why did all the leaves on my wisteria dry up and fall off?

Question

Why did all the leaves on my wisteria dry up and fall off?

Answer 1

If it has received sufficient watering and has no other symptoms, then it is likely a fungus causing that. Treat the plant with a fungicide (like neem oil) and that should fix it. If it has been recently planted, it could be due to air pockets in the soil which are preventing the roots from taking up water. If this is the case, flood the area with water and tamp the soil down around the plant to collapse the air pockets.