At this time year, many shrubs, trees and climbers are beginning to harden up their new growth as part of their annual effort to increase their woody framework. A little explorative fiddle with this new growth and one will feel more resistance when bending the stem than when it was soft and pliable earlier in the season. We term this material ‘semi-ripe’. When certain shrub or tree cuttings take a longer time to root, semi-ripe material is often ideal as it is tougher and less likely to wilt at higher temperatures or rot away in moist conditions.
We have been taking a number of semi-ripe cuttings on the Wisley Propagation Team including Viburnum, Philadelphus, Berberis, Eucryphia and Rhododendron. Please see the RHS advice page on semi-ripe cuttings for technical information.
Most of these cuttings were simple and straightforward, non-flowering stem-tip cuttings; but the Berberis were done as ‘mallet’ cuttings, where a little of the previous season’s growth is left at the base of the cutting. I invariably demonstrate this to trainees with a little “knock, knock” as I show how the cutting looks like a little hammer. They humour me, but I know they think I’m lame; as long as I know I’m cool that’s ok.
A shady start
We root these cuttings under polythene to provide humid conditions which keep the cuttings turgid; this year we have tried this outside in the shade area to avoid the heat of the glasshouse, which can be detrimental to the vulnerable material.
We recently took some exciting semi-ripe cuttings of a particular variety of box called ‘Bowles’s Blue’, a 1,000 of which are to be grown for the Garden Bridge project in London.
Nick Coslett, of Palmstead Nurseries in Kent, came to take more than 1,000 cuttings with RHS Executive Vice President Jim Gardiner, Wisley Propagation Team member Katie Benallick and Wisley Apprentice Nick Drury.
Jim Gardiner said that ‘Bowles’s Blue’ is a good strong variety of box with excellent colour, and he has never known it to suffer from box blight. Nick Coslett informed me that Garden Bridge designer Dan Pearson had selected the variety and that nearly 1,000 of them will form a hedge in the planting scheme.
The cuttings will be rooted in coir (coconut fibre) plugs under a misting system, with heat provided beneath them to encourage root formation. They will be planted out in early 2018. So when you see the ‘Bowles’s Blue’ in London, think back to its humble semi-ripe beginnings.