If you are building a backyard iAVs…or even a small commercial unit…beds that are up to six meters long are easy to level and will (all other things being equal) drain in a timely manner.
Beds that are much longer than that will be more complicated when it comes to levelling…and you’ll reach a point where you have to think about different drainage arrangements…to ensure that complete and timely drainage occurs. This is the realm of the more experienced horticulturist…probably working in a controlled-environment cropping greenhouse.
We recommend a fall of 1:50. Short beds…up to 3 meters long…will drain well enough if they are flat. Up to 6 meters long, and they will need a slight fall…and upwards of 6 meters, ensuring adequate fall gets more complicated.
The other consideration is the logistics of working with the beds. Shorter beds are easier to get around for day-to-day operations…like seeding/planting, plant culturing/trellising, harvesting – and maintenance.
Shorter bed lengths – up to 6 meters – is also consistent with our recommendation to have a series of smaller tank/bed modules rather than one large fish tank and longer sand biofilters.
The width of beds should be not more than 1.2 meters…so that operators can reach into the middle of the bed with undue stretching.
The depth of a biofilter will depend on the type of plants being grown, but 300 – 400mm is suitable for most purposes.