How to boost Astilbe colour

Q: I have a few astilbe that originally had dark red plumes on them when they were planted approximately five years ago. Each year, the plants emerge and grow into large very healthy plants, with several plumes, however the plumes no longer show any color. They are simply a greeny-beige neutral colour. They are in partial sun, in good rich, well-drained soil, and get regular watering. They have never been fertilized. Do you think fertilizing them might help bring their colour back? —Lynn

Astilbes probably should be divided about every three to five years, anytime during the dormant period (November to March). This is to ensure vigour and flower quality. Incorporate organic matter when replanting newly divided astilbes. Every spring, apply a good layer of mulch (no more than 2 inches thick when settled but leave 2 inches from the crown) to help maintain soil moisture and nutrition.

Supplemental water is important during the growing season and must be consistently moist, especially if plants are in full sun. Use an all-purpose granular fertilizer, as directed on the package, early in the
growing season depending on overall plant health.

Astilbes will grow in either sun or partial shade.