Bottle Tree and Leaf Drop

Q. Our bottle tree in Scottsdale is 11 years old and this summer had a crazy amount of leaves dropping. So, we watered longer but only once a week. It also gets some water when the lawn is watered, and right now, that is 3 times a week. The leaves are very, very light green, turning brown on the edges first and then completely brown and then dropping leaving it very sparse. Are we not watering long enough, or is it getting too much water?

Bottle trees sold in the nursery are not really a bottle tree. Yes it has a tapering trunk but the REAL bottle tree has a trunk shaped like a bottle! It may drop its leaves naturally when the soil is dry or just before it starts to flower in the late summer or fall.

The true bottle tree (B. ruprestis) has a much fatter trunk, shaped like a bottle.

A. These trees normally drop leaves just before flowering at the beginning of their wet season. In Australia where they are native, that would be just before our fall months. Many “south of the equator” trees don’t pay any attention to their new environment and flower or drop their leaves just like they were growing south of the equator. If leaf drop occurred starting around September and got worse a few weeks later, their leaf drop may be a response to longer nights, something totally out of your control.

Maximum/minimum temps in Scottsdale, AZ, USA.

Maybe it Was to Hot

Our normal summer temperatures are are about 10F hotter than their maximum high temperatures where they grow naturally. In their natural environment, the beginning of Australia's monsoon season mean cooler temperatures. With these high temperatures and low humidity and if there was a some wind then it would mean the plants and soils would dry out sooner. Your tree may have got hit with a double whammy; high temperatures and intense sunlight.

You did the right thing. You increased the amount of water they received by increasing the amount of water and not the frequency of water application. The only thing I would add is to increase the area where water is applied and not just the amount while all the time not letting the soil dry out between irrigations. My guess is the tree was getting most of its water (and fertilizer) from the lawn. That’s also probably were most of its roots are growing.

These trees like to have their "toes" in water but not submerged. Next time this happens, try watering your lawn a little more often. I think the amount of fertilizer the lawn is getting is plenty for this tree.