Here is another installment in our fruit tree pruning series – this week we’re tackling grapevines. For a list of our other pruning blogs click here. On a recent sunny winters day I caught up with my friend Julie pruning her 11 year old vines at the beautiful Kina Cliffs vineyard. Julie and her team prune 8,500 vines each winter and what she doesn’t know about pruning grape vines isn’t worth knowing.
She gave me a beginners guide to the most important things to know about pruning grape vines, which the home gardener can put into practice just as easily as the commercial grower. The first thing to know is that grape vines put on a huge amount of growth each season and need a regular pruning regime throughout the year. The bulk of pruning is done each winter. When the leaves drop and you’re left with a big old tangle of vines, where do you start to knock your vine into shape for the coming summer?
The most fruitful wood grows from one year old canes. This means that each winter you want to prune off 90% of the old growth and leave just a few new canes for next years growth to come from. Last years growth is always cut back to the head which is the top of the trunk of the vine. On a commercial vineyard the trunk is just under a meter tall to allow for easy maintenance between the rows. Over time the trunk thickens and the head forms a gnarly old fist from which the new canes spring forth. The one year old canes growing from closest to the head form the new replacement fruiting canes, and the suckers that sprout straight out of the head can be cut to 3-bud spurs which then grow replacement fruiting canes to tie down the following winter.
There is quite an art to keeping the head of the grape vine well maintained and low. If you’re not careful the head can get higher and higher each season so the trick is to select new canes to keep that are lower down the head. You also want to make sure you don’t get two heads developing, so don’t be afraid to lop off part of the head to correct this. If you have a double head you get a big window of low productivity in the middle of the plant. Paint big cuts like this with pruning paste.
It’s pretty brutal watching 90% of the plant ending up on the deck, but it truly makes for productive healthy vines. You’ll find many different methods for pruning grapevines in books for the home gardener – most of them don’t cut back the vines as brutally as this commercial method. But the problem with these home garden methods is that the vine laterals that aren’t cut back keep getting thicker and thicker and you end up with vast trunks all the way along your trellis or fence.
These thick trunks can eventually break their supporting structures, harbor pests, and diseases and produce less vigorous new growth and poorer quality bunches of fruit. With the commercial method you strip out all but a few of the canes each year so this heavy upper story never develops.
The canes that are retained in this commercial method form the framework for all the fruitful new summer growth to come. The best canes to keep are 10-15mm in diameter – larger canes aren’t as fruitful. How many canes to keep each year varies by variety. For her Pinot Noir, Julie only keeps one cane to tie down per plant and three for the more vigorous Sauvignon Blanc vines.
For the home grape vine, leaving 3 or 4 canes for tying up is about right. Another good tip Julie showed me is to leave a couple of spare canes before tying down and that way if you break any of the canes while you’re tying them down you’ve got a replacement – once you’ve cut them off you can’t stick them back on if you need them!
The canes that are retained are wound around horizontal wires, about 20cm apart, being careful not to rub the buds off or crack the canes in the process. They’re then tied and cut off at around 10 buds along the cane, leaving them any longer overworks the vine and reduces the quality of the fruit.
By early summer the shoots are all sprouting up, off the new canes. When they’re around 15cm long Julie goes along and thins out double shoots to singles, leaving around 8 or 9 shoots per cane. The fruit will grow off these shoots and during the summer Julie tucks them up through wires into a vertical growing pattern that forces the canes up and exposes the fruit. Each shoot will produce 1-3 bunches of grapes off the lower buds making a harvest of 25-30 bunches per vine.
The bulk of the pruning work is done in winter but during the growing season the vines get laterals around the fruiting zone removed, the fruit thinned and a bit of leaf plucking too around Christmas / New Year to ensure maximum sun on the fruit. The canes are shortened, leaving just enough of a canopy to produce enough energy to ripen the fruit – leaving around 1m of canopy, above the fruiting zone is about right.
Heavy pruning produces consistent large bunches of healthy grapes from new fruitful growth. To sample the Kina Cliffs range of award winning wines visit Kina Cliffs. In the interests of research I’ve tried them and they’re all good.