How To Grow a Young Grapevine
When you buy a grapevine in Spring or Summer it is likely to be in its first or second year of growth. If you intend to plant it in the ground please do so as soon as possible to allow its roots to get established before winter. Incorporate lots of grit into the planting hole for drainage.
Don't expect grapes from a baby grapevine. All babies need to be nurtured for the first few years, then they are more amenable. Once it's 3 year old your vine will be ready to start giving you grapes, but don't be too greedy with your first crop or you could weaken the vine permanently. Expect grapes in September/October and limit the Year 3 crop to a few bunches only.
A south-facing aspect is ideal for grapevines as they love sunshine and warmth which they need to ripen the grapes. If you can put up a trellis, or plant against a wall or fence, you will gain that important extra heat needed for tender varieties. Aim to plant in a spot that gets at least 6 hours of sun a day.
Train your vine up a 6 ft bamboo cane so that you have a single central stem with a couple of side branches by Year 3.
The most important thing about grapes is that they ONLY produce grapes from branches that grew out in the previous year. 2 year old wood (and older) will NOT give you any grapes. So you need to encourage the habit of cutting out old side branches and tying in new wood each winter. Grapevines don't need a lot of fertiliser. If you overfeed them you will have lots of foliage and few grapes. A little feed once a month is fine.
If you plan to have a large vine, some kind of long term support is advisable. Sturdy end posts with 2 or 3 wires between at height intervals will give decent support.
Mature vines are usually hardy down to -15 degrees Celsius, but a young vine should be given winter protection in the first couple of years. A straw mulch around the base will help protect the roots so that even if the top growth dies off you have a good chance of it regenerating from the base the following May/June.
Grapes can be kept in pots for up to 20 years, provided the compost is free-draining (lots of grit) and you keep increasing the pot size. A mature vine will need a 25 litre pot to thrive. Also, pots can be taken into a greenhouse for an earlier crop.