Pruning Forsythia

Erika and I were talking about forsythia shrubs today. A few years ago I bought 2 bare-root forsythias. They came up and leafed out the first spring, came up and leafed out the second year and this year, they winter-killed. No idea why. According to my well-thumbed book, Tree & Shrub Gardening for Alberta by Don Williamson (a very informative book), forsythias “quite happily survive in zone 3.” The ‘Northern Sun’ and ‘Northern Gold’ species are hardy ranging from -33⁰ to -35⁰ C. I believe we are zone 2b, and I know that Zone 3 shrubs will survive very nicely in Central Alberta.

Today, Erika talked about the poor performance of her forsythia shrubs. We both believe that it comes down to pruning. This is what my guide states: (p. 165)

“Correct pruning is essential to keep forsythias attractive, but prune young plants only minimally. Flowers are usually produced on growth that is at least two years old. Mature plants should be thinned annually, removing old wood back to vigorous shoots and removing one or two of the oldest stems to the ground. Pruning should take place after flowering has finished.”

Tips for winter survival – these flowers grow best when the shrubs are buried under a protective layer of snow: “As long as there is dependable snowfall, simply pile some salt-free snow over your hardy cultivar in winter to enjoy flowers each spring.” If this protective layer is not provided, “a shrub may flower only on the lower half that was buried in a protective layer of snow.”

So this August I purchased a forsythia again, but this time in a container, a New Hampshire Gold. We will see how it survives the winter.