very interested in how you ended up setting this up - we've talked about adding a garage to the back of our property, and I'd love to set it up to have a garden on the roof!

I would worry that the plywood would rot after a few years. For my planters, which are made of aluminum, I had holes drilled every 6 inches on the bottom. I covered the bottom with a layer of geotextile (to prevent soil from draining out of the holes), then 1.5 inches of clay bleeds, then another layer of geotextile. Soil went on top of that. So far I have no drainage problems. I also insulated my containers with styrofoam. Will you send pictures? My garden is planted on a concrète terrace so it would be cool to have other ideas...

Julie

I guess you are a do-it-yourself-kind-of-guy, but wooden planter boxes are only temporary, just like you would not build a plywood boat for more than one season's use. You need plastic or fiberglass, and double-walled is best to keep cool and reduce evaporation. If you have a reservoir at the bottom and a fill pipe in a corner, you won't need to drain it. If you do need to drain it, it will travel to wherever the rainwater travels to.

cascio.offsite@gmail.com

Yes, plywood will rot. But no, don't fuss with fancy pipes when you have raised planters above a sloped concrete surface. Drain from holes in the planters right onto that sloped concrete surface! Problem solved.

By the way, you rock! This is a great project.

And why not cover the whole roof with vegetation?

And why not jackhammer up some of that sea of hardscape on the ground?

Plastic sheets

Raised beds and planters are frequently made from wood so don't let the above comments deter you. And if you use a particularly durable, rot-resistant wood like cedar (either eastern OR western red cedar, neither of which are 'true' cedars), redwood, teak or ironwood (Robinia), you can expect a lifespan of 15-25 years for your planters. But nix the idea of plywood (or OSB), even marine plywood, for the base as they all will rot much faster than the sides and also leach some toxic compounds. Instead consider using just a fine mesh or hardware cloth for the base, supported with cross pieces as necessary. If the mesh allows too much soil to drift through, line with landscape fabric. This also allows for much better drainage properties, which are critical in any sort of container plantings.

Also skip the rocks or gravel for drainage. Contrary to popular belief, this does not improve drainage in any sort of container/planter situation but actually impedes it by raising the perched water table (worth researching if doing a lot of container growing).

And do some research into green roof soil mixes. These are formulated to be very lightweight while still providing fast drainage and good growth potential for most plant types.