Nepeta 'Walker's Low' is one of our favourites, we use this at every Chelsea Flower Show as it's flowering right on time, and is such a beautiful plant to accompany other herbaceous perennials, especially iris. It starts flowering in May and continues for weeks, when its finished flowering cut it right back and it will have a second flush later in the year. This plant is highly attractive to bees. Plant in full sun and a well drained soil. Height and spread 40-50cm.