First of all, perennials need a well-drained soil and need to be divided every 2-3 years or they start dying out because of over-crowded plants in clumps.
In preparing a bed where your perennials are going, you can dig up areas of 2 foot by 2 foot and add potting soil with worm kelp, gypsum, bone meal, and incorporate these with native soil to provide the media needed to grow the plants you’re looking for in your perennial flower garden.
Ratio and application amounts of potting soil with worm kelp should be mixed at about 1:1 with native soil. Gypsum applied at a rate of 16 ounces mixed into soil and come back after plants are in soil and apply at a rate of 2 pounds per 100 square foot and reapply in June, July, and August. Bone meal at about 4 ounces per hole, applied at the bottom of planting area and then place the plant in the soil and back fill.
All plants need to have roots cut and pulled apart so we remove the problem of root entanglement. Once plants are in the ground and watered, come back and apply root stimulator to provide nutrients and help new roots to be formed.
Here are some bullet-proof perennials for out in the country.