How to grow rosemary — overwintering + 'Tuscan Blue'

How to grow rosemary — overwintering + 'Tuscan Blue'

Rosemary (Salvia rosmarinus, formerly Rosmarinus officinalis) is a Mediterranean evergreen shrub that delivers fresh aromatic leaves year-round in mild climates and a single pungent harvest in colder zones. It is botanically a true sage — the genus was reclassified to Salvia in 2017 — and shares sage's love of full sun, lean soil, and sharp drainage. The Royal Horticultural Society awards multiple rosemary cultivars its Award of Garden Merit, and a handful of US-bred cultivars (notably 'Arp') extend the plant's hardiness several USDA zones north of the species's native range.

Track your rosemary's overwintering schedule in Growli: Add the cultivar to the Growli app and you'll get a frost alert tied to your local first-frost date, with the exact move-indoors window for container plants.

Rosemary varieties — what to grow

'Tuscan Blue' is the classic upright cooking rosemary — vigorous, deep-blue flowers in late winter, olive-green needle-like leaves. The RHS lists it in its plant database as suitable for culinary use; it is one of the most widely sold rosemaries in both UK and US garden centres.

'Arp' was selected in 1972 by Texas herb grower Madalene Hill from a wild plant near Arp, Texas, that survived an unusually cold winter when surrounding rosemary died. North Carolina State Extension trials confirm 'Arp' survives down to roughly -23°C (-10°F) when established and well-drained, making it the most reliably hardy upright rosemary for USDA zone 6 and warmer parts of zone 5. 'Madelene Hill' (also sold as 'Hill Hardy') is a slightly more compact sport of 'Arp' with milder flavour, closer to traditional Mediterranean rosemary.

'Prostratus Group' rosemaries grow 15-30cm tall and trail 1-1.5m wide — perfect for cascading over walls, in raised beds, or in large containers. They are less hardy than upright forms (USDA 7-10) and culinary use is the same.

UK retailers — variety availability

• RHS Plants, Crocus, Hayloft, Sarah Raven carry the full upright range plus Prostratus Group. 'Miss Jessopp's Upright' is widely stocked and is RHS-recommended for UK hedging.
• B&Q / Homebase usually stock generic "rosemary" (unlabelled cultivar, often 'Severn Sea') from spring.

US retailers — variety availability

• Mountain Valley Growers, The Growers Exchange, High Country Gardens, Burpee all carry 'Tuscan Blue', 'Arp', 'Hill Hardy', and prostrate types.
• For cold zones, order 'Arp' or 'Madelene Hill' specifically — generic supermarket rosemary is rarely the hardy cultivar.

Soil — drainage is non-negotiable

Rosemary in waterlogged soil dies. Replicate Mediterranean hillside conditions:

• Texture: Sharp, gritty, free-draining.
• Amendments: Mix 30-40% coarse horticultural grit, perlite, or sharp sand into potting compost.
• pH: Slightly alkaline, 6.5-7.5.
• Fertility: Lean. Rosemary in rich soil produces lush soft growth that doesn't overwinter well.

In heavy clay soils — common in much of the UK midlands and US midwest — grow rosemary in a raised bed, gritty mound, or container. Avoid planting in a low spot where water collects after rain.

Sun

Full sun: 6+ hours of direct sun per day, ideally 8+. South-facing positions in both UK and US gardens. Rosemary tolerates light shade in extremely hot climates (US zones 9-10) but produces stronger flavour in full sun.

Planting

Rosemary is slow from seed and rarely grown that way. Use a transplant or cutting:

From transplant (recommended):

1. Plant after the last frost — late April in southern UK and US south, late May further north.
2. Dig a hole wider than the rootball; backfill with native soil mixed 50/50 with grit if your soil is heavy.
3. Set the crown level with the surrounding soil.
4. Water in once. Do not water again for 7-10 days.
5. Space upright cultivars 60-90cm apart for hedging; prostrate forms 45cm apart.

From cutting:

Take 4-inch semi-hardwood cuttings in late summer. Strip lower leaves, dip in rooting hormone, and pot up in pure grit or a grit-heavy mix. Keep barely moist; roots form in 4-8 weeks.

Watering

Rosemary is drought-tolerant once established. Overwatering kills more rosemary than any other cause:

• First year (establishing): Water weekly during dry spells. Roots are still shallow.
• Established plants in beds: UK and most US rainfall is sufficient. Water during prolonged drought (3+ weeks without rain).
• Container rosemary: Water only when the soil is completely dry to a depth of 2 inches. Typically every 7-10 days in summer, every 14-21 days otherwise. Terracotta pots help.

A drooping rosemary is more often overwatered than underwatered. Check the soil before adding more.

Pruning

Rosemary becomes woody and bare at the base over time. Light annual pruning keeps it productive:

1. Wait until after the spring flowering ends (typically May-June in UK, March-May in US).
2. Trim back the year's new growth by about a third with sharp scissors.
3. Cut into green growth, never into bare wood — rosemary rarely resprouts from old woody stems.
4. Shape the plant as you go.

For culinary use, snip 4-6 inch sprigs whenever needed throughout the season. Spread harvests across the plant rather than stripping one branch bare.

Overwintering — the cold-zone question

This is the single biggest issue for rosemary growers north of USDA zone 7 or in the cooler half of the UK.

Zones 7+ / mild UK: leave in-ground

Most upright cultivars survive zone 7 winters in well-drained soil. Avoid winter mulching directly against the trunk (it holds wet against the bark). Improve drainage if rosemary failed in your garden in previous winters.

Zone 6 / UK north and east: choose 'Arp' or 'Hill Hardy'

These cultivars survive winters that kill 'Tuscan Blue'. Plant in the most sheltered south-facing spot you have, with sharp drainage. Mulch lightly with grit (not bark or compost) to keep the crown dry.

Zones 3-5 / coldest UK: overwinter indoors

Below zone 6, container culture is the realistic option:

1. Grow rosemary in a 12-inch terracotta pot with gritty mix.
2. Sink the pot in a sunny garden bed for summer.
3. Lift the pot and bring indoors in late October, before the first hard frost.
4. Place in a bright, cool indoor spot — an unheated conservatory, porch, or cool bright south window. Aim for 4-10°C overnight.
5. Water sparingly — once every 2-3 weeks when fully dry.
6. Move back outside in late April / early May after the last frost.

The single biggest indoor rosemary killer is a warm dim room: 20°C+ with low light dries the plant out and causes leaf drop. A cool bright spot mimics the Mediterranean winter the plant evolved for.

Pests and problems

Rosemary is largely pest-free outdoors. Watch for:

• Powdery mildew — uncommon outdoors, common on stressed indoor plants. Improve air circulation, reduce watering, move to brighter spot.
• Spider mites on indoor rosemary — fine webbing, stippled leaves. Increase humidity, rinse foliage. See houseplant pests.
• Rosemary beetle (UK only) — small iridescent green-purple beetle. Pick off by hand; widespread infestations are rare on a healthy plant.
• Root rot — wet feet. Move to better drainage immediately. Often unrecoverable.

Pet safety — rosemary and pets

The ASPCA classifies rosemary (Salvia rosmarinus) as non-toxic to dogs, cats, and horses. Pets nibbling fresh rosemary needles are safe. Cooking-quantity rosemary in pet food is considered safe.

Rosemary essential oil is a different story. Concentrated essential oils, used in aromatherapy or pet products, can cause GI upset and central nervous system effects in cats, which cannot metabolise the concentrated phenols. Keep undiluted essential oils away from pets, and consult a vet before applying any rosemary-based products to animals.

If a pet ingests an unusually large amount of any plant material and shows symptoms, call the ASPCA Animal Poison Control Center at (888) 426-4435.

Propagation — taking cuttings to keep your favourite cultivar

Rosemary cuttings root readily and are the standard way to multiply a known good cultivar (especially the cold-hardy 'Arp' and 'Hill Hardy'). Cuttings come true to the parent — seed-grown rosemary varies wildly in flavour and hardiness and is not recommended for cooking gardens.

Method:

1. In late spring or early summer, cut 10-15cm semi-hardwood stems from the current year's growth.
2. Strip leaves from the bottom 5cm of each cutting.
3. Dip the cut end in rooting hormone (optional but speeds rooting).
4. Pot into a 70/30 grit-to-potting-mix blend, with the stripped section buried.
5. Place in a bright sheltered spot out of direct midday sun.
6. Keep barely moist — over-misting causes stem rot.
7. Roots form in 4-8 weeks. Tug gently; resistance means roots.
8. Pot on into 9cm pots once well-rooted. Plant out the following spring after hardening off.

Take 2-3 cuttings every year as insurance against losing the parent plant to a hard winter.

Companion planting

Rosemary is one of the best companions for carrots, cabbages, and beans — its strong scent confuses carrot fly and cabbage moth. Plant rosemary near a vegetable bed (in its own container, since vegetables prefer richer soil) rather than directly in the bed.

Good neighbours for rosemary itself: thyme, oregano, sage, lavender, marjoram — all Mediterranean herbs sharing dry sunny conditions. Avoid moisture-loving neighbours (mint, parsley, basil) which will either dry out or drown rosemary depending on whose water regime wins.

Culinary use

Rosemary's resinous pine-camphor flavour pairs especially well with:

• Roast lamb — slip whole sprigs into slits in the meat.
• Roast potatoes — toss chopped leaves with olive oil and garlic.
• Focaccia — press fresh leaves into the dough before baking.
• Roast chicken — stuff the cavity with whole sprigs.
• Infused olive oil and vinegar — warm gently with rosemary sprigs and strain.

Rosemary dries well but loses some of its resinous edge. For best flavour, use fresh or freeze sprigs whole in zip-top bags.

Related articles

• How to grow basil — the warm-season counterpart
• How to grow thyme — another Mediterranean herb
• How to grow oregano — same dry-sun conditions
• Types of herbs — Mediterranean vs moisture-loving vs annual
• USDA zone & frost-date lookup — for timing the move indoors

Reviewed and updated by the Growli editorial team. Pet-safety claims sourced from the ASPCA Animal Poison Control Center; cultivar hardiness data via North Carolina State University Extension and the Royal Horticultural Society. For questions about anything here, open Growli and ask — or email hello@getgrowli.app.