Tansy is an old herb and cottage garden plant — flat clusters of bright yellow button flowers on aromatic foliage that smells strongly of camphor when bruised. The flowers are similar in form to feverfew and chamomile but larger and held in flattened corymbs atop tall stems. It blooms from midsummer into autumn and is virtually indestructible.
As a cut flower, the button-like yellow clusters add a wild, naturalistic quality to summer arrangements alongside coneflower, scabiosa, and grasses. Note: tansy can spread aggressively by both rhizomes and seed — plant where you can manage it.
Aphids
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.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
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.