Q. You told someone that a bottle tree lacked water when its leaves turned brown and fell. I have a large, Australian bottle tree that was here when I bought this house 12 years ago. Every summer it blooms and makes seedpods that eventually fall. It also loses leaves as the person in your article described. However, it grows new leaves so it looks eventually much as it did.
A. Bottle trees from Australia are “dry deciduous” trees. In other words, during the dry season of the Australian desert they drop their leaves. When rain returns, they grow their leaves again.
If these trees get water stressed in our climate and suffer from a lack of water, they drop their leaves. They “think” they are going through a dry season so they drop their leaves to protect themselves from drought.
During the summer here, if they are not receiving enough water they will also drop their leaves. They are conditioned to drop their leaves from millennia of evolution on the Australian continent.
If you want them to keep their leaves through the summer, then give them more water or, possibly, water more often. It is hard to say which is the right thing to do but my guess is they should be given more water when they are watered.
Plants use 500 to 800% more water during the months of July and August when compared to January in our desert climate. When bottle trees mature, they develop a swollen trunk that they use for storage of water that allows them to survive periods of drought, thus their name.