I always knew that it'd be a bit of a risk trying to grow a passionfruit vine in a container, but due to our location in the north this tropical plant simply would not have done well in the ground during winter.
The vine was growing quite fine for many months until it started losing leaves at the bottom. The problem got worse and worse and we knew we had to figure out a solution right away. The problem was that any solution we read about could also have been the problem!
So, after testing, we came to a conclusion- we were underwatering. Read more about how we figured this out below.
Note: Please keep in mind that my passionfruit vine is potted and trellised. I bring it inside in the winter as we live in Zone 6b with cold enough winters that would kill the plant. This more than likely influenced the issue that will be described below and may not have the same solution for those growing a plant in the ground.