This apparently easy technique is the second most frequent cause of Bonsai-related problems. Underwatering or allowing the compost to dry out completely will instantly kill or badly damage most trees; however overwatering can just as equally cause ill-health and eventual death from rootrot and disease.
The most important rule to remember is that trees should be CHECKED for their water requirement daily but should only be watered as required. Never, never water to a routine, this can lead to continually sodden compost which literally suffocates the roots. The surface of the compost MUST be starting to dry out between waterings, then the tree can be thoroughly watered again. The time between waterings can vary from 12 hours to 7 days depending on factors such as prevailing temperatures, wind and humidity levels.
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.
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.
People are conditioned to believe all the plants transpiration takes place in the leaves, but if that was true, how would a plant that was totally cut down spring back from the roots? The first few inches of soil are crucial to all of a plant’s functions; even a mighty oak does most of its feeding and drinking and much of it’s “breathing” in the top foot of soil. It is this reliance on a shallow soil profile that allows us to grow trees in such shallow pots in the first place. 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.
Some quick watering tips:
- 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.
- Sure it’s raining, but is it enough to get good flow-through? Better safe than sorry; water anyway. Been raining all week? Prop up one end of the pot a few inches to increase drainage.
- Using 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 (Get one with a mist setting; it’s great for occasional wash downs of the foliage). Keep in mind that if that hose has been lying in the sun for a few days, that first blast can boil a tree (literally!).
- Once a week or so, water by totally immersing the pot in water until the bubble trail quits. This assures top to bottom watering and lets the pot and soil soak up their maximum holding capacity, making it easier to keep them watered during the rest of the week. (I think this is the best tip in here, especially for novices)
- 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. Plants don’t transpirate (breathe) above 85°, so when 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”; kind of counterproductive. AND the water sitting on a leaf in the midday sun can act as a lens, burning leaves. So watering early AM beats all these problems and gives you a few uninterrupted minutes with your trees, and that can be a real stress beater!
- If you have flowering bonsai, don’t water the flowers; it’ll make them pass almost instantly…
- This is the most important part of bonsai care. 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!
Full sun will make the bonsai tree more yellow in most cases, while full shade (not advised) will force the glaucus, blue-green colour to come out. Blend the light requirements and you will have a healthy tree.
Some Light/Shade tips:
- It is very important for you to identify what type of bonsai you have, as different types of trees have different light requirements.
- Remember all trees live outside year round in their native habitat. Thus, the more sunlight they receive, the better they will grow.
- Some very general guidelines for temperate climate, woody trees are: Most conifers require a lot of light, full sun all day is preferable. Most broad leafed trees like a lot of light but will do well in partial shade. Some broad leafed evergreens like azaleas are shade tolerant.
- Tropical and semi-tropical trees are equally variable, and must be approached on an individual basis.
- Most trees will not survive indoors without supplemental, artificial lighting.
- For indoor wintering of tropical and sub-tropical trees in cold climates, many enthusiasts prefer fluorescent bulbs, one warm spectrum and one cool spectrum in the same fixture. Commercial fluorescent “grow” lights are also available. Place the trees as close to the bulbs as you can. Leave the lights on for 16-18 hours a day.
- Incandescent “grow” light bulbs are available but are not of much use unless used for one or two plants that don’t need a lot of light. These bulbs get very hot and will burn foliage if placed too near a tree.
- When a tree gets diminished light levels, water and fertilizer must be applied with less frequency.