Tabletop bottom options

I'm rebuilding my square foot gardens this spring - but off the ground in tabletop form this time.  There seem to be three options for the bottom of the boxes:

1. plywood with drainage holes and landscape fabric on top.  Strong, but subject to rot.
           

2. hardware cloth, supported underneath with wooden braces and with landscape fabric on top.  Not subject to rot, but dries out quickly.

3. hardware cloth (or other type of support) with rigid foam insulation on top.  Strong and retains moisture better.

Option 3 looks attractive but option 1 appears to be the most common choice.  Option 2 is also popular. I could use some help with my decision. 

Ted

if you can get metal spring frame from bunk beds, then put one cinderblock beneath it on each corner and middle. you can put cinderblocks on top for the walls. Then place cardboard inside on the bottom and fill it up with mel's mix. Place worms in the mix via a worm tube or vermicompost bucket like the ones I use. the worms and microorganism will eat the cardboard later on, but with it consume the mix will stay in place. It will not fall out through the frame. The cinder blocks are 8" high. if you top them with a cinder block cap, the walls will be 12" high. I would put mulched 3/4 the ways up and mel's mix to the top. it will get water and not rot out.

Ted, As you live in the great white north, I hope Trolleydriver will see this. He made an herb table top bed in the style I make mine. He can tell you how it over-wintered and his opinions. The only thing is that the Mel's Mix will freeze up there and I don't know if worms can survive. If you don't have worms in the beds, then not an issue.

Option 1 - All of my beds are table tops with plywood bottoms, the oldest Oct 2014. I just went outside to look at the bottom of the oldest and it looks great, just staining around the drainage holes. If you are trying to get away from the bind weed you can simply set the plywood bottom on treated wood "rails" or bricks spaced every 2 feet. If you are going for height, then legs of treated or stacked bricks will be need plus an underneath supporting frame. See photos in link below.

In this thread, my husband made a 3.5'x3.5' table top using scrap pieces of 3/4" exterior (rough finish) plywood. Just remember that if you make a table top bed, say 4'x 4', the actual interior measurements will be 45" x 45" so cut the lengths of the boards appropriately. I can't help you with Options 2 or 3.

https://squarefoot.forumotion.com/t19807-new-table-tops?highlight=Table+top

So far my Herb Table Top appears to have overwintered well.  I put a top on it (made out of some old pieces of wood) for the winter.  I have not yet checked the underside of the plywood bottom and I can't see what that plywood is like on the inside. The exposed edges seem to be fine.

Here it is



















 

Thanks for the information and the ideas.  Those are lovely looking gardens.  Mine will not be quite so professional looking as Sanderson's or Trolleydriver's because of my skill level.  I'm now leaning toward plywood bottoms.

My old 4 x 16 on-ground garden lasted 6 seasons. It did not contain Mel's Mix, was hard to weed and was a convenient restaurant for rabbits and other creatures.  I expect my tabletop gardens (3 4x4s) with Mel's Mix to be more productive although smaller in overall size. I may add a fourth one next year.