How to Grow Basil
In this article, we share a comprehensive guide to growing basil at home.
Quick Guide Information
Common Name: Basil (Sweet Basil)
Scientific Name: Ocimum basilicum
Family: Lamiaceae
Life Span: Annual (Short-lived Perennial in frost-free climates)
Time Till Harvest: 50-75 days from seed
Light Requirement: Full Sun
Optimum pH: 6.0 - 7.5
Basil is one of the most widely grown culinary herbs, valued for the way fresh leaves lift a dish far beyond what the dried version can offer. It originates from the tropical regions of Asia, which explains why it is frost tender and thrives in warm, humid conditions.
Choosing a Variety
Most home gardeners grow sweet Genovese basil, the classic pesto variety, which performs best in warm, relatively dry conditions and is moderately prone to downy mildew in humid weather. Thai basil is a good alternative in tropical and subtropical parts of Australia, since it tolerates heat and humidity better and is slower to bolt to flower. Purple varieties such as 'Dark Opal' share similar growing requirements to Genovese basil, with the main difference being leaf colour and a slightly more peppery flavour.
Propagation, Planting, and Maintenance
Basil is easy to start from seed, with germination typically taking 5 to 10 days at temperatures above 20C. Seeds can be sown directly in the garden once the risk of frost has passed, or started earlier indoors and transplanted once the weather has warmed.
Basil also propagates readily from cuttings. Take a 15cm cutting of healthy, non-flowering growth and place it in a jar of water. Roots will typically develop within 1 to 2 weeks, after which the cutting can be moved into soil.
Choose a warm, sheltered spot in full sun with fertile, well-draining soil. Basil does well in garden beds or pots, and pots can be an advantage in cooler or wetter climates since they can be moved to protect the plant from the elements. Space plants 20 to 30cm apart to allow good airflow.
Basil is a relatively heavy feeder given how quickly it grows. Work aged compost or worm castings into the soil before planting, and feed potted plants every 3 to 4 weeks with a diluted liquid fertiliser through the growing season.
Basil is frost tender and growth slows noticeably below about 10C, with damage or death likely at 0C or below. In cooler regions, plants should be started well after the last expected frost and brought to a close before the first frost of autumn.
Pinch off flower spikes as they appear to keep the plant producing leaves rather than seed. Regular harvesting from the top of the plant encourages bushier growth. Once a plant has been allowed to flower and set seed, leaf production drops off significantly and the plant is best replaced.
Growing Indoors and in Pots
Basil grows well indoors provided it gets enough light. Aim for a bright, north-facing windowsill that receives at least 6 hours of direct sun; where this isn't available, a grow light will make a noticeable difference to leaf production. Use a pot at least 15 to 20cm in diameter with good drainage, and let the top few centimetres of soil dry out between waterings rather than keeping it constantly wet. Indoor basil is more prone to leggy, weak growth than garden-grown plants, so rotate the pot regularly to keep growth even.
Harvesting and Storage
For the best flavour, harvest basil in the morning once any dew has dried, and before the plant flowers, since essential oil content is highest at these points. Pick from the top of the plant, just above a pair of leaves, rather than stripping individual leaves from lower down.
Fresh basil doesn't store well in the fridge, as cold temperatures cause the leaves to blacken. Instead, keep cut stems in a glass of water at room temperature, similar to fresh flowers, where they will last about a week. For longer storage, basil freezes well when blended with a small amount of oil or made into pesto, and this generally preserves flavour better than air drying, which basil tends to lose a lot of its aroma during.
Common Problems
Downy Mildew - This fungal disease appears as yellowing on the upper leaf surface with grey to brown fuzzy growth on the underside. It spreads quickly in humid, poorly ventilated conditions and has become a significant issue for basil growers in recent years. Improve airflow between plants, avoid overhead watering, and remove affected leaves promptly.
Aphids - These small sap-sucking insects can cluster on new growth. They are rarely catastrophic and can usually be managed by hosing plants down or using a soapy water spray.
Bolting - Basil is quick to flower and set seed in hot weather or as it matures, after which leaf production slows. Regular pinching of flower buds delays this, but eventually plants will need to be replaced with fresh seedlings.
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