Hempy bucket
In the next few chapters, we are going to build a passive hydroponics setup consisting of two Hempy buckets with an automatic weight-based irrigation system.
Overview
A Hempy bucket is a simple non-transparent bucket with a hole on its side, filled with coconut coir soil, perlite mix. It functions as a passive hydroponic setup by retaining water at the bottom 5 cm / 2 inch section containing pure perlite. We are essentially tricking our plant into thinking it found a natural water pocket at the bottom of the bucket.
Or visit the Gbox420 GitHub page and download the entire project.
Single Hempy table with nutrient and waste reservoirs
Three weight platforms: Hempy bucket, nutrient reservoir, waste reservoir
Double Hempy bucket table with nutrient and waste reservoirs
2 x Hempy bucket
2 x Hempy + 2 x Waste weight platforms
2 x Self-priming pump (12V - 2A)
Mounted on the bottom side of the weight platform
Hempy module - Gbox420
Arduino automation
Arduino automation
Hempy table - With four weight platforms
User interface
The UI for controlling and monitoring the Hempy buckets is provided by the Main module. The Main module wirelessly queries the Hempy module every 5 seconds for the latest sensor readings and sends user commands as soon as a button on the web page is pressed. You can check out the structure of the Command - Response packages in WirelessCommands_Hempy file in GitHub.
Hempy interface - ESP link - Gbox420
The start of the watering is controlled based on the bucket's Dry weight:
When the module first starts up it starts watering as soon as the .InitialNextWatering weight in Settings.h is reached.
After the first watering, the NextWatering weight is automatically calculated from the Wet weight minus the Evaporation weight.
Watering happens in multiple cycles:
When the Wet weight is unknown: Overflow target's worth of water is pumped into the bucket, then the system waits for the water to drain until Drain time is reached. The cycle continues until the Waste bucket's weight is increased by Overflow target.
When the Wet weight is known: Water till the Wet weight is reached, then continue adding Overflow target's worth of water and wait for it to drain. The cycle continues until the Waste bucket's weight is increased by Overflow target.
When the Overflow target is reached the bucket's Wet weight is updated and the next watering weight is calculated from the Wet weight minus the Evaporation weight. As a general rule of thumb set the Overflow target to 10-15% of the Evaporation target.
Throughout the entire watering process, the pump's total ON time is measured, this should not reach the pump's TimeOut. If the timeout is reached a problem with the pump/weight sensor is assumed and the watering logic gets disabled. An email alert is triggered via Google Apps Script at the next Google Sheet reporting:
Hempy interface - Home Assistant - Grafana
Review
After the trial of the two Hempy buckets, both plants had their roots all over the coco soil and the taproot going around the bucket’s water reservoir. The roots showed no sign of root rot, not even the parts that were constantly underwater. The only aspect I was not satisfied with was the water consumption. By design Hempy buckets are water to waste systems, meaning a large amount of the nutrient mix just ends up overflowing into the drain buckets. Over the test, 210 liter / 55 gallon of water was flushed through the Hempy buckets, part of it ending up as runoff. In my opinion, this is wasteful. On the plus side, the runoff can be used to feed other plants around the house.
Compared to regular soil pots Hempy buckets seem to provide a more balanced water source. Thanks to the reservoir at the bottom the plans would still be in good shape if a feeding is missed when watering by hand. Having drain tubes and an overflow bucket made handling the wastewater a simple task.
The automatic irrigation is awesome, not having to worry about the watering schedule was a huge comfort. My only job was to refill the nutrient reservoir every 2-3 weeks. As coco soil is closer to a hydro setup set the pH of the nutrient mix around 5.8 instead of the usual 6.3 used in traditional soil grows. Make sure to use a nutrient solution designed for coco soil or a hydroponics system, coco coir tends to binds some of the calcium and magnesium in the nutrient solution. I noticed a slight increase of pH in the reservoir over the 3 weeks it took for it to run out, but even on the last day the pH was below 6.2. This slight fluctuation of pH is perfectly fine as long as it stays within the 5.8 - 6.3 range.