Rosemary

Rosemary used to be classified as Rosmarinus officinalis; it was recently moved into the Salvia genus, which tells you something about its relationships but does nothing to change what it wants: full sun, gritty soil, minimal water, and temperatures that stay above about 10 to 15°F. In zones 7 and warmer, it can become a substantial shrub — four feet tall, woody at the base, covered in small blue flowers in late winter when almost nothing else is blooming. In zones 6 and colder, it's a container plant or an annual, and there's no shame in treating it that way.

The most common rosemary failure, even in mild climates, is not cold — it's poor drainage. A rosemary plant sitting in waterlogged soil will die slowly and look like a drought casualty: needles brown from the inside out, branches that snap instead of bend. The plant uses water in very small quantities, and its roots cannot tolerate sitting in wet for more than a day or two. Plant in raised beds, amend heavily with coarse grit, or grow in terracotta pots that breathe and dry out quickly.

Gardeners in zones 6 and colder can grow rosemary as an annual or bring it indoors for winter. Container plants need a pot at least 12 inches wide, a well-draining cactus or Mediterranean mix, and a south-facing window that gets six-plus hours of direct light. Indoors, the main problem shifts to spider mites: look for fine webbing and bronze-stippled needles in dry heated air. A weekly mist and good airflow help. Bring plants in before the first hard freeze — rosemary doesn't recover from a hard frost the way some woody herbs do.

The cold-hardiest variety available to most gardeners is Arp, which may survive mild zone 6 winters with good drainage and a sheltered south-facing wall. Hill Hardy is similar. Neither is reliably zone 6 — they are zone 6 possibilities, not zone 6 guarantees. If you lose one in January, it wasn't a management failure; you were at the edge of the range.

Harvest by cutting stem tips or side branches, never more than one-third of the plant at a time. Rosemary is slow-growing and does not recover quickly from heavy harvesting, especially in the first year. After two or three seasons, established shrubs can handle more aggressive cutting. The flavor is present year-round, but the oil concentration tends to peak in late spring and early fall, when growth slows and temperatures moderate.