With their lovely purple stems and purple-veined leaves on a shiny, dark green background, Thai basil plants are grown not only for their culinary uses but also as an ornamental specimen. Keep reading for more information on Thai basil uses.
About Thai Basil Plants
Thai basil (Ocimum basilicum var. thyrsiflora) is a member of the mint family and as such has a particular sweet flavor reminiscent of anise, licorice and clove. Popular among the cuisines of Thailand, Vietnam, Laos and Cambodia, growing Thai basil has a pleasing aroma similar to sweet basil and is generally used fresh in recipes.
Also referred to as ‘Sweet Thai,’ Thai basil plants grow to a height of between 12 to 18 inches (30-46 cm.) with leaves 1 to 2 inches (2.5 to 5 cm.) long on purple stems with purple flowers. Like sweet basil, Thai basil is a perennial.
How to Plant Thai Basil
If we look at how to plant Thai basil in the home garden, our first concern is obtaining the plants. Thai basil can be purchased from the nursery or started from seed. If your choice is to purchase from the nursery, pick up a rosemary plant as well. Rosemary and Thai basil work well planted together as they enjoy similar well-drained soil, water, and fertilization.
Handle the plants carefully, as they are quite delicate. Plant the new basil in a sunny area, water in and fertilize with a nutrient rich fish emulsion or seaweed solution two to three times during their active growing season.
Sun is a key ingredient. Thai basil plants need at least six hours of direct sunlight to flourish.
Water weekly but keep the water off the leaves; water from the base. Over-watering will cause the leaves to yellow and drop, and under-watering will make flowers and buds suffer, so it is important to attain a balance when watering Thai basil.
Harvesting Thai Basil
When harvesting Thai basil, remember to be gentle as the leaves bruise easily and you don’t want that to happen until you are going to use them. Harvest the leaves in the morning when their essential oils are at their peak and the flavor of the growing Thai basil will be at a premium. Also, water the Thai basil prior to harvest to intensify the flavor.
Growing Thai basil tends to be more compact than other types of basil, so harvest at the top of a group of leaves; otherwise, the stem will rot. If you make a mistake, cut the stem all the way back to the next set of leaves. Unless, you are growing Thai basil as an ornamental, cut the flower off several days before harvest so the plant can focus all its energy on the leaves. When you harvest your growing Thai basil plant, take it down to about 6 inches (15 cm.).
Thai Basil Uses
Now that you have harvested the basil, what are you going to do with it? Some Thai basil uses are to infuse with vinegar or oil, to flavor Pho with mint and chilies, make tea, or pair with most any chicken, pork or beef dish. Recipes online include one for making Thai basil beer and a recipe for Thai basil pesto with peanuts, rice vinegar, fish sauce and sesame oil, which will keep in the refrigerator for a week. Yum!
Thai basil is usually used fresh, preferably soon after harvesting, but you can also chop it up or run it through a food processor and freeze in ice cube trays. Once frozen, remove from the tray and store in resealable bags in the freezer for up to two months.
Thai basil may also be used as an aromatherapy treatment by bruising the leaves and inhaling their aroma. They can also be bruised and rubbed beneath the eyes and on the forehead for a relaxing reprieve from a long stressful day.
A cousin of the popular sweet basil, Thai basil has a somewhat stronger flavor with a hint of licorice and is popular in the cuisines of Southeast Asia. Freshly picked leaves can be added to salads, soups and sandwiches or dried for winter use. The plant is somewhat smaller than most sweet basil varieties, with smaller leaves. The stems and flowers are purple, making the plants right at home in ornamental gardens. The flowers make beautiful garnishes and look lovely in bouquets.
Like other basils, Thai basil is a heat-loving plant and is especially susceptible to frost damage. Seeds and plants should not be put into the ground until the soil is warm (65 to 70 degrees F) and the weather has settled. Even a 50-degree night will slow the plant's growth for some time afterwards.
To get a jump on the season, start basil seeds indoors, three to four weeks before planting time. Basil has a lower germination rate than many seeds, so plant four to six seeds per pot. Once the seedlings have their first set of true leaves, thin to one or two plants per pot. Protect basil plants from wind and sun for the first several days.
Thai basil prefers soil that is lightly moist, slightly acidic, well-drained and rich in organic matter, such as compost. It thrives in full sun but will tolerate part shade.
To get the highest yield of tender and flavorful leaves, pinch the tip of each branch, starting in early summer when the plants are 6" tall, to encourage bushiness. However, if you want to enjoy the beautiful flowers, allow some stems to grow, so they can form buds and blooms.
Related article: Make Your Own Pesto
Gardening: With basil, pinching makes the difference
I’m growing a ‘Sweet Thai’ basil under lights in my office and every time I walk by and stroke it, it emits an incredible licorice aroma that knocks my socks off. This new variety from Burpee Seed is scheduled to go into the OPC display garden, but I’m having a tough time giving it up. Thai basil is grown for culinary use as well as display because it produces attractive purple flowers. While the flowers of ‘Sweet Thai’ are not as showy as ‘Queen of Siam,’ the flavor aroma is stronger.
Pinch, pinch, pinch. One of the secrets to growing big flavorful basil plants is learning to pinch, When seedlings are 6 inches tall, pinch the central stem back by half, about 1/4 inch above a leaf axil, to force the plant to branch and make more leaves.
As the plants produce more branch stems, continue to pinch them back to encourage fresh growth. For a larger harvest, pinch the main shoots back by 1/3. About mid-summer basil plants begin to form buds that then develop into flowers. Once the plant flowers it begins to age – growth slows and the essential oil in the leaves decrease and flavor is reduced. So continuous pinching to prevent bud formation is the secret to great flavor.
Knowing how to harvest makes all the difference with basil. (Photo: Pixabay)
Many gardeners find pinching and pruning a daunting task and just avoid it, but it is one of the secrets to great gardening and worth the time to learn. Google “how to prune basil plants” and “when to prune basil plants” and you will find all kinds of how-to videos that will take the mystery out of this simple task.
When the plants are small, pinching out tender stems using your pointer finger and thumb is easy enough. As the plants grow you might choose to use a needle nose scissors.
If you’re a basil buff and you know how to start plants from seed, today the world is your oyster. Richters’ Herb catalog carries more than 3 dozen varieties of basils in their 2020 catalog. (www.richters.com ). Basils started from seed in mid-July will ensure a flavorful harvest in fall.
For fresh eating, 2 or 3 plants will feed a family of four. If you plan on making pesto, freezing or drying these herbs plant at least 5 or 6 plants.
The best way to store any leftover seeds is in their original packets in a glass jar in the refrigerator A layer of rice or the little packets of moisture control granules found in pill bottles will help keep the humidity below 50 percent.
When to Water
One inch of weekly water through the growing season keeps a garden plant healthy. More increases its risk of root rot. In loose, well-draining soil, 1 inch amounts to roughly 6 gallons for each 10 square feet.
A rain gauge helps determine when to water. If, at the week's end, it registers less than 1 inch, provide enough supplemental water to make up the difference. If the gauge holds 3/4 inch of water, for example, provide 1 1/2 gallons of water for every 10 square feet of soil.
Potted Thai basil dries out quickly. To test it, insert a finger into the top 1 inch of potting soil. If it feels dry, water the plant until liquid runs from its drainage holes. During summer, the plant may need watering twice a day.
- **Adding compost at planting time provides garden Thai basil with the necessary nutrients for the entire growing season.
- In loose, well-draining soil, 1 inch amounts to roughly 6 gallons for each 10 square feet.
- A rain gauge helps determine when to water.
Sweet basil (Ocimum basilicum) has multiple cultivars — Thai basil, O. basilicum var. thyrsiflora, is one variety. Thai basil may sometimes be called anise basil or licorice basil, in reference to its anise- and licorice-like scent and taste, but it is different from the Western strains bearing these same names.  : 92
Occasionally, Thai basil may be called cinnamon basil, which is its literal name in Vietnamese, but cinnamon basil typically refers to a separate cultivar.
The genus name Ocimum is derived from the Greek word meaning "to smell",  which is appropriate for most members of the plant family Lamiaceae, also known as the mint family.  With over 40 cultivars of basil, this abundance of flavors, aromas, and colors leads to confusion when identifying specific cultivars. 
Three types of basil are commonly used in Thai cuisine.
- Thai basil, or horapha (Thai: โหระพา ), is widely used throughout Southeast Asia and plays a prominent role in Vietnamese cuisine. It is the cultivar most often used for Asian cooking in Western kitchens.
- Holy basil (O. tenuiflorum), or kaphrao (Thai: กะเพรา ), which has a spicy, peppery, clove-like taste, may be the basil Thai people love most.  : 93 .  It is also known as Thai holy basil or by its Indian name, tulasi or tulsi it is widely used in India for culinary, medicinal, and religious purposes.
- Lemon basil (O. × citriodorum), or maenglak (Thai: แมงลัก ), as its name implies, has undertones of lemon in scent and taste. Lemon basil is the least commonly used type of basil in Thailand.  : 94 It is also known as Thai lemon basil, in contradistinction to Mrs. Burns' Lemon basil, another cultivar.
Thai basil is sturdy and compact,  growing up to 45 cm (1 ft 6 in),  and has shiny green, slightly serrated, narrow leaves with a sweet, anise-like scent and hints of licorice, along with a slight spiciness lacking in sweet basil.  Thai basil has a purple stem, and like other plants in the mint family, the stem is square. Its leaves are opposite and decussate.  As implied by its scientific name, Thai basil flowers in the form of a thyrse.  The inflorescence is purple, and the flowers when open are pink. 
Thai basil is a tender perennial  but is typically grown as an annual. As a tropical plant, Thai basil is hardy only in very warm climates where there is no chance of frost. It is generally hardy to USDA plant hardiness zone 10. Thai basil, which can be grown from seed or cuttings, requires fertile, well-draining soil with a pH ranging from 6.5 to 7.5 and 6 to 8 hours of full sunlight per day.   The flowers should be pinched to prevent the leaves from becoming bitter. Thai basil can be repeatedly harvested by taking a few leaves at a time and should be harvested periodically to encourage regrowth. 
Thai basil is widely used in the cuisines of Southeast Asia, including Thai, Vietnamese, Lao, and Cambodian cuisines. Thai basil leaves are a frequent ingredient in Thai green and red curries, though in Thailand the basil used in drunken noodles and many chicken, pork, and seafood dishes is holy basil.  : 178 In the West, however, such dishes typically contain Thai basil instead, which is much more readily available than holy basil. Thai basil is also an important ingredient in the very popular Taiwanese dish sanbeiji (three-cup chicken). Used as a condiment, a plate of raw Thai basil leaves is often served as an accompaniment to many Vietnamese dishes, such as phở (Southern style) , bún bò Huế, or bánh xèo, so that each person can season to taste with the anise-flavored leaves.