I am looking to construct 12 - 60 foot growbeds...2 feet wide and 14 inches deep. My intial concept was to use 24' water pipe cut in half (schedule 40), until I found out the cost....about $40 a linear foot. Second idea was to use black culvert pipe, again cost is an issue. I've tried contacting a firm in New Orleans that produces shallow fish raceways that could be adapted as growbeds, but to no avail. I am concerned about doing a plywood/pond liner construction due to durability issues over the next few years. Am looking for suggestions and appreciate the advice. Thanks, Mary
We are using concrete blocks stacked two high with liners in high tunnels. We used a crushed rock on the floor, but I am sure sand would work as well. Liners are about 250 bucks each at 45' lengths. USDA is matching on high tunnels as far as I know, but require everything to be on ground level. If you go this route, we have both plywood and block raceways and I would highly suggest the block. It is much easier to work with.
I built my raft tanks on the ground with 3/4" electrical conduit as posts, pressure treated 2x4 as frame and marine plywood as sidewall. I put a 2" layer of sand on the floor to level it up and lined it with 20mil reinforced poly ($0.32 sq ft) . So far so good.
What type of system? Raft beds or media beds?
You can get food grade HDPE plastic in rolls that are 4' wide and 1/16 inch thick, then you just need a frame to hold it. This should work for you using a wide variety of framing options. Only really tricky part is folding the ends.
I would love to get a good step by step on folding the endsHope this helps
I used a blunt chisel and hammer and on the line i marked i punched the plastic.not damaging the plastick but making a shallow groove for the bendthen the bend comes out a square corner and the fold looks niceflat plastic
the first folds
the two sides and the end
the inside of the box
chisel on top and the shape of the piont
the groove in the plastic bellow
I wanted to add this the other day.
This is a chisel I made using a +-8 mm x 50mm flat mild steel and sharpening the chisel end to this shape. With this you can’t damage the liner by hitting to hard.
I used a wood strip under the plastic to do the punching on
The two flats stops you from going through the liner
after this you get a perfect bend.
The thing not figured in this pricing is that all the pond liners are going to need a complete box constructed to support it and the gravel.
As far as using pond liner, I know the EPDM stands up well against gravel wear and tear, but the moist space between the gravel and a wood box is very attractive to termites. I still use EPDM but I will no longer endorse it's used against wood in termite territory. I don't know if any of the other pond liners are any better proof against chewing insects that are going to love the most space between them and wood. (The space between any liner and a wood box is going to have condensation in a humid climate since when the grow beds flood the plastic will be cool.)
There are several liners that are sturdy enough to support water with a radius on the ground without ripping out of the edging on the frame but I'm not sure if any of them will handle doing that with gravel. The HDPE plastic is sturdy enough to do such a thing with the bottom supported on the ground. Any type of liner to do up at table height though is going to need the bottom supported so suddenly this becomes a pretty costly method in terms of needing nursery benches or something to support the bottom of the liner as well as a frame to support the top edge if it's HDPE plastic or complete sides (that won't bow out) if using a lighter weight pond liner.
I think this is a bit portion of why few commercial operations use large scale media beds.
Have you looked into masonry grow beds? Ferrocement or block or brick?