The most important aspect of Bonsai care is watering. How often a tree should be watered depends on several factors (such as species, size, pot size, season, substrate composition and climate), which means that it is impossible to say how often to water.
Nevertheless, understanding a few basics will help you observe when a tree needs water.
As a general rule, it’s really not advisable to go more than 10 days without watering, again, this can vary depending on maintenance, but it’s not something you should exceed often.
How regularly should I water my bonsai?
How often a bonsai should be watered depends on too many factors to give a precise rule. Therefore, you must learn to observe your trees and know when they need to be watered. The following rules will help you to water a tree correctly:
Water your trees when the substrate becomes almost dry
This means that you should not water a tree when the substrate is still wet but only when it starts to dry. You can use your fingers to control the substrate to about a centimeter deep. With a little more experience, it is possible to see (rather than feel) when a tree needs to be watered.
Never water out of habit
Always observe your trees individually, rather than watering them daily out of habit, until you know exactly what you are doing.
Use the right substrate mix
The substrate mix has a big influence on how often you water your trees. For most trees, a mixture of akadama, fine gravel and sifted potting soil mixed at ½, ¼ and ¼ ratio works well. However, a mix that holds more water (using more sifted potting soil) can be used when you can’t water your trees often enough.
What are the factors to know when to water your bonsai?
Different needs for different species
Each species has different needs. Outdoor species like maple, Chinese elm… will need to be watered more often than a tropical species grown indoors like ficus. Grown outdoors, bonsai is exposed to sun, light and wind, which dries it out more quickly. However, rain can change the frequency of watering.
Watering through the seasons
A tropical bonsai grown indoors will need to be watered more frequently in summer and winter, when it is hotter because of the sun and dry air caused by heating.
Outdoor bonsai will need to be watered more frequently in summer, because the sun is stronger, temperatures are higher and exposed to drying winds. In autumn, winter and spring, bonsai may be exposed to heavy rainfall, which may affect the frequency of watering.
Sun and light
The sun is an important element that influences the frequency of watering. Indeed, the light and the rays of the sun can heat the bonsai and its pot and thus increase the evaporation of water and the transpiration of the plants, even in winter.
In a simplistic way, we can say that the more a tree is exposed to the sun during the day, the more the watering frequency is reduced. However, it is also important to know that a bonsai receiving morning sun will dry out less quickly than a bonsai placed in the afternoon sun.
Exposure to wind
In addition to drying out the surface of the substrate more quickly, the wind can increase the transpiration of the tree, i.e. the evaporation of water by the leaves, on certain species. And thus, reduce the watering interval.
Temperature and humidity level
A high temperature increases the transpiration of the bonsai and thus reduces the drying time of the soil, even if the weather is cloudy. However, this is true when the air is dry. Another factor to consider is the humidity level which plays an important role in the watering cycle. A high humidity level decreases plant transpiration and water evaporation, thus reducing the drying time of the soil.
The size of the pot
The size and depth of the pot play an important role in the frequency of watering a bonsai. Indeed, a bonsai placed in a small pot with a shallow depth will dry much faster than a bonsai placed in a large pot. A larger volume of soil gives a larger water reserve and thus increases the drying time. The drainage of the pot is also a consideration.
The substrate or soil mixture
Some components of the substrate or soil mix have a better water retention than others such as peat moss, vermiculite, sphagnum moss, clay, etc. The more these elements are present in your substrate mix, the more drainage will be reduced and the water retention capacity increased. As a result, watering should be more frequent.
Also, that other components have a less good water retention like, for example, pozzolan, river sand, etc. The higher the percentage of this type of component in the bonsai soil mixture, the less frequent the watering.
In addition to the composition of the substrate, it is also necessary to take into account the granulometry. Some components such as Akadama, river sand, gravel or pozzolan have a grain size that promotes aeration and drainage. The larger the space between the grains, the more often you need to water.
How should I water?
When we see that the plant needs water, we must water thoroughly, that is to say water until the soil is completely soaked.
We will need a watering can with very fine holes so that the water will gush out gently.
The bonsai are watered in two times: once so that the moisture opens the pores of the soil, and after a few minutes, a second time, until the water comes out through the drainage holes.
The tray that accompanies the indoor bonsai is used to prevent the residual water from dripping onto the furniture. After watering, this tray should not be filled with water.
The water level should not reach the holes in the pot. A bonsai that is always wet will see its roots rot.
On the other hand, there are bonsai which, having a very pasty soil, cannot be watered well by the method mentioned, because the water slides on the sides of the pot and does not penetrate any more in the soil.
This is the case of bonsai from China: Carmona, Sageretia, Ulmus, etc.
In order for the soil of this bonsai to soak properly, we can place them on the plastic tray that accompanies indoor bonsai, and let them soak in water for about ten minutes.
You should also water in this way the root ball of the bonsai which by forgetfulness has dried up and is no longer well soaked.
Never water with a sprayer which is used to remove dust or to provide moisture to the plants: THEY ARE NOT USED FOR WATERING. They only moisten the surface of the soil and the water does not reach the roots.
What time of day should I water my bonsai?
The time of day you water is not very important; however, it is best to avoid watering in the afternoon, when the substrate has been heated by the sun and may be cooled sharply if cold water is used.
How do you water a bonsai when you go on vacation?
This is a question that many bonsai owners ask themselves, once the vacation is approaching. The ideal solution is to entrust your bonsai to a close friend or family member. This person will be able to control and adjust the watering according to the different factors that affect the watering, such as the weather or the temperature. This is the most economical solution, especially if you have several bonsai trees.
A second solution is to have the bonsai kept by a professional. For a relatively small fee, he will water and care for your bonsai during your vacation. As a professional, he will also know how to react to unforeseen events.
Another solution that is a costly affair and requires DIY skills is the installation of an automatic watering system.