Sorrel is a hardy perennial herb grown for its tart, lemony leaves, used in soups, sauces and salads and in the classic sorrel soup. It is one of the earliest greens of the year, up as soon as the ground thaws, and it tolerates cold well, which makes it useful when little else is ready.
Plant it once and it returns each year. Sow in spring or set out divisions 12 inches apart in sun or part shade; it tolerates clay and ordinary soil. Harvest the young leaves for the best flavour and texture, cutting from the outside, and pull the flower stalks as they appear so the plant keeps making leaves instead of seed. In hot weather the leaves toughen and turn more acid; a summer cutback brings a fresh flush in fall.
Divide the clump every three or four years to keep it vigorous. The leaves are high in oxalic acid, which is where the sourness comes from, so it is a seasoning and a soup green rather than a salad bulk. Slugs like the young leaves. Rabbits and deer will graze it, so it belongs inside the fence.
Rust
Orange to brown raised pustules on the undersides of leaves, with yellow spotting on the upper surface. Heavy infections cause leaves to yellow and drop.
Remove and destroy infected leaves. Avoid overhead watering and improve air circulation. Apply a sulfur or copper-based fungicide if it spreads. Clear plant debris in fall.
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.
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.