Rue

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.

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.

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.

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.

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.