Rue

Start new plants from seed, cuttings, or division

Set rue out in spring or fall, spacing plants 18 to 24 inches apart in full sun to partial shade on well-drained ground. Propagate by seed, stem cuttings, or division of an established clump. Individual plants are short-lived, about five years, so a bed needs replacements coming along. Rue also self-seeds readily and will often replace itself if you let a few seedlings stand. The wide spacing suits a plant that finishes 2 to 3 feet tall and equally wide.

⚠ Handle seedlings and cuttings with gloves. Rue is not a plant to eat your way through: ingestion in quantity causes stomach pain, vomiting, exhaustion, confusion, and convulsions, and may be fatal.

Mulch the crown for winter in cold zones

In the north end of its range, surround the plant with mulch going into winter. Keep the mulch off soggy ground and do not pile it where water collects. Rue is hardy to zone 4 but it is a Mediterranean subshrub that hates wet feet more than cold. Mulch buffers the crown through freeze and thaw, while the real killer is root rot in poorly drained soil, which is why drainage matters more than depth of cover.

Cut back to old wood in early spring

In early spring, before the new blue-green growth pushes, cut the plant back hard into the old woody framework. Take out anything dead or damaged at the same time. Rue is a subshrub that turns woody and bare-legged with age, and it is short-lived, roughly five years. Cutting into old wood while it is still dormant forces fresh shoots from the base and keeps the plant dense instead of a bundle of leggy sticks.

⚠ Wear gloves and long sleeves. Rue sap causes contact dermatitis, and the irritation follows contact plus sunlight, so prune on an overcast day or in the evening and wash any skin the sap touches with soap and water before you go back into the sun.

Shear once over the summer to stop it going lanky

Trim the shoot tips back by a few inches at least once during the summer to hold the mound shape. Do not wait for the spring cut to do all the work. Left alone through the growing season, rue grows woody with lanky stems that flop open and expose the center. A single summer shearing keeps the branching tight and the habit compact.

⚠ Gloves and long sleeves again, and avoid cutting in bright midday sun. Summer is exactly when sap on skin plus strong UV produces the worst blistering.

Check for swallowtail caterpillars before you reach for anything

Through the summer, look over the foliage for the bird-dropping-mimic caterpillars of black, anise, and giant swallowtails. If you want the foliage intact, handpick them off; otherwise leave them and let them finish. Rue is one of the few Rutaceae hosts these butterflies will lay on, and the larvae are almost never numerous enough to hurt an established plant. The chewed leaves are the point of growing it for most people.

⚠ Do not spray this plant. Foliar insecticides and Bt (Bacillus thuringiensis) both kill swallowtail larvae outright, and insecticide is rarely justified here. Handpicking solves it in nearly every situation. Wear gloves when picking, since the sap blisters skin that then sees sun.