The perennials not to plant fall include tender varieties, late bloomers, and plants at the edge of their hardiness zone. These types need a full growing season to toughen up before facing winter cold. Putting them in the ground in fall often means losing them by spring.
I learned this the hard way with lavender in my zone 6 garden years ago. Three plants went into my beds in October, and none of them made it through that first winter at all. The same lavender planted in spring survived five years before I finally had to replace it.
Some plants fail in fall because they don't have enough time to grow roots before the ground freezes hard. Others get caught by freeze-thaw cycles that heave young roots right out of the soil over winter. Still others have their bloom cycle thrown off by late season planting stress.
University of Maryland notes that late summer and fall bloomers do best when planted in spring instead. These plants put all their energy into flowering at the same time they should be growing roots for winter. Moving them in fall interrupts this cycle and often kills them.
You should avoid fall planting perennials that sit at the edge of their hardiness range in your zone. Lavender struggles in zones 5-6 when fall planted because it needs that first full summer to harden off. Butterfly bush and tender salvias fall into this same risky group in cold areas.
Chrysanthemums are spring only perennials even though stores sell them in fall. Those fall mums rarely survive winter in your beds because they have no time to grow roots before frost. Buy your mums in spring if you want plants that come back year after year for you.
Skip fall planting for any perennial you just divided from a mature clump in late summer. Fresh divisions need time to recover from root damage before they can handle winter stress at all. Wait until spring to give your divided plants their best shot at survival in your garden.
Gaura and penstemons also make the list of risky fall choices in your colder zone garden. Some ornamental grasses do too when you're pushing their limits. These plants have borderline hardiness that makes fall planting a gamble for you each year.
Check your plant's hardiness zone rating before you decide when to plant it in your garden beds. Anything rated for your zone or colder handles fall planting well in most cases out there. Plants rated just for your zone work better when planted in spring to play it safe.
Save your risky plants for spring planting and stick to proven hardy varieties this fall instead. Your safe bets include hostas, daylilies, and coneflowers. Most ornamental grasses rated two zones colder than yours work great too. These tough plants establish fast and sail through winter without help from you.
Read the full article: When to Plant Perennials: Expert Guide
