About the timing of pruning, seasonal rhythms and long term thinking
It’s been a fragrant past couple of weeks in Grimsby.
A succession of fragrant shrubs have been in bloom, from Korean spice viburnum to lilac to the lovely dwarf Korean lilac. These early blooming shrubs are now approaching the last of their blooms.
Once the last of your Korean spice viburnum or lilac blooms fade, or any of the early blooming shrubs for that matter, including the earlier forsythia, now is a good time to prune.
Shrubs that bloom this early in the season did not have time to form blooms this year. Instead, they adapted to form blooms on last year’s growth. This makes the timing of your pruning particularly important.
It’s not complicated. It just means that the timing of your pruning will affect what your shrub will look like next year.
The easiest way to go about it is to remember when your spring shrub is done blooming. That is a great time to prune it.
Don’t wait until the end of summer. You’ll cut off all that new growth that would have been setting next year’s blooms.
A useful reminder is the natural act of deadheading. Once your blooms are finished, you may already be reaching for your secateurs to remove the bent brown lilac blooms. With pruners in hand, you can give the rest of the shrub a trim as well. Prune to size if it has overgrown its area. Prune to shape if you are looking for a different form. Or simply maintain its shape by adjusting where the new growth will appear.
This is also a good opportunity if you have an early blooming shrub hedge. Forsythia is a good example. Once it finishes blooming, which happened a few weeks ago, you’re good to hedge it.
There is an interesting effect that happens if you prune immediately after bloom. There will often be new growth, and that growth may overshoot the space you have available. Your lilac may put out shoots that extend beyond its current location.
That does not mean later trimming is forbidden.
I’ve noticed that shrubs that bloom on old wood will often still bloom even if you remove a little of that newer growth. You just do not want to remove all of it.
That becomes especially important in older hedges that are too thick to let sunlight into their interior, where new wood may already be struggling to set.
So if you’re wondering, yes, you can always chop a branch later. It’s not going to prevent the entire shrub from blooming the following year.
But if you give it a solid haircut late in the season, you are removing next year’s blooms.
Every shrub is slightly different. Some put out a lot of new growth from the base. Others continue mostly from established stems.
So even though the rule is general, and shrubs that bloom on old wood bloom on previous year’s growth, it helps to observe your own shrub and see what that means in your specific scenario.
Gardening is a practice that happens over years and features a lot of slow repetition.
If you’re new to gardening, know that pruning at the wrong time will not kill the shrub.
If you need to make an emergency intervention and remove half your lilac because it has overgrown its space and you have to do it in August, you may not have blooms the following year as the shrub recovers.
But the shrub is by no means dead.
That absence of blooms is often the feedback that tells you your timing was a little off.
You can adjust from year to year.
Most of our lives do not happen on such a long timescale. Gardening often happens in a single action repeated once a year. To make adjustments, you make that adjustment a year later.
Shrubs are not the only thing getting pruned right now.
As the weather has been good and we’ve had both a lot of rain and a lot of heat in Grimsby, perennials are racing towards the sky.
Some of the early blooming perennials, such as peonies, are now in full bloom.
However, your later blooming perennials, such as agastache, Joe Pye weed, Autumn Joy sedum, and perennial mums, are still mostly putting out foliage and have not started setting blooms.
If they are getting large and you would like to keep them a little more compact, or if you would like to increase the quantity of blooms, now is a good time for what some call the Chelsea chop.
In essence, this means pruning your perennial by about a third of its current height.
This encourages branching.
Where you make one cut, instead of having one stem continue, you may have two, three, or even five stems emerge.
Each of those stems may now set a bloom.
Depending on the plant, you may end up with more blooms overall. Some may be smaller, but the overall effect is larger.
Joe Pye weed is a good example. If happy, it often grows in whorls of five. Wherever you cut, you may get five new stems, each producing a bloom.
The trade-off is that the plant now has to gather resources and produce all that expanded growth.
In many cases, that trade-off is desirable.
Plants such as Autumn Joy sedum and mums bloom late already. Delaying them by a week or two can extend your bloom season significantly.
This matters in Canadian regions where bloom time is already limited and truncated by the arrival of cold temperatures.
Not all perennials respond equally well to the Chelsea chop. Some do not need it at all.
The four above are particularly happy with a good cut.
We have a large Joe Pye weed at home and last year I gave it a partial cut simply to reduce its size.
It responded very well. There were more blooms, and they appeared slightly later than the untouched sections.
This year I pushed the experiment further.
I left the center crown untouched.
Around it, I gave the surrounding stems a light chop.
Then the outer ring of the clump received a deeper cut.
What should happen now is three layers of bloom timing: untouched, shortened, and deeply shortened.
Because the clump is circular, I’m curious whether they will all bloom together a little later, or whether the bloom will stagger between the different layers.
I’m looking forward to August.
As the shrubs fade and the perennials grow, you may also notice that hedges have really filled in.
Specifically, yew hedges are now wearing a bright lime green coat.
That lime green is the new growth.
Yews usually have one strong flush of growth per season, and it happens right about now.
I could hedge them now.
But I’ve noticed that if I jump the gun and hedge too early, there is still quite a bit of energy left in the plant and it feeds another flush of growth.
That means touch-ups later.
A good rule of thumb is to watch for the lime green to begin turning darker.
It does not have to fully transition before you start hedging, but that colour shift is an indicator.
If you hedge as soon as the lime green starts looking scraggly, that is fine, especially in a small garden where a second trim is easy.
If you enjoy that bright green, you can leave it until it disappears and prune later.
I usually prefer the middle ground.
One cut, but before the hedge looks untidy for too long.
It depends on the style of your garden.
Formal gardens benefit from earlier hedging.
Wilder gardens tolerate later hedging.
Weather matters too.
Hedging, like any pruning, is mildly stressful for the plant.
If conditions are dry and hot, it may be worth waiting until after rainfall.
If the hedge is healthy and irrigated, sometimes the practical reality of your schedule wins.
There is usually an in-between.
In this in-between period where spring turns into summer and many plants are in transition, the timing of your actions can change your garden significantly.
But it is not difficult.
The plants will tell you when they are ready.
And remember there is flexibility as well.
We all lead busy lives and sometimes the available moment is not the exact right one.
But it often is not the wrong one either.
It may simply create a slightly different effect.