The record breaking hours of sunshine, with the associated high average temperature, during the spring seems to have brought on some of the later summer flowering plants so that they are already flowering. The daisy tribe, chiefly the border stalwarts such as Rudbeckia, Echinacea, Helianthemum and the like, are generally considered to be ‘late flowering perennials’. They bloom after the ‘high summer’ flowers that are associated with the traditional herbaceous border; delphiniums are the epitome of these ‘original’ border constituents.
Even though, in these unprecedented times, there was no physical ‘Chelsea Flower Show’ this year, there is a horticultural trick, commonly known as the ‘Chelsea Chop’, which would have delayed the flowering, slightly shortening the flowering height, of the later flowering border perennials. Obviously, this is performed in May, so too late to do it now, but all is not lost.
It has long been known that June flowering herbaceous border plants, like the aforementioned delphiniums, will flower again, albeit a little half-heartedly, if dead-headed as soon as the first flush of flowers has faded. The same is, unsurprisingly, true of their later flowering cousins. If your rudbeckias, and their ilk, are already flowering then they will have a second flush, even later into the autumn, if dead-headed in a timely fashion.
Another quirk of this year’s very high levels of sunshine, during May, seems to be that many plants generally propagated as stem cuttings, in July / August, were already showing a propensity to root much earlier than that. With that in mind, it’s worth having another go at attempting to describe how I go about taking cuttings (I employ the same basic technique to practically every plant that produces a fitting type of cuttings material).
I have a bed of penstemons which have been in situ for almost a decade—and they are beginning to show it. They flower non-stop, from mid-summer right up to the frosts, as long as they are dead-headed regularly. The problem with this is that it’s hard to find cuttings material which is, if you read propagating manuals, ‘preferably non-flowering shoots’. The theory is that high summer, with good light levels and a ripening sun, induces the highest plant hormone levels, in turn conferring the best chance of cuttings making roots.
Choose non-flowering shoots that are thick enough to yield cuttings that are able to be pushed into loose compost. The sharper your knife the better when it comes to dealing with cuttings material and for trimming them—if you can’t sharpen your garden knife, to the required degree, then it’s worth investing in those craft knives which have disposable blades. The science behind using sharp knives is that you want to cleanly cut the plant tissue and not crush or bruise it. A clean cut damages fewer cells which in turn reduces the damage to the cutting and gives it a better chance of not succumbing to bacterial or fungal infections.
The cutting needs to be about finger length and pencil thickness. The softer the shoot the fatter and shorter the cutting will need to be if it is to survive being inserted into your cuttings compost. What comes next is all about preparing the cutting so that it is in the best position to be able to survive long enough, bearing in mind it has been severed from the parent plant, for the time it takes to initiate and grow new roots.
To this end, the shoot you harvested from the parent plant needs to be trimmed off, at the bottom, to a point where the sharp cut is made just under a leaf joint (because that’s the place where the new roots will grow from). At the same time cut off all the leaves, except for a couple at the tip, severing them at the point where their stalks meet the stem. Leave as little stalk material as possible as this will die back and could promote rotting in the main stem if left too long. The leaves are removed in order to prevent needless moisture loss from the cutting because, until new roots are formed, it has no way to replace the water which it will inevitably lose by evaporation.
If the tip has large leaves, a tricky judgement call, then these should be cut down to size, with the sharp blade, as a further aid to reducing water loss. The tip itself needs to be left intact as it is important in the rooting / growing process because it is the source of vital plant growth hormones. By now you should have cuttings which are trimmed off at the base and have been completely denuded apart from the small leaves at the tip. They are now ready to be inserted into pots full of cuttings compost.
I get the best results from using a multi-purpose compost mixed with at least 50% grit / perlite to keep the mixture ‘open’ (full of air and free draining). It is important to use only fresh, sterile, compost because, once again, the aim is to reduce the chances of the cuttings succumbing to rot and diseases, caused by the pathogens more prevalent in old compost.
Air is vital to the rooting process because, just like human cells, plant cells require oxygen to sustain life and rootless shoots need to be able to absorb this from the air pockets in an ‘open’ compost. For this reason, it is vital that the cuttings compost is only gently firmed into the plant pot and not rammed in to the point where it has no air pockets left.
It should be firm enough to support the inserted cutting, but loose enough that the cutting can be pushed in without excessive force. For particularly soft, or thin, shoots it may be necessary to make a preparatory hole with a pencil or cut section of bamboo cane.
Your cuttings should be inserted around the edge of the pot, this is said to increase oxygen availability to aid rooting. Bury to a depth where at least the bottom most leaf joint is an inch, or so, beneath the surface. The pot should be of a size that it can have a short cane inserted into the middle, taller than the exposed sections of plant material, and small enough to allow you to cover it with your preferred lid / bag.
Short cuttings can be inserted into seed trays of compost and placed in a lidded propagator, as you would for germinating seeds, but taller ones will need deeper plant pots. Stand the filled pots in trays of water, to saturate them, and spray the new cuttings with clean water to aid water retention at this delicate stage in their journey.
I have always used the method which I was first shown which uses a polythene bag (not so easy to obtain these days) over the pot, held away from the cuttings by the bamboo cane, and secured around the pot with string or a large elastic band. The idea is that the polythene bag, preferably see-through so you can keep an eye on your cuttings, performs the same job as a propagator lid in maintaining a humid atmosphere—to keep your cuttings alive until they have had time to produce roots and uptake water for themselves.
This will takes at least a few weeks, maybe longer, and, in the meantime, they should be placed in a warm and light place, not so sunny that they ‘boil in the bag’, where you can largely forget about them. Once there are signs of growth, from the tip, you can gradually allow them to acclimatise to normal atmospheric conditions by cutting holes in their bag, or opening up the vents on a propagator lid, until they are sufficiently rooted to have their covering removed altogether. It is unlikely that every cutting will root so it is necessary to remove unsuccessful ones, which show signs of rotting off, before they infect their healthy pot mates.
I didn’t mention ‘hormone rooting powder’ above because it shouldn’t be necessary if the chosen plant material is at the right stage to root by itself. Having said that; rooting powder also contains ingredients which are designed to reduce the chances of rotting off so may be worth using for this aspect alone. For the same reason, in the past, it used to be common practice to water and spray the new cuttings with a chemical control against rot and disease. In today’s, less chemically dependant, climate this ‘belt and braces’ approach seems a little over the top when good hygiene should suffice.
Judging by the continued, lockdown induced, compost shortage I am hoping that there are now a lot more people that have actually found time to make use of their gardens. I am sorry to have largely banged on about cuttings this month, which maybe considered a more ‘expert’ aspect of gardening, but making your own plants, via whatever sort of propagation you can manage, is one of those horticultural tasks that might spark the kind of joy to foster a more long-term love of gardening.
Raising plants from seed is another variety of ‘propagation’ and requires no special skills at all—just follow the instructions on the seed packet! Fortunately, for the novice gardener, there is a whole tribe of flower seeds which are perfectly suited to sowing now; the ‘biennials’. These include many of the classic ‘cottage garden’ type blooms and some, like ‘Sweet Williams’, which make ideal cut flowers. Their chief quirk is that they need to be sown in the year before they are due to flower, hence the term biennial because they need two growing seasons, with a winter in between, in order to produce their blooms. Foxgloves are also in this group and, although less suited to cutting, it’s hard to imagine a cottage garden, in fact any garden without a few majestic spires of foxglove popping up all over the show.
For now, in these weird times, I just hope that you are continuing to make the most of your garden 🙂