Nepeta cataria.

The herb with a thousand roles: for domestic cats first, who lose every shred of dignity the moment they smell it; but also for humans, who have made a calming tea from it since antiquity; and for gardeners, who appreciate its spectacular insect-repellent power. The scientific name Nepeta cataria already says a lot: Nepeta, according to Pliny the Elder, comes from the name of the Etruscan city Nepete (today's Nepi, in central Italy), where the plant was particularly abundant in antiquity; cataria derives from the Latin cattus ("cat"), for obvious reasons. A member of the Lamiaceae family (alongside mint, lemon balm and sage), catnip has been cultivated in Europe and Asia since antiquity. Dioscorides mentions it as a digestive and calming remedy, and European settlers brought it to North America in the 17th and 18th centuries, where it quickly escaped gardens to naturalize everywhere — including Québec, where it is still regularly encountered along country roads, on abandoned farms and in pastures.

A robust perennial plant 60-90 cm tall, with the square stems characteristic of the Lamiaceae, and oval, toothed, slightly downy leaves in a soft silvery grey-green. In summer, spikes of small white flowers spotted purple draw bees and bumblebees in considerable numbers. The famous feline property comes from a particular volatile molecule, nepetalactone, which curiously mimics feline pheromones — about 65 to 70% of adult cats react to it; for the others, it's genetic. Kittens under six months never react. The typical effect lasts 5-15 minutes: ecstatic rolling, compulsive rubbing, salivation, then a phase of gentle bliss — entirely harmless and non-addictive. A surprising fact: big cats react as well (lions, tigers, panthers). On the human side, a light infusion (1 teaspoon dried per cup, 5 minutes of steeping) has traditionally been used as a calming bedtime tea or for difficult digestions — at moderate doses, the effect is gentle, relaxing, with no particular psychoactivity. On the gardener's side, nepetalactone is also a potent natural mosquito repellent — a 2001 Iowa State University study measured it as up to ten times more effective than DEET (the synthetic compound in classic anti-mosquito products) at equal parts. A few crushed stems in a pocket, or rubbed on the skin, effectively chase off black flies and mosquitoes in hot weather — useful when you're working outdoors in summer.

Grower's tip: Don't confuse this with ornamental "catmint" (Nepeta × faassenii, Nepeta mussinii), a cousin grown chiefly for its decorative blue flowers, which has no effect on cats. Nepeta cataria is the real catnip. Start indoors 6-8 weeks before transplanting, or direct-sow in late May in Québec. Germination is capricious; the seeds benefit from cold stratification (two weeks in the freezer in a sealed bag) before sowing. Once established, the plant self-seeds generously (sometimes too generously) and stays perennial for decades. To harvest, cut the flowering stems at full bloom, tie them in bundles, hang them upside down in a shaded, dry, airy spot for 2-3 weeks, then strip the leaves into an airtight jar.

Note: if you're growing this plant for a cat, it's best grown out of reach until harvest — otherwise the feline will trample, chew and flatten it to the ground long before you can harvest a single leaf.

• Open-pollinated. Hardy perennial, zone 3. Insect-pollinated; crosses with other Nepeta (rare in vegetable gardens) — low crossing risk.
• Height: 60-90 cm.
• Flowering: June to September.
• Exposure: full sun; part shade tolerated.
• Well-drained, rather dry, moderately rich soil. Very low requirements; tolerates poor and stony soils.
• Start indoors 6-8 weeks before transplanting (cold-stratify 2 weeks beforehand), or direct-sow in late May. Abundant self-seeding once established.