Grapevine help

[ameno]

^That's also a good idea.

[Plot70]

I would just plant them at an angle to loose some of the height.

[ameno]

If you're in Australia then I worry that mid July may actually be a bit too late. Sap starts to rise very early in vines, and they bleed profusely if you prune them from late winter until mid spring.
Try cutting off a thinner branch (around pencil thickness, or maybe slightly more) as a tester and monitor it to see how much it bleeds over the following 24 hours. If it's little to none then it should be safe to perform your desired more drastic beheading. If it bleeds quite a lot then it's now too late and you had best wait until next winter to do it, and do it a bit earlier (before midwinter, to be on the safe side).

Although one final question: how tall is this fence you want to hide? Vines can easily be trained pretty much entirely horizontally, or even downwards, so a vine with a dormant trunk height of 1.5m can easily be kept under about 1.7m even during the height of the growing season, as long as you tie in the new growth horizontally and prune any side shoots over the course of the summer.
My grape vines are trained along wires about 1.5m off the ground, and every winter I just cut them back to the main framework about level with the top of the wires, then as they grow over the summer I tie in all the new growth horizontally or else just cut it off (grapes need heavy summer pruning, anyway, or else they very quickly become and overgrown rampant mess).
So depending how tall the fence is, you may not need to cut them back at all. And at the very least, I think cutting them down to 50cm is probably too much.

[Sonja]

Hi Ameno, thanks for your reply. The vines are about 10 years old with trunks at a height of about 1.5m with no branches below that height. We want them to hide a fence line on our small farm, but we also have really gorgeous views over the fence line so if they are too high they will block out the view but not the fence 🙈. The trunks are thick and very mature looking. I’m in Australia so it’s winter over here. Our vines are totally dormant right now 😊

[ameno]

You can trim the trunk if it is thick and old enough, and it will grow new buds from under the bark. If the vine isn't old enough, though, it won't resprout and will die. You also need to make sure to leave a decent length of trunk (at least 6 inches) above the graft union (a bulge in the trunk a little way above ground level).

It's probably best not to do something so drastic, however, and this is not the time of year for hard pruning, anyway. How tall are the plants now, and why do you need them so short?

[Sonja]

Hi, we have been lucky enough to get our hands on some mature Shiraz grapevines. The only problem is the main stem/trunk is too tall for where we want to put them. Does anyone know if we can trim
the trunk down to approx 500mm off the ground? Will new branches/stalks grow still?