Watering your Bonsai

By far the most e-mail I get concerns watering. There are may instances where someone has purchased a Bonsai from a non specialist supplier, and been told to "water it every few days", this is wrong. You must use your judgement to ensure the tree gets enough water for its needs and if this means watering it two or three times a day at the height of summer, or indeed not watering it for a month or so during the winter, then do so.

Of the things your bonsai need to survive, water is going to prove to be the most difficult to provide in the right quantities at the right times. Too little water and your tree will shed leaves or needles, then branches in an effort to stay alive. Too much, particularly in a poor draining compost and the roots will rot away.

Ideally the soil should be moist at all times and be moist all the way through. Splashing a drop of water onto dry soil, in the mistaken belief that it will soak in does not work. You must water the tree long enough to ensure the soil is soaked through. However, occasionally it is beneficial to allow the soil to become dryer than you might think it should, allowing this to happen lets fresh air into the root mass.

As the root mass begins to fill the available space, the whole rootball becomes compact. When this dries out shrinkage occurs, pulling the roots and soil away from the pot. Although as I've stated above, some air must be allowed to get to the roots, this particular situation is dangerous, as the root hairs will soon be killed. While this probably will do no long term harm if caught in time, It will 'check' the tree and may, in extreme cases cause leaf shedding.

The illustration to the right shows a compacted root mass, in need of repotting.

When watering any tree, but particularly one that has dried out, you must ensure that it is thoroughly watered. The illustration to the right shows a tree where the root mass has shrunk back from the pot and a light watering will flow into the space opened up and out through the drainage holes. This gives the impression that the tree is well watered, but has no real long term benefit.

If your tree has dried out to this extent, your best course of action is to stand it in a bowl of water, until it is thoroughly soaked, say a couple of hours, then rest the tree in the shade for a day or so.

If you allow to much moss to grow on the soil, you will find that it will act like a raincoat, stopping the water getting through to the soil and allowing the water to run off over the edge of the pot.

You should try to have a large container full of rainwater, filling your watering can from this, as most tap water now has chemicals added.

Your can should have as fine a rose as you can get to avoid washing the soil away.

You will need to allow for the container the tree is in/on. A 'slab' type pot has much more soil exposed than a standard pot and will dry out quicker, so keep an eye on such trees.

the tree to the right is an Olive and will need careful watering.

Trees in shallower pots will dry out quicker and you may consider placing them in a less sunny location.


Over watering

Under no circumstances should you stand your trees in a bowl of water for more than a few hours. Prelonged immersion in water may kill the roots and of course the tree.

Nor should you water a tree that doesn't need it. More bonsai are killed by this than any other cause, watering the tree every day while the compost is still wet, will cause root rot and the death of the tree. Only water the tree when it needs it!.


If you must submerge your pot in water, watch out for Liverwort, as the spoors are distributed in water. Liverwort is a small flat plant related to mosses. This plant is indicative of poor drainage.
The plant reproduces in two ways. Firstly it has a small umbrella like flower (?) that produces spoors (Like a mushroom), pick these off as soon as you see them.
Secondly on the flat plates that make up the plant you will see cups, each of which contains spoors that, if submerged are released into the water and then onto the next tree you put into that water. Dabbing the liverwort with malt vinegar will kill it and any spoors in the area, however you should bear in mind that vinegar is acidic, so don't overdo it.

A Liverwort, showing the 'cups'

If you use a hosepipe you must have as fine a nozzel as you can get and bear in mind that you should not aim the hose directly at the soil, It will wash out of the pot.

Try not to get water on the leaves while they are in full sun. Some people think this recommendation is because the droplets may act as a lens and cause burning on the leaves. This is not the case. If you live in a 'Hard' water area, as I do, you will find that rapid drying out of droplets causes chalky deposits to be left on the leaves and they are a sod to remove.

Watering systems

On the whole automatic watering systems are an evil. (all right I admit it I've got one ) With a lot of trees to water and not much time to dedicate to each, I find it a good idea for those trees still being developed. But please don't become to reliant on this, as the needs of each tree and the depth of the pot it's in affect the amount of water it will need.

Holiday Watering

This can prove to be a problem, even if you do have an automatic system, you should still try to get a friend, or neighbour to check it's functioning OK. If you haven't got an automatic system try to come to an arrangement with someone you trust and have them water your trees, perhaps in return for some favour you could do for them while they're away.

If you only have a couple of trees there is an alternative.

Stand the trees in the bath (with the plug out of course), on piece of old cloth, or capillary matting (available from garden centres). Leave the tap dripping on the matting, this should supply enough moisture for their needs while you're away. I've used this method and provided you push the pots well into the material they'll be OK for a couple of weeks.

Allen. C. Roffey Sunday, July 15, 2018 15:09