Part 3 of a series by Eugene Howell
Of the four basic requirements for keeping a bonsai tree healthy, we’ve already discussed the first two in this series and they’re linked to at the bottom of this page. Today, while discussing how to care for bonsai, we’re going to talk about water.
All bonsai enthusiasts and gardeners intuitively understand that a plant needs water to survive. In fact, the lack of water will kill a plant faster than any other lacking need.
For the bonsai grower the question becomes “how much water should I give it and how much is too much?” Some people believe that if a little water is good, then more water is better. Unfortunately this is not the case as evidenced by the fact that most houseplants die from one cause, too much water. The interesting thing is that a plant getting too much water will show the same symptoms as one getting too little. To understand why, we need to know how roots function.
A plant’s roots are the structure that absorbs water and nutrients into the plant. To do this there are thousands of “root hairs” on all the smallest roots. Through osmosis, water and dissolved minerals pass into the root hair and enter the circulatory system of the plant. The amount of water absorbed depends on the amount of water given off by the leaves. The more that’s given off by the leaves, the more that’s absorbed by the roots. There is a limit to the maximum amount of water that can be given off by the leaves at any particular time. So, if there is more water surrounding the roots than can be absorbed by them, the roots will be subjected to a very unhealthy condition.
The reason this is unhealthy is because all soils contain millions of fungi and bacteria per teaspoon. And the one thing fungi need most to begin multiplying at a phenomenal rate is constant wetness. When roots are subjected to soggy conditions for days at a time, fungi begin attacking the roots and root rot sets in. This kills the roots, thus the plant is no longer able to absorb water. So a plant that has too much water reacts the same as one with too little. The plant begins to wilt, the leaves begin to curl and start turning brown. Eventually the leaves die and the plant soon follows.
No one wants to lose a valuable bonsai, especially one you’ve worked so hard to create. So what do you do to prevent this? The first thing is to make sure your tree is planted in a good bonsai soil mix. Through hundreds of years of growing bonsai, the Japanese have learned that bonsai soil needs to be fast-draining yet moisture-retentive.
Here in Florida we have adapted their formula to take advantage of the materials reasonably and economically available in our area. The basic formula for the soil we use is one part of very coarse sand (usually sold for sand-blasting), one part ground pine bark and one part Turface. This mixture will allow water to drain almost as fast as the sprinkler pours it on, yet will retain sufficient moisture so the tree can get through our hot summer weather for up to 24 hours following the application of water. If the tree is in very little soil, such as in a shallow bonsai pot, then watering twice daily may be necessary during the summer.
The timing of the daily watering is important. Studies at various universities have shown that when the root system of a plant reaches 90 degrees F, activity within the roots comes to a halt and when the temperature rises only a few degrees above 90, the roots begin to die. During the hottest part of the year, if your bonsai trees are in full sun for the entire day, especially those in black or dark colored pots, watering about mid-day will cool the roots and help protect them from the intense afternoon heat.
During Florida’s cooler winter months, when the water in the soil does not evaporate as rapidly and the plant does not use it as quickly, the moisture level in the soil will usually last at least 48 hours, and in some cases up to 72 hours for dormant trees.
Using a soil mix that contains more organic material than described above can increase the risk of root rot. But if you use such a mix you’ll have to check your bonsai trees each day to determine if water is needed. To do so simply stick your finger in the soil to feel if the soil is damp. If it feels cool and moist, no water is needed. If it feels dry, it’s time to water.
The safest way to water your bonsai trees is to use a good, well draining, bonsai soil and water once a day, but if in doubt, touch the soil to check and make sure your bonsai are not being over watered.
Photo Credit: Gary Howell