Basil stands first among the “warm” herbs, those with such highly volatile oils that a mere brush against the foliage releases a burst of fragrance. It's a member of the mint family (Lamiaceae) and shares mint's characteristic square stems, preference for moisture and lush growth in rich organic soil with good drainage.
My first vegetable garden was a municipal allotment with access to a mountain of composted manure from the local zoo. Fed liberally from this wealth of zoo-poo (mostly elephant and lion), the basil grew to jungle-sized stature. (That year I could have stuffed my pillows with it!) The herb's essential oils produce their most luscious scent and flavour when fed with natural fertilizers; incorporate garden compost and composted manure into the bed or container to produce superior plants.
Basil grows best in a cool location with part shade to full sun and consistent moisture; it quickly wilts in hot, dry weather, causing loss of flavour and permanently stunted plants. Manure and compost supply the trace elements essential to basil's flavour; feed with water-soluble fertilizer every two to three weeks to maintain new leaf production. Harvest leaves individually or take sections of stem, leaving at least 15 centimetres and three sets of leaf nodes behind. New stems will sprout rapidly. Pinch off flower buds to extend leaf production, or allow them to grow and provide a happy feast for pollinators.
Sweet basil (Ocimum basilicum, 60 cm) is the most familiar plant, with slightly puckered leaves and white flowers. The eight-centimetre leaves of ‘Sweet Genovese' and ‘Di Genova' are perfect for pesto-making; enhance the flavour by including leaves of ‘Thai Siam Queen', a purple-flowering variety with stronger flavour and fragrance. To produce a large supply of pesto, the crinkly leaves of ‘Lettuce Leaf' and ‘Napoletano' are the largest, lime green and beautiful. Dwarf basil (O. b. ‘Minimum', 20 to 30 cm) forms dome-shaped mounds with tiny, tasty leaves topped by white flowers. ‘Spicy Globe', ‘Minette', ‘Marseillais Dwarf' and ‘Green Bouquet' grow into rounded shapes perfect for clay pots or edging a bed.
Purple-leafed basils (O. b. purpurescens, 40 to 60 cm) are prized for their flavour, vivid colouring and leaf form. With flowers from bright pink to purple, the leaves are plain to ruffled or deeply cut burgundy-purple. Flat-leafed ‘Dark Opal' and ‘Osmin Purple', puckered ‘Red Rubin' and frilly ‘Purple Ruffles' make striking displays in a large clump by themselves, or mixed with other herbs and annuals. Scented basils (O. b. citriodorum, O. americanum) combine the herb's basic anise-mint-clove flavour with undertones of lemon, lime and cinnamon. The heirloom variety ‘Mrs. Burns' Lemon' is intensely flavoured, and has six-centimetre leaves and white flowers.
Hybridizers have bred edible ornamental plants, aiming for rounded, compact forms with flat tops carrying white, maroon or purple flowers. The blooms of new basil hybrids are carried on shorter inflorescences—10 to 13 whorls of six flowers tightly arranged along each rachis (spike)—that cover the dark green foliage for several weeks. Early- and late-maturing varieties allow for an extended season of blooms (plants will re-flower if first blossoms are removed). Hybrids can be grown from seed, and include ‘Lemon Sweet Dani' (65 cm); compact ‘Magical Michael' (25 to 35 cm), with red veined leaves and stems and fragrant burgundy flowers; and ‘Thai Magic' (30 to 45 cm), with green leaves and purple stems and flowers. They are magical plants in every respect, and a pot outside your door is sure to attract desirable attention.