Summer Heat Spikes and Bonsai–

Every now and then in many locales we can see a blistering heat spike that is 20 degrees higher than normal. Ignoring these spikes, and not making some adjustments to bonsai, is perilous…

Tree roots are familiar with an Elysian climate below the soil surface, a moderate one, where roots are protected from damaging heat and cold. Because the roots of bonsai are not living in such an insulated lap of luxury, we need to offer them protection from extremes when they occur.

Aside from being very careful with watering trees (and even the surrounding area to bring down temps) when there is a big heat wave, wing into action with several adjustments to your bonsai benches:

  • move pots closer together; tree’s foliage provides shelter for hot pots
  • move pots into the shade; getting foliage and pots out of the sun helps tremendously
  • rotate pots so that lower branches shade the south-facing pot sides, which is the hot side
  • set boards up to shelter the south-facing slope of pots

How to deal with a heat spike: First option, move pots into the shade

Second option: Place small plants under benches

Third option: Rotate pots so that the branches shade the south-facing side of the pot

Fourth option: Lean boards against the south-facing slope

Fifth option: Pack the pots closer together, allowing tree’s foliage to shade neighboring pots

You may choose to do several of these options. Bear in mind that trees in smaller pots experience greater temperature problems than those in larger pots.

And then as soon as the heat wave passes, return the trees to their former locations. With these adjustments one can pass through very hot days with little affect on the trees.


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  1. clark says:

    We just had a complete shade awning fabricated out of 1-1/2″ x 1-1/2″ steel , with 52% shade cloth stretched across the top to help aid in lowering the heat on our trees ,

  2. dirk says:

    I use shade cloth 70%, on a rail so i can retract and apply whenever needed. Took time to build, but trees are happy, so am i. I use 4 of the 5 options mentioned above. Thanks for the board trick.

    • crataegus says:

      That’s very heavy shade. If you’re in a desert area, that might be ok. 50 or 55% shade cloth is about max for most deciduous tree species. For general application I recommend 40% for a wider range of species. Pines generally can only handle light shade. Unless you frequently are past 105F.

  3. John says:

    H There
    I found that here in Australia if you have old towels then these can be placed over and around the pots and soaked with water to stop the roots from cooking. JC

  4. Paul Krasner says:

    How about watering several times a day with particular attention to spraying cold water on the pots? Also, one other tip. Test hose water with the fingers before spraying. On really hot days, where the hose sits in the sun, the water can come out smoking hot and will kill many trees.

    One other question, does showering the foliage help reduce stress on the trees? Should foliar feeding be avoided on days like this?

  5. Graham says:

    Had to do some similar things up this way too, all on the ground (under benches) or shade except my heaviest beast which is the only one on the bench.

  6. Janis Vandervort says:

    I have moved all of my trees to the bottom next to a 7′ concrete block wall…I water every evening and spray leaves. Also moved the larger trees to the top of patio table with umbrella up. Time will tell if I’ve done the right thing.

  7. Bruce Williams says:

    Thanks much for the good advice.

  8. John Wiessinger (Ithaca,NY) says:

    In my opinion, this is an extremely important topic. I’ve found that my pots in upstate NY get really hot on sunny days. I’ve used many of the solutions Michael has shared and then came up with another that has worked well for me. I went to the hardware store and purchased a roll of insulation that is used for wrapping duct work in a house. The material is double-sided with aluminum with a thin insulation core. I either cut the material to surround pots or, more easily, simply cut rectangles that can be placed over the soil surface of individual pots. This latter remedy is ugly as sin, but really does make a major difference in temperature.

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