How flood tables work
Cycle
A pump fills the tray, the medium soaks, then water returns to the tank
Between
Stored moisture covers the plant until the next flood
Media
Rockwool cubes or any hydro pot mix can sit in the same tray
Refresh
Recirculating water redissolves dry salts and brings new oxygen
Feel
If the medium is still moist, skip a cycle. A moisture meter beats guessing from the surface
Manual flood depths
Tray
About 6 inches deep with a flexible side drain you can raise or lower
LECA
First fill about 4 inches, then leave 1 to 1.5 inches in the tray because pebbles hold little
Coir, peat, or vermiculite-perlite
Flood about 3 inches, then drain
Rockwool
Four-inch cubes only need about a 2 inch flood
Return
Less water comes back than you poured. The medium kept some
Automation and safety
Lift
Place the garden above the reservoir so a pump can fill and gravity can drain
Timer
A short-cycle timer runs the pump. A float switch is optional extra control
Slow drain
The return should be slower than the fill so the tray actually floods
Overflow
A high drain at max water level is required if a timer, not a float, stops the pump
Scale
Several tables can share a central tank, each with its own pump, plus a makeup reservoir
Media notes
Lava: Red rinse water is iron-oxide dust, not dye. Rinse well, then use. Fine leftover dust is not a plant emergency.
Support: Stake plants if lightweight perlite shifts during floods.
Kits: Store systems remove most home-build leaks. Parts also come from hardware and garden shops.