The best days of the year for planting

Mark Cullen gets to work in his garden. Submitted photo.

“At the plant we planted a plant.”

Interpretation: At the factory we put a botanical species in the ground.

The English language is confusing, but some thoughts are not so hard to express. Such as, “fall is for planting”.   Autumn arrives this coming Wednesday September 22nd.  We recommend that you circle the date, the second equinox of the year.

Plants know all of this.  Their calendar is set by day length and is engineered into their DNA.  Therefore, a lilac that normally flowers in May will sometimes produce flowers in late September when the day length is about the same as their spring flowering period.  Their natural system for telling time is not foolproof.

Truth is, these are the best days of year for planting, bar none.   As the days shorten and temperatures adjust downwards, the soil holds an abundance of warmth accumulated in the summer which encourage roots of winter hardy trees, shrubs, and perennials to develop even while the top portion of the plant is finished growing for this year.  The new roots support new growth come spring, which is why a fall planted tree, for example, will often outgrow a spring planted tree of the same size and species.

Coincidentally, this coming Wednesday is National Tree Day here in Canada.  Not only is it one of the best days of the year to plant, but it is also recognized through an act of federal parliament as THE day of the year when we pause and celebrate the role that trees play in our lives.

They sequester carbon and produce oxygen and they provide many more useful functions.  While we spend our days on other distractions like working for a living or playing golf, trees are filtering toxins out of rainwater, providing habitat and breeding grounds for wildlife, cooling the atmosphere, and generally making the world a better place to live.  Indeed, it is because of trees that our world is liveable at all.  

The best-selling author Peter Wohlleben in his landmark book The Hidden Life of Trees noted that trees create rain.   If we were to cut down all the trees in North American, rain would only fall in the 50 kilometres closest to oceans and large lakes, where open water helps to create clouds.  The rest of our continent would be a desert, just as the Sahara is a desert now. A long time ago, the same Sahara was a jungle in which a lot of rain once fell.  People cut down the trees to create grazing land and, well, here we are.

Planting a tree any time is a good idea, but planting a tree now is the best idea of all.  Same can be said for planting flowering shrubs and perennials.   The same principles apply.  Which is why it is also a good time of year to dig up and divide perennials.  Any perennial with a fleshy or fibrous root system that holds together when you dig it up will work.   This is the best time of year to dig up peonies, divide them with a sharp knife or spade and either move the root clumps around your yard or give them away.  Be sure to plant peonies with the top of their roots no more than 10 centimetres deep in their new soil and if the soil is heavy and clay-based plant them only 4 or 5 centimetres deep.  

Fall is a good time to transplant young shrubs, trees, and evergreens also.   Note that the more fibrous the root system, that is, the denser and hairier the root structure, the more it lends itself to moving around your garden.  A shrub like burning bush or an evergreen like boxwood can be a decade old and still transplant well.   A root of heavy wood, like that of walnut or chestnut, will not transplant well at any time.

Birch and oak trees are best to dig and replant in spring.  We have not figured out why this is so, experience just tells us that it is.

There is no substitute for experience, we have observed. It was experience down countless generations that taught plants how to deal with the marvels of autumn.

Mark Cullen is an expert gardener, author, broadcaster, tree advocate and Member of the Order of Canada. His son Ben is a fourth-generation urban gardener and graduate of University of Guelph and Dalhousie University in Halifax. Follow them at, @markcullengardening, and on Facebook.