Meadow sage (Salvia nemorosa) is the hardy perennial salvia of the border: upright spikes of violet-blue, purple, pink or white flowers, 18 to 36 inches tall, over aromatic grey-green leaves. It is reliably cold-hardy to zone 4, tolerates heat and drought once established, and bees, bumblebees and hummingbirds work it from the first spike to the last. 'Caradonna', 'May Night' and 'Blue Hill' are the standard cultivars.
It blooms in early summer and reblooms if you cut the spent spikes back to the basal leaves as soon as the first flush fades; a plant sheared by half in midsummer comes back for a second show into fall. Give it full sun and soil that drains, 12 to 18 inches apart, and water only until it is established. Wet, heavy soil in winter is the usual reason a salvia dies, not cold.
It stays in a clump rather than running, and deer and rabbits leave the scented foliage alone. Divide every three or four years in spring when the centre opens up. It pairs with anything yellow or silver, and its spikes read well against the mounded forms of catmint and lady's mantle.
Root rot
Plants wilt, yellow, and stunt even in moist soil; lower stems and roots turn brown, soft, and mushy and the plant may collapse. Most common in heavy, wet, or poorly drained ground.
Improve drainage and stop overwatering, and never plant too deep. Lift and destroy badly affected plants along with the soil around the roots. Grow in raised or free-draining beds to prevent it returning.
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.
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.