Most trees that die are lost to dehydration, either from lack of watering or from being kept in a low humidity environment (indoors) too long.
Different soils dry at different rates, trees differ from species to species in water requirements and even different styles of pots dry out at varying rates, so each pot must be checked regularly until you become more familiar with the plant in question. The other end of the spectrum, over-watering can damage plants nearly as quickly; it is in finding the proper balance of soil, water and air that you will develop a healthy root system and thus a healthy bonsai.
What it DoesEdit
Watering accomplishes three things for your bonsai.
First, and most obviously, it provides H²O for your tree. Secondly, the water that flows through the soil carries nutrients your plant needs and washes out the excess salts that might otherwise build up. Third, and least obvious, the flow of water pushes out the old, spent gasses in the soil and pulls in new, fresh atmosphere. The porous quality of bonsai soil allows for quicker water flows and better gas exchange; this is why bonsai soil is so granular; it helps develop a dense mat of roots to support a dense mass of foliage.
Here are some basic hints, tips and tricks to stop your little tree dying of thirst.
=Water Three TimesEdit
The old Japanese adage is to water three times; once for the pot, once for the soil, and once for the tree. By going back and forth over your collection three times it allows the water to soak into the soil and the pot and leave water for the tree to take in.
Don’t just water the soil. All parts of a plant absorb water to some degree; 35% of the water intake for a plant doesn’t involve the root system at all. Washing off the foliage also keeps dust and pollutants from clogging stomata or breathing holes in the plant’s leaves.
Even if it's been raing, it is best rather to be 'safe than sorry'; water anyway. If it has been raining all week, prop up one end of the pot a few inches to increase drainage.
Using a HoseEdit
If you use the hose to water, too much water pressure can blast soil out of pots. Be sure to get an adjustable spray nozzle to allow for different needs i.e a nozzle with a mist seeting, for wash-downs of the tree's foliage. WARNING: Keep in mind that if that hose has been lying in the sun for a few days, that first blast can boil a tree .
- Water early in the day. If you must, water late in the day, but be aware that leaves your plants more vulnerable to fungus and slugs as the day cools down.
Plants don’t transpirate (breathe) above 85°F, so if you water in midday, you temporarily cool the leaf enough to start transpiration, which allows the moisture inside the leaf to escape in the 'exhalation'. Also, the water sitting on a leaf in the midday sun can act as a lens, burning leaves.
- If you have flowering bonsai, don’t water the flowers; it’ll make them pass almost instantly…
Watering is a learned skill; in Japan an apprentice is given pruning shears on his first day but he won’t touch a watering can for another four years!