Spring Watering Tip-

There are a lot of things we might say about watering bonsai. I’ve tried a few times on this blog to mention some of them. Some are hard to make sense of in words, but as ever I’m willing to try. This one is about watering recently repotted trees.

At post-repotting time we need to be awake to one change-up, and that is that the interior soil mass (the part that was returned to the pot) may dry out much faster than you’d think.

  • If that interior area is full of fine roots, it will dry out fast after repotting.

This pine is beginning to develop a solid mass of soil and roots, and this is the area that we’ll take our moisture ‘read’ from when deciding when to water. When dry, it will look very light colored compared to the surrounding new soil.

If you cut all the fine roots off in repotting your tree, shame on you, but that’s a different issue. For the sake of this example, we’ll assume you have fine roots, and that we’re talking only about established trees with a solid mass of roots and soil. There are myriad other situations, such as proto-root balls with stringy roots that don’t yet hold soil together, but these photos show what we’re hoping for and working towards.


A deciduous tree with a very mature ‘loaf’ of roots and soil that is returned to the pot, to be surrounded with new soil.

Especially with conifers, we usually don’t prune any branches at the same time as repotting. And so…

  • In repotting refined bonsai, we’ve created a situation where fewer roots are going to be supplying the same upper water need.

This interior mass we’re talking about, this is the area you should watch to determine when to water. Ignore, for a few weeks at least, taking your moisture reading from the new soil you’ve settled in around the original mass. There’s no active roots in the new soil yet and it won’t be drying out fast.

  • Another thing to keep in mind when repotting is to keep a portion of this old soil mass exposed, not covered with new soil, so that you can see when it’s drying out.

Freshly repotted beech, showing the two zones of soil—the older soil that is a bit green and mossy near the roots, and the newer soil that is gray (sphagnum moss covering new soil, actually). The older soil will be our indicator when to water, and is not covered with new soil on top but is exposed.

In many cases you’ll be watering when the new soil is still moist. So we ignore that area. Again, I’m only commenting on watering repotting bonsai with more mature root structures.

  • To sum up, only read the moisture level where there are roots to determine when to water.

Wordy post. Hope some of that made sense!

Here’s a previous post about watering that might spread a broader net around the issue of watering:


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  1. bindibonsai says:

    Reblogged this on Bindi Bonsai.

  2. Ann Mudie says:

    This all makes perfect sense to me – thanks!

  3. Reblogged this on Scratch Bonsai.

  4. Sage Smith says:

    Thanks for sharing your words of wisdom, as always

  5. Steve Varland says:

    Thanks Mr Michael, As usual you get to the ROOT of an issue! ( I couldn’t help myself )

  6. Daniel Dolan says:


    The photo you selected to show the established root mass is excellent. I understand that one could go several cycles of repotting, allowing the new roots time to reoccupy the container and at some point trimming the new perimeter roots, repotting and the cycle repeats. When, after numerous cycles, do you painstakingly comb out the center mass of roots when repotting….as is sometimes instructed?

    I recall an account by Peter Tea when he was in Japan that they had a monumental JBP with an 8″ trunk with a central root mass so dense that water would hardly penetrate it….and the challenge of watering this tree.

    With an refined older tree……..do you just never touch this area again?

    Thanks as always.

    I wanted to use Google translate, but I thought better not to.


    • crataegus says:

      Tends to be about the soil at the end of the day. The soils the Japanese use have great longevity, even though akadama does tend to break down somewhat over time, when mixed with pumice/scoria that interior area might remain untouched for decades. Still has penetration and fine root growth. Eventually some areas are teased out, but not often.

  7. backcountrydan says:

    Hey Michael, when do we get to see full pictures and a story about the limber pine in the first photo…? I’ve seen it in person a couple of times, but haven’t seen a post. Waiting until it’s picture perfect? 🙂

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