So. as those of you who follow me on Twitter will already know, I had some slight issues with the way the concept of the Chelsea chop was explained on Gardener's World on Friday 8th June. 140 characters is just not enough to explain why so I have decided to blog on the matter as I have had enough of people being given incorrect information. The comment that set me off was that the Chelsea chop was to be performed in the weeks following Chelsea Flower Show. this is just not true as the concept is that Chelsea Flower Show is the reminder that the chop needs to be performed forthwith, and with good reason which I will come to.
So what is the Chelsea Chop? Well as we all know, summer flowering herbaceous perennials such as Heleniums, Lysmachia, Sedums and countless more, like to grow upwards really fast as the daylight hours lengthen, and can very easily get to the point where they are getting unruly and falling over, even before they have flowered. So the idea of the chop is that the plants get cut back, whilst the daylight hours are still lengthening, in order that they don't collapse, but also, and far more importantly, so that they plant breaks from buds under the site of the pruning and becomes a bushier and therefore easier to control specimen. Many people like to perform this in mid-May and put any staking into the ground that they are going to use at the same time.
The important thing to remember is that this can actually be done a number of times. Take, for example, a Verbena bonariensis that you have lovingly raised from a seed. It will want to grow upwards as a single stem. However, this is no good to anyone as no sooner that it gets wobbled by the wind it will be over on its side and it also will just be a single stem with a flower on top. So. once the seedling has three or four sets of true leaves, cut it back above its second set of leaves and the buds there will then move into action and break so that it has two stems. Do this again and again as the plant grows and you will end up ith a beautiful, multi-branched plant that is not so tall it needs its own scaffolding system to keep it upright and which will produce multiple heads of flowers. Each time you cut for cut flowers in the house it will break again and become a better and better plant. As growers we do this with all herbaceous stock in order to produce quality plants.
Earlier in this tome I mentioned the importance of daylight hours and I shall now explain why. The "thing"with plants is that they are far more aware of the seasons than we are. In order to get all plants growing at their optimum daylight hours need to be long, so your herbaceous border knows that even though it might be a nasty wet day that it is still the beginning of June due to the fact that it's light for a long time. Its at this time of year that plants put on leaf, grow upwards and in summer flowering perennials in particular, get themselves to the point where they will begin to think about flowering. Timing your chop is vital as the plant will sulk for a week or two afterwards and you need it to get going again before the summer equinox at the end of June when the daylight hours decrease and the plants realise they need to flower and set seed. Therefore, in the UK, a month before this date is Chelsea week, and hence it is a good reminder that actually it is really last chance time. Obviously, if you have plants that have fallen after this date then cut them back as it will do no harm to the plant, but you may forgo many flowers that season.
Also commented on was the idea that one plant can be cut back to different levels for flowers in succession, rather than all at once. This is a great idea but I must offer one word of advice. Once the plant has flowered once, if you let it set seed it will be very slow to flower again and you will be disappointed by the second and third flushes. This is easily overcome by making sure that you deadhead the plant before it sets seed as this will fool it into thinking that it hasn't flowered and off it will go again.
Finally please always make sure you prune plants back to a bud. Plant stems at the tips have growing hormones in them and you need to cut back quite close to the bud to push those hormones back into the buds rather than let them continue up the stem. Also if the stem is left too long you run the risk of bacterial or fungal infection getting into it and the plant dying or suffering due to that. Also always ensure that the prunings are removed and composted and not left in the plant. And be quite mean and tough, cutting back by at least half if you are only going to do it once. The plants and your garden will thank you for it.