How to Avoid Burned Leaves on Deciduous Bonsai

Preventing burned leaves on deciduous trees in the summer involves two things: 1. We need a lot of fine roots. 2. We need to water frequently. Let’s break that down a bit.

If we don’t have a lot of fine roots, it won’t matter how much we water because few roots won’t be able to support the water needs of the tree at 95 F/ 35 C. If we overwater before we have many roots, we won’t get many more to emerge. And if the tree is in a poor soil mix, we won’t get many fine roots for that reason, too.

If we do have a lot of fine roots, and yet don’t water more than once a day at 95 F/ 35 C we will likely get burned leaves on our beeches, maples and other deciduous trees anyway. On a hot sunny day be ready to water 3 times a day. If your lifestyle does not allow that, then set up a watering system for the one or two watering cycles that you can’t do by hand.

Both of those requirements must be met to prevent burned leaves. Take a look at these photos:

This is the soil of the Japanese maple also shown in the next shot. There are many fine roots all the way to the top of the soil surface. They even climbed up and went into the fertilizer pellets on the surface. That kind of fine root growth is what you want to prevent burned leaves. If you don’t have fine roots bumping happily along the top surface of the soil and through your moss you can be sure it has not colonized the pot and it is only growing along the sides of the pot, which is the worst place for them. On the sides they will get scorched by sun hitting the pot, and will suffocate in a pool of water at the bottom—and that is a very unhappy and unstable tree.

Japanese maple, Acer palmatum, at the end of August.

Red maple, Acer rubrum, at the end of August.

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  1. Dylan says:

    Great post (and recent frequency of post). I was thinking my maples were getting too much sun because the soil always seemed wet but the leaves were getting the edges singed. I think this cleared up a lot. Thanks for the Juniper article as well, I was definitely confused about that bit of information as well.

  2. art rodriguez says:

    do we get the fine feeder roots to grow above by spreading some sifted spagnum moss ?

    • crataegus says:

      Yes! Sphagnum is a great help in getting fine feeder roots to colonize the top layers of soil. And that sphagnum moss is a great nursery for live moss to grow, too.

  3. G.Hues says:

    I think I need to add more pumice to my mix …for my maples…..I’m assuming you use a fair amount in your mixes?
    Cheers Graham

    • crataegus says:

      Yes, I do use a lot. Depending on the tree, I can use as little as 30% pumice or as much as 70%. For the maples I would say about 50% is a good starting place. If you grow pines you might well wish to use a bit more pumice. But if you’re using akadama as your secondary particle you don’t need to worry about soggy soil, really.

  4. Alex says:

    Hey Michael, do you keep any of your maples underneath shade cloth?

    • crataegus says:

      I haven’t, but I think it would be a good idea even in the mild summers I have. Just 20% softens the direct sun. In Japan we did have shade cloth over the deciduous, but the summers there were more intense.

  5. Al says:

    Hi Michael, i have two Bloodgoods 6′ high 20′ apart facing south west in the cooler area near San Francisco. Planted last season. The dirt down deep is clay! They are doing very well except at this time the leaves get scorched possibly by sun and continuous light breezes from the bay. I have defoliated them and i know they will bud again prior to winter.
    1. Do you think more frequent watering might help? I might start doing that 3 times a day! I see other maples in the sun not scorched and i see some in semi shade… scorched.
    2. Their leaves are usually green underneath but one of them just turned all leaves green. Why?
    Both trees come from the same source.
    If you go to you will see a Yin Yang i just built. There i have a Hefner maple in each center. Being in the back yard they do not suffer as much as the Bloodgoods. Anyway, thank you very much in advance. Have a great day!

    • crataegus says:

      I don’t have much other than to agree with you that possibly more watering might help. But if they’re in the ground, periodic deep watering is the way to go. Not sure what the color shift is that you describe, other than the Bloodgoods can have green areas occasionally here and there.

  6. Dianna Harris says:

    Terrible sunburn in the Pacific NW June 27th temps over
    100 F. My shimpaku’s, black pine’s, white pine, maples, and many more. I’m just sick. I went out to water yesterday evening and found horrible damage done by the sun. They look like they’ve been flocked with rust colored paint. I moved all of them last night to the other side of the house so they’re in the shade now. I know not to over water… can you please tell me what else I can do for my (some are over 30 years old) precious bon’s.
    Ty D

    • crataegus says:

      Hello Dianna, I’m sorry to hear of these plant damages. You’ve got the main thing, don’t overwater. If you can mist them a bit without getting water in the pot that helps a lot. For a year they will look ragged, there’s not much to do about that, but you want to prevent root rot and any more damage. On mild days they should get more sun. Don’t lose hope. It sounds like you’ve got the right instincts.
      For the future you may look into shade cloth for your growing area, that can help prevent severe sun stress.

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