The basic concept of bonsai is straightforward. A plant's normal growth is limited by cutting its tap root and growing it in a shallow container. Over time, the plant takes on a mature yet miniaturized appearance. New growth is pruned and shaped, and the main branches and lateral roots often take on a gnarled appearance. As an art form that's been refined through centuries, bonsai has a number of very specific types and styles. However, there's nothing wrong with simply trying to achieve an interesting or pleasing form with your bonsai, without worrying about formalities.
Choose a Plant
Any relatively small tree, shrub, or woody herb can become a bonsai. Little inexpensive plants from a nursery or "volunteer" seedlings from your yard will work just fine. You might also choose to start from seed, although seed-grown trees will need a couple of years in a regular-depth pot to get established before being planted as bonsai. Hardy evergreens, ficus, and woody herbs such as rosemary or scented geraniums (Pelargonium) are all good "beginner" choices, but it's hard to resist a cute little maple seedling or squirrel-sown oak-ling.
There are different styles of bonsai, from gnarled and twisted forms to waterfall shapes to little groves of symmetrical trees. Choose a starter plant with an idea in mind of the "look" you are aiming for. Yews and other tough evergreens can be heavily pruned right away to give your bonsai its initial form. Most young plants will put out new branches readily, so don't worry about making a mistake. If you don't love the shape of your bonsai, let it grow out a little and then prune it again.
Pick a Pot
You can find specially designed ceramic bonsai containers, but you can also be creative. You'll want a container that is fairly shallow for its width, and it must have one or more holes in the bottom for drainage. A terra cotta saucer with a hole drilled for drainage can make a good bonsai pot. A good rule of thumb is that a bonsai container should be only 2 to 3 times as deep as the diameter of the plant's trunk. When you're starting with a young plant or seedling, use a somewhat deeper container and transplant to a shallow one as the plant matures.
If you want to start a bunch of potential bonsai specimens without investing anything in containers, try recycling shallow plastic containers. The black plastic containers Chick-Fil-A uses for half-pints of slaw are perfect for little plants. 16 oz. cottage cheese buckets aren't very attractive, but they work. Bonsai pots need excellent drainage. A hot metal skewer or old soldering iron works great for melting holes in the bottoms of plastic containers (be careful, of course, and work in a well ventilated area).
Remove your future bonsai plant from its pot, and knock as much soil off the roots as you can. Take a good look at its root system. To grow in a shallow pot, your little tree will need strong lateral (sideways-growing) roots. Cutting the tap root back will encourage lateral roots to form. You don't want to leave it with no roots at all, so try to make your cut just below where some roots have branched out from the main tap root.
Pot it up using barely moist potting mix, and water it sparingly to settle the soil around the roots. Especially if you have just removed most of its root system, your new bonsai will probably need a little extra humidity while it gets established. A clear plastic bag can make a good humidity dome, as long as you use a couple of sticks or skewers to prop it up so the plastic doesn't touch the leaves.
Pruning right away will give the plant less foliage to support with its reduced root system. This is also a good time to start establishing the future shape of your bonsai. As with pruning any plant, start by taking out small or crossing branches, or anything that just doesn't look vigorous. Then begin to establish the future shape of your bonsai. Prune back to a single tallest central branch or "leader." Remove any branches that seem to interfere with the symmetry (or asymmetry) that you'd like your plant to have.
The remaining branches can be tied or wired into fairly precise positions. You may want to change the spacing between branches, straighten them, or twist them into a wind-blown shape. Strings or wires should be loose enough that they don't cut into the bark as the bonsai grows. Initially, your new bonsai will probably have a pitiful, hacked appearance. But give it time to recover, and continue to selectively prune and adjust as it grows into its new shape. In time you'll have a fine little specimen!
A simple plant in a pot is fine, but you may enjoy landscaping your bonsai. You can keep it simple or get as elaborate as you want. Add rocks and pebbles, tiny companion plants, bits of moss and lichen, or create entire miniature scenes. Have fun with it, and don't be intimidated by all the mystique of the "ancient art" of bonsai. If you can grow a plant in a pot, you can grow a bonsai specimen. Try your hand at it, and see what you can do!
Photos by Jill M. Nicolaus. Mouse over images and links for additional information.