Perennials are return again mainstays or backbones in the garden. Popular perennials include hostas, coneflowers, and daylilies. These flashy plants will live for many years if the conditions are favorable and if they are not overcome by pests or disease. Now that I've introduced what a perennial is, given examples of perennial types, and put my two sense to our delight for them in the garden border that leaves the title question... Is it okay to plant perennials in the fall? The answer being absolutely and most definitely!
Berry Smoothie Heuchera (fall foliage)
Fall is a great time for perennial planting and the lazy gardener, like myself, likes the cool temperatures, warm soil, and even soil moisture to establish these plants with ease. In fall you literally only have to prepare the site, including fertilizer, plant, and water in once. Mother nature can take care of the remaining watering. This is kind of similar to the spring, but the warm trends of early summer may warrant the need to water more often. In fall roots are able to stretch out, establish themselves, and to further expand in early spring making them more drought tolerant once summer comes.
Heath aster (fall blooms)
The best time to plant in fall is 6-8 weeks prior to your ground freezing solid. This gives the roots ample time to strike out before the ground freezes. Earlier is just as good too. If the ground in your area doesn't freeze solid you can plant all fall and winter, though make certain the perennials will thrive in your area by checking the hardiness zones. Some perennials do not do well in warm climates.
Amsonia 'Blue Ice' (fall foliage/great roots)All in all, fall is great time to enjoy all the colors and coolness while you are planting and planning next years garden.
Enjoy your fall, David Burton