Astilbe is a perennial plant that will bloom in the summer with tall flumes in shades of white, pink, red and purple. This is a shade loving plant that prefers wet soil and lots of fertilizer. Feed the astilbe every two weeks during the growing season with a 5-10-5 fertilizer, according to package directions. The various colors you can choose from will make it difficult to decide just what plants to grow as companions, as there are so many that will complement or provide a lovely contrast. Just make sure that any companion plants have the same, or similar, requirements for water and fertilizer. Astilbe is hardy to USDA Zones 4 to 8.
Hosta is grown for its beautiful foliage; some varieties are variegated, others solid, some with almost blue leaves. Planted in front of astilbe, the contrast would be very attractive. For best results, grow hosta where it will get morning sun and afternoon shade. Give it an inch of water a week and fertilize once in the spring and then again in the middle of the summer with the same fertilizer you use for the astilbe, and the hosta will do well for you. Hardy to USDA Zones 3 to 8.
Ligularia is a perennial plant that produces tall spikes of attractive yellow flowers. Planted behind the astilbe you will get an instant shot of color in a somewhat shady spot in the garden. Water and fertilizer requirements are the same as for the astilbe. Ligularia is hardy to USDA Zones 4 to 8.
Impatiens seem to be everyone's favorite shade plant, and for good reason. They are colorful and very easy to care for. Choose white impatiens if you are growing the deep purple astilbe. Impatiens like plenty of water and fertilizer, 5-10-5 every month. Impatiens is hardy to USDA Zone 7b to 11.