Do Bonsai Trees Need Drainage Holes?

Yes, bonsai pots need drainage holes. Drainage holes allow the water to drain from the soil. Most bonsai pots already have drainage holes built inside.

Growing bonsai trees, shaping them into different forms, and maintaining their health is an art form that requires patience and skill. You may be interested in growing bonsai trees and perhaps you have even learned some things about the art. But you may be asking a crucial question: do bonsai trees need drainage holes?

Bonsai trees need to be planted in pots that have drainage holes. Drainage holes allow for:

  • Water to drain from the soil
  • Aeration of the soil

Bonsai pots function with the art of the tree’s appearance, but their essential function is to keep the tree healthy.

Choosing a pot for your bonsai tree can be a fun experience of matching the color and shape of your tree with the color and shape of the bowl. With choices that include deciding whether you want your pot to be masculine or feminine, it is easy to lose sight of the big picture: the pot must first and foremost support the health of your tree. Keep reading to learn more about bonsai trees and why they need drainage holes. 

The Need for Drainage Holes in Your Bonsai Pots

Drainage serves two important functions in the growth and maintenance of your bonsai tree:

  • Preventing water accumulation in your tree’s soil
  • Allowing air and nitrogen to get to the roots

This may sound simple, but when you consider that bonsai trees are grown in small and often shallow pots you can see why it is important for the bonsai tree owner to keep an eye on these two factors.

Bonsai trees are just small trees. That sounds obvious, of course, but it is important to state plainly because it means that your bonsai tree needs everything a large tree needs: sunlight, air, and water.

When you provide your bonsai with drainage holes in its pot you are giving it the proper function of two of those essential items for health and growth.

The Drainage in Drainage Holes

bonsai tree care

True to their name, drainage holes allow water to drain from the pot so that it does not build up in the soil and, in particular, around the roots. Your bonsai tree’s roots are susceptible to rot if water is allowed to accumulate around them.

Why should bonsai roots be so susceptible to rot in the first place? One reason is that they sit in small and shallow pots where even a little water accumulation is going to make a big difference. For this reason, in addition to drainage holes, you will also want to use bonsai-specific soil that is engineered to allow water to pass through it quickly. 

Another reason is that a bonsai tree’s weight is made up mostly of water, sometimes as much as 85 percent. And the leaves can be made up of as much as 90 percent water. This is an indication of how much the tree needs water and how sensitive it is to having too much. Watering a bonsai is a delicate balance.

Yet another reason has to do with the maintenance of the tree itself. Bonsai trees need regular root trimming to shorten the roots that are circling around the main root, also called the taproot. This involves:

  • Removing the tree from its pot
  • Trimming off between ¼ and ⅓ the length of the roots that are curling around the taproot
  • Doing the same to the roots in the lower root structure
  • Leaving alone the tiny, hair-like roots coming off the taproot

Once that is done, you have fresh and new roots exposed to the soil and to the water. These new roots can be easily damaged by water accumulation and begin to rot away. Ensuring good drainage for your bonsai tree is as basic to the plant’s health and long life as watering it is.

Here is an article about why bonsai pots are so expensive that might be interesting for you.

Aeration from the Bottom Up

When you read the word aeration, you likely think of it in relation to lawns. The idea of aerating your lawn is to use a tool to poke holes in the dirt or remove plugs of dirt so that air can get to the roots of the lawn.

It is the exact same principle when applied to your bonsai tree. The roots of your bonsai tree need air in order to thrive. In particular, the roots crave the nitrogen that makes up 78 percent of the air in the earth’s atmosphere.

The main difference between aerating a lawn and aerating a bonsai tree is that for a bonsai tree the principle of aeration has the reverse application. Instead of drilling holes through the top of your bonsai tree soil, aeration happens from the bottom up, and the drainage holes in a proper pot for bonsai trees allow that to happen.

How Many Drainage Holes Should Your Pot Have?

bonsai pots

Knowing you need a pot with drainage holes is one thing, but how many holes should a bonsai pot have? Is it possible to have too many drainage holes in a pot?

Yes, it is possible to have too many drainage holes, just as it is possible to have too few. The right number of drainage holes is not based on exact science, but more on a rule of thumb. Generally speaking, you want to base the number of drainage holes on the number of times you have trimmed the roots.

So, working backward, this is how it breaks down:

  • A stable and mature bonsai tree can have between 1 and 3 holes depending on what your tree needs (check moisture levels in the soil either by hand or with a monitor)
  • On a bonsai tree’s second pruning, it should have 2 holes
  • On a bonsai tree’s first pruning, it should have 3 holes

The younger the bonsai tree is, the more drainage holes it will need. By the time it gets to an older, more stable age, you will have been caring for it for about three years, so you will probably be able to judge for yourself how many drainage holes it needs. Just make sure it has at least one.

What about the Size of the Holes?

Why Are Bonsai Pots So Expensive

The size of the holes is often a topic of discussion among bonsai gardeners because if they get a pot they like that does not have holes or if they make their own ceramic pots, they need to make their own holes.

Remember about surface tension in water? It applies here. If a hole is too small, the water will not drain quickly unless it is forced. If it is too big, soil will leak out (this article will discuss that in a moment) and possibly make a mess if it is an indoor plant. Ultimately you would want it too large rather than too small.

When looking at the size of drainage holes, or possibly when making them:

  • Do not go any less than ¼ inch diameter
  • Do not go any more than an inch

Many bonsai pots will have a mixture of these two sizes (roughly). When going by the number of holes you need, use the larger holes for the count to be safe. But feel free to adjust as needed.

The Downside of Drainage Holes

The problem with drainage holes is that if they are doing their job, they can let out more than just water but the soil as well. Your bonsai tree needs to keep that soil to stay healthy, you would likely prefer not to have the mess wherever you have set up your tree.

Keeping the soil where it should be is actually pretty easy. You simply need to find some material to cover the holes and there are a variety of possibilities:

Any of these methods should work fine, but the most common solution tends to be some kind of fabric mesh.

Conclusion

If you want to grow and train a bonsai tree, you are in for a long but rewarding task where patience and careful skill win the day.

Be sure that you give your bonsai tree the drainage that it needs by choosing pots that have the appropriate number and size of drainage holes. 

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