How to Grow Rue in Australia

Rue (Ruta graveolens, family Rutaceae) is a small, evergreen, semi-woody shrub of the citrus family. It is grown for its blue-grey, finely divided, strongly scented leaves and clusters of small yellow summer flowers. The store sells rue seeds of the common species, which forms a mound 60 to 90 cm tall. It thrives on neglect in lean, free-draining soil and full sun, from Perth to Hobart. The mistake that hurts gardeners is handling it bare-armed: its sap can blister skin that then meets sunlight.

Three mistakes that matter

1. Handling it with bare skin. Sap on the skin followed by sunlight, even on a cloudy day, can raise blisters within one to two days. Dark marks can linger for months. Wear gloves and long sleeves for every job, as Safety explains.
2. Burying the seed. In a Brazilian trial, seed left on the surface came up better than seed covered by 5 or 10 mm of soil. Press it onto damp mix and keep it in the light, as Germinating the seed describes.
3. Rich, wet soil. Rue rots at the root in soil that stays wet, and it lives longer and shrugs off frost better in poor, dry ground. Plant it in full sun with sharp drainage, and feed it very little.

When to plant

Warmth decides when rue seed comes up. Trays held at 18 to 25°C usually show seedlings in one to three weeks, and one laboratory study found the best rate at 30°C. That puts the main window in spring in the south and in autumn and late winter in warm zones. One sowing is enough, because each plant lasts about five years and often self-sows.

At the cool edge of a window, start seed indoors on a heat mat and plant out once frosts have passed. In the far north, sow early in the dry season so plants settle well before the wet season build-up.

Site, soil and setup

Rue comes from south-eastern Europe, where it grows on rocky, well-drained ground, and it does best when the garden copies that. Give it the hottest, sunniest, best-drained corner you have, and keep it back from paths where bare legs brush past.

Container growing

A pot suits rue well: it gives perfect drainage and keeps the plant away from children and passing skin. Give one plant a pot of at least 20 L and 35 cm across, filled with a premium potting mix. A heavy terracotta pot dries out evenly and stops a full-grown plant tipping over.

• Watering: water when the top 3 to 5 cm of mix is dry, and never leave the pot standing in a saucer of water.
• Feeding: fish and seaweed blend at half strength, about 12 mL per 9 L, fortnightly in spring and summer, only if leaves look pale.
• Position: full sun on a patio or step, set where people do not brush against it.
• Renewal: pot a plant on, or replace it with a rooted cutting, once roots fill the pot.

Germinating the seed

Rue seed is one of the easier traditional herbs to raise. It needs no special treatment: fresh seed asks only for warmth, moisture and light. A thousand seeds weigh about 2 g, so each seed is small but easy to handle. A packet of 50 gives far more plants than most gardens need.

Seed testers in Brazil chill rue seed for seven days at 5°C, a step their rules list for breaking dormancy. Chilled that way and kept at 20°C under constant light, seed on paper wetted with plain water gave 82 per cent within four weeks. In a Tunisian study, germination peaked at 30°C and reached 88 per cent within ten days. At home, sow two seeds for each plant you want and expect most to come up.

No source names a chemical treatment for this species, and none is needed. For more on seed treatments in general, see soaking, scarification and cold stratification.

When nothing comes up

• Buried too deep. Seed under a layer of mix emerges poorly. Sow again on the surface, pressed in, in bright light.
• Dried out. Surface seed dries fast. Cover the tray with clear plastic or glass until the first leaves show.
• Too cold. A winter windowsill can hold seed back for weeks. Move the tray to a heat mat or a warm, bright spot.
• Old seed. Rue seed stores well, but it keeps best cool and dry, not on a warm shelf. Sow within two to three years.
• Given up too soon. Keep the tray moist, warm and in the light for four weeks before sowing again.

Sowing Seeds

Start rue in trays for the most even stand, or sow it where it is to grow once the soil is warm. Both routes begin with seed pressed onto the surface, as Germinating the seed explains, and gloves for handling the seedlings.

Starting in trays

• Fill a punnet or cell tray with fresh seed raising mix, firm it lightly and water it well.
• Press two seeds into each cell, uncovered, and mist the surface.
• Stand the tray in bright, indirect light at the warmth given in When to plant, and keep the surface just moist.
• Thin each cell to the strongest seedling once true leaves appear, wearing gloves.
• Start trays about seven weeks before you plan to plant out.

Sowing direct

Rake the bed fine and level, water it, then scatter the seed thinly and press it onto the surface with the back of a rake. Mist daily until seedlings show, then thin them in stages to 45 to 60 cm apart. Seedlings about 5 cm tall move well to a fresh spot.

Planting out

• Plant out when seedlings stand 5 to 8 cm tall with several true leaves, after the last frost.
• Harden off first (stand the pots outdoors a little longer each day for a week, so they adjust to sun and wind).
• Wear gloves and long sleeves, and plant at the same depth as in the pot.
• Water in with seaweed solution at half strength, 15 mL per 9 L.
• Water twice a week until new growth shows, then only in long dry spells.

More on the step from pot to garden is in hardening off seedlings before planting out.

Care by growth stage

Drainage and restraint decide how well rue grows. Over-feeding reduces the essential oils that give rue its scent and makes it soft and floppy, so feed at half strength at most.

If growth stalls in very poor sand, a light application of all-purpose controlled release granular (NPK around 14-5-10) scratched in each spring can help.

Trimming and Cutting Back

A yearly trim keeps rue dense and stops it sprawling open in the middle. Trim in the evening, in gloves and long sleeves, and wash your skin afterwards.

• Cut back in early spring, once fresh shoots start breaking along the old stems.
• Cut to just above those shoots, into the old wood if the plant has grown leggy.
• Pinch the tips of young plants in spring for bushier growth.
• Cut off spent flower heads before the seed heads ripen, unless you want seedlings.
• Take cuttings of young shoots in spring to replace an old plant.

Cuttings root readily: see how to take cuttings for the method.

Companion planting

Choose neighbours that want the same sun and lean, dry soil, and keep rue out of the vegie beds.

Grows well with

• Lavender, another grey-leaved shrub for hot, dry, free-draining ground.
• Thyme, a low edging that suits the same poor soil and full sun.
• Rosemary, which takes drought and sharp drainage in the same way.

Keep apart

• Vegetable seedbeds: in one study, rue leaves in soil held back germination of radish and tomato and seedling growth of those two, zucchini and cauliflower.
• Paths, play areas and gates, where bare skin brushes the foliage.

Rue is often planted beside roses to keep insects away. In a replicated garden trial in the United States, roses interplanted with rue carried no fewer Japanese beetles than roses grown alone.

Harvesting Leaves

Pick leafy shoot tips once a plant is bushy, usually from about 16 weeks after sowing, and take them before the flower buds open.

• Wear gloves and long sleeves, and pick late in the day.
• Take no more than a third of a plant at one picking.
• Cut the soft upper shoots with secateurs, and discard yellowed or damaged leaves.
• Tie loose bunches and hang them in an airy, shaded place indoors.
• Dry until the leaves are crisp and crumble when rubbed.
• Wash gloves, secateurs and any bare skin with soap and water afterwards.

Store dried leaves in a closed, labelled jar in a cool, dry, dark place, well away from kitchen herbs. The leaves and sap carry furanocoumarins (psoralens): see Safety.

Traditional use and history

Rue is native to south-eastern Europe and the Balkans, and it is grown in gardens across temperate and tropical regions. Maud Grieve, in her 1931 herbal, records that the Romans brought it to England. She calls it one of the oldest English garden plants.

The name herb of grace probably comes from those holy water brushes. Shakespeare used it twice. Ophelia hands out rue in Hamlet, and a gardener in Richard II plants a bank of rue, the sour herb of grace. Grieve places that second passage in Richard III, a slip.

European herbalists also recorded rue as a household herb against fleas and other insects. Cooks in some European countries once added it to salads and bitter aperitifs. Its long record of medicinal use has faded, and the Missouri Botanical Garden notes that doubts over effectiveness and safety discourage it.

Safety

Happy Valley Seeds sells rue as seed for growing, as an ornamental. Nothing here is advice to eat or take any part of the plant. Anyone considering using a plant should first seek advice from a qualified health practitioner.

Two plants share the name: goat's rue (Galega officinalis) is a legume, and meadow rue (Thalictrum species) belongs to the buttercup family. Neither is this plant, so check the botanical name. If someone collapses, stops breathing or has a seizure, call triple zero (000). For any suspected poisoning, call the Poisons Information Centre on 13 11 26 without waiting for symptoms.

Common problems

No seedlings. Usually seed buried too deep, kept too cold or allowed to dry out; see Germinating the seed and its list, When nothing comes up.

Tall, pale, floppy seedlings. Too little light on a windowsill stretches them, so move trays to brighter light and turn them daily. Read more

Plants that collapse in wet ground. Root rot follows soil that stays wet, most often on clay or in a pot without drainage; see Three mistakes that matter.

Open, sprawling plants. Shade and rich soil both make rue loose and floppy, so move it into full sun, stop feeding and trim it hard in spring.

Old plants dying out. Rue is short-lived (see When to plant), so keep a rooted cutting or a self-sown seedling coming on.

Seedlings everywhere. Cut off spent flower heads before the seed ripens, and pull unwanted seedlings in gloves.

Pests and diseases

Rue has no serious pest or disease problems of its own, so trouble is most likely at the seedling stage.

Damping off (Pythium species and Rhizoctonia solani). Seedlings rot at soil level and collapse, most often in wet, crowded trays. Use fresh seed raising mix and clean trays, avoid overwatering and thin seedlings for air flow. Read more

Green peach aphid (Myzus persicae). This widespread aphid has been recorded infesting farmed Ruta chalepensis, a close relative, in Brazil, so check soft rue tips in spring. Hose colonies off with a strong jet, or squash them by hand in gloves. Read more

Common garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). Both graze seedlings at night in damp weather. Hand-pick them after dark, or scatter an iron-based snail bait thinly as the label directs. Read more

Prevention first

• Keep seed trays clear of rain and hose splash, which spread damping off.
• Water the soil, not the leaves, and let established plants dry out between waterings.
• Check soft shoot tips weekly through spring and summer.
• Clear boards, leaf litter and loose pots from around seedlings, where snails shelter.

Tips

1. Keep a pair of gloves and a long-sleeved shirt near the rue bed, so no quick job is done bare-armed.
2. Clip young plants into a low hedge for a knot garden: rue takes regular trimming and keeps its blue-grey colour all year.
3. Label every plant with its botanical name, because rue, goat's rue and meadow rue are easily confused at the nursery.