Seasonal Pruning for Size Control

(Originally posted: April 21, 2020)

After reading my last post, you may have been left with a burning question “don’t different trees and shrubs get pruned at different times of the year?”

The answer is yes, BUT… (and you knew that ‘but’ was coming didn’t you?) in the last post we were only discussing the removal of undesirable branches- ones that should be removed to promote good health and proper structure of our trees and shrubs. We were not discussing routine pruning for size control or rejuvenation of our plants. For this type of pruning the timing is everything… so let’s start that discussion here!

Old Wood vs. New Wood

To understand pruning times, we must first discuss the type of wood that trees and shrubs will bloom on. Let’s start with the seemingly not-so-straightforward woody plants: the ones that bloom on old wood. In these plants, flower buds were set last season and it is those buds that will bloom this year. Many of our showiest landscape plants (such as magnolias, serviceberries, dogwoods, lilacs, and rhododendrons) fall into this category, and if you look around the neighbourhood (while social distancing of course), you can often see these buds getting plump and ready for their floral frenzy.

Flower buds on a Cornus kousa (Kousa dogwood) getting ready to pop!

So what happens when you go crazy and do a size-reducing spring prune on these spring-blooming beauties? You remove all their flower buds! (The horror!) So leave these plants alone! In general, these trees and shrubs get pruned right after their bloom period has wrapped up- which also happens to be before they start setting their buds in preparation for next year’s show. So, at this point in the season, we only remove the undesirable branches. Yes, you will sacrifice some blooms by doing this, but don’t forget this is for the health and structure of the plant… we leave the size control (if necessary) for later in the growing season.

An assortment of spring beauties- none of which are pruned until after their flower show (if pruning is necessary)!

OK. So the hard part is over (phew). Let’s move on to the easy plants: trees and shrubs that bloom on new wood. These plants set their buds and bloom on those buds during the same growing season. Because these plants have quite the ‘to do’ list to accomplish before they can actually show-off their blooms, these plants are generally summer-flowering (at the earliest). For these trees and shrubs, the time to prune is now! Seize the day and prune away! No time like the present… OK you get the picture. Some common examples of these plants include:

• Hydrangea arborescens (such as the common ‘Annabelle’ hydrangea); shown below

• Hydrangea paniculata (such as the common ‘Grandiflora’ or Pee Gee hydrangea)

• Buddleia spp. (butterfly bush); shown below

• Caryopteris incana and Caryopteris x clandonensis (bluebeard); shown below

• Hibiscus syriacus (rose of Sharon)

Hydrangea arborescens still standing in the spring with it’s pretty dried flowers that provided some interest in the garden over the winter months (left) and another patch of H. arborescens that has been cut down for the spring (right, foreground). This patch is located in a common area so tending to these plants is not really an option for me, but if it were, I would be inclined to prune these shrubs back even further- cutting each stem just above a pair of buds located 10-20 cm up from ground level (oh, and I would remove all the leaves caught up in the base of the plants too!)

A Buddleia (butterfly bush) before and after pruning. Yes they get pruned HARD; pruned down to about 20-30 cm (8-10 in) with all weak growth removed. The photo on the right shows the shrub after some additional branches were removed to achieve a more uniform distribution of branches.

Spring pruning of Caryopteris incana ‘Jason’ (Sunshine bluebeard). Shown during it’s glory days last season (top left) and the same patch after spring pruning (top right)- not much left to see! The best way to tackle this shrub, in my opinion, is to grab a handful of branches and cut the whole thing down by half (bottom left); this removes bulk and allows you to ‘see into’ the shrub better so that the strongest stems can be selected to remain; old, weak, and dead stems can then be pruned out until you are left with a simple branching framework. The plant can then be taken down to a height of 20-30 cm (8-12 in) tall (bottom right).

And there you have it! Hopefully these last two posts have helped shed some light on the various goals of spring pruning. I will continue to provide more examples of pruning in future posts.

It’s now time to head back to the garden, secateurs in hand, and get to work on all those woody plants that flower on new wood.

Have fun and happy gardening!

Temper your Enthusiasm

(Originally posted September 15, 2019)

The crisp nights and cooler days have arrived- a sure sign that fall is around the corner. Fall is generally a time of yard work and many people become very enthusiastic to tackle outdoor chores- even people with no interest in their yard whatsoever throughout the rest of the year tend to catch the ‘gardening bug’ during the autumn months. Often this enthusiasm is directed at whacking back various trees and shrubs in their yard. While there is certainly lots to do before the snow flies, pruning is the one task that we want to minimize at this time of year. (Sorry Edward Scissorhands wannabes!)

Let’s start with the effect that pruning has on a tree or shrub… it promotes new growth. New growth is tender and needs time to toughen up to the environmental conditions around it. At this time of year, our frosty mornings are just around the corner. If we prune now, new growth that emerges will not have the time to properly harden off before the cold weather hits, which can ultimately lead to death of the new plant tissue… therefore you will get dieback. On deciduous trees and shrubs (ones that lose their leaves for the winter), this dieback would be apparent in the spring; on evergreens it could become obvious during the fall and winter months. Dead new growth is not the nicest thing to look at on a plant that is supposed to stay green for the winter!

Furthermore, plants are using this time to start shutting themselves down for the winter. They are gathering sugars and carbohydrates from their leaves and storing them in their stems, trunks and root systems; valuable energy to help the plant survive the winter and flush out new growth in the spring. Removing the leaves before they fall doesn’t allow the plant to relocate these sugars to their ‘winter storage facilities’ and therefore the plant is robbed of it’s energy sources for the months ahead. Additionally, the stimulation of new growth through pruning counters what the plant is trying to do. Instead of putting energy towards properly ‘shutting down’ it is putting energy towards new growth; this can weaken the plant going into the winter.

While it is true that plants can rebound from a late season prune, it is not an ideal time for this gardening task.

So… if you feel the call of the pruning saw, hedge shear or lopper- ignore it! Opt to warm up some apple cider, mosey through the garden, and start your ‘to do list’ for next year. Those shrubs and trees that you are just dying to hack back now will still be there in the spring and they can be first on your ‘hit list’ for a dormant season prune come a mild day in March***! Not to mention, with all that energy [properly] saved-up for a spring flush, the plant will be able to quickly rebound from your ‘haircut’.

Can you hear that?

That is the sound of your shrubs and trees breathing a huge sigh of relief.

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***While any plant can be pruned in the dormant season, it is important to note that if you prune anything that flowers early in the growing season, you would most likely be removing flower buds. For these plants it means that a hard prune = no flowers for the upcoming growing season. While some people may gasp in horror at the thought of this, sometimes it is a necessary evil in order to renovate an overgrown shrub. More on pruning and timing of pruning in future posts… I promise!

Remember these early season beauties? A prune at this point in the year (or any time leading up to their flowering period) would remove their flower buds. Believe it or not, plants such as these are already prepared for their 2020 show!

Clockwise from top left: lilac (Syringa sp.), serviceberry (Amelanchier sp.) magnolia (Magnolia sp.), Dogwood (Cornus sp.)

Deadheading Technique #2: The Haircut

(Originally posted: July 27, 2019)

We are still in the thick of summer deadheading- the constant attempt to tidy perennials, prolong their bloom or encourage a repeat bloom (depending on the perennial). If you like non-precise gardening tasks, this type of deadheading is for you! I call it ‘the haircut’ but it is also called shearing.

Remember our catmint (Nepeta) friends?

Well here are the three amigos again; one plant has already been sheared (a week prior to taking this photo), and two are still waiting in the foyer, reading their magazines, patiently waiting for the hairstylist (me)… who is taking her sweet time in completing the task!

I am going to keep this super easy: this deadheading technique involves grabbing a handful of stems and cutting them shorter. If there is new growth emerging from the base of the plant, you will want to avoid cutting this growth- it will be responsible for rejuvenating your plant! Once everything has been cut back, you can shape the clump if you wish. It really doesn’t get simpler than that! You can use secateurs for this task or hedge shears. I find hedge shears make a much bigger mess that requires cleaning (unless a drop sheet is put down first… something that I am known to do). I also find that I have much less control over the finished product with hedge shears so secateurs are certainly my ‘go to’ for this type of work.

Back to the task at hand…

Here are a couple photos of the finished ‘catmint project’. If you are thinking that the newly sheared plants look horrible, you would be correct. With that said, all you have to do is look at the middle plant to see how much better the plants will look in one short week. Also note how the clumps have been shaped to be slightly ‘dome-shaped’. I do this because I find it looks tidier overall.

Let’s do one more example of shearing… this time it is Geranium getting the haircut. In this case, the new growth coming up from the centre is left untouched- with this new growth, the plants will fill-in in no time!

If this method of ‘whacking things back’ is a little too crude for your liking, you can always cut each stem individually to a point just above a leaf (also called a node). It is from this point that the plant will branch and send out new growth. I tend to do this for Salvia spp. so that I don’t end up with unsightly ‘chopped-up’ leaves that are left on the plant; for larger-leaved perennials like Salvia, I find that looks especially bad! This plant tends to reach a point in the growing season where the removal of spent flowers to lateral flower buds (next post!) starts to make the plant look funny. Taking down the stems helps provide a reset.

Here are some common perennials that can be sheared:

• Cranesbill (Geranium spp).- the ones that get long and sprawling after flowering; spreading/dwarf varieties do not get sheared. If your Geranium is rambling over-top of other perennials, it is eligible to be sheared!

• Oriental poppy (Papaver orientalis)- cut to the ground including foliage

• Thread-leaf tickseed (Coreopsis verticillata)- when there are more spent flowers clinging to the plant than nice ones, it is time to give the plant a light shearing

• Spurge (Euphorbia spp.)- CAUTION! The milky sap that comes from the cut ends of this plant is an irritant to skin and eyes. Be sure to wear gloves, long sleeves, and eye protection. Euphorbias also harmful if eaten.

• Lavender (Lavandula spp.)

• Artemesia spp.

So there you have it! Quite possibly the simplest gardening task that can really clean-up the look of your perennials. Get out those hedge shears or secateurs and let the make-overs begin!