Are your astilbe (Astilbe) plants growing directly beneath the tree? Any plants grown directly under trees tend to suffer because trees have extensive root systems. As a result, the tree roots absorb the majority of water and nutrients in the soil. This is particularly distressing to astilbe, which prefers moist soil. Unfortu-nately, there's little you can do short of moving your astilbes to a spot where they'll have moister soil and replacing them with a plant that better tolerates dry conditions. Do you know what variety you are growing? Different astilbe varieties have varying amounts of fullness to their plumes. Many newer hybrids have larger plumes. It could be that your astilbe plumes are opening fully but are not as large and colorful as other types you've seen.