Creating a Growing Medium

Today started with the tedious process of hauling a ton of various growing media up to the roof via the ladder-and-hatch on our top floor. I'd previously, over time, gotten a bunch of stuff into that 3rd-floor hallway; but getting it up the ladder to the roof was slow, plodding work. And while some media are fairly light (like charcoal and vermiculite), others are pretty damned heavy (like peat moss and compost).

I'm using the Square Foot Gardening method outlined by Mel Bartholomew in his seminal book, Square Foot Gardening (catchy title, huh)? I have a copy of the original edition, published in 1981, in which Mel, "a retired engineer and efficiency expert," comes across as a big ol' hippie.....especially in his cover photo. But the process is sound, and it was crucial to this endeavor. The book has been revised multiple times since 1981, with a complete overhaul and rewrite in 2006. So I may be using some seriously outdated information. We shall see.

One of Mel's biggest messages is that for container gardening, particularly on a hot rooftop, you cannot use regular potting soil. It gets compacted too easily and quickly, and holds too much weight when wet.  You need something loose that will drain well, yet retain a ceratin amount of water for your overheated, thirsty plants. Mel crafts a recipe for a good container growing medium which SFG devotees refer to as "Mel's mix."

Of course, like any recipe, there are variations, and you have to make do with what you've got. But my version is pretty close to his recommended one: 1 part each of peat moss, vermiculite, and compost, and then some soil additives thrown in: fertilizer, lime, charcoal. The peat moss and compost are pretty standard gardening media. Vermiculite is a mineral which, when heated to a certain temperature, expands like a kernel of popcorn. It's incredibly lightweight, yet it retains moisture, air, and plant food very well, releasing them slowly as plants demand them. Having a lot of vermiculite is crucial to having a friable soil that drains easily. The lime is for pH balance, the fertilizer is to give an extra boost to the young seeds, the charcoal aids in air circulation, raises the pH, and also retains water and nutrients like the vermiculite.

After many, many trips up and down the ladder, I began to mix my soil up on the roof, taking breaks when the wind got too strong. I started by "fluffing" up the peat moss (which comes compressed into a giant bale), then mixing the three main ingredients (peat, vermiculite, compost) in a trashcan. I'd basically throw in a 5-gallon bucket of each, which cumulatively would fill the can about half full. Then snap on the lid, roll the can around a bunch, dump the mixture into the corn planter, rake the soil around to mix it more.... and repeat.

At day's end, the container was about half full (4 half garbage cans' worth of additions) and I was exhausted.

Peat after fluffing.

Mixing the soil in the planter.

The site at end-of-day. I covered the planter to ensure the soil didn't get blown out overnight.