Rosemary

Rosemary (Salvia rosmarinus) is an aromatic evergreen shrub in the mint family, native to Africa, Europe, western Asia and the Mediterranean. Its botanical name used to be Rosmarinus officinalis, and you may still see it sold under that name.

It can grow into a shrub 4–5 feet (1.2–1.5 m) tall, but it’s winter-hardy only to USDA zone 8, so in colder places such as Wisconsin it’s usually grown in a pot. Its small blue, mauve, pink or white flowers appear in spring and are popular with bees and other pollinators.

Be honest about seed. Rosemary can be grown from seed, but germination is very irregular and slow, and it can take up to three years to get plants big enough for a good harvest. Seedlings also won’t necessarily match a named variety. It’s much quicker and easier to start with a bought plant or a cutting.

If you do sow seed. Start seeds indoors 10–12 weeks before your last frost. Press them onto the surface of the mix and cover them only very lightly, because they need light to germinate. Even in ideal conditions, germination takes 14–21 days and is often uneven. Plant seedlings outside once they’re at least 4 inches (10 cm) tall, after hardening them off.

Taking cuttings. Cuttings from an established plant are the best way to propagate rosemary. Take 4–6 inch (10–15 cm) tip cuttings from shoots without flowers in late spring or early summer, strip off the lower leaves, and root them in a medium such as perlite.

Where to plant. Rosemary needs full sun and light, free-draining soil, and it hates wet roots, especially in winter. In heavy soil, use a raised bed or a container. A pot should be at least 12 inches (30 cm) wide and deep, with plenty of drainage holes, filled with a soil-based mix with some added grit. Spring, once the soil starts to warm up, is the best time to plant.

Watering. Rosemary is fairly drought tolerant. Water new plants during dry spells in their first year; once established in the ground, they shouldn’t need extra water. Potted plants need watering in dry weather, but never let the compost get waterlogged. Overwatering is the biggest cause of decline and death, so let the soil dry on top between waterings.

Pruning. Trim lightly every year after the flowers fade to keep plants compact, but don’t cut back into old wood.

Winter. In the UK, established plants survive temperatures as low as 18 °F (−8 °C), though harsh frosts and cold winds can damage them. Cover plants with fleece during very cold spells, and protect potted plants, which are especially vulnerable to cold. Where winters are colder than zone 8, keep rosemary in a pot and bring it indoors before the first fall frost. Indoors it needs a sunny window, ideally with at least 6 hours of sun a day. Some varieties, such as ‘Arp’ and ‘Madeline Hill’ (also sold as ‘Hill Hardy’), are hardier and can survive in zone 7.

Rosemary is generally pest- and disease-free. Wet soil, especially in winter, can make the roots rot, so make sure drainage is always good. Poor air circulation and high humidity can cause powdery mildew, and botrytis is also common. Indoors, watch for aphids, mealybugs, whiteflies and spider mites.

In Britain, the rosemary beetle has become widespread since the mid-1990s. Rosemary is also a high-risk host for the bacterial disease Xylella fastidiosa, and gardening experts advise buying British-grown plants to reduce the risk of importing it.

Because it’s evergreen, rosemary can be picked all year, though the tender young shoots of late spring and summer taste best. Pick small amounts as needed and don’t remove more than 20% of the growth at a time.

For drying, cut sprigs before the plant flowers. Hang them in a warm, dark, well-ventilated place; once dry, strip off the leaves and store them in an airtight jar.

Pet poison experts list rosemary (under its former name, Rosmarinus officinalis) as non-toxic to cats, dogs and horses.