Automated Watering Machine Has What Plants Crave: Fertilizer

We’ve seen countless automated plant care systems over the years, but for some reason they almost never involve the secret sauce of gardening — fertilizer. But [xythobuz] knows what’s up. When they moved into their new flat by themselves, it was time to spread out and start growing some plants on the balcony. Before long, the garden was big enough to warrant an automated system for watering and fertilizing.

This clever DIY system is based around a 5L gravity-fed water tank with solenoid control and three [jugs] of liquid fertilizer that is added to the water via peristaltic pump. Don’t worry, the water tank has float switches, and [xythobuz] is there to switch it off manually every time so it doesn’t flood the flat.

On the UI side, an Arduino Nano clone is running the show, providing the LCD output and handling the keypad input. The machine itself is controlled with an ESP32 and a pair of four-channel relay boards that control the inlet valve, the four outlet valves, and the three peristaltic pumps that squirt out the fertilizer. The ESP also serves up a web interface that mimics the control panel and adds in the debug logs. These two boards communicate using I²C over DB-9, because that’s probably what [xythobuz] had lying around. Check out the demo video after the break, and then go check on your own plants. They miss you!

Don’t want to buy just any old peristaltic pumps? Maybe you could print your own.

18 thoughts on “Automated Watering Machine Has What Plants Crave: Fertilizer

    1. Of course plants need fertilizer. Epiphytic plants, such as most of the orchids you see, do best with a small dose of fertilizer (125 PPM) with every watering (or every other watering during the dry season). And if you have mounted orchids that have their roots gripping a stick (instead of being shoved in an artificial pot of bark) you need to mist them daily and fertilize them weekly.

      I go through about 20-30L of fertilized water per week, and that’s for about 2 square meters worth of ornamental plants.

      I don’t know how many plants [xythobuz] is tending, but 5L per week is very believable for a small table full of ornamentals. I expect the water and fertilizer usage would be much higher if growing fruits or vegetables, like tomatoes.

      1. Very interested in hearing more about your work with orchids, we have several potted ones and after they bloom it seems almost impossible to get them to bloom again, but does (very rarely) happen

        1. Standard phalaenopsis need a temperature drop sustained for a few weeks to induce flowers. You need to drop the day and nighttime temperature 5-10c. For example, If your normal house temp is 25c, you need to drop it to ~18c. This is best done in autumn when you can just leave windows open to let the house cool.

        2. My mom routinely got her orchids to bloom at least once a year, sometime 2-3 times. I think she used a lot of Miracle Grow. She kept them in her basement, next to the furnace, in the winter. Outside in the summer (rural Missouri).

    2. My hand watered hydroponic hot pepper garden in inert (coco-coir) medium would beg to differ. It didn’t need heavy fertilization but, it did need liters of water a day per plant and there wasn’t any nutrition at all coming from anywhere but the water.

    1. I don’t see mention of the type of fertilizer; but it looks like a complete one or two part mix. Those are often PH buffered pretty well.

      A couple of years ago I started mixing my own fertilizer from salts for hydroponics, and that requires a lot more finicky PH adjustment. You can really tell how buffered the commercial solutions are when you see how much more PH adjustment solution it takes to change it compared to something simpler.

      So its likely nothing is being done or really needs to. PH seldom needs to be even close to ideal. In fact, it took me several weeks to even realize I should test my PH and realized it was so far off. My ideal target was 5.2ish but the unadjusted solution that I used several times…. closer to 3.5.

      They lived, didn’t die off badly. Were not happy though. YMMV obviously will depend on plant type. It probably matters that my solution was completely unbuffered and was pushed around quite easily by any PH modifying solution so, its likely it didn’t stay 3.5 for very long.

  1. My cheap submersible pump pump rusted, so I started using a sipon instead. Just need to place the water tank higher and let gravity does it work. As for controlling the flow, I attached a servo to a fish tank air valve. It won’t work with extra stuff in the water as it would crystalized and plug up the valve eventually.

  2. Why are you adding complexity to a simple process !?!

    Did this over 25 years ago using PWM on injector valves to control rate and distribution of various chemicals to down-stream irrigation on a 5 acre seed house. This method was then easily scaled to an order of hundreds of acres of greenhouses and growing fields.

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