Tips for a Thriving Perennial Garden:
Space perennial plants based on their mature size. Give them plenty of room to grow and spread so that they don't get overcrowded, as this leads to stress, competition for water and nutrients, and poor air circulation (which can encourage disease).
Water consistently and don't allow plants to wilt in between watering. Water often during the first growing season after planting. Established perennials are more drought tolerant and can be watered less frequently.
Perennials tend to bloom in cycles of 4 to 6 weeks, with a 2-3 week break in between. Deadhead and fertilize as needed after each bloom period and most will re-bloom.
Some (but not all) perennials need to be dug up and divided every 3 years or so to encourage renewed growth and vigor.
Remove dead plants and plant debris from the garden each fall as some diseases and insects can overwinter in debris and then reemerge during the next growing season to cause issues.