Globe thistle is one of the most striking plants available to the cutting garden — perfectly spherical, steel-blue flower heads the size of golf balls on tall, branching stems above deeply cut, silver-backed foliage. The blue is intense and unlike anything else; bees and butterflies work the flowers constantly. It is also one of the easiest perennials in difficult conditions: drought, poor soil, and neglect don't bother it.
Cut when the spheres are showing full blue colour but before they fully open. At this stage they last 7–10 days in water. For dried use, harvest slightly earlier and hang upside-down; the spheres hold their form perfectly.
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.
Crown Rot
Lower leaves yellow and wilt; the base of the rosette turns brown and soft, sometimes with white fungal threads at the soil line. Plants collapse in wet conditions.
Remove and destroy affected plants. Improve drainage and avoid overhead watering. Do not mulch directly against the crown. Space plants for airflow and avoid replanting in the same wet spot.
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.