Sweltering temperatures have arrived with the Central Coast and Sydney having already sustained a few 40° Celsius days in November. Trees will wilt before your eyes, especially with the dry desert wind driving this heat from the interior.
Watering your bonsai becomes paramount as the trees try to get rid of heat through transpiration. Unlike us, a tree cannot move into a cooler area when it gets too hot and so must remove the heat from its cells by pushing water through the xylem from the roots to the leaves. Water is a good conductor of heat, ‘picking it up’ on its way up the tree to the leaves and subsequently the atmosphere. Missing a watering at this time of year can be catastrophic for your tree so be sure to water every day at the least, with two or three watering applications required on those very hot, dry days. Consistent watering in the morning will set your tree up for the day and should it require more at the end of the day, you can top it up when home from work. Note too, that rootbound trees will dry out more quickly than others.
Some enthusiasts will put their more water loving trees such as Swamp Cypress and Australian natives into water trays. This will ensure adequate moisture and is easily monitored for uptake. Be mindful of which species you place in a tray as pines and junipers will resent being in water. Shohin trees can dry out in hours due to their small pots and size. Placing them on a suiban or other flat tray covered in sand and then burying them to just under halfway on the pot will help them get through the heat. The humidity produced allows the trees to absorb water through their leaves and reduces the ambient temperature for them.
For trees such as pyracantha and crab apples, keeping the water up to them is imperative should you wish to keep the fruit that is developing. They will drop the fruit quickly should they be under any water stress.
With the holidays coming up you may be getting away for a week or two. An automatic watering system is great for these times and if set up correctly will deliver a good supply of water to your trees. Test it out several times before you go and have someone pop by whilst your gone to double check it’s still on and functioning properly. Power outages can reset some systems. If your friend or neighbour is going to water for you then be sure to teach them by having them watch you a few times. Nonetheless, be prepared for a loss or two.