Herb · Rutaceae
Rue
Ruta graveolens
Give it full sun and lean, dry soil, and rue holds its blue-green shape for years with almost no fuss.
Full sun
Every 7–14 days
80–120 days
USDA 4–9
Overview
Rue is a tough, blue-green evergreen herb with a long history in old gardens and apothecaries. It grows as a woody perennial, reaching 2 to 3 feet (60 to 90 cm) tall, and carries small mustard-yellow flowers through the summer. People once cooked with it and used it in folk medicine, but today it earns its keep as an ornamental and as a host plant for swallowtail butterflies.
What makes rue easy is also what trips people up. It wants lean, sharply drained soil and full sun, and it shrugs off drought and cold down to 5°F (-15°C). Rich ground and frequent watering do it no favors, and soggy roots are the fastest way to kill it.
The one thing to respect is the sap. Rue is rich in furanocoumarins, and brushing the sap onto your skin and then stepping into sunlight brings on painful, blistering burns. Handle it with gloves and long sleeves, site it away from pets and children, and keep it out of the kitchen.
Care
The short version: full sun, lean and sharply drained soil, and a deep but infrequent drink only once the top half of the soil has dried. Cut it back hard each spring, feed it little or not at all, and always wear gloves when you handle it.
Light
Rue wants full sun, the more the better, and it holds its tight blue-green shape only in bright light. It will take some afternoon shade, but a shaded plant stretches, flops, and grows thin.
Water
Less is more here. Water deeply but only every 7 to 14 days, and let the top half of the soil dry out first. Rue is drought-tolerant once established and hates wet feet, so soggy ground is the surest way to rot the roots.
Soil
Plant it in lean, sharply drained soil, sandy or loamy, the kind most herbs only tolerate. A pH anywhere from 6.0 to 7.8 suits it, and poor ground actually keeps the growth compact and sturdy.
Temperature
Rue is genuinely hardy, taking heat to 95°F (35°C) and cold down to 5°F (-15°C). That toughness is why it returns year after year in zones 4 through 9 with no special protection.
Humidity
It prefers things on the dry side, around 30% to 50% humidity, in keeping with its Mediterranean roots. Damp, still air is the main thing to avoid, since it invites the rot the plant is already prone to.
Feeding
Feed rue lightly in spring or not at all. It thrives in poor soil, and a heavy hand with fertilizer only grows weak, floppy stems that fall open and lose their tidy form.
Pruning
Cut rue back hard in early spring to clear out the old woody growth and bring on fresh, compact foliage, then tidy it after flowering. Always wear gloves and long sleeves and prune on a cloudy day, because sap on bare skin followed by sun causes blistering burns.
Repotting
A container-grown plant needs moving up only every 2 to 3 years. Repot when roots circle the pot or push through the drainage holes, water runs straight through, or new growth turns sparse and stunted.
Size & spacing
Rue forms a rounded shrub 2 to 3 feet (60 to 90 cm) tall and 18 to 24 inches (45 to 60 cm) across. Give each plant that much room so air moves freely and the foliage stays dry.
When to plant
Rue is a hardy perennial that takes its time getting started. Sow the seed indoors in late winter, set young plants out in spring once the frost has passed, and look for its mustard-yellow flowers across the summer, roughly June through August.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 6-8 weeks before last spring frost
- Plant: spring, after danger of frost has passed
- Harvest: Mustard-yellow flowers in summer (roughly June-August); grown ornamentally - do NOT harvest the foliage for eating due to toxicity and phototoxic sap.
Hardiness
USDA hardiness zones: 4–9
Temperature: down to -34°C
Troubleshooting
Rue is forgiving once it settles in, and most of its troubles come down to too much water or too little pruning. Read the early signs below and you can usually set it right with a change of habit rather than a rescue. Match what you see, then act before the roots or the shape go too far.
Wilting, yellowing, and a plant that slowly collapses
This is root rot, and with rue it almost always traces back to wet feet. The plant resents soggy ground, so heavy clay or constant watering rots the roots from below. Cut back the water at once, work grit or sand into the bed to open up drainage, and pull out any plant whose roots have already gone brown and mushy.
Fix:
- Reduce watering immediately and allow soil to dry
- Improve drainage by amending with grit or sand, or relocate to a raised/well-drained site
- Remove and discard severely rotted plants
Bare woody stems with leaves only at the tips
An unpruned, leggy plant lets its base turn woody and sheds the lower leaves, leaving green only at the ends. Too little light makes it stretch and worsen the look. Cut it back hard in early spring and the plant pushes out fresh, compact shoots, but give it full sun or it stretches right back.
Fix:
- Cut back hard in early spring to encourage compact new shoots
- Ensure the plant receives full sun
Blue-green leaves chewed down by caterpillars
Those green-and-black banded caterpillars are swallowtail butterfly larvae, and rue is one of their favorite host plants. Most gardeners leave them be and treat the chewed foliage as the price of raising butterflies. If the damage bothers you, pick the caterpillars off and move them, and skip the broad sprays that would kill them outright.
Fix:
- Tolerate the caterpillars where butterflies are desired, as rue is a valued host plant
- Hand-pick and relocate caterpillars if damage is unacceptable
Toxicity
Treat rue as a plant to admire, not to touch or taste. Its sap holds furanocoumarins that cause severe sun-triggered skin burns, and the foliage is toxic to cats, dogs, horses, and grazing animals if eaten. No part of it is safe to eat, so handle it with gloves and keep it well away from pets and children.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Moderate
A cat that nibbles rue or brushes the sap tends to drool, throw up, and run loose stools, then turn dull and withdrawn. The same oils can leave the skin red and irritated.
Dogs Moderate
Watch for drooling, vomiting, and diarrhea after a dog chews the foliage, often followed by low energy and a patch of inflamed skin where the sap landed.
Horses Moderate
Horses get an upset stomach from grazing rue, and the sap can blister or inflame the skin, especially on pale, sun-exposed muzzles and legs.
Rabbits Toxic
Don't let rabbits near it. The furanocoumarins make the foliage unsafe to eat, and a curious rabbit can end up with a sore gut and irritated skin.
Livestock Toxic
Grazing animals that eat rue can suffer digestive upset and photosensitization, where sun-exposed skin reddens and blisters after the plant builds up in their system.
Birds Caution
There's little reason for birds to peck at the bitter foliage, and the same phototoxic compounds make it a plant to keep out of reach rather than offer.
People Caution
No part of rue is a casual nibble, and the real hazard is your skin: brushing the sap and then stepping into sun brings on painful, blistering burns. Wear gloves and long sleeves whenever you handle or prune it.
Always handle rue with gloves and long sleeves, and avoid contact on sunny days, because sap on skin followed by sunlight causes painful blistering burns (worse than parsley or celery). The plant must NOT be eaten by people or animals and is not used as a modern culinary herb.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
A couple of named forms turn up in gardens, grown more for their foliage than for any difference in use. These are the two worth knowing.
'Jackman's Blue'
A compact form grown for its unusually deep blue-green foliage that holds its color all season.
'Variegata'
Its leaves are splashed and edged with creamy white, giving the plant a softer, mottled look.
How to propagate
Rue spreads readily enough from seed or cuttings, though both ask for a little patience and, in the case of cuttings, a pair of gloves.
SeedModerate
Start indoors 6-8 weeks before last frost, or sow outdoors in spring; germination can be slow · Several weeks to germinate and a full season to establish
Start rue from seed indoors 6 to 8 weeks before your last frost, or sow it straight into the spring garden. Press the seed onto the surface rather than burying it, since light helps it sprout, and keep the soil evenly moist until the seedlings appear. Be patient, because germination runs slow and the plant takes a full season to settle in.
Stem cuttingsModerate
Take softwood or semi-ripe cuttings in late spring to summer · 4-8 weeks to root
Take softwood or semi-ripe cuttings from late spring through summer and root them in a gritty, well-drained mix, where they take hold in 4 to 8 weeks. Always wear gloves while you cut and handle the stems, because the sap can burn skin in sunlight.
Myths
Rue is a safe culinary herb you can cook with as freely as other Mediterranean herbs.
Old recipes used it, but modern guidance does not treat rue as food. It is toxic to eat and its sap brings on severe sun-triggered skin reactions, so today it earns its place in the garden as an ornamental and historical herb, not a kitchen one.