Aquaponics 4 You

 Hydroponic Flood & Drain Systems

Article 1-1 Flood & Drain Systems


Answer: These irrigation systems are based on a very simple concept: plants grow in individual rockwool blocks in a large shallow tray. The tray is flooded with nutrient solution until the rockwool cubes and roots are wet, then the tray is drained to allow air back into the cubes. Rockwool soaks up the food and water like a sponge, so irrigation generally takes only a few minutes at a time. Gravity draws excess water from the cubes and keeps the roots healthy.

The simplicity of this system lends itself to many uses in horticulture. Large-scale commercial propagation systems using the flood and drain concept are becoming more common every day, since crops rooted in rockwool blocks can be transplanted to potting soil, hydrocorn, larger rockwool blocks, and even nutrient flow (NFT) and aeroponic systems.

Flood tables have also become popular for intensive crop production of shorter crop plants (to about a meter tall). Herbs, flowering ornamental crops (miniature roses, poinsettias) and even cherry tomato plants work well in this garden system.

Indoor growers working with short crop plants find this system very productive gardening under lights, especially with horizontal shades for intense light levels. Since the crop grows directly under the lamps, and virtually all the light is directed down onto the crop, the need for reflective material on walls is eliminated. Instead of crowding crops into the corner of a room in a desperate effort to capture light lost by inefficient reflectors, these tables work better placed in an open area for easier temperature control and greater air movement through the crop. Open sides makes it easy to maintain the garden. Remember that better air movement through the garden can mean fewer pest and disease problems, too!

Although the system is simple, successful growing is based on careful planning and preparation, since everything is growing so fast! A 4' x 8' garden might hold 20-30 small bushes, using one or two 1000 watt lamps with horizontal reflectors. Two or three 16" oscillating fans move air through the garden towards a "Dayton" 465 CFM or 550 CFM exhaust fan, which carries the hot air away from the garden.

A 20 to 30 gallon reservoir under the flood table holds the nutrient solution. A "Little Giant" (1 AT) water pump in the reservoir moves the food up through a short length of 1/2" polyhose to a "bulk head" fitting in the table. The nutrient mix is pumped up into the table until the cubes are completely watered (usually under 1O minutes), then the pump is shut off and nutrients drain back to the reservoir. Use an air pump (4.2 PSI air pressure ) with 2" or 3 12" air stones to aerate the nutrient solution in the reservoir.


Irrigation and drainage:
A single 3/4" poly hose supplies nutrients from the reservoir to the plants on the flood table. Drill a 1" hole in the flood table, in one of the flat areas on the bottom of the tray (and through the plywood support for the table).

  • Insert a 3/4" bulkhead fitting (thru- hull) through the hole, with the threaded end pointing down. (use 2 washers- one on the inside of the tray, and one underneath).
  • Tighten the bulkhead nut onto the bulkhead securely.
  • Push one end of the 3/4" poly hose onto the bulkhead fitting, and connect the other end of the hose to the pump in the reservoir. Shorten the hose if necessary to avoid crimping or bending the hose.
  • Fill the reservoir with nutrient solution, plug in the pump and flood the table to check for leaks. Check where the bulkhead is connected to the table, and where the 3/4" hose fits on the bulkhead.
  • When the pump is shut off, the nutrient solution should drain back to the reservoir.

Gardening With The 'Flood and Drain' Systems
Flood tables. are ideal for intensive, high-yield cultivation of short crops (plants to one meter tall). We'll describe the use of this system with 4" 'Grodan' rockwool blocks, but gardeners have used other grow mediums (hydro-corn in net pots for example) successfully too. The main differences in using hydro-corn are in frequency of irrigation and in use of an opaque cover. For the table (6mil. black and white poly works fine) to protect roots growing out of the net pots from the heat and light of the lamps. Let's look at a typical cycle of crop production using the flood table. We'll consider the three stages of growth on this table: the transition stage associated with transplanting cuttings into the 4" cubes, the "green growth" stage, and crop production stage.

During this growth stage, rooted cuttings or seedlings growing in small rockwool cubes (mm 40-40 'Grodan' cubes) are transplanted to prepared 4" Grodan rockwool blocks and placed on the table. The purpose of this stage is:
  • To develop new roots into the larger blocks.
  • To allow the plants to gradually adjust to 'green growth' conditions.
  • Remember that we are dealing with very young plants. They have small root systems in the starter cubes; they've been growing under low light levels they've had very mild fertilizers and low levels of air movement.

    Our goal is to progress as quickly as possible in conditioning the transplants to handle the intense growing conditions of their 'green growth' stage by gradually increasing light levels, nutrient strength, etc. It is important to make the transition stage go smoothly, with no set-backs to the crop. This is a good time to develop "two-way communication" with your plants. Of course plants can't talk, but they do use 'body language'! Growers who learn to recognize the signals plants give off will garden very successfully. For example, if you raise light levels to the crop by moving lamps closer, you'll watch plants closely to see their reaction. If they all wilt, raise the lamps back to their original height and try again when they have better root systems established. Dealing with living things can be very challenging, but once you know your crop's likes and dislikes, it will be easier each time you repeat this stage.
    Transition Stage - Activities

    1. Prepare the reservoir:

    • Use 20-30 gallons of water in reservoir.
      • Mix a mild 'green growth' fertilizer solution: (Nutrient strength 600-800 PPM; pH 6-7)
    • Temperature 21°C = 70°F
    • Connect air stones to air pump with clear air hose, place stones in fertilizer reservoir and plug in the air pump to aerate nutrient solution.
    • If reservoir is cold (e.g. sitting on concrete floor) use an aquarium heater in the solution to maintain proper nutrient temperature 68° - 72°.

    2. Transplant into 4" blocks:

    • Prepare 4" Grodan blocks using PL 4.5 water solution. Soak 24 hours, rinse well. Remove protective plastic wrappers from small (mm40-40) propagation cubes and plant into the large holes of the 4" blocks.
    • Leave wrappers on 4" blocks.
    • Put plants onto table, spacing them evenly.

    3. Feed the plants:

    • Turn on the pump and flood the table to soak cubes with nutrients (about 10-15 minutes).
    • Shut off pump to drain the table

    4. Set up lighting:

    • A single 1000 watt lamp and reflector gives adequate light for 20-30 new transplants.
    • Position lamp about one meter above plants. Turn on lamp and monitor temperature closely. Best temperature for new transplants: 23°C = 75°F.

    5. Establish air movement above plants:

    • A single 16" oscillating fan will do for these young plants. Do not blow air directly onto plants! You'll overwork their small root systems!
    • Set up oscillating fan 2 - 3 feet (up to one meter) away from table.
    • Raise fan on stand so air is moving above the transplants.
    • Leave fan running 24 hours a day.

    6. Set up exhaust fan:

    • Use exhaust fan at far end of garden from oscillating fans. Run exhaust fan 24 hours a day.

    7. Hang or mount thermometer at top of plants:

    • Watch temperature closely.
    • Maintain 23°C - 75°F during light cycle.

    8. Shut off Lamps after 18 Hours of Lighting: maintain cooler temperature during the 6 hour dark period: (18°C = 65°F best.)

    9. Maintain moderate growing conditions:

    • Monitor progress of your crops as you gradually increase light levels, food strength, etc. Signs that plants are adapting to new conditions are:
    • Increased root growth into 4" blocks. . Roots start to grow out bottom of 4" blocks.
    • New top growth and branching.
      • within 7-10 days, your crop should be actively growing in full light levels, with full food strength (1600-1800 PPM) green growth fertilizer mix. You are now into green growth stage!
    • Properly watered new transplants likely won't need irrigation for 2-3 days or longer! If plants look healthy and rockwool is still damp, don't water or feed!

    1. Establish good growing conditions:


    • One or two 1000 watt lamps with horizontal reflectors - directly over the crop, about 18 inches ( .5 meter ) above the plants.
    • Exact lamp height above the plants is determined by temperature. Position a thermometer so it's level with the top of the plants, then raise or lower lamps until the thermometer shows the correct growing temperature (30°C - 85°F).


    • Nutrient strength 1600-1800 PPM (parts per million). -pH: 5.5-6.5
    • Nutrient temperature: 21°C = 70°F.;

    Air Movement:

    • Use two 16" oscillating fans to move fresh air through the garden. Position the fans about .5 meter (about 18" to 24" away from the table, and direct air flow through the garden towards the exhaust fan.
    • Use oscillating and exhaust fans 24 hours a day.

    Watering and Feeding:

    • Don't overwater! Most crops will only need to be fed once every 2 - 3 days. If plants look healthy and rockwool is still damp, don't irrigate your crop yet!
    • Your nutrient solution was started at the beginning of the transition stage, and you've added more nutrients to increase food strength to 1600-1800 PPM. Drain and replace nutrients after 17 days.

    Monitor plant health and height:

    • Check underside of leaves for signs of spider mites and eggs. Check every plant!
    • Use 'sticky cards' to check for signs of flying insects.
    • Handle pest problems immediately! -Raise lamps as crops grow to maintain correct temperature (30°C - 85°F). -When plants reach 10" -12" (.3 meter), consider changing to crop production stage.

    1. Summer (Long Day) crops: For 'long day' crops such as miniature roses, basil, bush tomatoes

    • Continue 18 hour days, 30°C temperature.
    • Change to 'flowering and crop production' fertilizer mix
    • Nutrient strength: 1200 -1400 PPM.

    2. Autumn (Short Day) Crops: For 'short day' crops such as chrysanthemums, poinsettias:

    • Reduce 'daytime' temperature to 27°C = 80°F. Gradually reduce light hours to shorten day length from 18 to 12 hours.
    • Use 'autumn' light (high pressure sodium, 'compatible' sodium lamps).
    • Change to flower nutrients formula.
    • 'Dark period' temperature: 15°-1 8°C (60°-65°F).