The Art of Watering Bonsai

Really the only logical place to begin is with water. Water is the most important aspect of bonsai because when we strip away all of the design aspects of bonsai we’re left with just a tree.

Trees, like plants and people, need water to survive. If you don’t water them they will die. If you water them too much they will die. The most important task you have when caring for bonsai is to keep them alive. What differentiates bonsai from nearly any other art form is that your media is alive. If your plant dies your art dies.

Watering is widely regarded as the most difficult art to master. From my understanding of apprenticeship in Japan, watering is the second task you are given to learn (the first task being cleaning and straightening up the nursery). In fact, many bonsai masters claim they have not “fully mastered” watering after 30 or even 40 years of working on trees.

Any variation off the exactly correct watering technique will obviously be watering too much or not enough. While determining the exact moment your tree is thirsty may take eons to learn and perfect, watering in a manner that keeps your tree alive is much easier than most people make it.

Over Watering

I wanted to start with over watering because it’s exactly what killed my first few bonsai trees and it’s my suspicion that it’s what is most likely to kill your’s. Getting into an over watering cycle is easy to do and the results happen quickly. This is how it will happen:

  1. You water your tree.
  2. You come back the next day to check on it and the soil looks dry, so you water it again.
  3. Then the next, same story, rinse and repeat.
  4. When you come to check on your tree you notice that it’s drooping a little. “Wow it must really need more water than I’m giving it” and you water again.
  5. On the fifth day you notice that the leaves are starting to look yellowish and pale. The petioles (little stem that connects the leaves to the branch) have become weak and the leaves will fall from the tree when you brush them with your hand.
  6. Eventually all of the leaves fall from the tree. The thin, limber limbs become stiff and brittle. Your tree is gone. Dump it out. Save the pot.

You can see how at the end of my first month I had a stack of empty pots and a sad pile of sticks behind my house. When I began to be interested in bonsai again (at 25) I was fortunate enough to have the internet filled with bonsai info to assist me. Also, perhaps a 25 year old had a little more ability to understand instruction than a 10 year old.

I believe the majority of over watering occurs for a few reasons. First, almost every bonsai book, website, or video explains that bonsai need to be watered frequently. Many instruct you to water at least once a day and sometimes more during particularly hot weather. So, is everyone wrong? I watered everyday just like the bonsai pros said and it killed my trees.

What the books, websites and videos typically don’t explain is that they are generally talking about mature, established trees in ideal soil. Let’s break that down. Mature trees are larger and have far more complex branching and root systems than their younger counterparts. While it is certainly true that young trees need lots of water to grow vigorous shoots, mature trees need far more water to maintain their compound and extensive systems. Established trees, meaning ones that have been trained as bonsai for many years and have likely remained in the same pots for some time, have large clusters of compact feeder roots. Unlike full-size trees whose root systems may look like a giant web, established bonsai root systems look and work like a giant sponge.

Finally, ideal bonsai soil drains incredibly well. There are an infinite number of theories on the best mix for bonsai soil, but for the purposes of this moment, I’ll just say that professional bonsai sit in soil that is a mixture of large and small particles of both water retaining substrate and non-water retaining substrate. Image thousands of soil particles that fit together in a way that creates millions of tiny holes and crevices for bonsai roots to meander through. Unlike the soil in your back yard which may be filled with clay and decomposing organic material, bonsai soil uses material like lava rock, pumice, sand and other materials that won’t compact and do not retain a great deal of moisture.

As you can see, any professional watering in a professional environment will recommend that you water frequently because the trees they are growing are in ideal condition and require copious amount of water to thrive. If you’re like me then you bought a starter tree from a nursery. It is a young tree. Likely cut down from a full size tree or just a sapling, and plopped down in a cheap commercial pot. Maybe if you’re lucky it’s in “bonsai soil.” Even then I can guarantee that your soil and conditions will retain about 1000 times more moisture than our friend’s in Japan.

If you want your tree to live you’ll learn to find out exactly what it needs.

The best way to practice good (maybe not great) watering techniques is simple. Everyday you stick your finger about a half inch in the soil. If you can feel damp soil, and I mean when you pull your finger out of the soil the air makes it feel cool, then you don’t water. This is obviously an art and not a science. you will not be perfect today, tomorrow or the next day. I cannot tell you the perfect degree of wetness your soil needs to be before you water. Just follow your instincts. If its damp it doesn’t need water. If it’s dry, water it. If your plant is still alive at the end of the month you’ve at least beaten the curve.

Under Watering

Honestly I feel that this rarely occurs. I’ve never met someone who sort of likes bonsai. If you like it, you’re probably obsessed. If you’re not obsessed than a time consuming hobby like bonsai is probably not for you. While I do not believe there is a great deal of under watering going on, there are two very important notes to make while we’re on this topic.

The first comes from Ryan Neil. At the moment I won’t touch on Ryan’s history. At a later date I promise to detail as much as I can about the various people that make bonsai what it is today. It suffices to say that he is an important dude and more info on him can be found here.

Ryan makes an interesting point about bonsai that I think is commonly lost or misrepresented by much of the community. Junipers don’t like to be dry. Neither do Pines or any of the other species that folks are always saying prefer to be dry. Just because there are junipers that grow near the desert or in dry climates, doesn’t mean that junipers prefer to have dry soil. A tree, really any plant or animal, exists in an environment because they can survive there better than all the others. Yes, a juniper can live in the dry mountains where a maple would die, But this is just because the juniper developed adaptations to live in that environment while the maples did not. Obviously this does not mean that your trees should be sitting in a pool of water in their pots, but it does mean that withholding water for the sake of a plant’s “preference” does nothing more than hold it back from its true potential.

The second point is made by Jonas Dupuich on his blog Bonsai Tonight. Again, I’ll elaborate on Jonas and others in posts to come. The central point he is making in this post is that things like surface moss can obscure your ability to successfully evaluate your need to water your trees. While top moss retains water very well, it can hide the fact that the soil underneath is drying out.

There are a million facets to the topic of bonsai watering. Hopefully I’ve detailed enough to keep your plants healthy and alive. Please feel free to leave any questions you may have. If I have answers I’ll give them. If not, I’ll do my best to find out who can.


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2 Responses to The Art of Watering Bonsai

  1. Anonymous says:

    Can you make a few recommendations for the person who works 9-5 mon-fri and isn’t able to check on their trees during the hottest part of the day?

    • Thanks for that great question! I happen to have a regular day job as well and do not get to spend very much time with my trees either. I would suggest a few major things that should help keep your trees from drying out:

      1. If possible select a spot for your trees that gets the most sun in the morning and gets less sun throughout the day. The summer sun is hottest after 12 noon and can scorch delicate leaves like maples. You could also put your trees in a spot that gets partial shade or broken light (this is what I do). I find it works pretty well even for trees like pines that may prefer direct sunlight.

      2. Use a blend of soil that contains a larger proportion of organic ingredients, like pine bark. Pretty much all the professional sources you read will promote the use of mostly inorganic soil holds very little water. It’s true that this is ideal for growing and sustaining professional bonsai. Unfortunately we don’t all have the time to care for our bonsai like the pros. A soil mix that retains more water can save you in the summer!

      3. A less evasive measure, especially if you won’t be repotting soon, would be to cover the surface of your soil with damp sphagnum moss. you can buy it dried at many garden shops and it’s relatively easy to pull apart, soak, and place. It basically helps by retaining a good amount of water and also shielding the top soil from the scorching sun.

      You could always install an automatic watering system, but that is expensive, and more importantly you won’t learn anything by watering that way.

      Hope this helped, and best of luck!

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