Fall Planting in the North
I just came home from a road trip with a load of terrific end-of-season sale perennials. The conventional wisdom used to be that fall planting in the colder zones was chancy, but by paying attention to the details and being faithful with the after care, the odds can be very favorable. The only exceptions are marginally hardy plants that you might want to try. Those need an entire growing season to establish first.
Timing is important in fall planting. New perennials should be in by Sept. 15. Evergreen trees and shrubs should be in no later than October 15, but deciduous trees and shrubs can go in up until the ground freezes. The further north you live, the sooner it must be. The herbaceous plants (perennials) must get their roots established before the ground freezes. That doesn't happen overnight. If you do plant later for some reason, be sure to pay attention to the section on mulching and cross your fingers, your odds are getting worse.
The ways to go about improving your odds depend largely on which came first, the horse or the cart? If you have the choice, choose the plant for its suitability to the site where you will plant it. However if, like me, you bought on impulse, we must hope we have a suitable site. Ordinarily, I stick things into open spots in the garden until I find the perfect place sometime later. Some perennials, though truly cold hardy enough for our zones, cannot tolerate wet roots in winter. Delphiniums and lavenders come to mind. If the soil is clay you may be out of luck hoping to establish these plants now. If the soil conditions such as pH or texture must be changed for the plants to succeed over the long term, then fall is not a good time to plant them.
When planting in the fall, don't get into such a hurry that you forget to properly prepare the planting hole. Research in recent years has blown away a lot of conventional wisdom about planting. Plant trees and shrubs with their root flare at the soil line. This is not necessarily the soil level in the pot or on the root ball. Hurried or sloppy work during the production of the plant often leaves it too deep. The greatest cause of failure to thrive and early decline in woody plants is problems associated with being planted too deeply. Some perennials also are sensitive to the depth of planting. Peonies are especially sensitive, but Iris and Dicentra are too.
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