This month following on from my thinking about how long plants live last month I am going to talk more about how to rejuvenate plants in your garden.   First a couple of star plants at the end of June here: –

Lychnis coronaria: –

Geranium ‘Patricia’: –

I mentioned rejuvenating old shrubs such as Weigela and Philadelphus by a particular pruning method, which I shall go into more detail about this month, and how to rejuvenate herbaceous perennials.   You may wonder why I am talking about pruning in July, but the two shrubs mentioned are pruned after they finish flowering which is usually later June so that they produce wood this year for flowering next year.  The forsythia which has died, is also pruned after flowering finishes for the same reason – usually May.

When we moved here all the shrubs were overgrown – gangly, flowers high in the sky, etc.  You have two choices faced with that – digging them out and replacing them with something else, or rejuvenating pruning to give them a new lease of life.  So, I followed best gardening practice to rejuvenate them – a pruning technique of cutting one stem in three out over a three-year period, taking the biggest/oldest stems first and pruning them right to the ground, to make the shrub throw up new young shoots.  Try as I might to take meaningful photos of the process, none of them come out clearly enough to show big old stems, new growth, etc, so here is a wordy description instead.   

 Look at the base of the shrub.  See how many branches/trunks it has.  You are aiming to cut out a third of these as near to the ground as you can. Say it has seven stems, for the first year, I would try and remove the oldest/biggest two from nearest the middle as I can.  This SHOULD cause it to throw up new growths from the cut areas.  In the second year, remove another two of the more central largest/oldest stems, and by the third year, you can remove the last three of the original old branches, and you should be left with just the growth that has happened in the past three years.  It looks rather drastic when an enormous branched stem gets pulled out of the mass of the shrub, and for the first two years the plant looks very uneven and even more leggy than when you started, but all of the shrubs, no matter how old or “deformed” they were, responded well to this treatment, producing new branches with lots of leaves and flowers, and I have carried on pruning them in this manner each year subsequently, to ensure that they keep throwing up new young shoots.  These two photos of the pruning of the Weigela does demonstrate HOW MUCH is still removed each year though by the pile on the path:-

Shrubs of over 25 years in age that have not been pruned in this manner before have stems that resemble tree trunks, and need not just a pruning saw, but sometimes even an actual carpenters bowsaw to cut through them – and that is a two-person job, not just so that one of you holds the other growth out of the way, but as the cut goes deeper and deeper into the trunk the weight of the branch and all the growth on it above the saw weighs more and more heavily on the cut and makes the process of sawing much more onerous.  The other person needs to (carefully) support the weight of the branch being cut so that the saw will still move, whilst NOT pushing back so far that there is a jaggedy split in the trunk which can let infection in.  Much like tree pruning, it is helpful to make a cut on the other side of the trunk being cut before starting the main cut so that minimises the likelihood of a jaggedy split.  After pruning, I feed the plants with blood fish, and bone. 

Having said that, I found that this year whilst the Weigela flowered earlier because of the warm winter, the Philadelphus flowered later because of the very cold weather in May and early June.  It didn’t really start flowering til the hot weather around the summer solstice, so it has not yet been pruned this year.  Here is Philadelphus coronarius flowering on 20 June:-

The long-lived Shasta daisy Leucanthemum x superbum was here when we moved in and I still have large clumps around the garden: –

The largest clump was planted in the gravel garden when we made it more than 14 years ago, and it is still there, spreading ever further outwards, and leaving a bald center patch.   I leave the top growth on the Leucanthemum x superbum all winter for the mini beasts to overwinter in and took the photo below after clearing that away at the beginning of March 22.  As you can see the Leucanthemum x superbum leaves are heading outwards leaving a huge bald spot in the middle (in front of where the tete a tete are flowering) They leave their dead or aged woody stems and roots where they were and grow new roots/stems on the edge and work their way away from their original site. 

This happens with grasses too, here is a clump of (I think) Molina caerulea with a bald center in a garden I visited in September last year: –

Which brings us to the method of rejuvenating old hardy perennials, and why you are recommended to lift your herbaceous perennials every three years or so and split them so that you can discard the old woody material and replant the younger parts.    So, if you look at the picture of the grass above, dig up the whole plant, and using a spade or kitchen knife (I keep a large carving knife for these purposes!) I would divide the plant into quarters so I can get to the old, bald, middle, which I would cut away carefully and compost, leaving the outer stems of the grass with their roots.  This would probably make at least six new plants.  To maintain the impact of the large clump, I might plant two or three of these smaller clumps back where the original had been – checking the soil isn’t compacted under where the original clump was and giving them some blood fish, and bone as I did so.   We are told the best time to do this is in the autumn when the ground is still warm and the plants will be able to re-establish themselves before the winter, but for me, it’s best to do it in the spring after clearing the top growth, as I am much less likely to put my eye out on the old stems, and the ground is usually much softer after winter wet than it is in the (often) bone-dry autumn.  I think spring would be the best time for me to divide deciduous grasses too – i.e. when you have cut the old stalks back and when you can see the new shoots growing, though I have divided a pot-bound Festucca glauca (which is an evergreen that you “comb” of its dead growth in spring, rather than cut to the ground) with a bald patch in the autumn and put it in the ground in clumps successfully. 

Subshrubs, particularly grey-leafed ones such as Lavender, Helichrysum, or Santolina can quickly become woody, and splay out from the base.  As we all know (and I am BAD at being ruthless enough) you have to chop lavender down to just above where the new leaves start on the stems after the flowers have gone over in the summer to keep them compact.  The same is true for Santolina.  As you can see here from this Helichrysum italicum, (Curry Plant), I snapped at Wisley in May, they splay even before the flowers have really got going, particularly if they are grown in too rich a soil, or where they get a lot of water – a problem if you have them as part of a mixed border where other plants need the more enriched soil:

What I have done with my Santolina chamaecyparissus is prune half of it back to the tiny beginnings of grey leaves on each stem and left the rest for the summer – a very ugly compromise, but one where I still have a live plant, and then taken cuttings from all the stems I have drastically pruned and then done the same the following year with the remainder of the gangly part.  This did rejuvenate my Santolina chamaecyparissus a bit, but it never really put on masses of new growth was always oddly shaped and leggy, and over this past winter wet gave up completely.  So, reluctantly I have concluded that these may not be suitable candidates for rejuvenation.  So, I try and take as many cuttings as possible from them to make new plants.  

I mentioned above that the Philadelphus coronarius was flowering a bit later than expected, and next month I am going to report on other observations in my garden of how the exceptionally wet mild winter and wet cold spring have affected things so far this year.   Let’s finish with a close-up of some plants doing very well at the end of June here – the rambling rose Rosa ‘Sander’s White’ with the honeysuckle Lonicera periclymenum ‘Serotina’ in the foreground: –

Sheila May, July 2024