Nights are cool and getting a bit longer. Plants respond to these cues by switching from leaf production to root growth. They create weather-proof seals over their growing shoots, seals that will not pop until next spring. They ramp up starch production in the leaves. In a good year a plant has stored enough energy by midsummer to remake itself next year plus hold some in reserve. If good times continue through fall the plant may be equipped to grow three times as many leaves next year.
We do a lot of pruning in late summer, focusing on what we want to keep small and shaped to our liking. We reduce that plant’s foliage now when it has stored enough starch to be healthy and is unlikely to respond by creating a bunch of new shoots, as it does if cut while it’s growing in spring.
What we prune now, we don’t need to cut again until this time next year. For some plants the interval is two years.
We have written about this many times, covering both why and how-to. For example, elsewhere on GardenAtoZ.org:
However, since the questions keep coming we keep trying to refine and improve the message. During our webinars, Too Big Too Much, and Trees and Shrubs for Small Spaces (available to our subscribers' in the library) you asked about keeping a tree small. We promised you a new guide in time to use it this year. Now’s the time!
This Saturday’s webinar, Pruning Evergreens, Shrubs and Trees is hereby open to all, no subscription required. We’ll cover this guide and take live questions. Simply use this link at 8:30 Saturday, August 22. 2020. (Join at 8:15 if you are new to Zoom or our webinars, so you can catch the Q&A warm-up session).
The password is Prune
We will also post the recording of this webinar on our public youtube channel, Janet at Garden A to Z. (It will be uploaded after the event; we will post its link on our Webinar page. Send us an email to subscribe to our weekly webinars and receive the ticket to each new webinar plus the keys to all recordings.)
We want you to prune smarter, so you too can do less work but still have good-looking shrubs and trees that stay the size you want.
Although the goal is to maintain plants at a certain size, our first example is pruning a tree that’s already too big because that’s the starting point for most people. This happens because we don’t expect the plant to get so large and don’t anticipate the geometric progression that comes with all that starchy energy described above.
Many plants can double in size in a year, which is great when an 18” shrub grows into the 36” space you wanted it to fill. It’s less of a gift when that plant doubles again in its next year and looks down on you from six feet.
We start this guide with an over-large tree rather than a shrub because knowing how to prune a tree to make it smaller is also the key to understanding how to maintain shrubs at the same size indefinitely.
Don’t take on a whole tree at once. View the tree as a collection of branches, and decide which will be the main limbs.
There is no right or wrong answer. Don’t look up into the interlaced or overgrown canopy to make your main branch choices. Look at the main divisions from the trunk or the trunks themselves in a multi-trunk tree. Designate a framework of a few branches that, between them, can gracefully fill all the air space above the tree. Commit to them, because you will address them one at a time now and when you cut again, each year or two.
In the process of choosing your keepers, some losers may become apparent. They may be dead-, damaged- or crossing wood. We remove them, first thing. We’ll come back to “crossing wood” in a minute.
In pruning, you'll address each main limb separately.
Follow each main limb to its tip or tips and cut back to a side branch. Choose the side branch for being gracefully situated and having tips that end one year’s growth inside the current canopy.
You can gauge the year’s growth by measuring a new branch from near the top or high on the side of the tree. New growth has smooth, no-bark-yet wood. How long are the new branches, how many inches long from their tip back to where bark is beginning to develop? For a healthy Japanese maple like this, the growth rate may be 12 to 18 inches. So the side branch we leave to take over as tip should have a tip end 12 to 18 inches short of the tip we’re removing.
You will cut more than a year’s growth into the tree, since the side branch has some length of its own. Perhaps it diverges from our main limb 30 inches inside the canopy. We cut out a 30 inch length of wood to put that side branch into the new tip position.
There are probably multiple side branches on our main branch. Once we choose our new tip, we cut back all other side branches so they do not reach quite as far as our new leader. We want orderly, graceful growth of followers behind one leader, not a line-up of equals vying for top position.
For an explanation of how plant growth sorts itself out and how you can help it remain orderly, watch our webinar, “Too Much, Too Big”:
Then move to the next main branch, shorten it and shorten its long side branches. Continue pruning one main limb at a time. Stay focused, don’t be drawn out of turn to limbs associated with a different main branch. Before you know it the whole tree is done.
When we designate our main limbs, we choose them for being well distributed. Each should grow toward and fill its own piece of sky. So a main branch that begins on the south side of the trunk should grow up to the south. It should not reach across the center of the plant and grow into a part of the canopy that rightfully belongs to the north- or west-side main limb. Branches that do stray are called crossing wood.
Crossing wood may sway, rub on and injure other branches in their crossing but that isn’t their main offense. They are most undesirable for becoming more woody than green. Since few leaves form in the dense shade inside the canopy, they do not produce their fair share of leaves and energy. At the outer edge, they do leaf out, shading out rightful resident branches. Remove crossing wood, the sooner in the tree’s life, the better.
Once all main limbs are shortened, the whole tree can grow for a full year before more pruning is required. Prefer to prune only every two years? Then cut a tree with a 12” growth rate to be 24” smaller than allowable.
How to cut such long pieces, such thick wood as required to reduce a tree already several feet too tall and wide: With a sharp handsaw. It’s rarely possible and never safe to use a chainsaw for this work. No chainsaws while on a ladder. No chainsaws whirring away and injuring bark of nearby limbs.
How to get into a tree this size, high enough to make these cuts? Clever foot work and a good ladder, or hire a competent arborist. If you hire help, be prepared to hear you “shouldn’t head back.” Thank that person for the consultation and find another helper. If you were with us for our free webinar
“Too Much, Too Big”:
you heard about heading back. You know it’s okay but you don’t need the extra work of teaching someone else.
We do not say it is easy to reclaim a tree once it is this size or larger. Which is why you should begin cutting trees – and shrubs – as soon as they reach your maximum allowable size. Don’t wait until they qualify for major reduction pruning.
Now step down to the ideal situation.
This Japanese maple just reached maximum allowable size.
It has about three main limbs, in our estimation. (Remember, there is no right or wrong. You pick the ones you want and stick with them year by year.)
We would remove one of the two lower branches that grow out to scrabble for the same bit of sky – our choice for removal is the lower one (red ink), for the sake of the person who mows beneath these limbs. If you were able to circle this tree and consider it in the round you might choose differently because one or the other looks better to you from your chosen angle. That’s okay!
In this case you can use a sharp handsaw, loppers, even hand pruners to cut back each main limb, standing on the ground or a short stepladder. Hooray!
As you cut, branches accumulate on the ground. Expect to become a bit anxious. A third generation grower of apples told us, “If I am not scared when I see all the branches on the ground in the orchard, then my pruning crews haven’t cut enough.”
Lay the branches on the ground and keep comparing the number of leaves removed to the number left on the tree. Aim to leave twice as much foliage on the tree as what you remove but don’t be surprised or worried if you remove half. If the tree is healthy it’s already set itself up pretty well for next year and will not only produce two leaves for every one remaining now, but will have some starch in reserve, too.
Now imagine this tree as a bush. You probably don’t designate main limbs, but you do cut all the tips at a certain height and width.
If you stop there with shearing everything to an outer limit, that’s a mistake. Everywhere your shears cut through a much-branched area, there remains a concentration of tips. Each will branch and grow most vigorously from its cut end, creating a very dense shell. Interior foliage and branches will be shaded out. Dead wood will build up, along with pests. The plant will look cluttered. Leaves will be smaller and less healthy as the ratio of leaf to wood declines. Pruning will be tougher every year as the wood at the perimeter becomes thicker.
Just as you shortened side branches all the way down a main branch, creating different levels of growth and letting light penetrate and sustain those levels, you need to thin a shrub’s outer “shell.”
After you shear – or before! – cut back the most heavily branched tips so that light can penetrate the canopy and keep new growth coming from within. If you shear first, then go back over the shrub, patting the cut tips with an open palm. Where your hand meets the greatest resistance, reach in and shorten that branch by at least one year’s growth.
You can do this thinning before you shear. If you do you, you actually make less cuts. However, most gardeners need to pat and clip a few times in order to understand which branches they are looking for, to be able to find them before shearing.
Join the webinar 8/22/20 or watch the recording of our webinar Pruning Evergreens, Shrubs and Trees.
If the tree you’re pruning is an evergreen, keep some things in mind about needle- and evergreen leaf regeneration. Some evergreens will not produce new foliage on a branch that is totally bare.
So if you cut one of these listed below, make every cut to right above a leafy side branch or green bud.
If you leave a bare branch on these, it will remain bare, nothing but woody clutter:
Cypress and falsecypress
Cut to those leafy side branches, let light reach them and watch the plant become more dense. This arborvitae was very overgrown four years ago when we first cut it back to reclaim the path and garage roof. It had been mistreated, too, albeit unknowingly. That is, the lower part, most reach-able and most in the way, had been shorn while the upper part was left to grow wider and taller. As the upper parts bellied out they cast more shade on the base so the foliage became very thin from the ground to six feet.
At that first pruning we cut back the top as well as the bottom, letting light in
Right after the cut the lower part seemed naked. That’s because the only way we could reduce any branch was to cut off the green concentrated at the outer edge and clip to just above the tiny bits of green that had survived all the shearing. We would have liked to cut the top harder at the same time but remember we had to leave at least as much green on the plant as on the ground. Most of this plant’s green was in the top.
In the four years since then, the tiny bits of green on the lower half became branches with their own side branches.
...we were rewarded. We could cut back to significantly leafy branches on the bottom. On top, we could cut back more than before, no longer worried about starving the plant.
Every time we prune this arb now - we’ll move it up to every other year – it will have more internal growth.
Eventually that arborvitae will be full again, and smaller overall. If the gold mop falsecypresses featured below could do it, any shrub can.
...be early in your cut
Can you even tell we’ve made the first cut on this arb, a channel from ground to tip as deep as two years of growth?
You may not see it because there is such a depth of green to work with. The difference is that we began cutting this arb before it became badly overgrown.
The first cut served as our guide. We circled the plant, cutting vertical strips to that same depth and thinning too, as we circled.
Done now. Does it look okay, still soft and feathery? It can grow for two years now before we cut it again.
We cut that arborvitae once in exchange for two springs of no work, no heartbreaking loss of the brightest and best growth. Two years of enjoying the luscious gold green new foliage.
...are no different. If you have been doing your pruning in spring and doing more shearing than anything else, you have probably pruned some plants two or three times each season to keep them even in form and prevent overgrowth. Want to do less?
Then prune once more, now. Put them on the late summer once a year schedule so that you do not have any spring pruning to do.
Join us for this weekend's webinar. See more about pruning more kinds of plants, and have the chance to ask questions as they come to you.
If you miss this free webinar, watch the recorded version on our youtube channel, Janet at Garden A to Z while you sharpen your tools.
Hop onto our new Forum (we have just opened this new, improved version) with any follow up questions. You can post photos there, and everyone can cut to the chase!