You might be wondering if bonsai trees can be left outside in the garden without any protection when it rains.
Most bonsai species thrive OK under normal rain because they grow in nature in outside open spaces like forests. That said, too much or continued rain may damage the bonsai trees depending on the potting soil, climate, and their growth stage.
Should you protect bonsai from rain?
There are four things you should consider if rain is good or bad for bonsai.
- Is normal rain good or bad for bonsai?
- Can bonsai get too much rain?
- Do you need to water bonsai trees when it rains?
- Is rainwater good for bonsai?
Is normal rain good or bad for bonsai?
Except for a few indoor bonsai species, most bonsai species grow in nature in outside open spaces like forests, parks and backyards without any protection from the rain. This means that most bonsai trees can thrive OK under normal rainfall. Rain just acts as watering by the grower.
There is one condition. Keeping bonsai under the rain is totally OK as long as the pots drain water and the soil dries enough. You have to be careful if the soil is covered with moss. It might keep the moisture in the soil much longer than we want.
Can bonsai get too much rain?
Now you know that normal rainfall will not damage bonsai. But what happens if it is not a “normal” rainfall? Does the amount/period of rainfall affect bonsai trees?
Heavy rainfall in a short period of time
Heavy rainfall does not harm your bonsai trees per se but the soil may flow out of the pots because of the downpour especially when recently repotted. As bonsai pots can contain a very small amount of soil, losing a tiny amount may be harmful.
Normal but continued rainfall
As I said earlier, rainfall acts as watering by the bonsai grower. But if it continues to rain, it might cause problems for bonsai trees. There are three factors that affect a bonsai tree’s water needs: soil, climate/weather, and bonsai species and their growth stage.
Continued rainfall may be harmful to the bonsai trees if you are using normal houseplant soil or if you haven’t repotted your bonsai trees at recommended intervals. Normal plant soil contains lots of organic matter (=compost) which keeps the water in the soil and does not drain as much as we want for bonsai. The soil may always be wet and the roots will be waterlogged.
In addition, high humidity prevents water in the soil to dry. In the humid zone at high temperatures, water need is about half compared to high temperatures under the same climate because moisture tends to stay in the soil when it is humid.
Water in the soil tends to stay longer for older, coniferous trees that do not need water as much as younger, deciduous/flowering trees.
If you are interested in how often to water your bonsai trees, please read the following post.
Do you need to water bonsai when it rains?
During the growing season when the bonsai foliage becomes dense, leaves may act as an umbrella from the rain for the soil. In a short drizzle, say 1 to 2 hours, the rain may not fully penetrate into the soil of the pot.
Also, those with dense foliage such as Japanese maple, Chinese quince, and camellia need lots of water because water evaporates from the leaves as well. So, when it rains, check whether the water is actually seeping into the soil. If not, you need to water your bonsai trees.
Is rainwater good for bonsai?
Rainwater has an acceptable level of acidity of around pH 5.5 for the irrigation of bonsai trees. For the majority of bonsai tree species, soils with a pH between 5.5 to 6.5 generally provide the best growing conditions, and rainwater fits within this range.
Among tap, rain, and bottled water, rainwater is always the first choice for irrigating bonsai trees because it is good for bonsai growth.
For a more detailed explanation of this topic, please check the following post.