How to Grow Thai Basil in Your Herb Garden

How to Plant Thai Basil

Like sweet basil, Thai basil plants are easy to grow. Start seeds indoors about six weeks before your last frost date in the spring. Plant Thai basil seedlings outdoors in late spring when soil temperatures are around 70 degrees and night temperatures are consistently above 50 degrees.

Seed Thai basil about a quarter-inch deep in a spot with moist, well-drained soil and full to part sun. Plant or thin Thai basil seedlings to put about 12 inches between plants. You can also plant Thai basil seeds or seedlings in containers.

Thai basil plants bloom in mid-to-late summer, depending on your region. Pinch back the tiny purple flowers to keep the plant from setting seed and encourage leaf growth.

Thai Basil Plant Care 

Light

Thai basil plants grow best in a spot that gets at least six hours of direct sun per day. In very hot climates, the plant prefers part sun; choose a spot with morning sun and afternoon shade to shield it during the hottest part of the day.

Soil

Plant Thai basil in rich, well-drained soil that holds moisture well. Work organic compost into the soil a few weeks before planting or add one part compost to two parts potting mix if growing in containers.

Water

Keep your Thai basil plant’s soil consistently moist with regular watering during periods without rain. Consider dressing the soil around the plants with an organic mulch like hay or straw to help maintain soil moisture.

Temperature and Humidity

Thai basil prefers the warm, humid conditions of its native region. Wait until daytime temperatures are consistently above 70 degrees and night temperatures are above 50 degrees to plant seeds or starts outdoors. Temperatures below 50 degrees can stunt the plant’s growth. Later in the season, harvest Thai basil before night temperatures hit 40 degrees, which can damage the leaves.

Fertilizer

If you plant Thai basil in rich soil, it shouldn’t need any fertilizer. If you’d like to promote more vigorous growth, feed the plant with a balanced fertilizer every few weeks during the summer. This is especially beneficial when you’re pinching back plants to promote growth or harvesting frequently.

Types of Thai Basil

There are several cultivars of Thai basil, including:

• ‘Siam Queen’ (Ocimum basilicum ‘Siam Queen’): This award-winning cultivar is known for its tender, highly aromatic leaves, which retain their scent at higher cooking temperatures than other types.
• ‘Queenette’ (Ocimum basilicum ‘Queenette’): Compact with long purple stems and relatively showy blossoms, this Thai basil cultivar is ideal for ornamental and culinary use.
• ‘Thai Magic’ (Ocimum basilicum ‘Thai Magic’): This cultivar offers a mild, sweet flavor with dark magenta flower clusters that pop against bright green leaves.

Thai Basil vs. Holy Basil

Thai basil is just one of the dozens of varieties of Ocimum basilicum. It’s sometimes confused with holy basil, also known as tulsi (Ocimum tenuiflorum). Depending on the cultivar, Thai basil and holy basil may have a similar minty, peppery, or licorice-like scent, but the plants are two distinct species. Both have slightly serrated leaf edges and grow tiny purple flowers, but Thai basil has dark purple stems, while holy basil has green stems.

Harvesting Thai Basil Plants

Harvest Thai basil by picking the upper sets of leaves from each branch, which will encourage growth. Harvesting lower on the plant can inhibit growth. Frequent harvesting, as often as every other day, will encourage more vigorous regrowth.

Store Thai basil by placing the stem ends in a glass of water, then covering the glass with a clear plastic bag. Keep the glass at room temperature, as refrigeration damages basil leaves. Change the water every few days and use as needed.

How to Grow Thai Basil Plants in Pots

Thai basil grows well in containers. Put a single plant in a 12-inch deep pot with drainage holes and rich, loose potting mix. Use a plastic or glazed ceramic pot, as porous materials like terra cotta will let the soil dry out too quickly.

Pruning

Once a young Thai basil plant has six to eight sets of leaves, pinch off the top set of leaves to encourage branching and fuller growth. Do this on subsequent branches and use the leaves in recipes.

Propagating Thai Basil Plants

You can propagate healthy, mature Thai basil plants using stem cuttings. You’ll need sharp scissors or pruners, a small glass or jar, and water. Here’s how to do it:

1. Examine the mother plant and choose a healthy-looking stem with several leaves.
2. Make a diagonal cut about six inches from the stem tip and just below a leaf node. Remove the leaves on the lower half of the stem.
3. Place the cutting in a jar of water so the leaf nodes are submerged.
4. Keep the cutting in a warm place with lots of bright light. After a few weeks, you should be able to see roots growing from the stem.
5. When the roots are at least an inch long, you can pot up the cutting and care for it as usual.

How to Grow Thai Basil Plants From Seed

Directly seed Thai basil a quarter-inch deep, with a few seeds every inch. Space rows about 18 inches apart. Thin seedlings to eight to 12 inches apart to give mature plants adequate airflow and room to grow. Keep soil moist.

You can also start Thai basil indoors by seeding in flats or trays around six weeks before your region’s last frost date. Harden off seedlings gradually for a few weeks before planting outdoors.

Common Pests and Plant Diseases

Watch out for plant damage from common pests like aphids, slugs, and Japanese beetles. Pick off Japanese beetles and drop them in a bucket of soapy water. Use insecticidal soap to treat aphids and diatomaceous earth or slug baits to kill slugs.

Plant diseases like fusarium wilt and bacterial leaf spot can affect Thai basil plants. The best way to avoid these is by watering the soil directly to avoid getting the leaves wet.