Prior to building this system we had all of our germinated 1020 shallow trays with their own white, leak-proof bottom watering tray. This, not surprisingly, requires a human to lift up each micro tray, and fill up the bottom watering tray with a hose – sometimes up to 3 times a day when it was hot! Talk about a giant time-waster!
The reason we went with bottom watering in the first place is due to the improved growth that resulted from not wetting the young foliage. When we started out and were still top watering invariably we’d get foliage sticking together, then humidity increases, then airflow gets restricted and viola, mold growth! The bottom watering solved the mold problem by and large, along with some fans to help improve airflow. It also served to better buffer the moisture availability to the young seedlings so we had less losses from wilt (though we still had some, because you can’t watch it every hour of every day).
This system does away with the individual white, leak-proof bottom watering trays, and instead we put (4) 1020 shallow germination trays into a sump tray. This helps us limit the number of “fill up” points in the system.
All of these sump trays sit on a level platform so that any water in the bottom will be evenly distributed throughout the tray.
Next each tray gets (2) 45″ long pieces of 1/2″ Schedule 20 PVC pipe. These pipe segments act as a spacer to help support the 1020 trays and to keep them from collapsing (they get rather heavy when the soil is saturated, and their lips just barely reach across the sump tray – not enough to make it secure). These pipes also ensure ample volume underneath the 1020 trays for water and/or wicking medium.
We then filled each tray with about 1/4″ of sand, so that just in case our platform ever deviated from level (known to happen when our clay soils get wet) they could still carry and retain moisture throughout the bottom of the sump tray.
For the water inlet we used 180 Shrubblers – which allow you to regulate the flow rate at the emitter head by simply twisting it. We also drilled two outlet holes just slightly lower than the inlet to make sure the water level in the trays would self-regulate (i.e. not swamp our delicate micros). We drilled these outlets just below the top of the PVC pipes so that there would always be a little bit of air between the 1020 trays and the water.
Each tray also has a 1/4″ inline valve that allows us to shut off the water supply to any individual sump tray when it is not in use.
The entire rack is run off of a single 3/4″ solanoid valve that is controlled by the Galcon AC 6S Irrigation Timer (this timer allows for cyclical irrigation patterns as well as intervals as small as 5 seconds). We currently have it run for 4 minutes 3 times a day and that keeps all of the sumps topped up nicely with minimal overflow.
Here’s a quick video tour of the system so you can see how the components connect and how it operates.
Any questions about the DIY process please drop them below!