French tarragon is a sterile perennial herb that must be propagated by division or stem cuttings — it produces no viable seed. It differs fundamentally from Russian tarragon, which is seed-grown but lacks the pronounced anise character that makes French tarragon indispensable in classical French cuisine: béarnaise sauce, fines herbes blends, and tarragon vinegar.
Plants thrive in lean, fast-draining soil and decline quickly in wet or overly fertile conditions. They go fully dormant after hard frost and re-emerge in mid-spring. Clumps become woody after three to four years and should be divided to maintain the vigor and flavor intensity of the foliage. In zones 4–5, a layer of dry mulch over the crown after dieback reduces winter heaving.
The primary flavor compound is estragole, also called methylchavicol. Herbalists have traditionally used tarragon to stimulate appetite and ease mild digestive discomfort. A fresh leaf applied directly to the gums was a folk remedy for toothache, attributed to mild numbing properties.
Clubroot
Swollen, distorted roots; wilting in midday heat; stunted growth and yellowing foliage. Plants recover poorly even with watering.
Remove and destroy infected plants with roots. Raise soil pH toward 7.2 with lime. Improve drainage and rotate out of brassicas for several years.
Black Rot
Yellow, V-shaped lesions spreading inward from leaf margins, with blackened veins. Severe cases cause wilting and leaf drop.
Remove and destroy infected plants. Use disease-free seed, rotate brassicas on a 3-year cycle, avoid overhead watering, and keep tools and beds clean.
Downy mildew
Yellowing on top of leaves with grey-purple fuzz underneath. Spreads rapidly in humid conditions.
Remove affected leaves. Improve air circulation. Avoid overhead watering. Copper spray as preventive.
White Rust
Raised white to cream-colored pustules on leaf undersides, with yellow blotches on upper surfaces. Infected tissue may swell or distort.
Remove and destroy infected leaves. Improve air circulation and avoid overhead watering. Rotate brassicas and avoid planting in previously infected soil.
Alternaria blight
Brown circular spots with yellow halos on leaves; spreads rapidly in wet weather.
Remove affected leaves immediately. Water at the base only. A copper-based fungicide can help if caught early.
Damping Off
Seedlings collapse at the soil line with thin, water-soaked stems; seeds may fail to emerge or rot before sprouting.
Sow in well-draining mix, avoid overwatering, and ensure good airflow. Remove affected seedlings and let the surface dry between waterings.
Root-Knot Nematode
Swollen galls on roots, poor vigor, wilting in heat, and reduced fruiting. Containers and sandy soils are more prone.
Use clean potting mix in containers. Avoid replanting in infested soil. Maintain plant vigor with mulch and steady watering. Solarize affected garden soil.
Cabbage Worm
Pieris rapae →Ragged holes in leaves and green velvety caterpillars on undersides; dark green frass collects in leaf crevices and head.
Handpick caterpillars and eggs. Apply Bacillus thuringiensis (Bt) weekly during egg-laying. Use floating row cover to exclude white cabbage moths.
Flea Beetle
Alticini →Small round shot-holes scattered across leaves; tiny dark beetles that jump when disturbed. Heavy feeding stunts young plants.
Use floating row covers on seedlings. Remove crop debris and weeds that harbor beetles. Apply kaolin clay or spinosad if damage is severe.
Aphids
Aphididae →Clusters of small soft insects on new growth and flower buds.
Knock off with a strong jet of water. Ladybirds and lacewings are natural predators. Insecticidal soap as last resort.
Cabbage Root Maggot
Delia radicum →Seedlings wilt suddenly despite adequate moisture. Roots show surface scarring and interior tunneling from small, creamy-white larvae feeding at and just below the soil line. Young transplants may collapse and die; older plants produce stunted, loose heads.
Apply floating row cover immediately after transplanting to prevent adult flies from laying eggs at the soil line. Drench soil with beneficial nematodes (Steinernema feltiae) before planting. Remove and dispose of infested plants and surrounding soil. Rotate all brassicas to a new bed each season.
Cabbage Looper
Trichoplusia ni →Ragged, irregular holes in outer and wrapper leaves caused by pale green caterpillars that arch their bodies in a looping motion when moving. Heavy populations consume leaf tissue down to the midrib and bore into forming heads.
Apply Bacillus thuringiensis var. kurstaki (Bt) at the first sign of feeding, targeting larvae while they are small. Reapply every 5–7 days during wet weather. Use floating row cover to exclude egg-laying adults. Hand-pick caterpillars on small plantings. Parasitic wasps are effective natural controls; avoid broad-spectrum insecticides that kill them.