When I first moved to my current garden, I gardened strictly in containers for the first two years. I covered my 800 square foot deck with everything imaginable, leaving barely enough space for eating and sitting. During that time, I learned a lot about container gardening from both failures and successes. The three most important lessons I learned are: anything can grow in a container; the potting soil matters a great deal; and containers must be cared for and freshened up throughout the year.
Anything Can Grow In A Container
Anything that grows in the ground can grow in a pot. Containers are not just about annuals. More can be added to the garden by varying the contents of your containers. For example, two years ago I planted a culinary herb garden near our Children's Garden. I found that it was too far from the house to duck out while cooking for a quick snip at an herb or two. So, last year I relocated the herb garden into pots on the deck. I have one huge pot with dill, chives, and basil; one with rosemary, tarragon, and various kinds of thyme; and a few smaller ones with different varieties of basil. I usually grow any new roses I want to try in pots: everything from the small Clotidle Soupert to the rampant climber Cecile Brunner. Evergreens, shrubs, grasses, vines, even trees can be grown in pot. I have had a lilac growing for five years now in a pot on the deck and each year the blooms get better and better.
When growing shrubs and trees in pots for the long term, I've learned to treat them as really large bonsai plants. Each year, I renew their soil by removing some and adding organic amendments and manure. Also, every few years I trim off the outer most roots of the plants on one side to allow more root development without the danger of the plant becoming root bound. With this treatment, my lilac is still growing in its original planting pot.
The Potting Soil Matters a Great Deal
As regards the potting medium, consider again what will be growing in the pot. For tropical plants that like a lot of moisture like elephant ears, I use a heavy potting soil with lots of organic matter added to it that will hold moisture well. This year I am mixing the organic Gardeners' Gold potting soil with dehydrated cow manure. For my roses, that mixture would kill them because the water would sit too long close to their roots. So for roses, I could take the same Gardeners' Gold, but to it add perlite and cow manure so that the proportions are 1:1:1. This yields a rich, well draining soil. For a plant which likes leaner soil, take out the cow manure and use a less organic potting soil as a base.
Containers Need Year-Round Care
Once the container is planted, the care for that container does not stop there. Since containers are their one ecosystem, I must be very attentive to watering, particularly during heat waves, and fertilizing. Usually, I water every morning and sometimes again later if the weather has been particularly brutal. I also fertilize once a week with fish emulsion, sea weed emulsion, or a liquid complete fertilizer.
Containers add so much to my garden and plant knowledge. It is a great way to experiment with different plants and combinations without the commitment of planting in the ground. Also, seeing how a plant thrives in a pot with a specific planting medium helps me understand under what conditions it will thrive in the ground.