Basil

Growing Conditions

Basil is one of the most cold-sensitive common herbs. It dies at frost and sulks in soil below 50°F. Nighttime temperatures below 50°F slow growth and cause leaf blackening. It needs warm soil, warm nights, and full sun. In cool climates, starting transplants indoors and waiting for genuinely warm weather before planting out pays off significantly.

Cold climates: Start indoors 4–6 weeks before last frost. Do not transplant until nights are consistently above 55°F — in Zone 5, this often means late May or early June rather than at last frost.

Warm climates: Direct sow after soil warms for a simple, continuous supply.

Sowing & Planting

Start indoors ¼ inch deep at 70°F. Transplant at 4–6 weeks old, spacing 12–18 inches apart. Direct sowing after last frost also works — thin to 12 inches. Basil transplants easily with minimal root disturbance.

Care & Maintenance

Water consistently at the base — basil is susceptible to fusarium wilt, which is spread by soil splash. Mulch lightly. Feed with balanced fertilizer every 3–4 weeks or top-dress with compost midseason. The most important maintenance task is pinching flower buds: remove them as soon as they appear. Once basil flowers, leaf production slows and flavor declines. Pinch from the top, cutting just above a leaf node — the plant branches and produces more leaves.

Common Problems

Fusarium wilt causes sudden wilting and dark streaking in stems — no cure; remove and destroy affected plants; don’t replant basil in that spot for several years. Downy mildew appears as yellowing on upper leaves with gray fuzz underneath — choose resistant varieties. Aphids on new growth — control with water or insecticidal soap. Cold damage causes black leaves — prevent by not planting out too early.

Harvest

Harvest from the top of the plant, cutting stems just above a leaf node. Never remove more than one-third of the plant at a time. Regular harvesting encourages branching and more leaf production. For large harvests, cut stems down to the second or third set of leaves — plants recover quickly in warm weather.

Varieties

Genovese/sweet basil is the standard culinary type for pesto and Italian cooking. Thai basil has a spicy, anise-like flavor used in Southeast Asian cuisine — more heat tolerant than Genovese. Lemon basil has a citrus fragrance and flavor. Purple/opal basil is striking in the garden and used in vinegars. Lettuce leaf basil has enormous leaves and mild flavor. Downy mildew resistant varieties (Amazel, Eleonora) are worth choosing in humid climates.