Watering tip

Before the real summer heat hits, consider how you are watering your trees.

Have you ever seen your trees grow through spring just fine, only to get fried leaves at the first onset of early summer? Ever wonder why that happens?

Those trees just don’t have enough roots. Those are the trees that got overwatered, or simply never dried out, in the cool spring months. Their roots were never encouraged to hunt out water, so these trees could survive in the moist cool weather on about three roots. First hot day: bam, they get hit hard as they have a spindly root system, not enough to support their overlarge, over long leaves and shoots on dry hot days. (A bonsai version of a company that has overspent just before a recession…)

Especially on cool overcast days, if you can monitor them, water each tree only when it is really drying out and not by rote. Watering by a schedule is the surest way to have some really weak trees that show themselves in the hot summer.

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  1. juanbobsdad says:

    I am new to bonsai, but I must say that this sounds like hoo-do. Aren’t you mystifying the cause and effect? Isn’t this really about healthy roots?

    With a water retentive soil mix, “over-watering” will suffocate roots and cause root rot. Then the plant fails when the transpiration rate cranks up because the tree has insufficient roots to meet the water demand. The exact same trouble can be induced to a healthy plant by root pruning in these same environmental conditions.

    On the other hand with a well drained inorganic soil, one cannot “over-water”. Having healthy roots is then primarily a matter of proper plant nutrition (npk and micros), not watering habits. From my brief experience I would think every professional would use inorganic soil and some food like Osmacote for bonsai simply because it “automates” this tedium and frees the artist to do bonsai art.

    • crataegus says:

      I understand the skepticism. Watering seems straightforward. And yet in practice watering is mystifying. Watering is difficult.

      In theory your comments are correct. In practice it does not seem to work out that way. I rarely make comments on watering because it is one of those things that is best learned standing next to a teacher, not by words on a page. And that does sound like hoo-do, I know, I thought the same thing until I did it in Japan with my teacher and realized that for the previous 15 years I did not know what I was doing with a hose.

      Yes, it is about healthy roots, but also numbers of roots. If you have only a few healthy roots, later in the year we’re in big trouble. And that was what my post was about. Great extremes in seasonal and daily climate and weather are only supported by a large number of healthy roots. It is actually quite easy to over-water in an inorganic soil. A weak or recently repotted tree can be easily killed by too much root watering no matter what soil it is in. Like everything else in bonsai, watering is case by case. One tree at a time down the bench we are making multiple split second decisions regarding tree health, recent training, location, vigor, age, species, and what you did yesterday. If you automate or go by rote and stop looking and analyzing you no longer have bonsai but plants in pots. And some will be strong and the rest you will kill. And we’re not even talking about the finer points of bonsai: If you water a refined Japanese Maple like a Needle Juniper sitting next to it, you will never have good bonsai.

      Although it’s a famous product, Osmocote is a tricky fertilizer to use since it over-releases in the summer heat and can burn roots. Those growing 10,000 stock plants a year avoid it like the plague. It seems like a good product, releasing increasing amounts of fertilizer as the temperature rises, but there is no temperature cap to it. Better slow-release fertilizers are Apex or granular organics.


  2. Daniel Dolan says:

    Mr. Hagedorn:

    I am a member of the Midwest Bonsai Society in Chicago. I hope we will have you as a speaker soon. I appreciate your commentary and wish there were more care articles. A quick question following up your watering tip.

    Many bonsai authors and care descriptions frequently refer to the watering requirements for certain species as….” do not over water but keep roots/soil moist….never let dry out…”.

    Though still a novice, I have about 60 trees in training and watering is, as I have learned, difficult to master…without a master. How does your recommendation correlate with this familiar guide to keep moist.

    Typically, when our calcined clay soil [Turface] becomes brown with no interstitial moisture..one author Colin Lewis has advised that watering is OK but not necessary. However when this soil has turned light tan …one “must water.” I appreciate that these recommendations are without much context…the one constant being species care guides to “keep moist’.

    I would welcome you comments. I look forward to reading your book soon.

    Best regards,


    • crataegus says:


      Like Juan’s comment, yours is also excellent with no easy answer. It is precisely as you say, ‘without much context,’—and unfortunately, the context is as critical as the general rule. Or another way to put it is, the exception is as critical as the general rule, and the exceptions will continue to weaken your tree or kill it.

      This I know is not a comment that will give satisfaction. There are simply too many variables to accurately give advice about watering. But I should say that on my travels around the country, looking at root systems and soil components, Turface is one that gives some of the most unequal results. Sometimes a tree seems to do fine. Frequently very poor root systems emerge from mixes high in Turface. And so proper watering is confounded.

      Keeping a plant ‘moist’ is about as vague, I think you will agree, as whether aquamarine is considered a warmer or cooler color than cerulean. We simply cannot come to an understanding of proper watering through words. People smarter than I have attempted it, and I think, failed.


  3. Ben Griswold says:


    I really appreciate these important and very misunderstood thoughts on the fine balance of watering and soil dryness. In the past year I have begun to see the results of this concept being played out in one of my many experiments I am continuously performing in this art. The root systems of these trees are twice as substantial as the ones that are constantly wet, or “moist” =) In retrospect, I see now that this is the central repeating factor in nearly all the problems I have had with poor health, or death. I guess that’s why I feel the need to comment because I wish I had someone explain this to me years ago

    Part of the reason for my slow learning curve is that I did “alonesai” for many of my beginning years with only the occasional help of Masa from Japan Bonsai. I have learned these lessons on watering the hard way through killing many, many trees. Over-potting was the biggest cause of the death of my trees in the beginning since I was attempting to grow much of my own stock as big and as fast as I could. Brent Walston’s article on, “Why the Earth is Not Like a Pot”, was probably one of the most important articles I ever read in bonsai. This along with joining the Portland Bonsai Society last year directed my understanding of roots needing to seek water to colonize a pot quicker.

    I find, like Daniel and you alluded to, that I have had to unlearn all those vague suggestions in bonsai books concerning watering and soil composition. Amusingly, one book I have referred to loam as being a good soil component. So of course being persistent like many of us “enthusiasts” are, I had to find out what the hell loam was and where I could get it! Loam of course didn’t solve my problems, but I have learned some invaluable lessons… most of them through failure.

    Ive spent the first 9 years learning how to water, develop healthy root systems and basically keep trees in pots alive. Maybe now I will have some time to learn the art of bonsai


    • crataegus says:

      Everyone please read Ben’s comment on the post ‘Watering Tip.’ I agree with him—improper watering is the key cause of problems with bonsai. And without the foundation of a potful of roots that proper watering brings, all the other problems rain down on the weak tree. And we begin to think the ‘problem’ is something else entirely and not our basic care—
      Thanks, Ben,

  4. bonsaitico says:

    Hi Mike:

    Thanks for taking the time to share all these tips on bonsai culture. I cannot think of anyone else writing on these subjects. Somehow I feel your posts are preludes to chapters on your next book 🙂

    With the current reductionist trend going on in bonsai, I can only hope more discussion on the finer points of Bonsai come from people like you and spaces like these.

    Best regards,

    • crataegus says:


      Ah, discovered. I am always writing…and some of the next book might get inspiration from this blog, you never know.


  5. Lzyjo says:

    Interesting, I will be taking this into account. It’s been in the mid 90s for weeks and now I see my fear that the bonsai would dry out caused error in the opposite direction. I’ve really been over watering the bonsai, even in this hot weather I should be giving them a chance to dry out. Thanks for the great simple tip!

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