Sensing Soil Moisture: You’re Doing it Wrong!

If you compulsively search online for inexpensive microcontroller add-ons, you will see soil moisture measurement kits. [aka] built a greenhouse with a host of hacked hardware including lights and automatic watering. What caught our attention among all these was Step 5 in their instructions where [aka] explains why the cheap soil sensing probes aren’t worth their weight in potting soil. Even worse, they may leave vacationers with a mistaken sense of security over their unattended plants.

The sensing stakes, which come with a small amplifier, work splendidly out of the box, but if you recall, passing current through electrodes via moisture is the recipe for electrolysis and that has a pretty profound effect on metal. [Aka] shows us the effects of electrolysis on these probes and mentions that damaged probes will cease to give useful information which could lead to overworked pumps and flooded helpless plants.

There is an easy solution. Graphite probes are inexpensive to make yourself. Simply harvest them from pencils or buy woodless pencils from the art store. Add some wires and hold them with shrink tube, and you have probes which won’t fail you or your plants.

Here’s some garden automation if this only whet your whistle, and here’s a robotic friend who takes care of the weeds for you.

Automating Plant Care

[Daniyal]’s goal is to build an automated garden that allows him to grow plants in any environment he chooses. He’s got a good start with this rig, which is controlled by a Pi Zero connected via serial to an Arduino Mega clone, which  in turn controls a bank of relays and sensors.

Monitoring the environment is a temperature and humidity sensor as well as a series of  six soil moisture sensor spikes. The relays control the water pump(s?) and lights, allowing [Daniyal] to maintain specific conditions depending on what he’s growing.

[Daniyal] has ambitious goals for the project. The Pi has a camera on it, and he hopes to not only maintain the greenhouse from the Internet, but also figure out how to monitor plant growth automatically, so that the Pi can measure plant growth and adjust the conditions without his input.

We’ve covered a lot of very cool horticulture projects here on HaD, including radio-connected soil sensors, using G-cal to create an internet of lawns, and the Garden of Eden watering kit.

Growerbot turns gardening into a science

A backyard vegetable garden can be a hit-or-miss game. You’re really not sure if your crops are getting enough sun, shade, or water until it’s time for harvest and you see the results of a season of hard work. Growerbot, a hardware project by [Luke] that’s up on Kickstarter now, hopes to change that. This box will pull down how much sun and water your crops should get, and is smart enough to correct any deficiencies.

On board the Growerbot is a soil moisture sensor, light, temperature, and humidity sensors, as well as WiFi connectivity and a few relays to run pumps and turn on grow lights. The idea is to learn from mistakes and achieve optimal growth for everything connected to the Growerbot. If you’re trying to grow some heirloom tomatoes in the midwest, you can go online and get the growth profile for your area and precisely control environmental variables for the perfect crop.

As of now, there are settings for in-ground gardens, raised beds, and hydroponic setups. There’s not much in the way of ideal growing conditions aside from what is available from the USDA, but once Growerbot is released we expect the data to start flowing in.


[George Foreman] seedling starter for kitchen herbs

Sometimes the best kitchen hacks aren’t about the best barbecue, the rarest steak, or the baconiest bacon. Sometimes you need a little color on your plate, son, so why not grow your own herbs in a [George Foreman] rotisserie greenhouse?

[Sam] first saw his barely used rotisserie as his friend was throwing it out. Like any good maker, he quickly snatched it up and began work on some modifications. After removing the fun bits like the motor, heating element, and timer, [Sam] installed two compact fluorescent light bulbs to start a few herbs off right.

Kitchen herb gardens are surprising common, so much so that entire forums are dedicated to the practice. [Sam] doesn’t have any soil in his seedling starter yet but when he does, we expect he’ll be harvesting a nice crop of basil, oregano or cilantro in the spring.

Of course, [Sam] could use his seed starter to grow more “unconventional” plants, but some of us have been kicked out of a dorm for growing a pomegranate seedling, so we’ll leave it at that.