I am considering buying a roll of 800 gauge high density polyethylene to line my growbeds, is 800 gauge heavy enough? i'll be using pea gravel as grow media,a roll of (HDPE) is very expensive, i want to use plastic or rubber pond liner but i was concerned about the plastic leaching into the water!, does rubber leach? would leaching in ap systems gb or ft liner's hinder AP farmers from obtaining an organic cert?. thank you.
Hi Kevin, I belive I read at Friendlies Aquaponics site (Hawaii USA).....that rubber liner would not be able to get an organic rating.
Friendlies use the covering/sheeting thats used for green houses. They managed to get an organic rating. Maybe Chris will be able to tell you exactly what they use ?
Ok, I found a link...look at the 4th, number 7 question. The question starts out....Where can I get some net pots in large quantities... In the answer, they say what they use.
They do make PVC pond liner. I don't know if it would be 'organic'. It may be cheaper then the HDPE.
I'm curious to see what others say...?
Pea gravel may/will plug pretty fast. I've been reading where 3/4 inch grow media is recommended.....at least 1/2 inch. Hydroton is at least 1/2 inch (?)
Good luck...looking forward to seing some pictures of your system !
I've used the EPDM pond liner. I don't know about the organic cert but it is heavy duty stuff and will stand up to the gravel. However, it doesn't stand up so well against things like termites. I've been in the process of removing my lumber/liner beds and replacing them with Rubbermaid Stock tanks.
I would be more worried about leaching from the PVC liner though I know that food grade or at least drinking water safe PVC liners exist.
As to the pea gravel, just make sure it is from some pH inert type of rock. I would probably go for 1/2" river rock instead if the pea gravel is on the small side or made of lime stone.
Vinyl (UV resistant) and HDPE are both rated as safe for foods by the FDA. (this doesn't necessarily mean they're food grade plastics) Although you want to make sure you're using a UV resistant liner either way. Vinyl liners now are very heavy duty and some last as long as 20 or 30 years (unless chewed up by termites). Although I'm a big fan of solid tanks. . . But a liner is def. the cheapest way to get into it.
I can't know much for certain about any pebbles from here. (I would guess that beach pebbles are probably a good choice but it is only a guess.) If you can get a small sample of them to run some simple tests on, you might be able to save your self some trouble. One test would be to rinse the pebbles well and then put some in a jar and dump vinegar over them. If it fizzes up big time, avoid them. If nothing happens then they probably don't contain any calcium carbonate and won't buffer the system and may be fine.
If you are doing flood and drain media, I would definitely not use something like greenhouse film as the liner for the grow beds, since even a nice smooth media will probably abrade the plastic as you fill the beds and dig around planting/harvesting. See Friendlies gets away with using the film as liner since they are doing DWC or floating raft. So in the first place, the growing method is far gentler on the liner and second, if there is a leak, it's far easier to get at to patch or replace since it is just floating rafts to move and water to drain rather than unloading all the gravel.
I rather like liner but if you have any wood chewing insects on your island, be very careful of using liner in conjunction with wood. I've spent the last year replacing my lumber/liner gravel filled grow beds with stock tanks. A few of my old lumber/liner grow beds have been re-purposed to be wicking beds for soil growing since a bit of leaking isn't as problematic there and I figure they might last another year or two for that purpose before the wood rots and falls apart.
I'm still using a liner and metal fencing construction for my big fish tank and I've re-used a long piece of liner for a duck system where we placed the liner on the ground and edged it with metal instead of wood. I still have one bed that is liner and the wood is pressure treated on that one but I expect it might require replacement in the next two years as well.
I don't know much about the HDPE liner, if it is almost more like stiff plastic HDPE rather than a flexible rubber liner, the HDPE might be a better choice. I know it is possible to get food grade HDPE though I don't know if what your looking at is food grade and/or UV resistant. I don't know the grading of HDPE either so I'm not sure how thick or heave 800 grade is.
Good Luck with it in any case.
We use low density polyethylene that is 20 mils. This is a food grade liner that can be certified organic. HDPE is much more expensive. Rubber liners like EDPM will leach into the water. If it smells like a tire you don't want to grow food in it!!
If you are planning to make a commercial system I would discourage you from using media. There are so many advantages to using the raft system for a commercial setup The biggest if that everything on the farm is mobile. Without planting roots in media, everything can move around. When plants are small I keep them in a tight spacing then spread them out to a final grow out spacing after a few weeks. This saves me valuable grow out space increasing my overall yield! I put small plants into troughs at one and harvest from the opposite end which makes harvesting much more efficient. Check out some of my pics to see this.
Chris does have a point, for commercial production, raft systems are generally thought to be more appropriate.
The biggest selling point for me on media based growing is that it can be designed very low maintenance for a backyard scale food production.
If going commercial, there is going to be some one there to tend daily so rafts with separate settling tanks and bio filters are more scalable and much lighter weight to deal with. Rafts lend themselves very well to growing compact crops like salad greens and herbs with the methods Chris describes being able to spread them out for final grow out. Larger crops like tomatoes can also be grown in raft production but their large stature and need for support makes them harder to move down the length of a raft bed assembly line fashion.
I have not had much luck growing stuff in DWC in my systems but I'm dealing with extreme sub-tropical heat 6 months of the year so there are few crops that do all that well in a DWC bed for me and the very warm water needing supplemental aeration also limits the usefulness of DWC or raft beds to me. They might work ok for me November through April but not May-October. A true tropical or a temperate climate seems more appropriate for raft culture.