how to prune a new greenhouse grape

The green growth is not mature enough to grow on next year, cut it back and lay the remaining rod down to ground level. In February buds will form and you can disbud, leaving the buds you wish to grow towards the top. Tie back up and tie in the main rod on the lower part of the roof horizontal. Put up wires now.

Thank you! Not the answer I wanted to hear (all that lovely new growth gone to "waste"), but I'm sure you're right. I understand the vine may make 15-20 feet a year, so that's something to look forward to...

When the new rod reaches the first horizontal wire, do I just let it bend over at 90 degrees? 3 main horizontal support wires are already in place to support "vertical shoot positioning" laterals that will - hopefully - grow off it.

Thanks again; I've been worrying about this all over Christmas, because I know I have to do any pruning NOW!

MundyE

It takes years to get a vine into the required shape in your vinery.prune off the top Now, it will take all the energy away from the other growth. As said, lay the remaining rod on the floor of the greenhouse. In Feb/March, new buds will appear along the rod. You may want to tie the rod back at an angle, making more new rods up the side of your vinery. Auxins take the growth to the top, so if you leave the rod you have upright it will only give you growth at th top. A picture would help to show me the area in which you are growing your vine.

Thanks again! It's not a huge greenhouse (8x10ft), so I'd rather have all the growth in the eaves rather than up the wall (the Victorian preference, I understand) and train laterals up to a horizontal wire installed in the apex of the roof. This would also help shade the rest of the plants. Here's a pic: the vine is in the northeast corner of the greenhouse, planted into the ground so that the roots can get outside (no foundations with these new greenhouses, just a 6" solid base surround). The vine's brown wood reaches just above the level of the staging.

MundyE

I can now see what you want to do, but if you leave the green growth on, it will not be strong enough to take side shoots. You need to cover the roof of your greenhouse. You can leave it to ripen, but mildew is likely to kill most of it off and side shoots will be poor. You will need to shade your greenhouse roof as the sun will scorch the new leaves.

Thanks very much for that. I don't want to risk mildew, so I'll cut off all the green growth tomorrow! But do I then need to bend the stalk down, given that I'm not looking for lateral shoots until the main stem reaches eaves height. I actually want it to go upwards ONLY until then...

Oh, and I'll get some shading material up there between the glass and the vine. Once more, thanks for helping me out of a dilemma!

MundyE

If you leave the rod up as it is you will get buds developing in Feb/March. I would only let 3 grow, then this time next year you should have 3 small rods to develop. The best overall shading for a greenhouse is coolglaze which you can paint on inside. You then only need to shade the part you need at that time. It wipes off with a damp cloth. To help you also prevent algae build up on the inside of the glass, wipe it over with a cloth with malt vinegar on it. Mildew spores will hold up in algae also botrytus. Feed around the base of vine with Blood, Fish and Bone in March. Don't look to grow grapes this year, although you could try 1 bunch on each new rod.

I hope you dont mind me asking a question to Bob, Mundye.
I have an old grape vine that grows at the back of the greenhouse and runs along the eaves towards the door. The last couple of years my tomatoes have had blight. I have 4 roof windows but I'm concerned that the grape vine in full leaf is contributing to the blight. We've not had problems in the past so think maybe the blight has been due to the bad summers we've had. Were thinking of putting a vented window to replace a pane in the back to get a through draught, What are your thoughts Bob - if you dont mind ;-)

Hi Dawn, Happy New Year.
It is a good idea, often vents are in the wrong place. There are loover types, but automatic vents which work on heat i.e. if it's very hot they open and when it's cold they close. Better in the roof though. Fan heaters can be set to blow cool air. But most important all the year round is to keep everything clean, nothing that's not needed i.e. flower pots, wellies etc. should be left in your greenhouse. Brush the dormant rods on your vine with a weak solution of Armillatox.

Hello Dawn and Bob,

Good to hear other people's problems. Re my vine, I've now decided to leave it unpruned and see where the buds grow, then train the results along the eaves-height wire and grown laterals upwards from that (vertical shoot positioning, I think it's called).

I've got a solar-driven fan with a backup battery already installed at eaves height, as well as two automatic vents, so I hope I can keep the vine nice and airy. Thanks for the tip about cool glaze: sounds less cumbersome than netting-typw shading.

MundyE

OK, Mundy, let me know how it progresses. Good Luck.

Thanks Bob! I will...

Hi You Two and thanks Bob.
One of the windows has an automatic opener Bob but the fan on cold sounds a good idea, to get the air circulating. The grapes usually get mildew if I dont spray them but the spray (which I cant remember the name of) does work - I spray them periodically - for the first time when they come into bud.
I'll get some Armillatox for the vine too.
I did the greenhouse out with Jeyes fluid at the end of the summer so I think I give it a good do over again before Spring and tidy it up :-)

Hello Doctor Bob,

Don't know if you remember my vine question - but how right you were in your answer. Against your advice, I couldn't bear to cut back all the new growth on the single stem of my new vine over the winter, and indeed as you said the very top did get a bit of mildew.

This spring, however, new buds began to grow below the mildewed part, and I completely removed the lowest ones because I want the trunk of the vine to go to shoulder height before putting out laterals. I left 3 buds around 8in apart on the single stem and - as you said - the nearer the top of it, the weaker the bud.

Only the bottom bud looked really robust and, after I finally bit the bullet and trimmed the main stem (mildew and all) back to this strongest bud, it has romped away: about 18in in less than 3 weeks! I did think I was taking a big risk by pruning back to just one bud, but it's so muscular-looking that I backed it to survive anything!

So I've seen your advice working in action, and the vine and I are (touch wood) happily looking forward to this year's progress!

Thanks again, MundyE