Fall is such a comfortable time to get a jump on garden activities, with moderate temperatures, sunny skies and gorgeous fall colours to encourage us!
Autumn really is a good time to plant hardy perennials, as the air temps are moderate (even during heat waves like we are having now, things cool off nicely at night) and the ground is really warm (encouraging root development). Perennials that are hardened for outdoors can in fact be planted well into fall, but the very comfortable conditions right now make it a win-win for plants and gardeners alike.
Tip # 1 - Definitely water
Newly establishing perennials always require watering, and this includes fall-planted material. Add water to the planting hole, backfill to complete planting, then water the soil. Re-water daily for about a week (unless it pours rain). Even if air temperatures get cool your plant's roots need hydration as they settle into their new home and start growing. Once soil starts freezing, there is no more need for water.
Tip # 2 - Don't cut plants back
There is great polarization between gardeners who trim everything down in fall and those that leave perennials standing until spring, but it is safe to say that newly planted hardy stock should be left alone. If you prune these plants back now they risk being stimulated to re-grow, just as they need to be settling into dormancy. Leaving top growth standing also encourages snow cover, which is never a bad thing for perennials in our climate.
Tip # 3 - Break open roots at planting time
This rule applies to planting any time of the year, but you may find perennials and shrubs are extra root-bound in their pots when purchased in fall. It is essential to open these roots up when planting, otherwise, the root system may not take in the new planting hole - potentially causing winter kill or at the very least a stunted plant.
Some perennials have extremely dense roots. As an example, many of the grasses cannot easily be opened up by simply pulling roots apart by hand. In this case, it may be necessary to use a garden knife or even a small saw! Don't worry about damaging roots - it is healthy for them to be handled.
Originally posted on September 26, 2021