Here in the Pacific Northwest we’re having a devilish heat wave…and to protect your trees from very hot days there are a few precautions to take.

The most important precaution is to step up your watering. If you’ve been watering once a day at 80 F, you will want to step that up to two or three times a day at 100 + F. When I say ‘water’ I really mean ‘check.’ You might not actually water each plant, but five hours of intense heat and sun can dry out a pot in record time and so we check frequently.

The next precaution might be to put up shade cloth areas that will reduce the local heat by five degrees or so. This step can be significant, particularly for small pots or sun-tender plants.

Another precaution is misting. A hose does this just fine, spray the foliage and benches and gravel down with water. No need to soak the pots, this is just a refresher for the foliage and to cool down the pots a bit.

Finally—and this can make a huge difference—try to relocate trees and companion plants to shadier parts of the yard. This may be a tall tree or even a tall wall that protects an area from afternoon sun.

And cool yourself down with lots of watermelon…


  1. John Armitage says:

    Hi Michael

    Thank you for all that really useful information on watering. This year in the UK we actually saw some sun. Now that I grow mainly shohin I have had to install a watering system. My bonsai live 20km away from where I live ( see them only atr weekends) and I have had to rely on my folks. We have had watering “issues” this year. But a cheap watering system has meant I have avoided fatalities and everything is growing really well.

    Keep up the good work.

    John Armitage

    • crataegus says:

      Hello John,

      It’s been an eye opening year for all of us. Here in Portland, Oregon we’ve had 105F/40.5C this week and we’ve been watering and worrying nonstop. We have a climate that is considered similar to the UK (although we have a bit more sun and heat in the summer but nothing like this) with mild weather and cloud and a fair amount of endearing drizzle. For much of the year we can water the best way—with a watering can. Hose is used only when we need to use it…we can easily overwater with a hose. But when it’s hot, half the day can go by watering with a can!

      Thanks for the comment,

  2. Josef says:

    Hi Michael,

    Plenty of HEAT indeed! How foolish of me to buy a soil thermometer that maxes out at 100 degrees! In any case, I’m wondering about the soil temperature in my mica pots, as it seems rather high compared to the soil in terracotta or wood. What is your take on mica pots in general? Thanks for keeping the blog up with all the tips.

  3. David says:

    I discovered your blog just recently, but i’ve read most of it by now :-).
    I love your stories and information… Tx.
    I have a question on watering. Something i see with my maples when i water them is that the tips of the leafs burn.
    I can only water in the evening, so never in the hot sun. I thought it was because of the salt in the water, but still don’t understand why it is.
    If you guys have that hot temperatures, do you never water the leafs??? Or if you do, don’t the never get burned tips?
    Some questions from a Belgian bonsai addict 🙂
    Tx again for the interesting blog Michael.

    • crataegus says:


      Great questions. I think there is a lot of misunderstanding about watering delicate leaved plants like your maples. In fact, watering them in the full hot sun is never a problem. I’ve done it for years, in Japan, in Arizona, and here in Oregon. The tips of the leaves burning is usually an indication that they need more water. Watering twice a day rather than once should solve that problem. But once they begin to burn they will likely keep burning back a bit all summer no matter what you do to correct it now. Also, watering only in the evenings during hot days usually means that there are warm nights, and plants can dry out fast on a warm night so that they start the next day dry. Be very careful of this—

      The idea that watering leaves in full sun causes burning is something passed around by those in the gardening circles to bonsai to everywhere else and it is like a virus of misinformation. There is no truth to it. Your burning leaves are a separate problem. It may be due to salt, but too little water is another possibility. If the sun is really hot, these plants that are susceptible to burning may be placed under shadecloth in the summer. That will give you an edge, just keeping the temperature down.


      • David says:

        Tx Michael.
        Yes, misinformation is something that circles fast.
        I will keep in mind that watering leafs is not a problem in the hot sun.
        If i looked at the soil, i saw that this was not really dry, that’s why i didn’t water more. But maybe your advice is better. I will try it. Water more.
        I already placed the trees in the shade. Always better since i work long days…
        And not all my maples have the problem. I have one that’s always in the sun and never has this problem. That’s why i got confused about my watering.
        It’s a pitty to hear that they will always get the burning tips when they had it once… how does this come?? Are they more fragile after they had it once?
        Best regards

      • crataegus says:


        I might have been misleading. If your soil is wet, then don’t water it. But if it dries out even for an hour on a hot day you may see burning leaf tips as a result. One of the problems may be that those you see burning leaf tips on may not have as strong a root system as those with no problems. This may account for the fact that the soil is not drying out on those particular trees.

        And those tips will continue to burn only in that year. Next year you can avoid it with different culture. Have you tested your water for salts? You mentioned this and if the levels are very high, yes, that might be a part of the problem. Keep looking and thinking. Sometimes it takes a while to whittle down the variables.


  4. crataegus says:

    Hello Josef,

    I’ve seen thermometers break when maxed out. Hope yours survived…

    Mica is not so bad, really, they are dark so they soak up a bit of heat, but the material does not transfer it so readily. High fired ceramics is the worst for heat transfer. But terracotta and wood are the best. The terracotta in particular due to the porosity of the clay will be a bit cooler, because of evaporation.


  5. Elliott Farkas says:

    Living in the Hottest part of the San Fernando valley in Los Angeles, California, I am no stranger to extreme heat. I actualy chose to work night shifts so I can tend to my trees during the heat.What makes it worse for me is that because of the yard and sorrounding structures, I can’t put up any shade cloth. Last month we had a long heat wave that had temps over 105 f. daily for an extended period. I just spray the whole area with water and actualy soak towels with water and roll them up and coil them around the pots. I check and see who is dry and water accordingly. Some trees go into a semi dormancy in the middle of summer and will actualy get root rot if you water to much especialy the raw stock that is not yet in good draining bonsai soil.
    Also, my local wallmart was selling beach umbrellas that have a clamp at the base so you can sit at the beach in a chair with your own umbrella for shade. I bought about a dozen of them and clamped them to the bench or pot of the most sensitive trees. Since thay are about 3 feet above the tree, they provide shade from the noon day sun but allow the early morning and late afternoon sun to shine on them. They are all red, white, and blue stripped like the american flag, so my bonsai garden looks very patriotic. It gives my guests a good laugh. We get some very hot, dry winds here and I have had casualties so far. I even brought in some ficus retusa from Florida that went from 85 degrees and humid, into a box for a week, then into my 100 plus super dry windy heat and I didn’t lose a twig!
    Michael, you are a great artist and this is a great web site. I got the address from the bio they did on you in Bonsai Focus magazine (may/june 2009, issue #121). This is my first time here and I look forward to visiting regularly.
    Elliott (bonsai Eli) Farkas

  6. Mike Cole says:

    Sacramento are heat waves can reach 105-110 degrees. We have are having success putting “diapers” on the pots and surface of soil area. BTW, Costco sells watermelon flavored popsicles infused with botanical Gin.

  7. kiwijaz says:

    Ha ha – this post works for all of us who live on the ‘other’ side of the equator!

    Kind regards


    Ann Mudie
    157 Chestnut Lane, Pirongia, New Zealand
    021 072 0636

  8. Eugene Sekulow says:

    Thank you for the comments on watering, sun protection and reducing ambient heat in summer. I sadly learned the hard way and lost a very nice cryptomeria to sun scald. And nearly lost a lovely variegated ficus group the same way.

    Gene Sekulow

    Eugene A. Sekulow


  9. Gene Sekulow says:

    Excellent advice on shade. I speak from sad experience having lost a prized cryptomeria and nearly lost a beautiful variegated group ficus planting. And this in former Zone 5 now Zone 7. So much for no such thing as global warming. Cooling down the ambiance is good advice I had not considered.
    Gene Sekulow

  1. […] last two posts are prompted by the heat wave out west. One is a very timely tip on watering and the other is a story from his time as a bonsai apprentice in […]

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