excellent results results and the the raft system. system.
The NFT system. (Either fixed bench system, or sliding gully system.) The NFT system uses either fixed fixed Growing benches 18 meters meters long by 8 gullies wide or sliding gullies inside a structure. Gullies are made using the 100 x 50 rectangular Hydroponic gully with a flat base, do not use round pipes, as the true film of nutrient cannot cannot be achieved. Fixed benches are set up in rows, at a convenient height to work on, and grow plants to maturity. They may be inside structures or outside with a suitable covering in winter, e.g. cloche covers or roof only structures with wind break sides, and roll down plastic sides for winter. This depends on the crop grown and the area climate.
Spinach in warm areas for example example would be outside in summer, or inside a structure with shade cloth cover. Sliding gully systems are usually inside a structure, and have gullies custom manufactured to fit the structure size. More plants per square meter can be fitted into this area compared to the fixed benches. For both systems seeds are germinated in a sterile media such as as 25 x 25 x 40 Rockwool blocks, or in grow pots, again in a sterile media, such as Perlite, Vermiculite, Sterile Steril e Pumice or mixtures of these. Flood & drain trays are usually used for propagation, with horticultural lighting for consistent production year round. In the fixed bench system seedlings are transferred to a Nursery bench [18 meters long and 12 gullies wide] as soon as the roots are large enough to sit on the gully base. Young plants are grown on on in these Nursery benches benches until the roots or the tops of the plants are touching, at this stage they are transferred to the final Growing benches. A ratio of 1 Nursery bench to 9 Growing benches is ideal. Holes in the Nursery bench are drilled in a zigzag pattern to house as many plants as possible, while in the the Growing benches they they are spaced; 250mm to 280mm apart for Spinach Spinach . A hole sized sized to suit suit the chosen chosen pot or media, media, e.g. Grow pots pots require 48 to to 50mm holes, the same size also suits Rockwool cubes. Growing Growing benches benches hold from 450 450 to 525 plants depending depending on the hole hole spacing. spacing. The Nursery bench holds several thousand, the more the better. Benches Benches should should have have a fall fall of 1 in 40 40 down the the gullies, gullies, e.g. e.g. the top is 450mm 450mm higher than the bottom of an 18 meter long gully. The flow of nutrient is set at 1 liter per minute per gully. For sliding gully systems, the seedlings from propagation are placed into the gullies at one end of the system, and progress down the system, moved manually each time plants plants are harvested, harvested, until they reach full full size. Feed and return pipes are sized according according to the number of benches and flow rate required. Tank and pump size are also determined by the number of benches or sliding gullies and head required to reach to the highest point. NFT systems require nutrient to circulate 24 hours per day.
Propagation to end product.
1/. Seed Seed germinatio germination n in the propaga propagation tion stage stage takes 12 to 20 days depending depending on climati climatic c conditions. In winter the seed is planted, watered and placed on a hot pad to encourage germination and root growth. Once germinated they must not dry out at any stage of growth [if they dry out at any stage, dispose of the plants pl ants and start a fresh batch, as
they will never be top quality plants and will produce flower well before they are ready to harvest] Timed flood & drain systems are best for this stage. The seeds only require water to grow to the two leaf stage, and then require a nutrient solution at 3 to 5 CF. 2/. When seedlings are transferred to the Nursery bench or sliding gullies they should be sprayed if necessary for insects [aphids in particular] and any possible fungal problems. The Nursery bench is fed with the same nutrients as the Growing bench. CF 10 to 18 according to local air temperatures and the time of year. [The hotter the air temperature the lower the CF.] A pH of 6.0 to 6.5 should be maintained at all times, ideally 6.3. The Nursery stage takes 7 to 21 days according to time of year. 3/. Plants are transferred to the Growing benches and may receive an additional insect and fungal spray if necessary. Time to maturity varies with temperature, and time of year, but ranges between 21 to 60 days.
Nutrients and pH correctors.
Use a Spinach formula mix. Spinach has its own special mix. Nutrient formula mixes can be blended to suit your water supply. A copy of your water analysis or a sample of water for analysis is necessary for these customised mixes to be designed for you. pH correction is made to maintain a pH of 6.3 (6.0 to 6.5 is the optimum range) To raise the pH; Use Potassium Hydroxide. This product is purchased as a strong solution or in powder form and requires diluting with water, do not use at full strength as the nutrients can be destroyed by precipitation, and the crop could be damaged. Potassium Silicate can also be used to raise pH i f extra Silicon is needed for natural fungal protection. To lower the pH; Use Phosphoric and/or Nitric acids. The ratio required depends on the pH of the base water, and will be advised. In many cases a 50 / 50 mix is used. Again do not use at full strength. Dilute acids 500 to 1 with water.
Medias and equipment.
Suitable Medias for pots and plug production include; Sterile pumice. 1 to 5mm in size. 60% Perlite [super course] mixed with 40% vermiculite [medium]. Sterile potting mix (used with care). Course washed river sand. Suitable pre-made blocks include; Rockwool blocks. 25mm x 25mm x 40mm cubes are ideal for Spinach. Grow pots; Available in reusable (white) or disposable (green) types.
Test and control equipment.
It is advisable to have a fully automatic nutrient dosing system to control the pH and CF for Spinach if there are more than 10 benches in the system. Nutrient heating is advised in the winter months if temperatures of the nutrient fall below 14 degrees C. Spinach grows well at 14 to 24 degrees C but does not like temperatures over 32 degrees C, going to seed/flower very quickly.
Where Spinach is grown under protective structures, good air flow is essential for healthy plants, and temperatures over 30 degrees C must be avoided where possible. Evaporative mist cooling systems can be employed if high temperatures are a problem. Seed varieties. The seed suppliers should be able to supply samples of different varieti es, test these to see if they are suitable for your growing conditions, and market requirements
ppm Mineral levels for specific CF ranges for Spinach MINERAL
CF 10
CF 12
CF18
NITROGEN
33-100
40-120
60-180
PHOSPHOROUS
8-25
10-30
15-45
POTASSIUM
50-150
60-180
90-270
SULPHUR
13-40
16-48
24-72
CALCIUM
33-118
40-142
60-210
MAGNESIUM
8-25
10-30
15-45
SODIUM
3-35
3-35
3-35
CHLORIDE
3-35
3-35
3-35
IRON
0.7-3.6
0.8-3.6
1.2-5.0
MANGANESE
0.13-1.6
0.16-1.9
0.24-3.0
BORON
0.07-0.5
0.08-0.6
0.12-0.9
ZINC
0.03-1.0
0.04-1.0
0.06-1.0
COPPER
0.03-0.33
0.04-0.36
0.06-0.5
pH RANGE
6.0-6.5
6.0-6.5
6.0-6.5
Nutritional problems
Regular nutrient analysis and leaf analysis may be requi red to assist in producing top yield, especially in the first crop, or crops. The following are the leaf nutrient results required for a healthy crop. Nitrogen Potassium Magnesium
4.2 to 5.2 % 3.5 to 5.3% 1.6 to 1.8%
Phosphorous Calcium Sulphur
0.48 to 0.58% 0.6 to 1.2% 0.3 to 0.8%
Iron 220 to 245 ppm Manganese 50 to 85 ppm Boron 42 to 63 ppm Copper 45 to 65 ppm Zinc 50 to 75 ppm With NFT systems it is often advantageous to flush out the nutrient tank regularly to avoid a build up in toxic materials or to remove a nutritional mineral imbalance. Also if the nutrient gets dirty and you don't fancy drinking it, then flush it out. Plants respond to clean nutrient and there will be far less problems from disease if nutrient is regularly changed. Only nutrient analysis will show how long a specific system can run for until it’s out of balance; however 4 weeks is usually the maximum time between flushing. Remember, don't put cold water into the tank and circulate immediately, raise the
temperature to that required before turning on the pump. For run to waste crops this is also an essential, don't chill off the roots on a hot day or freeze them in winter. Pre-heat the water to be applied.