Thai herb plants, like the herbs of other cuisines, are what form the basis of the Thai flavor palette. Unlike some other cuisines, however, Thai herbs are rarely used alone, or even in pairs. In many cases, they are layered together so that they interweave and form a complex blanket of flavor, as in the famous Thai curry pastes.
Thai chilies are the first thing many people think of when they think of Thai cuisine. They come in several varieties, of which green and red bird's-eye chilies are the most common. These chilies grow on small bushes and are perennial plants.
Three types of basil are common in Thai cuisine: sweet basil, common basil, and holy basil. Sweet basil is similar enough to Italian basil that one can be substituted for the other if necessary. Common basil still retains a recognizable basil flavor, but stronger and less sweet. Holy basil is used more for scent and to steep in soups and liquids; it is not usually eaten, as the leaves are somewhat tough. All three types of basil plants are annuals.
Lemongrass is most accurately described by its name; it is a thick, tough grass stalk that smells powerfully lemony. Because of its texture, it is not usually eaten, although in some instances it is cut up very small and served in tiny amounts. Kaffir lime leaves are similarly used as aromatics rather than readily eaten out of hand. Kaffir lime zests and juice are used in recipes as well, though other limes may be substituted if necessary. There is no substitute for the leaves, however. Both lemongrass and kaffir lime plants are perennials.
Culantro is a close cousin of cilantro, and cilantro is often substituted when culantro is unavailable. Culantro has a darker, more intense, earthier flavor than cilantro. It is often used raw in salads, on soups and as garnish for any number of dishes. Culantro and cilantro are annuals.
Galangal and ginger are both rhizomes (underground nutrient storage systems for plants, separate from the roots), and are somewhat similar in flavor. Galangal has a slightly more citruslike taste, and is a bit more pungent than ginger. When fresh galangal cannot be found, fresh ginger can be substituted. Galangal has a papery skin, like ginger, but is thinner, straighter and has a slight orange tinge to it. Ginger is golden underneath the papery skin, and usually quite plump. It may branch off in several directions, while galangal usually only has a few small nubs shooting off the main rhizome. Both galangal and ginger are perennials.
Shallots and garlic are used as a basis for many Thai dishes. Thai garlic is slightly stronger and more pungent, but other garlic may easily be substituted. Shallots are sometimes fried and used as garnish, in addition to being sauteed as the base for many foods. Both shallots and garlic are annuals.
While it is good to use authentic ingredients whenever possible, Thai cuisine prides itself on using the freshest ingredients possible. For example, since culantro is not widely available in many parts of the world, its close cousin cilantro is often substituted because it is fresher. Gardeners growing Thai herb plants and cooks alike should keep this in mind. Gardeners will find that many Thai herbs will grow readily in the Northern Hemisphere. Tender perennials, such as lemongrass, ginger and kaffir limes, will need to overwinter indoors for success.
There is no such thing as a mild Thai chili. Thai chilies have varying degrees of heat and subtleties of flavor. Gardeners and cooks alike should taste-test particular chilies before committing themselves to large amounts, whether growing or cooking.
Although they are not herbs, Thai cuisine also uses a lot of peanuts, both in recipes and as garnishes. Individuals with peanut allergies should proceed with extreme caution.