Looking at grape plants, I noticed that they all say the height is variable, or only list the spread of the plant. Does that mean that as long as I provide a tall enough trellis, I could grow a grape plant as high as I wanted?
In the wild, grapes are a canopy vine, meaning the reach the tops of the forest trees for sunlight. I've seen them go up 85', but apparently they can go a lot farther. Of, course, it takes quite some time for them to reach that height.
So basically, yes. A grapevine will grow as high as any support you can provide. Here are some good things to note:
Grape vines are very heavy, and the taller the support, the more reinforced it must be. I've seen grape vines take down some very strong looking supports.
A horizontal support is better than a vertical one, for a few reasons.
- The stems and leaves will grow up, and the fruit will grow down. Sometimes a disease will affect the fruit only, or the leaves only. It's good to be able to spray only one of them, if necessary
- The aeration is better than on a fence type trellis. You are less likely to encounter diseases such as powdery and downy mildew.
- The area underneath is great for shade-loving plants, or if big enough, a great place for a picnic table.
- The leaves are all high off the ground, so there is no soil-foliage contact.
- The grapes hang down, and are really easy to pick.
Grapes can be kept small if necessary, but the major pruning is done in spring, so at the end of the season there is quite a bit of vines, weighting down the trellis. Make the trellis bigger than you think will be necessary.
With any kind of support, it's good to keep the lowest part at least 2' from the ground, to prevent rain from splashing from the ground onto the foliage/fruit.
I'm assuming you mean american grapes, the hardiest by far in this climate. Otherwise, this answer may not apply.
I grow a couple vines in my yard. They are NOT mature plants by any means having been in for 3 seasons now, but still, they grew about 10-15 feet this year after a very aggressive spring pruning. you will get the best fruit out of a well-pruned plant. The new growth encourages it to reproduce, and hence, grapes. If you're looking into it for privacy or shade, let it run rampant and you'll have some big vines in a couple years. After 3 years now, if i didn't prune, i bet the runs would be 40 feet when starting from a 1' plating.