Purple basil, a variety of sweet basil (Ocimum basilicum var. purpurascens), offers captivating visual appeal with its deep, rich foliage. This herb is celebrated for its unique color, ranging from violet to dark burgundy, and its slightly more intense, sometimes spicy, aroma compared to green basil. Beyond its ornamental value, purple basil is a flavorful addition to culinary creations, making it a popular choice for gardens and kitchens.
Planting Purple Basil
Start purple basil from seeds or young plants. If starting from seeds, sow them after all danger of frost has passed, when daytime temperatures consistently remain in the 70s Fahrenheit and nighttime temperatures are above 50°F. For cooler climates, seeds can be started indoors 4 to 6 weeks before the last expected frost date.
Plant in a location receiving at least six to eight hours of direct sunlight daily; this helps develop its deep purple coloration. Sow seeds 1/4 inch deep, covering them lightly with soil, and space them 10 to 12 inches apart. Water thoroughly after planting to ensure the soil is consistently moist for successful germination, typically occurring within 5 to 10 days.
Essential Care Requirements
Purple basil requires specific environmental conditions. Proper light, soil, water, temperature, and humidity are important for a healthy plant.
Light
Purple basil needs at least six to eight hours of direct sunlight daily. This intense light is crucial for robust growth and anthocyanin production, which gives its distinctive purple hue. Insufficient light can lead to a less vibrant color, causing the leaves to appear more green, and may result in leggy, weaker growth.
Soil
Purple basil thrives in well-draining soil that is rich in organic matter. An ideal soil pH is slightly acidic to neutral, typically between 6.0 and 7.5. Before planting, amending the soil with compost or well-rotted manure can improve its fertility and drainage. For container planting, use a commercial potting mix designed for herbs.
Watering
Consistent moisture is important for purple basil, which does not tolerate drought conditions. The plant generally needs about 1 to 2 inches of water per week. Water thoroughly when the top inch of soil feels dry, ensuring deep penetration. Watering in the morning helps prevent fungal issues by allowing the leaves to dry throughout the day.
Temperature and Humidity
Purple basil is a heat-loving herb, with optimal growth between 65°F and 80°F. Nighttime temperatures should remain above 50°F, as basil is sensitive to cold and frost, which can cause its leaves to blacken. While it generally thrives in average household humidity, protecting it from sudden cold drafts is beneficial, particularly for indoor plants.
Maintenance and Harvesting
Regular maintenance and timely harvesting are important practices for encouraging a bushy purple basil plant and ensuring a continuous supply of flavorful leaves. These actions promote new growth and prevent the plant from prematurely developing flowers, a process known as bolting.
Pinching back promotes lateral branching, leading to a denser, more productive plant. This involves removing the top set of leaves and the stem just above a leaf node, where new leaves or side shoots emerge. This redirects energy from height to foliage. Begin pinching when the plant is about 6 to 8 inches tall, removing about one-third of the plant’s top growth.
Harvesting leaves regularly also encourages continuous production and helps maintain the plant’s flavor. To harvest, snip off individual leaves or cut entire stems just above a set of leaves or a growth node. Harvest before flowering, as it can make leaves bitter. If flower buds appear, pinching them off promptly will delay bolting and extend the plant’s leafy growing period.
Troubleshooting Common Issues
Even with proper care, purple basil plants can encounter challenges. Addressing premature flowering, pest infestations, and leaf color changes helps maintain plant health.
One common issue is bolting, where the plant prematurely produces flowers and goes to seed. This often occurs due to high temperatures, water stress, or insufficient harvesting. To delay bolting, pinch off any emerging flower buds and ensure the plant receives regular, deep watering. While the flowers are edible, removing them redirects the plant’s energy back into leaf production, maintaining flavor and yield.
Purple basil is susceptible to common garden pests like aphids and spider mites. Aphids are small, soft-bodied insects that cluster on new growth; spider mites cause a stippled appearance and fine webbing. Organic control methods include spraying affected plants with a strong stream of water to dislodge pests or applying insecticidal soap. Maintaining proper spacing between plants helps improve air circulation, reducing conditions favorable for pests and diseases.
Purple basil leaves may lose their vibrant color and turn green. This is primarily due to insufficient sunlight, which impacts anthocyanin production. Other contributing factors can include genetic instability in some hybrid varieties or environmental stressors like extreme temperatures. Purple basil varieties are also less susceptible to downy mildew than green varieties.