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Annual / Perennial 
Genus: Ocimum Species: basilicum
Variety: tenuiflorum / sanctum
Full Sun - Partial Shade tolerable
Soil pH 6 to 7.5 Hardiness zones 4 to 9 as Annual 10+ as a perennial
Days to Germination: 7 to 14 days 
Days to Maturity: 75 to 85 days 
Foliage Color: Green to purple
Bloom Color: Purple / lavender
Plant Height: Avg. 18 to 24 inches 
Frost Sensitive - Don't plant it too early in the spring.
Holy basil is deemed 'Holy' in the Hindu religion as it is believed it helps achieve purity of the heart and mind. Its somewhat narcotic effects which have been authenticated by modern herbalists include alleviating stress, fortifying the nervous system, antioxidant, antibacterial and antiviral properties.
There are multiple varieties but the most common are Rama , Krishna, Vana and Thai Holy Kaprao [Gaprao]. In the culinary arts it is popular in Southeast Asia, particularly Thailand. Thai cuisine employs it in a number of dishes and teas. The fragrant green leaves are also used in potpourri and have a peppery sweet, clove like flavor. My experience leads me to describe it as a menage a trois between mint, cloves and habanero - very mild habanero, some sub varieties have a citrus kick.
The plant attains an average height of up to 1.5 feet, some conditions and cultivars are a tad taller, some shorter . It has a bushy growth habit and produces stems and leaves that range in color from light green to dark purple. Pinching back will encourage fresh growth.
1. Basil can be grown as a perennial only in USDA hardiness zones 10 and higher, Elsewhere, it is a tender annual that will die off with the first cool weather if not transported indoors.
2. Some variation among specific cultivars
Basic Care of Basil
Water - Basil requires ample and persistent water. Mulch to retain moisture in warm weather is advisable.
Delicate flowers on Basil are attractive however they are a sign your plant is going to seed and production will decline at this point. If you are not looking to harvest seeds, you should pinch off any flower stems as they appear.
Temperature - Basil thrives in warm temperatures and heat. It will turn black and die off in temperatures approaching the mid 30s F. Temperatures should be at the very least in the 70s around the clock.
Optimal Growth Temperature 65 to 85 F
Germination Temperature 70 to 75 F
Pests and Disease
Basil has some enemies, Beetles, particularly Japanese Beetles, love Basil as much as people do and have been known to completely skeletonize whole plants. Aphids are also a problem at times. Most varieties are also subject to various plant diseases such as black spot, gray mold and fusarium wilt.