At Wisley, permanent hardy displays are augmented with tender plantings that really pack a punch such as Penstemon ‘Sour Grapes’, Salvia confertiflora ’La Mortola’, Osteospernum ‘Serenity Bronze’, Cuphea llavea and Verbena ‘La France’. More muted in colour but statuesque in figure are architectural tender perennials including Amicia zygomeris (see photo, left), Solanum atropurpureum and Salvia guaranitica ‘Black and Blue’.
This extends the season of interest in many areas of the garden. Tender perennials can create a vibrant display in their own right as seen in Wisley’s Canal Borders, which are home to new seasonal tender displays each summer.
If left to be ravished by a British winter the majority of the plants within these displays would not survive, which is where the Wisley Propagation Team comes to the rescue.
From late July to early September softwood cuttings are taken to produce plants that are over-wintered in heated glasshouses, which are eventually planted out in May the next year. When the Propagation Team ventures out into the wild wider garden a survival kit is assembled; not for the safety of the propagator but for the plants themselves. This is comprised of a sharp sterilised pair of secateurs; a plastic box complete with ice-packs; clear plastic bags; plant labels; a spray bottle of water; a bottle of sterilising fluid and maps with bed numbers.
Sleepy gardeners plod off into the garden early in the morning as the parent plants are more turgid and not suffering from the heat stress of the midday sun. Healthy, non-flowering side shoots are selected with short internodes and stem-tips are cut from these side-shoots just above a node, so that there is no die-back on the parent plant. The cuttings are then placed in a sealed clear plastic bag and sprayed with water to stop them wilting. A label with the plant name is placed in the bag to aid identification and prevent embarrassing mix-ups. The cutting material is taken back to the glasshouses where it is placed in a fridge until needed. It will remain happy in there for few days, but the sooner the cuttings are struck the better.
Before the cuttings are prepared modular trays of cuttings compost, consisting of 70% coir (coconut fibre) and 30% perlite, are made up. Each cutting has its own cell of compost to root into, causing the least amount of root disturbance when the rooted cuttings are potted-off. To prepare the cuttings a sharp disinfected knife is used to make a cut just below a node, this is the area most likely to produce adventitious roots.
The cutting should be about 8cm (roughly 3in) in length; too tall and it may flop out of the compost cell and will produce a leggy plant.
Leaves are removed from the bottom half of the cutting to stop them rotting in the damp compost, if possible the tip of the stem is left, but any flower buds should be removed. Any large leaves are reduced by cutting them in half to reduce water lost though transpiration.
The cutting is then inserted in the compost half-way down the cell, and the compost is watered after all the cuttings have been inserted to ensure that it settles around the stems.
They are then placed under misting nozzles to prevent them from wilting and on top of heated matting to encourage root development. Shading protects them from bright sunlight. The cuttings take two to three weeks to root, after which they are potted off to be overwintered and continually pinched back to produce beautiful bushy plants.
Now I have successfully grown thousands of tender perennial plants I indulge myself by imagining myself to be a green-fingered knight with my trusty sterilised blade. I risk ridicule yet elicit respect by dubbing myself Sir Propalot of the Wisley glasshouses.