Astilbes require copious moisture to thrive in the landscape; in fact, a rain garden is an ideal setting for these plants. Adding humus to the soil and using mulch generously will help keep the root system moist for healthy plants. All impatiens are easy to grow from seed, if you start them indoors about two months before last frost. Impatiens like ample amounts of water, and even do well on the banks of streams and ponds. Sweet violets can be invasive, so you may need to take steps to keep them in bounds. Plants spread by prolific self-seeding, and deadheading the tiny plants is tedious, so a heavy mulch will reduce (but not eliminate) the spread of the plants. Yanking small seedlings when they emerge will also keep them from creeping into lawns or neighboring garden areas.
