Every May somebody asks me when they should plant the tree they meant to plant last year.
May feels right. The garden centres are full, the weekends are long, and the tree is in leaf so you can picture it on the lot. I still plant in spring when that's the window we have. I would rather plant in September.
Not because spring trees fail. Because in Durham Region, fall is when a new tree spends its energy on roots instead of leaves, and roots are what decide whether that tree is still alive in three years.
What the Tree Is Actually Doing in September
Above ground, the canopy is clocking out. Below ground, the soil is still warm from summer and the air has finally cooled off. That combination is the whole argument.
A tree that goes in now does not have to push a full flush of leaves through a July heat wave with a half-formed root system. It can sit in warm soil and grow fine roots until the ground approaches freezing. University of Guelph work on root growth puts that cutoff around 4°C in the soil — which, here, is often late October or into November, not Labour Day.
Tree Canada's timing matches what we see on jobs:
- Deciduous trees: from leaf-fall until freeze-up
- Conifers: from early August through the end of October — they need to be in a bit earlier so they can anchor before the ground goes hard
- Container trees: any time the ground isn't frozen, if you water them like you mean it
On our lots in Ajax, Whitby, Pickering, and the rest of Durham, I treat early September through late October as the real planting window. After that you're gambling on freeze-up.
Why Spring Feels Better and Often Isn't
A May planting has to survive its first summer immediately. That means you, or us, on a hose, once or twice a week, through whatever drought July decides to be. Miss two weeks in a heat spell and a $400 tree becomes a $400 stick.
Fall planting still needs water — autumn here is often drier than people remember — but the demand is lower. Cooler air, shorter days, less leaf area losing moisture. The tree is building the root plate it will use next June, not fighting to keep last week's leaves turgid.
The other spring problem is the calendar in your head. People book planting when they think of it, which is when the forsythia blooms. By the time we get a crew and a decent tree, we're into the first hot week. Fall bookings are quieter, the nurseries still have stock, and we can put the tree where it belongs instead of wherever was left on the lot in May.
The Two Replacements I Will Talk You Out Of
Planting is not just a hole and a tree. It's what you put back after something died.
Don't drop a new maple in a maple grave. If the last tree on that spot coloured up on one side in August and we diagnosed Verticillium wilt, the fungus is still in the soil. A new Norway or Japanese maple there is a second funeral. We plant something that isn't on the menu — honeylocust, bur or white oak, ginkgo, a conifer — or we pick a different hole.
Don't assume a beech is a safe native swap. American beech is a beautiful tree and a bad 2026 bet if you're not watching the foliage. Beech leaf disease — a nematode, Litylenchus crenatae ssp. mccannii — has been in Ontario since 2017 and is now through the lower half of the province, including the Lake Ontario shoreline toward Peterborough. Dark bands between the veins, leathery or curled leaves, early drop, dead saplings in a few years. There is no homeowner spray that fixes it. If you already have a beech, we look at it. If you're about to plant one, we talk about something else first.
That's the same right tree, right place conversation we have on every new plant — soil, wires, salt, the neighbour's Norway maple, and whatever killed the last one.
How We Plant It So It Lives
Most young trees we get called back to didn't fail because of a disease. They failed because they were planted like a shrub.
- Find the root flare and keep it at grade. Too deep is the usual killer. The trunk should not look like a telephone pole disappearing into a volcano of mulch.
- Cut the circling roots on container stock. If you don't, they keep circling and girdle the tree in five years.
- Water deep, not cute. A slow soak that wets the original root ball and the backfill. A daily sprinkle on the mulch does nothing.
- Mulch a wide ring, not a pile against the bark. Three inches, off the trunk.
- Stake only if it needs it, and take the ties off before they bite in.
We put that in writing when we plant. The first two seasons are establishment. After that, a Tree Health Care look once a year catches the boring problems — girdling ties, a lawn mower kissing the flare, a dry July — before they become a removal.
What I'd Plant in Durham This Month
For a normal residential lot, these are the ones that keep earning their keep here: red oak, sugar maple (on a clean site, not a Verticillium hole), swamp white oak, serviceberry, eastern redbud, honeylocust, Kentucky coffeetree, white pine. Urban salt and compacted clay change that list. So does a hydro line.
If you want a tree under wires, say so before we pick a 60-foot oak. That's a pruning problem you can avoid for a few hundred dollars and twenty years of peace.
The Window Is Open Now
If the tree has been on the "next spring" list since 2024, this is the season that actually matches the biology. We can still get it in the ground before freeze-up. After that, we wait until the soil can be worked in spring — and then we're back to babysitting it through summer.
I would rather see the roots working in warm September soil.
Want a tree in the ground in Ajax, Whitby, Pickering, or anywhere in Durham Region before freeze-up? Book a free site visit and we'll tell you what will live there — and what we won't plant.
