A Bioneer's Greenhouse Part 3 - Drainage

This is Part 3 in a series. Feel free to read Part 1 and Part 2 first.

In my last entry, I covered how to get water into my greenhouse, but not how to get it out. To be honest, I have put almost as much thought into draining the greenhouse as I have in watering it.

Obviously, the water hits the soil first, so soil is a significant consideration in drainage. I suspect that I will have to do some serious adjusting to my soil mixture for drainage purposes. If I make it drain too well, it will pass the water straight through before the plants have a chance to get any, and no amount of water will be enough. If I make it too dense, it won’t drain fast enough and will always be a puddle, which would kill the plants. They say that if you have clay soil and need better drainage, add organic matter. They also say that if you have sandy soil and need better water retention, add organic matter. It loosens stiff soil so water can penetrate it and it helps absorb water passing through sandy soil to improve retention. Based on this, I am intending on making my own soil almost entirely out of organic matter. I may adjust it a little this way or that with some pea gravel or clay kitty litter if it needs some help.

From there, the water drains down to the bottom of the beds. My plan is to make the floor of the greenhouse concrete. I just don’t want all that water draining right under my foundation. I also don’t want local trees to put some roots up in my greenhouse to steal all my water and possibly damage my beds. So concrete bottom it is. The beds, which will be about 3’ high, will be made of cinder block. On the bottom course of the interior walls, I will leave the mortar out of the vertical joints. This will allow the water to drain from the beds into the pathway. The pathway will also have soil on it, about 8” deep. There will be a perforated pipe inside a sleeve of landscape fabric running the length of the walkway. I will put a cinderblock block with chunks knocked out every 2’ or so along the length of the pipe, straddling the pipe. I will then mortar a stepping stone of some sort to the tops of the cinderblocks. The rest of the walkway will be filled with soil with some sort of shade and moisture tolerant creeping ground cover. Personally, I am hoping for Corsican mint, but to date my attempts to grow Corsican mint have been considerably less than successful. I am also hoping to put some mushroom logs in the pathway there as the shade and moisture will be perfect for them.

So the water trickles down through the soil and then drains to the center of the greenhouse, where it encounters more soil. From there, it drains into a pipe that will take the excess water off to the natural area behind my house. Depending on how much water I have there, and what I can convince the neighborhood of, I might just put in another distribution system and a little orchard of fruit trees. We’ll see.