Many bonsai owners mistakenly assume that underwatering “will keep their bonsai tree small”. Nothing could be further from the truth. Underwatering has a serious effect of killing the water absorbing capacity of your bonsai tree, resulting in death, or poor health, with which the tree may never recover from.
If you allow your bonsai tree to go without water for an extended period, what happens is the tree undergoes “drought mode”. Feeder roots and root hairs which are mostly near the soil surface are the ones responsible for taking in water, so when there is a lack of water, they will dry out and die, severely impacting your bonsai tree’s capacity to absorb water in the future.
It is through the evaporation of water from your tree’s leaves that pulls in water through the roots all the way up the trunk and into the branches (transpiration). On the leaves, tiny pores called stomata constantly open and close in response to hormonal changes brought about by external stimuli. During “drought mode”, especially in temperatures above 29 celcius, the tree stops aspirating (‘breathing’), due to the closure of the stomata to prevent evaporation, and this results in drastic lowering of gas exchange through the leaves. Thus, less carbon dioxide is absorbed by the bonsai tree, resulting in reduced photosynthesis, and carbohydrate production, which are needed to manufacture tannins and alkaloids. This will impact your bonsai tree’s resistance to diseases and pests.
What if you went on holiday for a week and forgot about your bonsai?
We hope that doesn’t happen. Get someone to water your bonsai.
One temporary way to “water your bonsai” while you’re away on holiday is to place the pot on a large, thick piece of cloth and make sure it is inserted a little way into the hole at the bottom of your pot/container so that it’s fully in contact with the soil. Let water from a faucet drip slowly onto the cloth
Drastic measures in case your tree went thirsty for extended periods...
Submerge your tree under a tub or sink filled with water as mentioned in part one, but don’t leave it there for more than a few hours, after which you remove the tree and let the excess water drain out through the mesh-covered hole and into the tray underneath or attached to the pot. If the tray is full, dip the pot slightly to allow only a low level of moisture to remain, and leave the tree alone for a couple of days.
It should become a habit for you to regularly examine the bottom tray. Draining excess water from the tray will ensure that any excess water in the pot has somewhere to go, and doesn’t collect around the roots.
Water daily, making sure that water flows to the bottom but doesn’t pool to the point of filling up the tray. Water left standing in the tray not only makes it impossible for the pot to drain, but encourages mold build-up. Depending on the type of soil (sandy soils require more watering), the climate, and the species, adjust your watering accordingly.
Pines and other conifers need less water. They benefit from moderate drying periods, as well. Deciduous and flowering trees require and welcome more water than conifers. Look for curled leaves on deciduous trees, indicating dryness. Wilting flowers (when they should be blooming) are an indicator of dessication.