When any tree grows in its natural habitat, it requires plenty of water, which the plant acquires by developing roots that penetrate deep into the soil and also stretch quite far around it. Though a bonsai tree is small is size, it also has similar requirements, obviously according to its proportion. Precisely speaking, nearly all bonsai trees require frequent as well as abundant watering, especially during the summer. Even if the bonsai trees are kept outdoors and exposed to natural conditions, including rain, it does not imply that the grower can do away with watering the plant. You should always bear in mind that the moisture retained by the tree's root ball is never sufficient to fulfill the tree's requirements.
Similar to any other tree, a bonsai also requires fresh water that does not contain any toxic physical elements or harmful chemicals. There is no doubt that though rain water is found to be polluted in some urban areas, it is still the best for these plants. Even well water is good for the plants, but you need to ensure that it is not limy or hard. If the water in your well is limy, you may soften it by using requisite equipment before providing it to the plants. On the other hand, you may also water softening tablets, which are available commercially. These tablets should be used as per the instructions printed on the packaging to reduce the pH level of the water, thereby softening it.
You can also use tap water for this purpose, but only after ensuring that it contains relatively less amount of chemicals that are used to purify the water from reservoirs. In fact, chlorine is most harmful for the plants, because it is extremely toxic to plants. If you have no choice, but to use tap water for watering your bonsai, it is suggested that you collect the water and keep it in the open for many days. When you keep the tap water outside for some days it will help the chlorine in tap water to evaporate. Irrespective of the water you may be using to water your plants, especially if you are using water from a well, ensure that it is not very cold. Using very cold water may give your bonsai trees a shock. Therefore, you may fill your watering cans several hours before you use them for watering, as this will help the water to become warm and its temperature will be same as that of its surrounding.
Great care needs to be taken while watering bonsai trees. It is best to water these plants using a fine rose to avoid damaging their delicate leaves or washing away the compost on the surface of the tray/ container. Using a watering can having a fine rose is alright if there are only a few bonsai trees to water. On the other hand, if there is a group of plants having different sizes, watering them may really turn out to be a major chore. In the second instance, you will be requiring sprinklers that are mechanically operated by a tap or robotically using a valve controlled electronically.
If you are using a watering can, you will also require a sprayer, if possibly a pressure sprayer, to mist on top of the leaves when the whether conditions are warm. On the other hand, if you are using a sprinkler device, it will work automatically, fulfilling your requirements.
However, it is not possible to predict how frequently you need to water a bonsai tree, because different species have dissimilar requirements. In addition, the climatic conditions in your place may also differ. Generally, the rule is to water the plant often, but in moderation, instead of watering them infrequently and liberally. At the same time, you need to ensure that the compost is always damp, but never be soaking. If the compost retains water in any way, it may result in root rot.
It is important for you to know that a bonsai tree needs maximum water when it is growing very robustly as well as when the weather conditions are hot. On the other hand, it requires very less water during the weeks after it has been pruned or its leaves and shoots have been clipped. There are two reasons for this - first, the pruned roots system is able to draw very little amount of water; and, second, very less water evaporates from the clipped leaves.
Generally speaking, you need to water the bonsai trees roughly once every week during the winter months. However, even this is subject to the overall humidity in your region. On the other hand, they should be watered several times during the middle of summer. If you find that the root ball of the plant is drying up, you should immediately immerse the tray in a basin filled with water. While doing this, you ought to be careful and ensure that the tree is not uprooted. At the same time, you must also keep the foliage damp by spraying/ misting water on it. In fact, it is particularly important for you to take care of the tree everyday, especially from spring when the warm weather is approaching.
Providing a bonsai tree with excessive water may prove to be harmful for the tree. For bonsai trees grown outdoors, too much rain during autumn and spring may be as detrimental for the plant as the extremely hot summer sun. In order to prevent water logging and avoid loss of soil, you need to make a sloping shelter, for instance using a clear polythene or plastic sheet over the tree. At the same time, you may angle the trays somewhat to ensure that any excess water will flow out of it by itself.
In you have placed the bonsai tray in a slanting position, you should keep an eye on the fact that the shape of the tree does not change. In case you are not growing water-loving trees like willow and wisteria, you should never place the container in a saucer or tray, because doing this may prevent the drainage of water, thereby leading to root rot.
Watering bonsai plants that are grown indoors do not pose many problems for the grower, because the climate indoors remains relatively stable. These plants should be watered no less than once or twice every week, subject to the size of the container it is growing in. If the pot is smaller, you will be required to water the plant more often.
Apart from watering the bonsai, the leaves of the tree should also be misted using water frequently, because sometimes the atmosphere indoors may become very arid. If you have a central heating system at your home, it will only aggravate the problem, and it will be necessary to spray the plant with water more often, particularly during spring. This is primarily because the new growing season of the plants start during this season and usually the heating is also on.
The frequency of watering bonsai trees actually depends on several factors and, hence, it is quite difficult to offer any specific guideline. Therefore, it is strongly advised that you should learn to monitor your bonsai trees and learn when they actually need watering. Nevertheless, the guidelines discussed below may possibly help you to know when you should water your bonsai trees.
It is suggested that you should water the bonsai trees when the soil becomes somewhat dry. In other words, you should never water the trees while the soil in the container/ tray is still damp, but only when it becomes somewhat dry. You may use your fingers to test the soil up to roughly 1 cm (0.4 inch) deep. As you become more experienced in the matter, you will see (rather than feeling) the time when a bonsai requires watering.
Watering should never be done on a routine basis. It is advisable that you continue to observe your trees separately, rather than watering all of them on a routine basis daily. However, you can follow a routine when you are sure about what you are doing exactly.
In addition to watering the plants when they actually need it, you should also use the appropriate soil mixture. This is mainly because the soil mixture usually has a great influence on the frequency of watering the plants required by the plant. A blend of akadama, potting compost and fine gravel mixed together in proportion of 1/2 to 1/4 to 1/4 is appropriate for nearly all bonsai trees. Nevertheless, ideally you need to use a soil mixture that has the ability to hold more water, by including additional potting compost to the mixture. This will be useful on occasions when you are not able to water your bonsai trees on a regular basis.
As discussed above, you should only water the bonsai trees when the soil becomes somewhat arid. However, when a tree actually required to be watered, it needs a thorough soaking. Water the plants in such a way that its whole root system becomes damp. In order to do this, you should continue watching till the water starts flowing out of the drainage holes of the container. You may repeat the entire process some minutes later.
You should always water your bonsai tree from above with a watering can fitted with a fine nozzle, as this will not allow the soil on the surface of the container/ tray to wash away. If possible, you should collect and store rain water for watering your plants. Rain water is considered to be the best for bonsai or for that matter any other plant. However, if rain water is not available readily, you can also use the usual tap water after softening it.