How to container garden
Even if you don't have access to land for edible gardening, you can grow an outdoor container garden on your sunny porch, patio, balcony, or roof deck. Before we built raised beds in the backyard, I started vegetable gardening on the patio in food-safe plastic (HDPE aka #2) 5-gallon buckets, pictured below.
Front row: mixed lettuces and arugula. Back row, left to right: peas, tomato, and Queen of Night tulips (not edible, just pretty).
Just a quick note before we get started: my way is not the only way and that's ok. See, gardening is both art and science and gardeners are a creative, resourceful bunch who figure out all sorts of ways to make it work. If you do things differently than I do and you are pleased with your results, then rock on with your bad self.
1. How to choose a container
Generally speaking, bigger is better when it comes to containers. Smaller containers dry out faster because there's a smaller volume of soil to hold on to water. I prefer containers no smaller than 12-inches deep and 12-inches wide, which just so happens to be the dimensions of 5-gallon buckets. The 12-inch diameter is also convenient for spacing your plants, like square foot gardening...more on that later.
While terracotta pots are beautiful and long-lasting, they're also porous, which causes them to dry out faster by evaporation. Metal containers and dark-colored containers absorb more heat from the sun, speeding evaporation, causing them to dry...you get it, right?
That's why I like food-safe plastic. Actually, the buckets in the photo are self-watering containers. See, each container is composed of two nested buckets with strategically-drilled holes, creating a water reservoir that irrigates the inner bucket. The plans I used to make these self-watering containers no longer exists on YouTube (I looked and looked and I'm so sad!) but these plans from the University of Maryland extension illustrate the idea well.
2. How to choose "soil"
For container gardening, you aren't actually using soil at all. Technically (and here comes the nerd), soil is the foundation of our ecosystem, composed of minerals, air, water, microorganisms, insects, other invertebrates, and their waste. However, when you dig soil up out of the ground and put it in a container, it does not perform. Dug up soil is heavy and it becomes compacted under its own weight in the absence of invertebrates to till it with their buggy activities. In turn, compacted soil impedes the free movement of the air, water, and nutrients that plants need for nourishment.
Potting "soil" is actually a soil-less mix, usually made from peat moss, finely shredded pine bark, perlite, and slow-release fertilizer. You can also find peat-free potting mix, which usually contains compost and coconut coir instead. Peat and perlite are non-renewable resources and there is concern over the environmental impact of mining for them.
I reuse and replenish previously purchased potting soil by mixing it with finished compost. I have even grown plants in 100% compost to good results.
3. How to choose plants
All kinds of herbs do well in containers. Perennial herbs can be planted at any time and include lavender, rosemary, sage, thyme, oregano, chives, mint, tarragon, and lemon balm. Cilantro and parsley are cool-season herbs, best planted in the fall or early spring. Basil is a warm-season herb and will die if the temperature dips below 50F, so I plant mine after mid-May. Dill also generally prefers warmer weather, but it's not as sensitive as basil, so I plant it in April.
When choosing vegetables for containers, I let the seed companies and nursery growers identify them for me: recommended varieties are proudly proclaimed as "good for containers" on seed packets and plant labels. Other good keywords to look for in names and descriptions are any that indicate a diminutive size: "dwarf," "compact," and "mini-." For cucumbers and beans, choose "bush" varieties instead of long-vining ones. For tomatoes, choose "determinate" varieties that will stop growing at a genetically predetermined size (determinate tomatoes are better suited to wire tomato cages for support too). By contrast, indeterminate tomato plants continue growing until killed by frost.
Another clue is to look at the "days to maturity," as faster-maturing plants typically do not grow as large as a slower-maturing plants. I find this particularly useful for choosing root vegetables such as turnips, radishes, beets, and carrots.
Leafy greens do very well in containers. I like to densely sow all sorts of lettuces and mustards, thin them when they become crowded, and eat the baby greens for fancy restaurant-style salads. In a 5-gallon container, it looks something like this:
From left to right: 19 baby greens fit within a 12-inch diameter circular container with 2-inch spacing between plants. When the babies get too crowded, remove (and eat) 12 plants as shown, leaving 7 plants spaced 4-inches apart. When those plants get too crowded, remove 4 plants as shown, leaving 3 plants to mature.
4. How to space your plants
Following the 12-inch diameter container gardening model ("round foot gardening," anyone?), you can fit 19 of the following plants: dwarf peas, spring radishes, baby carrots, and salad greens for harvesting at the baby stage. Six or seven (the plant in the center always seems to get a little squished) of the following will fit: turnips, beets, bush beans, and mature leaf lettuce. Bok choy, mature Romaine lettuce, and bush cucumbers (allow the short vines to trail over the sides) will fit 3 per bucket. Lastly, you'll need a single bucket for each tomato, pepper, eggplant, broccoli, kale, and collard plant.
5. How to keep your garden from dying
In bold type, that section heading reads far more sarcastically than I intended. But anyway, have I stressed the importance of watering enough to keep your garden from drying out? Self-watering containers make it a little easier to survive summer heat, but you still have to ensure that the water reservoir remains filled. Make it a habit to check your plants for water every morning so that you don't come home to a wilted, distraught garden in the evening. Yes, even if it rained the night before. Checking your garden daily is good practice anyway, to catch any pest/disease problems while they are small and to see what looks like it might be delicious in time for dinner.
And there you have it. Happy gardening!