Thai basil care infographicThai basil, or Ocimum basilicum, has a distinct smell and flavor that make you imagine you’re seated in a restaurant at some exotic, distant land. It’s a perfect ingredient for different types of dishes, making it more savory.

We asked our expert gardeners about this fantastic type of basil, so you’ll know what to do if you decide to grow one.

What Is Thai Basil? Origin & Places Where It Grows

Thai basil (Ocimum basilicum var. thyrsiflora) is a pleasant-smelling plant from the mint family. It has a rich history in Asia, from where Alexander the Great brought it to Greece, spreading it to Europe.

Thai basil in a potThe Latin name means “a scent fit for the king’s palace.” It is a gentle plant that takes some effort to grow but is wholly rewarding.

Ocimum basilicum is a plant popular in Southeast Asia as a decorative plant and a flavoring in recipes. It can grow up to 1.5 feet and have blue, purple, or pink flowers. Yet, the Thai basil stem is always purple and square. That’s why it’s also called “purple Thai basil.

The leaves are shiny, narrow, and serrated.

Ocimum basilicum seeds can be brown or black and are also known as “nutlets.” There are many Thai basil varieties, and they mix well, so do play plant matchmaker.

How To Grow Thai basil? 6 Simple Steps

Ocimum basilicum can be grown from seeds or cuttings. Doing the latter is relatively easy and also helps you prevent crossing with other basils. This type is great when you want to preserve some of the more unusual varieties of basils.

To grow a Thai basil perennial from a cutting, do the following:

  1. Take a 4-inch section of the stem before it blooms
  2. Take off the leaves from the bottom part of the stem
  3. Put the stem in a small container with enough water
  4. Place the container near a window
  5. Change the water daily
  6. When roots emerge, move the basil to a small pot

Give Ocimum basilicum sandy, well-drained soil with 7 pH and at least 6 hours of sun each day. Space more plants at least 1 foot apart for small varieties and up to 3 feet for large ones. That is for air movement, which is vital to help Thai basil stay healthy; otherwise, they will make each other sick.

How To Water The Purple Basil? Taking Care of Draining

Ocimum basilicum is always thirsty but can’t stand living in a swamp, which means you have to take care of draining. Poor draining kills more of these plants than any other reason.

thai basil

It would be best to keep an eye on the soil the plant is in and water when it gets flaky or light. Never wait for your basilicum plant to start wilting before you ramp up the watering.

Growers who mass produce these plants in a greenhouse in the Southern areas might water them 2–3 times a day. If you’re not one of them, you can water your Thai basil once every few days. For those plants you’re growing in clay pots, ramp up the watering a bit.

How To Harvest Thai Basil? Pruning & Transplanting

Harvesting and pruning Ocimum basilicum is the same action. When you notice the plant has three sets of real leaves, it’s time for its first pruning.

Whenever you report or transplant your Thai basil, prune it above the second pair of leaves. Keep pruning every 3–4 weeks, cutting your plant down to the lower 33 percent of the main stem.

This kind of aggressive harvesting nets you about 20 cups of Ocimum basilicum leaves from that one plant. Still, you might want to go easy on your Thai basil and prune with a light touch. In that case, only cut off the topmost set of leaves, which you might be doing as often as once a week.

How To Plant Thai Basil? Pots, Seeds & Soil

In a pot, make a 1-inch hole in the soil and half an inch in diameter with your hand. Put in 3–4 Ocimum basilicum seeds into the hole. Cover the seeds with dirt and water the spot with a watering can until the water starts draining.

In the garden, sow Thai basil seeds at a depth of 1/8 inches and close together but not touching. If your region has unpredictable rainfall, seeding this plant in this way isn’t doable. Heavy water flow can wash away seeds and seedlings before they can establish roots.

Cover the soil with a transparent plastic sheet two weeks before the plant date. Remove the sheet when planting and later add mulch with straw to keep moisture and curb weeds.

If you can’t find that one, use whichever mulch you can find in your region, such as bark. You can use the lunar cycles to plant the Ocimum basilicum and plant it with the waxing moon.

How To Fertilize This Plant?

Use a 10-10-10 fertilizer mixed with water in a 50:50 ratio twice as often as the directions suggest. If you need leaves, go with a fertilizer rich in nitrogen. In that case, choose a dry mix that’s easy to add to the potting mix. When seedlings develop two pairs of real leaves, use a 14-14-14 fertilizer, again diluted 50:50 in water.

Fish emulsion is a good idea, as is organic fertilizer. You can try using kelp and add it once a week or once a month if the plants are in flats.

Where To Grow Thai Basil? Knowing The Best Environment

Ocimum basilicum can’t survive frost and grows well only in tropical weather, which means USDA zones 10–13. If your area’s lowest average temperature drops below 30–40 F, Thai basil can’t make it there.

You can grow Thai basil outdoors in northern climates, provided the weather has been warm for 30 days. It is, by definition, a tender perennial. But most people grow it as an annual in the northern hemisphere.

How To Start Thai Basil Indoors? Waiting Time Needed

Start about 5 weeks before the last frost but don’t make the mistake of starting too early. If you do that, your plant can become leggy, meaning with spindly stems with no leaves.

thai basil flower

In that case, you’ll be losing precious time while the plant recovers. Better start a bit later so that plants are small enough and don’t adapt too much to the indoor environment.

It takes on average 11 days for Ocimum basilicum to germinate, which you can do using plug trays or small cells. Some Thai basil growers prefer using two or three seeds per one large compartment, which reduces the effort to replant them. You don’t even need to bury Thai basil seeds; you might get away with only placing them on top of the soil and watering.

Still, it would help if you thought about pre-watering the soil, so the seeds don’t get moved around. Keep the seeds wet, cover the cell with plastic or newspaper but give them an air supply and put them in a dark, warm place.

What Is The Best Soil For Ocimum Basilicum?

We recommend that you use a soilless mix instead of garden variety potting soil brands.

Your options are:

  • Aged bark and peat to add drainage and prevent root rot
  • Perlite, sphagnum, and pasteurized wood chip mix to avoid diseases

Pasteurized compost is another option in your arsenal that can enrich the soil for Thai basil.

You can pasteurize your compost by:

  1. Making 1/2-inch squares in a garbage can lid
  2. Pouring compost through the lid to let the enclosures filter out large chunks
  3. Pouring in boiling water
  4. Mixing everything with a shovel
  5. Covering with the lid and let steam kill off diseases
  6. Repeating the process two more times
  7. Letting the soil cool for an hour

Through this method, you will end up with both pasteurized and warm soil, where Thai basil will feel like at home. If you want the same warm soil effect for indoor Thai basil growing, use an electric rubber heat mat. Keep the soil temperature as close to 70 °F as you can.

How To Pick The Best Container For This plant? Right Pot Sizes

Once your Ocimum basilicum seedling has germinated, it’s time to move it to a series of larger and larger pots. Clay and plastic pots are the two most serious contenders for growing Thai basil.

Clay pots look pretty but break way too often, are heavy to move around, and encourage water loss. Plastic pots keep the moisture and heat in place to help the Thai basil grow and are lightweight. Clay or plastic, pick those of dark color to protect the Thai basil roots from light. Also, make sure the container you choose has got drainage holes.

After your Ocimum basilicum sprouts leave, it’s time you start moving it from one pot to the next to give it more room to grow. You should do this every few weeks but be careful — a too-large pot might invite root rot. A good rule of thumb is to start with a 2–3 inch container and then move your Thai basil to a 4–6 inch one in a month. Be warned that you should never let the plant’s roots become too big for the pot it is in.

What Are Some Pests And Diseases of Thai Basil? Protect Your Plant

Grasshoppers and whiteflies are the two most dangerous pests of Ocimum basilicum. Cutworms, slugs, and spider mites are also notorious for chewing away from the plant with ease. You can spray the plant with a jet of water, which should knock off the pests but not harm the plant tissue. A homemade hot pepper and garlic spray also does wonders, as does a natural insecticidal soap.

You can curb cutworms by pouring wood ashes all around the Thai basil or use a cutworm collar at the plant’s base. Against slugs, install a 5-inch copper fencing. Copper reacts with the slug’s body on contact to zap but not kill it. You can curb all other insects by spreading fabric row covers over your Thai basil during the day.

Fusarium wilt is the deadliest disease of the Ocimum basilicum, seeing how it can kill seeds and remain in the soil afterward. Remove any plant you see Fusarium destroying as soon as you spot it before it can infect other plants.

Your best option against Fusarium is to plant hardy varieties of Ocimum basilicum, but you can also do these:

  • rotate crops
  • solarize the soil (covering it with plastic to increase the temperature)
  • proper removal of diseased plants and soil

What Makes Thai Basil So Special?

Tasting or smelling the Ocimum basilicum plant can remind you of:

  • cloves
  • lemon
  • rose
  • cinnamon
  • thyme
  • anise

This happens for a good reason: plant chemistry. Each aroma is a different chemical, and each Thai basil plant has a unique mix of these chemicals. Depending on the variety you’re growing, you will get a different ratio of scents and flavors.

What Does Thai Basil Taste Like?

The Thai basil flavor is like licorice or anise, with a hint of spiciness. Ocimum basilicum flavor will grow bitter over time, but you can pinch its flowers to stop that.

Thai Basil Taste

Can You Use Grow Lights For Indoors Thai basil?

Yes, since Thai basil enjoys the sun or anything that feels like it. Use warm or cool white fluorescent tubes, set them on a timer, and experiment with 12–24 hour lighting times.

Keep fluorescent grow lights 3 inches above seedlings and use only after germination. Place aluminum foil or mylar over the light source for a more generous light reflection.

What Are Some Fine Thai Basil Companions?

Tomato is the finest Thai basil companion, though you need to take some precautions. The two are often planted together for convenience, since their flavors go well in meals. They also have similar ideal growing conditions.

Plant the Ocimum basilicum about 3 feet away from the tomato and always on the south side. This is to avoid the tomato plant overshadowing the Thai basil. If you’re not interested in practical combos, plant the Thai basil with oregano or any flowers.


Does Thai Basil regrow after cutting?

Yes, Thai Basil can regrow after cutting. Trim the stem just above a node, and it will produce new growth.

Can I keep Thai Basil alive all year?

Thai Basil is a tender perennial, meaning it can survive for several years in warm climates. Indoors or in colder regions, it may die in winter.

Does Thai Basil go dormant?

Thai Basil may go dormant in winter or during periods of extreme heat. Keep the soil moist but not waterlogged, and it should resume growth.


In this article, you’ve learned that:

  • Thai basil is an ancient plant cherished for its smell
  • Ocimum basilicum varieties can mix, sharing their attributes
  • Growing Thai basil cuttings keep their unique smell and flavor
  • Well-watered soil gives vigor to Ocimum basilicum growth
  • Pruning is a must and produces plenty of Thai basil leaves
  • Planting Ocimum basilicum seeds on the surface of soil work fine
  • Kelp is a valid Thai basil fertilizer
  • The ideal Ocimum basilicum soil is warm and sterile
  • Plastic Thai basil containers work better than the clay ones
  • Tomato is an excellent Ocimum basilicum companion, both in the garden and in dishes

It’s not easy to accommodate plant royalty, but the effort is well worth it. Thai basil is a noble, gracious plant that you must handle with care, but your reward is an aroma you’ll never forget.

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