Selecting Plants. Perennial flowers are sold both in containers and bare-root. Plants should be healthy and show no signs of disease or nutrient deficiency. Container grown plants should be removed from the container to examine the roots. Healthy roots should be white and be able to hold soil. Do not buy plants with dark colored and/or tightly coiled roots. Bare-root plants should be checked to ensure roots have not dried out and that the young shoots are not wilting.
Container Plants.> Generally, container-grown plants can be planted throughout the season. Most often they are planted in the spring. Perennials that are grown in the greenhouse should not be planted until after danger of frost (32ºF) has past, much like annual bedding plants and vegetable transplants. Container-grown plants that have been exposed to outside temperatures throughout the winter can be planted as soon as the soil can be worked, about the same time trees and shrubs are planted. Fall planting of perennials promotes development of roots before onset of winter.
Bare-root plants. To avoid drying out, perennials bought bare-root should be planted as soon as possible. Roots should be spread out and soil placed and firmed between them when planting.
Planting depth. A majority of perennials should be planted out at the same soil level as they were in their containers or grown at (bare-root plants).