Here's something that I've wondered. What kind of support do you have to have underneath to hold up what must be very heavy? 15 gallons of water is close to 125 lbs. Plus all the logs/compost/dirt. And what is the bottom made of so that it doesn't rot away?
I'm in awe of your planters,
@gtaus.
Most people would use 4X4 legs. I used 2X4's for the legs. Yes, 15 gallons of water alone would weigh about 125 lbs., then you have to add in all the wet potting soil. My planter is 2X4 feet by 16.5 inches high and the 2X4 legs seem to be holding everything up well. Wood has a lot more strength vertically than it does laying horizontally. Even if my planter, filled with water, weighed in at 200 lbs., that still would make each 2X4 leg supporting only 50 lbs.
Other than the 2X4 legs, everything on my planter is made from 1X6 wood. The bottom of the planter is lined with a rubber liner about the same thickness as a pond liner. I had some old rubber roof liner that I used, but if you had to buy new, then look for a pond liner made for fish ponds. I went up the insides about 6 inches, but the water reservoir only needs to be 3 inches high. If you wanted to line the entire insides, then I imagine the wood would last even longer.
Like most everything you build for growing plants, you have to decide how much money you are willing to spend to get extra years of life out of the build. I bought regular 1X6 pine board, the cheapest option at the time. 1X6 treated pine would last longer, but cost more. 1X6 cedar board would last years longer, but at about 3X the cost. Again, I built these planters 3 years ago, before COVID, and the skyrocket price hikes in wood we have seen since then.
At the time of my build, even with the lower prices, it still cost me about $50 per planter just for the wood. Add to that the price of the 4 inch perforated drain pipes, the PVC pipes, and the liner, I think I had something around $80 into each planter.
IMHO, it was worth it because, in a normal year, I get more produce out of one 2X4 sub-irrigate planter (8 square feet) filled with beans than I got in my main garden plot which had about 48 square feet. And, last summer, we had a terrible drought and all my bean plants dried up and died in the main garden. I got no beans from my main garden last year.
If you are asking can you upgrade the materials on the planter to last longer, then, yes, that is certainly possible. But, at my age, if I get 5-10 years out of each sub-irrigated elevated planter, I will be more than happy.
