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A Drip Mist System for Bonsai

by Brent Walston


Eventhough I spend nearly my entire life thinking about and growing plants for bonsai, I find it too inconvenient to have to hand water my own bonsai. I switched to an automatic system years ago. In some ways it is more advantageous than hand watering. The disadvantage is that you don't get to see your bonsai everyday to spot problems, unless you have some other routine for visiting every plant every day.

The Advantages of Automatic Watering

The advantages of automatic drip mist watering bonsai are convenience, reliability, adequate and timely watering, and ease of inline fertilization. With an automatic drip mist system you can apply water very slowly for a long period of time and do it precisely when the plant needs it the most, just before the heat of the day. I usually water for an hour or more around noon with a fine mist that thoroughly saturates the root ball.

How to Set Up Your System

The type of drip system you use makes a big difference. Spray stakes and drip emitters (one emitter per pot) in general do a poor job of watering bonsai. In such loose mixes the water tends to go straight down rather than out. I prefer a drip mist system sometimes called a drip spray. This uses conventional drip system parts but the emitters are sprayers. There are various types, but mine are Olson 'O' jets. These fit into a rigid poly 1/4 inch riser that snaps into the standard 1/2 inch poly drip tube. I place these about every three feet along my bonsai benches creating a complete coverage mist. As long as the pressure is about 30 psi or higher the mist is almost fog like and it works well, especially if there is a little breeze to stir the mist. At lower pressures the O jets tend to 'pattern' and you can get dry spots.

For my larger bonsai that are lined up singularly on a narrow bench, I just put these mist heads in strategic positions so that the top of the soil gets a pretty much direct spray. I don't worry about the foliage. It does get wet from the fog like mist, but the water is mostly directed at the rootball.

You can operate such a system just by connecting to a hose bib and turning it on and off manually. But the beauty of such a system is that it can be easily automated with a hard wired irrigation timer and electric 24V solenoid valve. Battery operated timers are just too erratic for this purpose. With this system you can pretty much leave for a week or two and your plants will be fine if you have someone check everyday to see if the system came on, and if this person has the wherewithal to fix it if it breaks. In general, a hard wired system is pretty fool proof if you have a nice fresh backup battery.

Although these mist heads have larger diameter orifices than traditional drip emitters, a filter is still a must. Fine mesh filters tend to clog too often for me and really are not necessary since most fine particles will pass right through the emitter anyway. I find that about 60 mesh is right. This should be a fairly large filter so you don't have to check it too often and to give you a larger reserve. Netafim filters with 3/4 or 1 inch outlets are about the right size and have a choice of filter meshes.

Adding a Fertilizer Injector

I have been using fertilizer injectors for years, which you can plug right into your system. However, they do tend to waste fertilizer with an overhead spray system such as the above. I prefer to use the injector with a hose and hand water to fertilize. You can easily set it up to do either. If you have a regular drip system for your plants in training pots, then an inline injector is very easy and efficient. Good injectors are not cheap. There are two reliable companies making small professional non electric injectors, Dosatron and Dosmatic. I have been using Dosatrons for years. It is an all plastic/stainless injector that uses the flow of the water through it to operate a piston which pumps fertilizer concentrate into the water stream. They are fully adjustable from about 60:1 to 500:1 with about an 11 gpm flow rate. The work very well at both low and high flow rates. Price is currently about $300 US.

Reasonable Cost of the the System

This system minus the timer, valve and injector is very inexpensive. 50 feet of 1/2 inch tubing is around $5, fittings are about $.50 to $.75 and emitters and risers are less than $.50. Filters are about $15. That would get you started. Irrigation timers (found at almost any home supply stores) can be found for about $50 to $100. Get an all digital one, they tend to be more reliable than the old 'clockmotor' timers, and more flexible too. Electric solenoid valves are about $10 to $15. One hint on the valves, use an antisyphon valve with a good filter after it. Bugs can, and do, enter through the vacuum break. Drip parts can be found almost anywhere these days, but in case you can't find what you want or you want to see everything that's possible using drip systems, go to:

And finally

Don't rely too heavily on an automated system. Bonsai rely on a water supply every day in summer. Missing even a single day can often cause irrepairable damage. Always check every day to make sure the system did its job.

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