Native to southern Europe and southwestern Asia, creeping St. John's wort is a low, mat-forming shrub with evergreen to semi-evergreen leaves and 3-inch golden-yellow flowers, each with a brush of stamens, through summer. Red-brown seed capsules follow.
It earns its keep on dry banks and in dry shade where little else grows, and it knits together fast. That speed is the catch: it runs by rhizomes and stolons and will cover more ground than you gave it. Give it a boundary, or plant it where a mower or edging can hold the line.
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.