Wednesday, 11 November 2015 16:03

Constructing the Seeding Racks

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Flood and Drain Seeding Racks


A critical part of the whole growing process is the germination and initial growing cycle of the plants.  The quicker, more consistent growth of our herbs and greens from seed means we first of all convert more seed to plants, and also try to shorten the period of time from seeding to actual planting into the towers.

So, previously we had a misting system watering the seedlings.  A few issues associated with this technique.

  1. Inconsistent watering of each seeding pod
  2. Wasting water
  3. Wetting leaves

Due to the nature of the misting system, it was impossible to ensure that each of the 288 pods in a seeding tray was evenly and consistently watered. This is a major issue, as certain pods would dry out and we would therefore loose that seed.

Second, misting goes everywhere and therefore a percentage of the water is wasted. All the ground around the seeding area becomes wet, and all this water goes to wastage.

Lastly, as the misting system is from the top down, the leaves are wet. This introduces issues with the plants such as rotting etc.

The flood and drain technique is a far better process for watering our seedlings.  Initially we will have 32 seeding trays being watered (that is 9,200 individual pods). The flood and drain system will consistently water every one of these pods identically, thus eliminating the dried pods and loss of seeds.

Secondly, as the water is pumped into a tray, and then drained back into the sump tank, no water escapes from the system, and therefore eliminating the water waste.

Thirdly, no wetting of the leaves occurs, as the wetting process is from the flooding water, and therefore only the pod is exposed to the water.


The design of the system is a 5 shelf wire mesh shelving system, with 4 flood trays, 3 LED strip lights per tray, a sump tank and a pump on a timer.

Each flood tray can accommodate 4 seeding trays. Therefore each shelf is accommodating 1152 seeds.

The sump tank is a basic plastic tub, with a capacity of 120 litres. In this tub is a submersible pump (with a 2m head capacity).

The water is then pumped to the top tray, on one side, and slowly fills.

On the other side of the tray, there are two drains, with elbows. They have been positioned so that as the water reaches the outlet, the trays are sitting in water.

The water then flows out through the drains to the next tray below.  The drains have an elbow connection which positions a small tube to the bottom of the flood tray. Eventually as the top tray fills, a siphoning action starts, and the water drains out of the top tray to the next tray.  This repeats down the shelves to each flood tray. The bottom flood tray then empties into the sump tank.

So, all that needs to happen is to fill one and a half trays with water, then let the siphoning action move the water from the top tray down and back into the sump tank.

We plan to run the pump 2 or 3 times a day, to ensure that seeding trays receive sufficient watering throughout the day.

Two seeding racks with 5 shelves, four flood and drain trays. 

Added two 90 degree elbows for drainage. Two in case one blocks a little. The lower edge of the internal part of the elbow sets the water level, just below the height of the seeding tray


Just a standard 120 liter tub from bunnings, will be the sump tank



LED strip lights. Four per tray


The water will go into the top tray from this side, then drain alternatively down until the last tray drains into the sump tank

Up and running

One of the flood and drain racks is now complete. I have placed a number of seeding trays in the flood and drain trays and have run the pump.

All working well, except for a slight oversight. The tray have a slight angle to them so when you insert a tube it increases the water level height (ie the drainage height). I have over come this by lifting the seeding trays a little.

So I fill the top tray, and it starts overflowing into the second tray, let this fill about half way. Then stop the pump.  All the rest is gravity and siphon! 



Drainage. Once the water start travelling down the drainage pipes, a siphon action starts. The elbows have a small length of tube just reaching the bottom of the tray. So the siphon action will suck out the water from this tray and move it down to the next tray.

Bottom of the drainage from the tray above. Filling this tray.

Again, bottom of drain filling the next tray
Read 4065 times Last modified on Thursday, 12 November 2015 12:08

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