If you have a grapevine in your greenhouse this is the perfect moment to give it its annual prune, and I have been attacking my absolute beast of a vine. Grape vines make wonderful greenhouse plants in one way: the warmth and shelter makes for an environment much closer to the climates they like to produce fruit in than our usual British summer.
There is less dicing with late frosts and with the threat of rain at flowering time – which can wipe out a prospective crop – and of course there is a quicker and generally more successful ripening of the fruits. However they are really big and boisterously rampant plants, and if they are not kept in bounds you will quickly find them taking over, blocking lots of light for other greenhouse plants, and being far from their most productive themselves. So a good annual prune really is necessary.
Why now? As the winter wears on, grape vines start to get ready for spring, their sap rising, and if you prune once this has begun to happen they can ‘bleed’ sap, dripping for days or even weeks, and weakening themselves. Traditionally in fact this pruning is done before Christmas for this exact reason, but if you had time to set aside to prune your grapevine in the run up to Christmas then you are a more organised person than me. Early January will do just fine, but do get your skates on.
Mine in fact isn’t quite in the greenhouse. It has slowly wound its way up the uprights of my veranda, and then I have trained it along near-horizontal wires under the clear polyurethane roof. But the principle remains: it is a limited space under cover and the thing needs to be kept in bounds. It is also worth noting that vines are at their most productive when well pruned: all that energy gets forced into fruit production rather than into reams of vegetative growth. So our task is to direct energy where we want it.
Over the past few years I have trained my vine so that one long branch runs along the edge of the veranda roof, and several branches grow off of it, along those near-vertical wires. This is my permanent framework, and if you don’t have this, this is your first task: train your chosen branches along a framework in summer, and then cut back to it in winter. You will also need to ‘stop’ (chop off) the ends of your permanent framework branches a couple of years in a row before they get the message. Once you have this permanent framework in place though, it is pretty easy to keep the growth pruned back to it. With sharp secateurs prune all growths arising from these side shoots back to a couple of buds.
I have been doing this repeatedly for several years now, and these parts start to take on the gnarled and encrusted appearance that justifies calling them ‘fruiting spurs’: likely to produce all flowering and fruit-producing growth, no soft, fast and useless vegetative growth. At this stage I also remove any old and shrivelled up bunches still hanging. They have been a good food source for the garden’s blackbirds so far this winter, but there are very few left now, and it is time for them to make way for coming growth.
I love the look of the newly pruned vine, tidy, all in parallel rows, and yet still gnarly and Arthur Rackham-esque. In early summer the leaves will unfurl lime-green and new against what each year becomes older, more cracked and more woody. A grape vine is a beautiful plant, and all the more so when it is given a firm hand.