Wood – wood will not stay useful for long if exposed directly to soil. This is mostly because of the moisture that comes from healthy soil and regular watering. Now, wood containers are my favorite, because I love working in wood, wood is generally inexpensive, and it lasts if you use it correctly.
So first, having built or purchased your wooden container, you will use some kind of exterior varnish (I like the kind made from polyurethane, available at home improvement stores). You will put at least 2 coats of varnish on every inch of the pot, inside and out, including the bottom. This is to protect the wood from the weather. Note that if you want to “go the extra mile” you can stain the wood just about any color before you varnish it.
Second, you must have some kind of liner for the inside of the pot. I like to use heavy duty yard trash bags. This plastic is not too terribly heavy-duty, but is fairly durable. Of course your container must have a drain hole in the bottom. If not, drill a hole in the bottom center about 5/8″-1″. Now, if your container is 18″ high, you will start from the corner of your trash bag and measure up about 24″ and cut. so you will now have a plastic bag triangle. take the corner of the bag, which is now the bottom of a funnel shaped bag, and thread it though the hole in the bottom of the container, pulling about 2″ of the bag through the hole (from the inside to the outside).
With one hand, hold the piece of the bag at the bottom hole from the outside of the container. With the other hand, push the bag out to conform to the sides of the container. Lay your drainage rocks at the bottom of the bag. Now, from the outside bottom of the container, cut off the last 1″ of the bag sticking through the hole. The rocks will hold the bag steady so you can put the soil in, and you now have drainage at the bottom of the container. Fill with dirt, cut off the excess plastic at the top, and plant something. Remember, with this treatment your wooden containers should last a long time, but not forever.
Plastic – there are 2 types of plastic containers that I like to use, at opposite ends of the spectrum. The very plain, and the very ornate.
The very plain plastic containers are generally in the standard pot shape, and they tend to be the color of terracotta. I like these because they are very inexpensive. I like to use them for applications where the pot itself is not all that visible, such as the rear of an area with several pots. The main consideration here is that you should use these in areas where the pot itself is not subject to direct sunlight. Sunlight will fade the color, and degrade the integrity of the pot. And, of course, these pots are not terribly attractive.
On the far side of the continuum are extremely ornate plastic containers. These are generally made to look as if they were made from ornamental stone, so they are very attractive and suitable for use around entrances to the home and other focal points. These are considered a replacement or alternative to expensive cement or stone containers. Look online and at gardening stores for alternatives here. And note that since these more decorative pots will be placed in focal areas, they will probably be exposed to direct sunlight, and therefore will have a more limited useful life. But they are available in nearly all colors, shapes and styles, so you can have a lot of fun with these.
Terracotta – the majority of pots and containers available for plants will be made from terracotta. It is attractive and versatile. Moisture glides through it and helps avoid over-watering. It is available in several colors, and an almost infinite array of styles. If you don’t live in the snow belt, these pots can stay beautiful for decades. Sadly, I live in the snow belt. So, to avoid replacing all my terracotta pots, at Halloween each year, which is generally just prior to the first freeze for us, we empty all our outside terracotta plants and store them in our garage, dry.
It is terracotta’s ability to transfer moisture that makes it both a great pot, and destroys it in the winter. When there are water droplets inside the terracotta (and there always is when you have it planted) and it freezes, the water droplets expand and cause the pot to deteriorate. A single winter outside in the snow will completely destroy most terracotta pots. Dry them and store them in a dry place in the winter, or you will lose them.