Scutellaria alpina, the alpine skullcap, is a species of flowering plant in the mint family, Lamiaceae.
This can be given perhaps every 3 or 4 weeks or so when watering during the growing season. The aim is just to keep the plants healthy and active in their limited volume of soil, not to encourage lush, rapid growth - hence the use of fertilisers at low rate only.
These plants are known for being fairly hardy when it comes to experiencing drought or cold temperatures.