Spearmint and peppermint--both members of the botanical genus Mentha in the mint family, Lamiaceae--grow in fertile, moist soils in sunny exposures. Their tiny flowers attract bees, and the plant stems and leaves dry well, so they can be stored and rehydrated for use in beverage teas or in potpourri. Both spearmint and peppermint are grown outdoors in herb and vegetable gardens in USDA winter hardiness zones 3 through 7.
Spearmint (Mentha spicata) is a naturally occurring species of mint native to western and southern Europe, including all around the Mediterranean Basin. Peppermint is also native to Europe but is the result of a genetic cross between the spearmint and the watermint (Mentha aquatica). Peppermint's botanical name is Mentha x piperita.
In the garden, spearmint can be problematic. It grows up to 3 feet tall but will spread indefinitely, sprawling and choking out nearby vegetation. Peppermint, on the whole, is much more well-behaved. It grows anywhere from 1 to 3 feet tall but spreads into a clump typically no larger than 3 feet in width, according to the American Horticultural Society's "A-Z Encyclopedia of Garden Plants."
When compared side-by-side, spearmint leaves are slightly smaller than those of a peppermint. Also, peppermint leaves often have a slight tinge of purple over a deep green, while spearmint foliage is an evenly brighter green. In summer, both mints produce upright spikes of tiny tubular flowers. Spearmint's blossoms, in dense cylinderlike spikes with separated whorls, look like spears. Spearmint blossoms range in color from pale blue to lilac or white. Blossoms of the peppermint are lilac-pink and occur in stem-tip clusters that are rather blunt and short in comparison to those of a spearmint.
Spearmint leaves possess a lighter, sweeter flavor that is much more palatable when fresh leaves are chewed, according to "Sunset Western Garden Book." By contrast, peppermint leaves' flavor is very strong and should be "dried first and used sparingly." A form of peppermint (Mentha x piperita f. citrata) is known as the lemon mint or orange mint, because the leaves emit a fragrance reminiscent of citrus or cologne, depending on your nose's acuteness.
Spearmint traditionally has been used to flavor food, jelly, cold drinks and toothpaste. The milder taste of the fresh leaves finds it used much more readily in fresh salads or in mint juleps or mojito beverages. Peppermint is also used in flavoring foods as well as in potpourri because of its more intense fragrance. Dried peppermint leaves flavor hot water to make tea much more fully than spearmint in general. Both mints are manufactured and sold in oil form.