Clay (Unglazed Terra Cotta)
Advantages: Weight of the clay adds stability; pots in the classic tapered shape are less likely to tip over than are tapered plastic pots. Porosity enables water to evaporate, which has two benefits: roots are less likely to drown if the plant is overwatered; and evaporation cools the pot, helping to prevent overheated soil.
Drawbacks: Clay is heavy, even before you fill it with soil. Evaporation means plants must be watered more frequently. Fertilizer salts build up on the outsides and rims of clay pots. And they are breakable. Another fault, though not of the clay itself, is that many good-looking clay pots are designed more for beauty than use: a pot that is narrower on top that it is at its widest point will probably have to be broken if the plant in it needs potting up.
Advantages: Lightweight. Inexpensive. Easy to clean and compact to store. Plants in plastic need less-frequent watering. Fertilizer salts do not build up. Plastic is not unbreakable (in fact, many plastic pots become brittle after a few years), but it’s not as fragile as clay.
Drawbacks: Tippy, especially if the plant is attractively large in proportion to the pot. Holds water so well it increases the danger of water-logging. Can overheat in a sunny spot, especially if the plastic is a dark color. There are now pseudo terra-cotta ones, complete with fake fertilizer sales, that look pretty convincing from a distance. But the beauty bottom line is still, well — they’re plastic.
Glazed clay pots don’t transpire water as fast as unglazed ones, but they still provide more evaporation than plastic. Salts are less of a problem on glazed clay. These pots can be gorgeous, but that’s not always a plus. Pots are there to support the plants; beware of using one that’s so pretty it upstages its contents.
Glass is uncommon for good reason, as it combines the faults of clay and plastic without offering the benefits of either (unless you count weight).
Galvanized metal tubs will rust where the seams are, no matter what the literature says, and Wood will rot. Containers made of these materials should be lines with heavy plastic and used as cachepots.
Tips on Putting Pots in Pots
- The outer pot is called a cachepot, from the French for “hide pot,” and it can be made of any material, in any shape. As long as you can put a potted plant in it, it qualities. Ironically, the one thing it is unwise to use is a valuable antique cachepot — or actually, a valuable antique anything. The minerals and algae that tend to collect on the inside of cachepots can discolor porcelain, bond to metal, or otherwise cause irreversible damage. Plastic lines are not reliable damage preventatives, though if you are determined to use an antique, a liner may help protect it.
- If the outer container is china or glass, use a plastic pot inside to minimize the chance of breakage if the interior pot hits it. If the outer container is metal, wood, or straw, line it with plastic for protection against rot, and use clay for the inner pot to give the plant roots a slightly better chance to breathe.
- Prop up the inside pot. Water is going to run out of it and collect in the cachepot, and if the plant sits in water constantly, the roots are likely to rot. Any water-resistant elevator will work: a piece of brick, an overturned saucer, or a short stack of plastic deli tubs (open end down). You can also just use a thick layer of pebbles, perlite, or styrofoam beads, though loose materials like these make routine maintenance more difficult.
- Remember to lift out the plant and empty the cachepot frequently; that water can get nasty. And if the assemblage is outside, mosquitoes can breed in it. Outdoor cachepots should contain small chunks of Mosquito Dunk (a biological control organism, widely available at garden stores).