A cousin of the commonly grown sweet basil, Thai basil (Ocimum basilicum) is becoming a popular herb grown in home gardens as culinary tastes expand. Like so many other herb specimens it is easy to grow inside as long as its basic sunlight and temperature requirements are met. Read on for uses, a comparison to other basil types, and step by step indoor growing instructions for Thai basil.
Uses for Thai basil
Similar to other basil varieties, Thai basil is typically grown for culinary uses, but it also has some medicinal properties. Its striking physical appearance also lends it to be a beautiful ornamental piece.
Culinary uses: Thai basil is used in cuisine originating from Thailand, Vietnam, Laos, and Cambodia. Most recipes call for fresh Thai basil but dried or frozen can be substituted if necessary.
Medicinal uses: Leaves can be bruised and the aroma inhaled, or the bruised leaves can be rubbed across the forehead and beneath the eyes to promote relaxation.
Differences between Thai basil and other types
Basil is available in over 40 different cultivars with varying characteristics. Some of the favorited types grown are sweet basil, lemon basil, Genovese basil (a variety of sweet basil), holy basil, Thai basil, and opal basil.
Thai basil is known for its differing flavor, appearance, and ability to hold up better in culinary uses.
Thai basil has a stronger flavor profile and aroma than the more commonly grown, sweet basil. Its flavor is described to be anise or licorice-like and is spicier in nature. Sweet basil has larger, brighter green, shiny leaves – the hallmark of Italian cuisines and pestos.
Plants have small, narrow leaves, dark purple stems, and pink flowers. The leaves smell like anise; essential oils present in leaf tissues have the highest odor intensity of the basil types (1). The most popular cultivars found in stores and markets have dark green leaves and white flowers; plants have a rich, spicy, pungent aroma.
It also holds up better under higher temperatures and prolonged cooking times than sweet basil.
Thai Basil in bloom. Image: drewwest75
How to grow indoors
Native to the tropical regions of southeast Asia, Thai basil prefers full sun, warm conditions similar to the sweet basil commonly grown in gardens and kitchen windowsills.
Thai basil plants grow well outside when they can take advantage of the hot summertime temperatures and long days. Grow naturally declines as temperatures drop in the fall and day lengths start to shorten; in most growing zones grow will halt completely in the winter.
In order to grow Thai basil plants indoors, it’s important to mimic the outdoor conditions of summertime. Provide plants with plenty of sunlight - supplementing with grow lights if necessary - and keep them in a warm location to encourage strong, healthy growth of plants and the best tasting foliage.
Adequate sunlight is needed to drive photosynthesis – the process of converting carbon dioxide and water into sugar plants use for food (2).
When growing Thai basil indoors, plants require a minimum of 6 hours of sunlight a day. Position plants in a south or west-facing window if possible.
South facing windows provide the most sunlight exposure in homes, with light streaming through them all day. Windows facing westwardly receive a long period of direct sunlight but often miss the hottest, most intense part of the day making them a great alternative.
If your home doesn’t have enough direct light from the sun for your basil plants, purchase a simple growing light to supplement natural sunlight.
Basil plants are very sensitive to cold temperatures. They thrive in conditions between 72-85°F. During winter months keep them away from drafty windows or frequently opened doors that let in cold air. Even a short dip down to 50°F will impede growth for a length of time afterward.
Supplies needed for growing indoors
With a few basic supplies, it’s easy to start growing Thai basil plants. Supplies are similar for growing most other herbs, sweet basil included.
Containers: Choose from either clay (either glazed or unglazed) or plastic pots based upon your personal preference and decorating style. A 6-inch pot is sufficient for a single plant; 3 plants can be grown together in a 12-inch container.
Growing Media: Commercial potting mixes and coconut coir both make an excellent substrate for growing plants. Both media are lightweight with excellent moisture retention.
Plants: Thai basil can be started from seeds or propagated through plant cuttings.
Supplemental lighting: Plants need a high amount of sunlight when grown indoors for maximum growth and yield. Often times indoor spaces cannot provide the full-sun conditions similar to growing outside; in this case, plants should be supplemented with light via grow lights. Thai basil responds well to either fluorescent or high-intensity discharge (HID) growing lights.
Photo taken by F Delventhal at Clagett Farm CSA.
The instructions for planting Thai basil varies slightly depending on the method and the desired end result. As mentioned previously full-sized plants can be grown via seed or stem cuttings.
Starting Thai basil from seeds:
- Fill container(s) with pre-moistened potting soil.
- Sprinkle a small number of Thai basil seeds across the top of the mix and cover lightly.
- Place container(s) in an area where the ambient temperature is at least 70℉.
- Keep the soil moist but not saturated.
- Thin plants after true leaves emerge when they reach a couple of inches tall. Keep the single, best-looking plant for a 6-inch container, the three best-looking seedlings for a 12-inch container.
Starting Thai basil from stem cuttings:
- Take a 4-inch stem cutting right below a node and remove all of the leaves from the bottom 2 inches of the stem.
- Place the cut end of the stem in a glass or jar of water, allowing it to grow until newly generated roots are a couple of inches long.
- Fill the container(s) with pre-moistened growing media of your choice, carefully planting the rooted cuttings.
Caring for your Thai basil plants
Thai basil plants are fairly low maintenance when grown indoors.
- Water containers when the potting soil is dry to the touch. Thai basil is native to tropical regions but prefers a well drained potting mix.
- Avoid getting water on the foliage when watering the plants. Water the soil directly if possible.
- Fertilize plants every 4-6 weeks using a water-soluble fertilizer at half strength.
Thai basil plants respond well to frequent harvesting; regularly removing foliage from your plants will trigger new growth, encouraging full, bushy plants.
- Harvest mid-morning on a sunny day when essential oils are at their peak.
- Using clean, sharp scissors or even your fingernails, snip or cut off stems right above the node where a pair of leaves originates.
- Periodically pinch off branch tips to encourage your plant to grow outward instead of upward for a fuller shape.
- If plants are overgrown, you can do a more severe harvest. Starting from the top of the plant begin harvesting stems, taking the plant down to 6 inches tall. Never cut into the woody parts of the stem; the plant won’t resprout.
- For the best flavor, harvest basil leaves before plants flower. If they do flower, remove flowers and wait to harvest for a couple of days.
After harvesting you can opt to use your fresh Thai basil, or you can preserve it by drying it, freezing it, or preserving it in oil.
To dry it in a food dehydrator, place washed leaves in a single layer on the food dehydrator trays. Dry at the recommended temperature until leaves are crispy.
To air dry, bind a clump of 6-inch long stems together to create a bunch. Punch some holes in a small paper bag and place the bunch inside the bag; the bag will catch any leaves that fall off. Hang the bag in a dimly lit or dark room where the temperature is warm and the humidity low.
To learn more about the different drying methods check out our how to dry herbs guide.
To freeze Thai basil, remove whole leaves from the stems, and blanch for two seconds, immediately placing leaves in an ice bath afterward. Dry completely and store in an air-tight container or freezer bag, separating layers with wax paper.
To preserve in oil, place blanched basil leaves in a blender or food processor, adding 1 to 2 cups of olive oil and a ½ teaspoon of kosher salt for each cup of basil. Pulse until blended. Then strain the mixture or leave it as it is for a stronger flavor. Use immediately, refrigerate in a glass container for up to a week, or freeze in ice cube trays.
Growing Thai basil in your indoor herb garden adds a variety of flavor to your Asian culinary adventures while contributing to the overall aesthetics of your decor with its beauty. Plants are low maintenance, preferring full sun locations and warm temperatures. When these conditions are provided you will be rewarded with lush, aromatic foliage for harvesting and use.
- Tangpao, T., Chung, H., & Sommano, S. (2018). Aromatic Profiles of Essential Oils from Five Commonly Used Thai Basils. Foods, 7(11), 175. doi:10.3390/foods7110175
- Smithsonian Science Education Center STEMvisions Blog. (2017, April 12). Retrieved January 7, 2019, from https://ssec.si.edu/stemvisions-blog/what-photosynthesis