Nice! Making some green happen around all that concrete and deck!

Is the wood redwood or cedar? If not the wood won't last many seasons for you. And if you do put a preservative on it you may as well line the inside with plastic, just in case. You'll get some drainage through the bottom, I would guess you'll need to drill holes but you can fill/wait and see as you can always drill holes from the bottom to adjust to the drainage you want.

What a bad idea.....integrating a non-treated wood planter into the structure of your house......wood destroying insects will soon follow......

What a cool project!
I think I would put in a false bottom so that only the top two-thirds is filled with soil. For example, the bottom foot might be filled with crumpled aluminum cans, plastic drink bottles, lava rock, etc., with a perforated false bottom over them (scrap plywood with holes drilled in it), then the soil. Ornamental gardeners often do this with large planters.

I'm a little concerned about the plywood on the broad side bowing out when the planter is full of wet soil. Have you thought about putting in a diagonal brace on the outside, between the horizontal 2x4s? Or you could toe in a few pickets that match your deck.

As a finishing touch, I'd be tempted to install a simple drain with faucet in the bottom to have control over dripping.

In terms of plant appropriateness, you will need a warm-natured species that likes warm roots if the broad side of the planter gets direct sun. Cherry tomatoes, malabar spinach, eggplant come to mind. If the planter is shaded, root warming is less of a factor.

It's too cold in Chi-town for formosan termites.

How about trailing sweet potatoes?

I didn't do treated wood because its twice the price and I plan to line inside with plastic and stain the outside to match rest of garden. Am I still going to have problems with wood eating bugs and whether damage? The box is only 3 and half feet high so not gunna hold much soil. I think the support should be fine. This was a spur of the moment thing...didn't think it out to much. On the other side im doing one identical so before I start what should I do different?

The wood is pine. Again im staining it and lining inside with plastic

@abnorm And I don't think this is such a bad idea. It'll take years for termites to eat that...if they even do..its pretty high up. After being stained I wont have to replace that for I'd say 5 yrars

Maybe Carpenter bees? Do you plan on supporting the melons with something? I read you can use pantyhose to hold them up. They will be to heavy without support to stay on the vine.

I think abnorm just said what he thought...... abnormally :). Could have been more polite and suggested a treatment for the wood rather than BAD IDEA!

Don't kid yourself.....Chicago has Termites.....and barbara I said nothing about Formosans

I don't care about the planter's longevity.....It's all about the structure.....On this forum I'm wearing my gardening hat (Zackey has my gifted plants)......On other forums I have fifty years of building experience under my hard hat

Let me say it again to be clear.....This is a STUPID idea

You have placed the built-in planter AROUND the deck balustades....altho those spindles are "treated" they are treated for above ground usage.....Decks and stairs are regulated because of the potential for serious injury if they fail. Insects will certainly find and nest in/around any soil in contact with the wood......the weathered P/T is hardly a deterent......The plastic liner will add a different enviroment for them to live between the tasty plywood/glue and the plastic.....stain is NO deterent to insects

Building codes dictate how we build for minimum protection from the elements.....Decks and stairs are built to shed water....not contain it. Use a planter box ON the deck.....use a container, build a window box........use a gutter on the railing

IF you had posted this thread with the professionals over at Building a Home or Porches and Decks you would get similar ridicule/replies to your construction efforts.......

and Nancy....from thisOldHouse...Not Norm (Abrams) = Abnorm

A platform for containers wouldn't have looked as 'integral,' but it would have been a much better idea. I'm sure there's a way to do this sort of thing, but it would take a professional designer do to it, and it would cost a bundle.

And why so deep? 12-18" would have been plenty deep enough and would have taken much less potting mix to fill it. Filling that size will be costly and most of it will never be used.

Still, since it is already done, experimenting this way is one way to learn from our past mistakes for future projects.

Dave