How many grape vines would i need for a pergola that’s 18ft by 13ft?

Question

The vines I’m looking into produce black grapes. They are already established vines and are to be removed for transplant.

Answer 1

Normally 8 - 12 feet spacing on a trellis. But assuming that you intend for the vines to grow up the posts and spread overhead on top of the pergola, I would say 6 plants, one on each post. That's if there is a post in the middle of the 18 foot span as well as corner posts. If there are only 4 posts overall, then one on each post will be okay, but won't create as dense a cover as fast as it would with 6 plants. I wouldn't put two on a post, but you wanted closer spacing, you could provide other vertical support with a trellis or wire.

If they are table grapes, prepare the soil well, with a deep and wide planting hole and rich composted and mineralized soil, it will provide high nutrient density, support more fullness of growth to cover the pergola and better quality fruit.

https://ucanr.edu/sites/gardenweb/Growing_Grapes_in_the_California_Garden/?uid=1&ds=436&email=yes

http://www.soilminerals.com/Agricolas4-8-4_MainPage.htm