Pruning is one of those things that sometimes takes an act of courage to start and also requires a little bit of faith at the end. You need courage to actually lop off chunks of a plant that you like and you need to have faith that the plant will recover afterwards.
Many years ago, I learned basic pruning techniques for common plants in the nursery industry, including various perennials, trees and shrubs. Of course, that class didn’t cover pruning methods for the thousands of other specialty ornamental plants that I grow now. For that, I’ve had to adapt what I have learned and apply it. Sometimes I find something that works, and other times I fail miserably and end up with an unsalvageable, mangled mess or the plant simply dies.
Today, I am going to illustrate my tried-and-true pruning technique for dwarf Jerusalem sage (Phlomis fruticosa ‘Nana’), one of my all-time favorite shrubs for my xeric rock garden. Despite being a “dwarf” Jerusalem sage, this plant is about 6 feet tall and 10 feet wide. It tends to get floppy after blooming and I’ve been using this technique for 14 years to keep it in shape.
Here it is beautifully covered with yellow blooms on June 5th in 2020.
And here it is this year, blooming on June 18th (2 weeks late because of our cold spring this year). You can see it doesn’t have quite as many flowers as it did back in 2020. I suspect I pruned too late in the season last year and that may have affected flower production this year. But, the most important thing to focus on is that this plant is almost the same size as it was 2 years ago, and it is still lush and full. That is quite an accomplishment and requires some pruning!
Although the flowers are nice, they only last about 2 weeks and then they’re gone. I mainly grow it for the foliage, which provides a consistent, grey-green backdrop that looks good in the garden almost year round. This is one of my garden’s stalwart performers, needing only a good soaking maybe 3 times during August and September.
Now that flowering has finished, it’s time to prune to keep this shrub from becoming a massive gangly mess. First, a quick gander at the spent flower heads, which look like a cluster of green stars. This is where the seeds would form if I didn’t cut them off.
Pruning my plants at this stage in July has several benefits.
- It keeps them more compact. Plants that aren’t pruned every year tend to get too large too fast. They become lanky and floppy, sprawling all over, and they tend to break more often under the weight of snow or ice in winter.
- It seems to reinvigorate them. The plants that I forget (or don’t have time) to prune seem to slowly die out over six or seven years, branch by branch. In contrast, my pruned plants maintain strong growth with a thick branches that support a full canopy. I’ve had this particular specimen since 2008. That makes it 14 years old and it is still going strong.
- It also removes or reinvigorates the branches that have just finished blooming and would otherwise die after setting seed. Over time, this leads to a build up of dead branches and old ratty seed heads.
- It allows plenty of time for the plant to recover and look good before winter arrives. I prune back hard, which leaves the plant looking bare and bedraggled for about 6 weeks afterwards. I don’t prune too close to winter because the new growth might not have enough time to fill in and harden off before frost.
By the time flowering is finished sometime in July, there’s typically 15 to 18 inches of new growth.
I use my trusty Felcos (Felco #2). These are the pruners I use for 95% of what I do around the garden. You can tell how much I use these – the red plastic came off of one of the handles a few years ago. The other red handle makes them easier to find when I inevitably put them down somewhere I shouldn’t have.
Here, you can more clearly see the difference in the vigor between a vegetative branch (left) and a flowering branch (right). The vegetative branches are more compact and leafy while the flowering branches are more lanky. Most of these flowering branches will die after the seed matures in fall.
Let the pruning begin! I wanted to get this done in the morning before it got too hot. I usually cut down near the base of the new growth where I can see the buds starting to produce new leaves (yellow arrows). That removes almost all of the new growth that was added on over the last year and keeps the overall size of the plant roughly the same from year to year.
Flipping things around so that the branch is right side up – here is a closer look at where I would prune the stems (yellow horizontal line). You can tell this new growth because the stem is a fresh silvery greenish-white color. Last year’s older growth (circled in yellow) is more tan. The yellow arrows point to the first pair of buds at the base that have already put out a few leaves. Pruning at the horizontal line will release these two buds and they will grow into new shoots yet this year.
Here’s what it looks like after pruning about 2 dozen branches. There’s a lot more to go.
I start low on the plant and work my way upwards. Here, I am about 30% through and the sun is starting to warm things up. I had better hurry…
You can cut back to buds as small as these depicted by the smaller yellow arrows, and sometimes I have to in order to get the overall shape that I want. However, occasionally the smaller buds won’t grow and the entire branch will die. So be careful when cutting back this far. You can also see the shamefully long branch stub that I left when I pruned last year (large yellow arrow). Although this is a technical no no from an aesthetic standpoint, I’ve not seen it have any overall detrimental effect on the plant’s health and it is quickly obscured by all of the new growth that is stimulated by pruning back the entire bush this hard.
It’s hard for me not to get distracted while doing chores around the garden. As I am doing one thing, I often see something else that needs to be done. For example, I wanted to get a picture of this prickly pear flower (Opuntia phaeacantha ‘Coral Sunset’), but kept forgetting to do so. This was the last flower on the plant for this year and if I didn’t get it now, it would be too late tomorrow. The flowers only last a short time.
But, no! I must push on and finish pruning. It’s getting even hotter out here, but an occasional cloud helps cool things off. This photo gives a sense of how much new growth I am removing.
This is also the time of year when this shrub starts dropping its older leaves. I just leave them to decompose as a natural mulch. A more fastidious gardener with an abundance of time would clean them up.
Here is the finished product half an hour after I started.
It looks pretty awful and bare, right? But, it will recover. I give it a good soaking immediately after the operation and will do so again 2 or 3 more times throughout August and September to help it along.
Here is what the plant looked like immediately after pruning in 2021 (left) and 2 months later in September 2021 (right).
And, now would also be a good time to show you how my Ozothamnus ‘Sussex Silver’ and Bupleurum fruticosum have recovered after pruning them back hard in April (here).
I was thinking of taking that Ozothamnus out because it is really too large of a shrub for this site. But, as long as I prune it back each spring, it stays manageable and I really like its silvery, willowy form.
Leaving you with one last shot of my dwarf Jerusalem sage from May 2022. Hope you found this pruning tutorial useful!
7/11/2022 to 8/26/2022: I’ve not been keeping track of temperatures, but it’s been unusually hot (above 90°F) for long periods of time. 0.25 inches of rain on August 9, 2022.
Notes: Rufous hummingbirds have left for the year. Crickets have begun singing.
Garden chores accomplished: Mainly watering and pruning.
Sometimes the hardest cut is the kindest in the long run. I have a couple of plants I always think of pruning to contain their size but usually chicken out. Must be strong. Your rock garden is quite beautiful.
I think pruning might be one of the hardest things to get started on in my garden. We have one large conifer in the rock garden that I’ve been wanting to cut back for years, and now it’s large enough I am worrying about disfiguring it. But, it’s going to have to be done at some point or come out completely. I’ve been chickening out on that one for three years now.