Category: Monitor

My herb garden consists of three roughly 30cm x 40cm pots, each containing a single plant—rosemary, basil, and chilli. The garden is located outside our upstairs window and receives mostly full sunlight. While that’s good for the plants, it makes it harder to keep them properly watered, particularly during the summer months. After losing my basil and chilli bush over Christmas break, I decided to automate the watering of my three pots, to minimise the chance of losing any more plants. So I went away and designed an auto-watering setup, using soil moisture sensors, relays, pumps, and an Arduino—an open-source electronic platform—to tie it all together.

I placed soil moisture sensors in the basil and the chilli pots—given how hardy the rosemary was, I figured I could just hook it up to be watered whenever the basil in the pot next to it was watered. I connected the pumps to the relays, and rigged up some hosing to connect the pumps with their water source (a 10L container) and the pots. When the moisture level of a pot got below a certain level, the Arduino would turn the equivalent pump on and water it for a few seconds. This setup worked well—the plants were still alive—except that I had no visibility over what was going on. All I could see was that the water level in the tank was decreasing. It was essential that the tank always had water in it, otherwise I'd ruin my pumps by pumping air.

To address this problem, I added a float switch to the tank, as I was aiming to set it up so I could stop pumping air if I forgot to fill up the tank. Using a WiFi adapter, I connected the Arduino to my home WiFi. Now that the Arduino was connected to the internet, I figured I should send the data into Splunk. That way I'd be able to set up an alert notifying me when the tank’s water level was low. I'd also be able to track each plant’s moisture levels.

Using the Arduino’s Wifi library, it’s easy to send data to a TCP port. This means that all I needed to do to start collecting data in Splunk was to set up a TCP data input. Pretty quickly I had sensor data from both my chilli and basil plants, along with the tank’s water status. Given how simple it was, I decided to add a few other sensors to the Arduino: temperature, humidity, and light level. With all this information nicely ingested into Splunk, I went about creating a dashboard to display the health of my now over-engineered garden.

With this data coming in, I was able to easily understand what was going on with my plants:

1. I can easily see the effect watering has on my plants, via the moisture levels (lower numbers = more moisture). I generally aim to maintain the moisture level between 300 and 410. Over 410 and the soil starts getting quite dry, while putting the moisture probe in a glass of water reads 220—so it’s probably best to keep it well above that.
   
2. My basil was much thirstier than my chilli bush, requiring about 50–75% more water.
3. It can get quite hot in the sun on our windowsill. One fortnight in February recorded nine 37+ degree days, with the temperature hitting 47 degrees twice during that period.
   
4. During the height of summer, the tank typically holds 7–10 days’ worth of water.

Having this data in Splunk also alerts me to when the system isn't working properly. On one occasion in February, I noticed that my dashboard was consistently displaying that the basil pot had been watered within the last 15 minutes. After a few minutes looking at the data, I was able to figure out what was going on.

Using the above graph from my garden’s Splunk dashboard, I could see that my setup had correctly identified that the basil pot needed to be watered and had watered it—but I wasn't seeing the expected change in the basil’s moisture level. So the next time the system checked the moisture level, it saw that the plant needed to be watered, watered it again, and the cycle continued. When I physically checked the system, I could see that the Arduino was correctly setting the relay and turning the pump on, but no water was flowing. After further investigation, I discovered that the pump had died. Once I had replaced the faulty pump, everything returned to normal.

Since my initial design, I have upgraded the system a few times. It now joins a number of other Arduinos I have around the house, sending data via cheap radio transmitters to a central Arduino that then forwards the data on to Splunk. Aside from the pump dying, the garden system has been functioning well for the past six months, providing me with data that I will use to continue making the system a bit smarter about how and when it waters my plants.

I've also 3D printed a nice case in UV-resistant plastic, so my gardening system no longer has to live in an old lunchbox.