There are several things I do when it gets hot.
- water early in the day or even the day before so the trees are well-hydrated ahead of the heatwave
- water often: after watering in the morning I’ll overhead water the trees, benches, ground and nearby fences throughout the day
- add a layer of white sphagnum moss (or mountain moss/yamagoke for azaleas) to the surface of the soil
- move sensitive trees into the shade: if the temps are high, I’ll move trees under benches or to corners of the garden where there’s less sun
- provide shade for the pots by moving pots closer together (the combined canopies can shade the pots), turning trees so lower branches better shade the pots where the sun exposure is direct (typically south facing in the US), or propping a board against the pot to provide shade: (see example at https://crataegus.com/2017/08/02/summer-heat-spikes-and-bonsai/)
- keeping trees on the ground can be helpful as this can insulate the pot and keep the temps on the roots down
- I also use shade cloth and can move more trees under the shade cloth during hot spells; covering the top and sides of the shaded are can make a big difference
- Setting trees on a tray with pumice provides extra water and keeps the pot cool - I do this a lot for accents and smaller trees, and sometimes I’ll bury the entire pot in a larger pot filled with pumice
Of course, it gets much warmer in other parts of the country and world. Am curious to hear from others about successful strategies for dealing with the heat.