Tarragon

Light and exposure

Tarragon wants full sun, at least six hours of direct sunlight. Give it the warmest, brightest spot in the vegetable garden. It is in the sun that it concentrates the essential oils responsible for its aniseed flavour; in the shade, it grows leggy, thins out and turns bland.

In a pot, choose a well exposed spot on the terrace. Growing in a pot has real value: it lets you bring the plant into a dry, cold place for winter, sheltered from the rains that make it rot in open ground.

Watering

Tarragon copes poorly with excess water. Water moderately, only when the soil is dry on the surface, and always let the soil drain between two waterings. A plant settled in open ground usually makes do with rain once it is rooted; it tolerates drought well.

In a pot it is trickier because the substrate dries out fast in summer but holds water in autumn. Water at the base, never on the foliage, and always empty the saucer. A tarragon that yellows and goes soft at the base is almost always a tarragon watered too much, not too little.

Soil and repotting

The ideal soil is light, free draining and rather poor. Tarragon comes from the steppes, it hates heavy, clayey, waterlogged soils that rot its crown. If your soil is compact, lighten it with coarse sand and gravel, and plant on a small mound so the water drains away.

At planting, forget the generous compost: soil that is too rich gives soft foliage, less fragrant and more sensitive to cold. In a pot, mix potting soil with a third of sand or perlite, over a good layer of clay pebbles. Plant a young plant bought in a small pot in spring, never a seedling from seed.

Temperature and humidity

French tarragon is semi hardy: the species is rated for USDA zones 4 to 8, that is winter lows of around -30 °C, but that hardiness only holds on well drained soil. It takes frost without any problem once dormant, while it is winter dampness that kills it, not dry cold. A mild, rainy winter is more fatal to it than a good frost on well drained soil.

The critical point is therefore drainage combined with mulch. As winter comes in, once the stems have browned, earth up and mulch the plant generously with dead leaves or dry straw to keep the crown warm and dry. On heavy soil or during a particularly rainy winter, it is better to bring the pot into a cold, dry, frost free room rather than risk losing the plant.

Pruning and upkeep

Harvest the stems regularly from May to September: this stimulates regrowth and keeps the clump compact. Cut above a leaf, take what you need and do not wait for flowering, which weakens the scent. French tarragon flowers little and its flowers come to nothing anyway.

At the end of the season, when the aerial part dries and turns brown, cut the dead stems back to ground level before mulching. In spring, a light clean up is enough to let the new shoots come through. An important point for the plant’s longevity: divide the crown every three years, because the clump exhausts itself and becomes woody at the centre.

Pests and diseases

Tarragon is tough, its troubles almost all come from dampness. Root and crown rot is the real risk in a damp climate: on heavy or overwatered soil, the crown blackens and goes soft, often in autumn or coming out of winter. Rust, a fungus that marks the underside of the leaves with orange pustules, appears in mild, damp weather, especially on crowded, poorly aired plants.

Prevention comes down to three actions: free draining soil, measured watering at the base, and enough spacing for air to circulate. As for pests, slugs nibble the tender young shoots in spring, and aphids may settle on the stems in summer; a jet of water or black soap deals with them.

Propagation

Remember first what does not work: sowing from seed. French tarragon produces no viable seeds. The packets of tarragon seeds sold in shops are Russian tarragon, another plant, hardier but completely without flavour in cooking. This is the classic trap; always buy a young plant in a small pot, never seeds.

Real propagation is done by root division, in spring or early autumn: dig up the clump, split it into pieces bearing roots and replant at once. This is also the action that regenerates an old plant. Taking stem cuttings in summer, in a sandy mix kept barely moist, also works and gives new plants true to the mother plant.

Month-by-month care calendar

Green Hub tips

• Never buy tarragon seeds: it will be Russian tarragon, flavourless. Get a French tarragon plant in a small pot, from a garden centre.
• What kills tarragon is water, not cold. Drain the soil and mulch the base as winter comes in to get it through the cold season.
• Divide the crown every three years in spring. The clump exhausts itself and turns woody at the centre, division regenerates it and gives you new plants.
• On heavy, damp soil, grow it in a pot: you will be able to bring it into the dry and cold in winter rather than risk losing the plant.