Protecting bonsai in summer

In summer, when air temperatures are very high, a bonsai can be damaged or even die unless we take special measures to protect it. A tree cools itself through its leaves, by evaporating water. At high temperatures it loses moisture quickly. When a bonsai gets too little water in the heat, the leaf temperature can reach a critical point. Wilting leaves are the first symptom of water shortage. In extreme heat a tree may go dormant prematurely (as it does in autumn). The leaves change color and drop — first the inner and lower leaves of the canopy, then the rest. When direct sunlight falls on a bonsai, the soil in the pot also heats up considerably. High temperatures can damage the roots too. Under these conditions the tree becomes less resistant to diseases and pests.

A tree can cope quite well with very high temperatures if you give it normal conditions to function. There are a few simple ways to protect a bonsai from extreme heat:

• Keep it out of direct midday sun, or rig up some kind of shade.

• Don’t stand a bonsai on a surface that gets very hot in the sun (stone, concrete, metal)

• Try to raise the humidity around the bonsai: mist it more often, and water the area around it.

• Make sure the soil in the pot never dries out completely.

• Watering at midday is another way to cool the roots.

• If you have many trees, stand them close together — huddle them up, so to speak. That way the branches shade the pots and more moisture is retained.

  Small bonsai need particular attention in summer. At this time of year they may need watering as often as three times a day.