The most traditional of flower pots is the classic terra cotta. Its sheer earthiness makes terra cotta the natural choice to anchor any plant. Plastic and fiberglass flowerpots are increasingly popular, but terra cotta has a long timeline in human history and a place in the gardener's heart.
Terra cotta refers to natural clay fired at a low (in the pottery and ceramic scheme of things) temperature. Iron compounds in some clay give terra cotta its familiar "rusty mud" hue, though terra cotta exists in other earthy colors. When the clay is fired, the minerals are partially melted, resulting in a hardened but still porous material. Humans have used terra cotta for many hundreds of years.
Terra cotta pottery was many an early civilization's version of plastic. Before modern production, terra cotta allowed cheap, easy production of decorative and functional pieces. Mediterranean pottery from the ancient Greeks and Etruscans was made from terra cotta. Chinese artisans created thousands of life size terra cotta soldiers to march into the afterworld with Emperor Qin Shi Huang, the "first emperor of all China." The soldiers are life sized and were individually crafted, displaying distinctly different bone structures and even facial expressions. Terra cotta craftsmanship flourished during the European Renaissance. Italian and German artisans became skilled with terra cotta, substituting it for scarce stone in their home regions. They brought their skills to England and France during the 14th and 15th centuries. Terra cotta was found useful for increasingly detailed architectural elements and for sculpture.
Terra cotta flower pots date to those times. Ancient Egyptians and Romans are reported to have put plants in pots. Flower pot use blossomed as Europeans explored the world in search of new herbs, spices, flowers, and trees. Explorer- scientists like Thomas Nuttall brought amazing plant discoveries to England. The use of "rude" terra cotta flourished as more common citizens caught the botany bug. Terra cotta flower pots were, and still are, produced in many countries. As we gardeners know, sometimes to our dismay, clay is found almost everywhere.
Using terra cotta in the age of plastics
Many thoroughly modern gardeners still crave the natural look and feel of unglazed terra cotta. Common clay pots are inexpensive and widely sold in either standard or short "azalea pot" sizes. Both shapes of clay pot work well for many plants. Unique designs in terra cotta, as well as thicker frost proof clay pots, are sold at some garden centers. Use the pot that looks pleasing for the size and shape of its inhabitant. Brick suppliers may offer even more unusual terra cotta pieces such as chimney pots or flue liners. It's hard to look at terra cotta and not think "what can be planted in that?"
No one pot material, even clay, is perfect for all plants. As Todd Boland points out in his article, Windowsill Orchids, care of plants in clay pots can be more touchy than of those in plastic pots. Terra cotta's porosity means that plants root zone may "breathe" more easily (probably good) and dry more quickly (possibly bad.) While terra cotta is breatheable, it cannot rescue a plant from an overly spongy, heavy soil. A terra cotta pot is not an excuse to scrimp on quality potting soil. Nor will clay wick enough water to act as a reliable reservoir to a flower in a hot, dry location. A thin plastic pot used as a liner to a clay pot can mitigate these effects while still allowing the "use" of terra cotta.
Given its composition and minimally processed nature, it's no surprise that terra cotta is altered over time by its environment. The slightly absorbent nature of a clay pot can foster the growth of algae or mosses, lending a feel of terra cotta's lengthy history. This works well with containers used in shade or wet situations. Soil minerals can seep into the pot and show as white streaks, also giving a pot that lived in look that some gardeners enjoy.
Terra cotta is breakable. It will also crack or flake if moist and allowed to freeze. Clay pots always weigh more than similarly sized plastic or fiberglass pots. This can be a help, stabilizing a top heavy plant, or a hernia in waiting, when a large plant must be moved. Given these limitations, larger clay pots are tricky to use in frost prone zones. In cold winter areas, clay pots must either be brought indoors or emptied and stored dry to survive the freeze.
To terra cotta, or not to terra cotta? That is the question with no wrong answer. Modern gardeners can choose, keeping their own preferences in mind and understanding both the pros and cons of clay pots. Terra cotta's long history and versatility probably means that clay flower pot tradition will continue for ages to come.