St John's Wort - Hypericum Perforatum
This is an attractive-looking, slender plant with bright yellow flowers that grows to a height of 30cm. For identification hold the tiny leaves up to the light to see the perforations. It is a valuable medicinal herb, used in homoeopathy. The oil is very effective rubbed into aching and tired muscles, and its tincture is a valuable antiseptic.
Sow outside in autumn or spring in any good garden soil, covering lightly. It grows in most garden soils in sun.