Sow the seeds in plug trays or flats containing a mixture of equal portions of peat and vermiculite and barely cover them with clean sand or vermiculite. Water the trays or flats from the bottom, and place them under a mist system or cover them with plastic. Germination of Achillea species is improved by exposure to light. Fertilize seedlings with 100 ppm nitrogen until plants are ready to be placed in the field. Do not fertilize the plants once they are in the production beds.
Excessive fertility causes weak stems and poor flower quality.
Place transplants in production beds in early May, approximately 8 to 10 weeks after seeding. Division Divide yarrows any time before or after flowering, although early spring is the easiest and most reliable time. Divide established A. millefolium and its hybrids every 2 to 3 years and A. filipendulina selections every 3 to 5 years to maintain plant vigor. As plants become crowded, disease problems increase and flower size and quality decrease. Grade the divisions.