Thoughts on watering-and the related subject of soil

When do I water my bonsaI?

One of the most common bonsai related questions, and one of the hardest to answer.  Why so hard? Because most folks asking are really hoping for an easy to cope with response- Once a week, every other day, something like that. No one wants to hear  “Well it depends…”

But thats a better answer. The tough part of bonsai care is dealing with variables. When considering bonsai variables, things break down to an equation like this:

R+E+P= Watering schedule.

These stand for

R- Requirements of the plant. These are usually the factors that can not be changed, things like water requirements or amount of sun light.

E-Enviromental factors.  Conditions in the growing area such as duration and intensity of sun light, wind exposure and temperature.

P-Planting mix. The easiest factor to control, such as Container type, particle size and component ratio.

If you get the feeling that how often to water depends alot on what a tree is potted in,you have grasped an important idea. Trees in sunny, windy locations, or trees that will by their genetic nature need a moister environment would all benefit from a potting mix that retains more moisture. Trees that require a dryer soil situation, or that are sighted in  shadier locale, would likewise prefer and do better in a mix that stays drier/drains quicker.

There are bonsai soils mixes packaged and available for purchase at many venues.  Using them right from the package will mean observing how much water is absorbed and how quickly it is used by plants. Additions can be made to customize the prepacked mixes, and most bonsai hobbyists will soon realize that buying soil in small packages is not cost effective.  It is much cheaper to buy raw ingredients, and allows basically infinite flexibility in creating soil mixes tailored to any situation.

So what materials can be used in a bonsai soil mix? Soil components fall into three types:

ORGANICS-high capacity to absorb water, offer some  nutrition (NPK) micronutrients and bioactivity. These items break down over time, which can affect the effectiveness of the mixture’s drainage.

Coffee grounds

Leaf mold-slow to rot leaves such as oak are best

Bark Chips-wide variety is available either as mulch or other horticultural uses-orchids

Coir-coconut shells, used in potting mixes and as animal bedding

Mulch-cocoa shells, hard wood

Shredded pine cones-not commercially available, easy to harvest in the right neighborhoods

Peat moss-breaks down quickly, hard to rewet once totally dry.

INORGANICS-provide weight, assure drainage, these never breakdown, absorb almost no water.

Sand-must be appropriately sized, swimming pool filter sand and mason’s sand are best.

Gravel-small gravel(large sand) with sharp edges work well, aquarium gravel is no good!

Poultry grit-harder to find as the old fashioned feed stores disappear

Crushed limestone/paver base-especially good for plants that need low Ph ( base)

Crushed brick-expensive

Lava rock-expensive

Akadama-a naturally occurring soil type imported from Japan, expensive

MANIPULATED ITEMS-somewhere between organics and inorganics, these items have been processed in some way. Usually longer lasting that pure organics, they absorb some water but also promote drainage.

Turface-a naturally occurring clay fired to high temperatures.

Floor Dry-diatomaceous earth fired to high temperature-available at NAPA

Haydite-shale expanded with heat.

Vermiculite-a mineral expanded with heat.

ITEMS TO AVOID

Perlite-heat expanded obsidian, it is very light weight and pure white-distracting.

Garden soil-breaks down quickly, contains weed seeds, disease vectors-bad news.

Compost-same issues as garden soil.

Beach sand-may contain salt

Particle size matters. Notice how when you open a can of mixed nuts the big heavy Brazil nuts are on top? It seems counter intuitive, but there are interesting physicals forces at work, that also affect how well bonsai soil mixes together and stays mixed.  Using play sand (very small) with large bark flakes ( big) will result in a mix that does not hang together. Using items of similar size will improve the mix.