Thai Basil, also known as Oriental basil, Asian basil or Bai Horapa in Thailand, is a cultivar of sweet basil commonly used in the cuisines of Thailand, Vietnam, Cambodia, and Laos.
"Siam Queen" is a large leaf cultivar of Thai Basil that has been cultivated to provide a distinctive set of traits preferred in Asian cuisine. It has an identifiable liquorice flavour not present in sweet basil, and its flavour is more stable under high or extended cooking temperatures than that of sweet basil.

It has a stronger taste than many other sweet basils. It is very fast and easy to grow, and also quite pleasing to the eye. It produces flower heads that are deep burgundy, which contrasted nicely against the pale green and burgundy leaves.

Use Thai basil for Thai, Indian, and Italian recipes. Fresh, it can be added to salads, and either the fresh or dried forms can be used to flavour soups, pasta, and vegetable dishes.
Thai basil matches well with rice, poultry, and seafood. In Thai cuisine, great handfuls of fresh Thai basil leaves are added to spicy stir-fries. Thai basil can also be steeped into a soothing tea and used to flavour vinegar and oil as dressing components.

Timing:
All basils are very tender herbs that cannot withstand frost and will only thrive with night temperatures above 12°C. It is vital that Basil is not exposed to the last spring frosts so if sowing outside be patient and sow in late March. Sow at any time if the plant is to be kept indoors. If sowing inside and planting outside, you can sow from late February.

Prepare the site:
If growing outdoors: Basil likes a fertile soil that has been well dug to allow good soil air circulation. Introducing well rotted organic compost or manure into the soil a month or so before sowing will help this. Before sowing ensure that the compost or soil is weed free and moist. If growing in pots then a general purpose compost is a suitable soil solution. Ensure that adequate drainage is allowed from the base of the pot.

Sowing:
Sow the seed thinly and if growing in pots sow enough for a few plants in each pot. Cover with ½cm of compost and firm gently. Basil seeds germinate in under a week. Once the seedlings have developed 2 pairs of true leaves, thin out the weakest seedlings, leaving each pots strongest.
If growing indoors in pots then weeds shouldn't be a problem. If growing outdoors then you can add an organic mulch around the plants to help aid soil moisture retention and prevent weed establishment. Add a small amount of fertiliser every month or so to any pot plants. Water at the base of the plant avoiding showering the leaves and stems.

Harvesting:
When harvesting basil, don’t remove single leaves as you need them. Pinch off the top section of a stem, stopping just at the intersection where two leaves emerge. This will prompt the plant to produce new growth branching off from the place where you removed the stem. Removing leaves individually will not achieve the same result. Rinse the leaves in cool water to remove dirt or grit and pat dry between paper towels before use.
Basil will grow all year round indoors but outdoor plants should be dug up and brought indoors before the first autumn frosts if you want to extend the plants growing season.

Storing:
Basil can be used in fresh or dried form. Cut the stems at soil level and hang bunches up to air dry in a warm room for about a week, then remove them from the stems Store them in a dry airtight container for up to 12 months. Basil can also be frozen for later use.

Companion Plants:
When interplanted, basil is said to improve the taste of tomatoes and peppers, as well as repelling tomato hornworms and aphids. Basil is also the one herb reputed to repel mosquitoes around its growing place.

Etymology
The word basil comes from the Greek βασιλεύς (basileus), meaning "king", as it is believed to have grown above the spot where St. Constantine and Helen discovered the Holy Cross. The Oxford English Dictionary quotes speculations that basil may have been used in "some royal unguent, bath, or medicine". Basil is still considered the "king of herbs" by many cookery authors.

Although Vietnamese and Loations also use the Asian varieties of basil in their cuisines, the purple-stemmed liquorice flavoured leaves have come to be identified as Thai basil.
Thai basil is often confused with Holy basil which has a smaller, slightly hairy leaves and an aroma more akin to that of cloves.