A few years ago three new bonsai came to the Cecchetti house hold, a forth was later gifted to me by a friend. As I’ve come to learn the care of bonsai is an endeavor of interwoven timescales and master class in asymmetric appreciation. To properly care for a bonsai you are keeping a plant in a somewhat unnaturally suspended growth state. The guiding of the growth comes slowly over many years of wiring, pruning, and watering. My understanding is that if done properly this slow growth can cause a bonsai to be well over 800 years old. As far as slow hobbies are concerned, it does not get much slower, unless you are willing to leave the biological for geological or astrological time scales. Interwoven with this slow growth the bonsai still need constant watering to stay alive. I found that ultra slow growth over the course of decades is compatible with all the other things going on in my life, but daily watering is not.
So like many things in my life I looked to automate the daily watering away. Initially this was so that my bonsai had some chance of survival while I travel. I’m not the first person to attempt to build a plant watering robot. A simple web search will list dozen of projects and a few kits that you can buy. One blog post I found claimed they spent two years and more time making the watering system than it could possibly save them in a lifetime of watering. I decided I’d keep this to a few weekends project and “good enough” would be ok here. I opted to build my own for a number of reasons. I haven’t worked with water pumps or tubing in the past and getting a feel for flow rates and valves seemed like a skill I’d end up using in the future. Second all of the kits I found feel into two categories, water 1 plant, or water an entire yard/garden. I’ve got 3 bonsai that all need love (4 now) and so I wanted to be able to easily dial the number of plants, pumps, and tubes up and down based on need. In the middle of all of this I was impressed by a fairly low tech solution that was a gravity drip system built from a water bottle turned upside down. However, I wanted to have one large basin that I’d refill not a half a dozen small bottles.
Every project has a few good dead ends and this one was no exception. One of the dead ends everyone seems to find is that the cheap moisture sensors you find online don’t accurately measure moisture levels. The “sensor” is just an electrical contract that when water touches closes the circuit letting you know the soil is moist but not a good indicator of by how much. When I stepped back and thought about it, measuring the actual moisture level across any area is a non-trivial problem. A quick search online reveals that dedicated devices are made to do this but that’s too expensive for my hobby project. I decided to forgo using a sensor and just put it on a timer. My then partner now wife Sarah recommended using a scale and reading when the soil dried up. I thought this was pretty clever, but haven’t upgraded the system to incorporate a scale yet. The downside is it requires a powered scale for each plant and some concept of measuring plant growth and adjusting weight over time. Perhaps I’ll add this in a later version.
For now here is the system and the bonsai.
If you wish to replicate the project here is the Bill of Materials.
1 Raspberry Pi
1 SD Card
1 12v DC Water Pump.
1 12v DC Power supply
1 5v DC Power supply
1 Relay Board
1 Coleman 5 gallon jug
1 PVC Tubing
1 Plastic container to store this all in.
Plans for version 2.
More pumps with watering spikes to directly deposit the water in the soil, I’d also like to build a misting system. However, that’s a project for another time.