Folded leaves indicate the plant has stopped growing. It is a self preservation mode to conserve water within the plant.
This occurs for 2 reasons:
1) Lack of water due to the roots inability to take up water from the soil (transplant shock) or lax of water ... aka: DRY soil.
2) High Heat
a) At less than 100 to 105 deg F 'air temperature' this is a combination of sufficient available water for the plant & heat.
b) Radiant Heat from the bright Sun can cause the surface temp of the plant leaves to be 20 or 30 deg F higher than the air temp. It is known that at approx 115 -120 deg F the plant leaves will fold down and the plant go into a self preservation mode regardless of availability of water in the soil. This is to protect the corm should the pstem be unable to recover after an extended period of high heat.
For the past month in the Southeast, radiant heat of the sun has been our problem along with soil water evaporation. This is the reason I've set up a sprinkler on my small banana patch (30 or 40 plants). The sprinkler water directly cooled the plant leaves and replaced the lost soil water. I was running the sprinkler 3 times a day for a couple of hours each time.
'Radiant heat' is also the reason I recommend that banana plant to be plant in locations to receive afternoon shade from the bright sun. ... Also, banana plants are not solitary plants and should be planted in groups so the plants can shade each other and the canopy to shade the pups.
@
zfallon84 ... Set up temporary shade to protect the plants from the bright sun. Our air temps have not been high enough to cause the folded leaves if the plants have water.