How to Grow Purple Basil From Seed

Purple basil is a warm-season annual that dislikes the cold, so timing comes down to warmth. Start seeds indoors about 6 weeks before your last spring frost, then set plants outside only once nights stay reliably above 50F and the soil has warmed. You can also direct-sow once frost is well past and the ground is warm. Give it plenty of sun, which deepens its rich purple color, and sow fresh batches through the season for a steady supply.

Purple basil is easy to start from seed, though it can germinate a touch slower than green basil, so be patient. Sow the small seeds about a quarter inch deep in rich, well-drained soil or moist seed-starting mix, pressing them in gently for good contact. Keep the mix evenly moist and warm, around 70F, and seedlings usually appear in 7 to 14 days. Give them bright light for stout growth and the best color, then thin or space plants 8 to 12 inches apart in full sun.

Purple basil grows much like sweet basil but needs full sun to hold its deep color, since shade fades the leaves back toward green. Water to keep the soil evenly moist but never soggy, watering at the base in the morning. Give it a light feed, and pinch the tips once plants reach 6 inches to keep them bushy and ornamental. Pinch off flower spikes as they form to keep the plant leafy and richly colored. Being a true basil, it is cold-tender, so gardeners in the North, from the Midwest to New England, should wait for soil above 60 degrees and settled warm nights before planting out; growers in the sunny South and Southwest not only get a longer season but tend to see the richest, darkest leaf color, since strong light deepens the purple.

Purple basil is both useful and beautiful in the garden, pairs well with tomatoes, and its scent helps deter many common pests. These four make especially good companions, and you can add any of them in one click:

Start picking once plants are 6 inches tall and bushy. Harvest by pinching whole stem tips just above a pair of leaves rather than stripping single leaves, which keeps the plant branching and colorful. Cut in the morning when the oils are strongest, harvest regularly to encourage new growth, and never take more than about a third of the plant at once.

Reach for purple basil when you want color as much as flavor, since its taste runs a little milder and more clove-like than sweet basil. Use the leaves fresh so they keep both color and taste: scatter them over salads and platters as a garnish, and steep them in white vinegar, oil, or a simple syrup to turn it a beautiful ruby-pink. Tuck a sprig into summer drinks, and plant it as an edible ornamental edging that doubles as a kitchen herb.

• Fading color: too little sun turns purple basil green. Grow it in full sun to keep the deepest color.
• Bolting (flowering): pinch off flower spikes as they form and harvest often to keep leaves tender and colorful.
• Cold damage: it blackens in a chill. Keep it warm and never set plants out until nights stay above 50F.
• Slow or patchy germination: purple basil can be slower to sprout. Keep the mix warm and evenly moist and give it up to two weeks.
• Leggy seedlings: too little light. Grow in full sun or under bright grow lights and pinch the tips to encourage bushy growth.