Yarrow, sometimes known as sun fern for its high light requirement and fern-like foliage, is an herbaceous perennial plant valued for its aromatic, ornamental flowers. The yarrow plant can reach up to 3 feet in height and develops flat, dense clusters of flowers in spring, summer and fall. Yarrow flowers are most often white, but they can also be yellow, orange, pink or red. Yarrow plants are hardy in zones 3 through 9, and require very little care to thrive in the home garden.
Purchase yarrow plants in spring or fall from a nursery or garden center. They are typically available as started plants in 1- to 6-gallon containers. Choose a planting location that receives full sun and has well-drained soil of average fertility.
Prepare the site by cultivating the soil to a depth of 6 inches with a garden tiller. Dig a planting hole of equal depth and twice as wide as the plant's current growing container. Place the yarrow plant into the hole, back-fill with soil and water thoroughly. Space plants 18 inches apart to allow room for growth.
Water yarrow plants only after the soil has completely dried, about once per week during spring and summer. Reduce the frequency of watering during fall and winter to once every two weeks, or any time the top 2 to 3 inches of soil are dry to the touch.
Remove spent yarrow flowers after they have faded to encourage further blooming. Cut back the dead flower clusters with pruning shears or pinch off with your fingers if possible. In some cases, deadheading may result in a second bloom in fall.
Stake tall yarrow cultivars to prevent them from falling over or drooping when they become too tall. Place a flower stake in the ground 1 to 2 inches from the base of the plant and secure it loosely to the stake with garden twine for the best results.