Tuesday, July 1, 2008

Container dirt is not just any dirt

(This is not dirt)
Container gardening is quite different from in-ground gardening. There are trade-offs. While I don't have the usual ground pests (deer, moles, raccoons, squirrels), I do have a somewhat limited list of plants to choose from. Winter crops normally grown in the ground, or in milder climates, are pretty much off my list, because roots in containers freeze easily. I can't grow most perennial fruiting bushes or trees for the same reason, since I don't have a suitable place to overwinter them. I can't grow gourds or winter squash because the vines and fruits are too big to train vertically in my small space. I grow mainly annual fruiting vegetables and leafy greens because they keep on giving, are fairly compact, and have simple needs.
What's amazing to me about vegetable gardening in containers is this: once I've set it up, it really doesn't ask too much from me. I water and feed and check for insect pests, and the plants just keep on trucking. One of the keys, I'm sure, is that I have intimate control over my soil.
I'd like to elaborate on potting mix for container gardening. A few years ago when I was just getting into this container gardening thing, I got into worms at the same time so I could make compost. I wanted an organic garden, but with no yard on hand, worms were a way to compost indoors. I bought a copy of Mary Appelhof's book "Worms Eat My Garbage", along with my first worm bin.
Next, I sought out a few books about soil (book suggestions follow below). Initially, I wanted to learn about soil so I could recreate the conditions in my containers. But I quickly learned that soil used in container gardening really is a horse of a different color. Container gardening has unique issues of drainage, aeration, and dessication that simply don't apply to in-ground gardens.
So, what makes a good container mix?
Good container mix needs:
1) superior aeration and drainage
2) ability to hold water in drying conditions
3) nutrients for plants
A lot of container gardeners use a soilless mix. Dirt from your yard won't work in a container- it compacts too much and won't breathe or drain correctly. Plants simply won't thrive in it.
A basic soilless mix contains:
1) sphagnum peat moss, leaf mold, or shredded fir bark (nutrients, moisture retention, and "body")
2) horticultural vermiculite (moisture retention, trace minerals and drainage)
3) sandbox sand, aka., builder's sand or sharp sand (for drainage- don't use beach sand, it contains salt)
4) compost (nutrients and moisture retention)
These four ingredients can be mixed in varying amounts. But usually, it's 2 parts peat (or 1 part peat, and 1 part leaf mold or shredded bark), 2 parts vermiculite, 1 part sand, and 1 part compost
Or, you can start your first year with pre-bagged potting MIX (not potting SOIL) and freshen and supplement it in the following years. I started my first year mainly with pre-bagged potting mix, but I've supplemented from there. I've since made my own mixes, too.
(NOTE: Don't add additional nutrients, below, if you are starting off with a pre-bagged potting mix made for vegetables. It's overkill- these mixes already contain food. Do read the bag, though- it might suggest you add occasional supplements for heavy feeders, like tomatoes, as the season wears on.)
To a basic home-made container mix, you will need to add nutrients. Nutrients include, but certainly aren't limited to:
Blood meal (nitrogen)
Fish meal (nitrogen)
Bone meal (phosphorus)
Wood ashes (potassium)
Green sand (potassium)
Crushed oyster shells (calcium)
Finely ground, uncooked eggshells (calcium)
Epsom salts (magnesium- good for sandy soil)
Worm castings (mainly nitrogen and magical water-retaining abilities)
Kelp (wide array of trace minerals)
Most folks add (at the very least) greensand and blood meal. I also add bonemeal, crushed eggshells, and a lot of worm poop. If I lived on a coast and had easy access to the stuff, I'd add composted seaweed.
Of course, a good pre-mixed, commercial vegetable food will do the job, too. I like the vegetable mix by the company Espoma (the mix named "Garden-Tone"). It has a great menu of trace nutrients. Even though their mixes are not completely organic, they derive their ingredients from natural sources- unlike, say, Scott's traditional mixes, which derive most of their ingredients from petroleum sources.
Some plants are heavier feeders than others. In my garden, tomatoes, squash, and peppers all get additional helpings of worm poop, usually once a month. To stave off blossom end rot, my tomatoes also get finely crushed eggshells and bone meal. And all my leafy greens get worm poop. I apply all of these foods as a top dressing, but scratch them in lightly with a garden fork.
In the fall, when every plant is kaput, I empty all of my potting mix into one giant outdoor box. (Side note: Last year I made the box from wire shelving, and lined it with burlap. This year I'm going to make a double-walled, insulated composting box so I can hot compost through the winter- the giant soil cube froze solid last year.) In between 2-inch layers of the leftover potting mix, I add thin layers of dead plants from the growing season, leftover rabbit hay, worm castings, blood meal, bone meal, and crushed eggshells. By the next planting season, all my mix needs is a good fluffing, a bushel or two of fresh vermiculite, and of course, some more worm poop. My vegetables are certainly thriving after following this cycle.
Here are a couple of books on soil for you to check out. Like I said earlier, they don't really address container gardening, but they are a great background on soil.
"Teaming with Microbes" by Jeff Loewnfels and Wayne Lewis. It's a great little book, written in plain language. The intended audience is home gardeners.
"Secrets to Great Soil" by Elizabeth P. Stell. It's from the wonderful Storey Publishing. I reference this book at least weekly. It's cleanly written, easy to understand, and is chock-full of great charts for composting and nutrients. Though it has only a small section about container mixes, it is full of adaptable and interesting information. Tool sharpening, anyone?
Two books specific to vegetable container gardening:
"The Bountiful Container" by McGee and Stuckey. It's a bit cutesy, but thorough.
"Movable Harvests" by Crandall and Crandall. It's a little dated, but is a great basic introduction to vegetable container gardening.


A.E.K. said...

Great post, I will refer to it again when I start my container garden next year.

Carolyn said...

Thanks for the informative Post. I have been wondering what you use. I used potting soil last year with not so good results. This year I used Garden Soil in my containers. So far so good. I try and work up the dirt each week for aeration. I will try your wintering method for sure!!

I'm picking up my worms tomorrow!!

d. moll, l.ac. said...

Wow, you really got it going on!

Laura said...

Amazing post! thanks a lot for all of that information! It sure explains why we only have one weed in all of our containers (one weed and no plants)...I bet we used potting soil, which must be just a step up from the heavy clay mixed with construction debris we have in our front yard.
All this time I thought you had a light load with gardening in containers - you do way more work than I thought possible; your plants must sing with health and happiness.

ilex said...

Laura- It's a lot of work, but only at the beginning. I really don't have do much once everything is in. After about mid-May, I'm little more than a harvester/ occasional weeder. But the right mix in containers is really critical.

And when in doubt, just add more worm poop. It is the magical elixir, believe me when I tell you.

Anonymous said...

Brilliant! Thanks for the intro.