Crop steering is a technique used in hydroponic and indoor growing to manipulate plant growth by adjusting environmental variables to influence the plants' hormonal balance, so they grow in a more vegetative way, producing more shoots and leaves, or more regenerative way, producing flowers, seeds and secondary metabolites.
The most common method of steering is by controlling the EC content in the substrate by precicely timing irrigations during the growth cycles. Even without EC sensors in the substrate, growers can experiment with irrigations and runoff to coax certain growth charachteristics from their plants.
By controlling irrigations and runoff, a grower can simulate drought stress on the plants without actually stressing them, which is one of the triggers for more generative growth. Larger drybacks and less runoff on irrigations will raise the substrate EC, which will create a larger osmotic differenctial in the root zone - which is a trigger for the plant to start focusing on reproduction
Conversley, if a grower increases their runoff, the substrate EC will lower, creating a more even osmotic differenctial in the root zone, which makes it easier for the plant to transpire and uptake nutrients, and is a sign for it to focus more on more vegetative growth traits such as leaves and shoots. However, this type of growth is also used during the 'stacking' or "bulking" phase of flowering, so the plants can create as many bud sites as possible.
Once the plants have stopped stacking and are begin to "swell" more, a grower can switch back to generative irrigations to begin raising the substrate EC again, influencing the plants to focus more on generative growth.
During the finishing stages, a grower can also taper down the use of nitrogen in their feeds to coax even more generative signals out of the plant. Simply replacing calcium nitrate with calcium sulfate and/or calcium chloride can do this without sacrificing calcium.
The more data you can log on your grow, the better. Bluetooth thermometers with a histroy feature are a decent starting point to get an idea of where an enviornment VPD can be dialed in.
Beyond that though, the possibilities are endless. There are a handful of expensive commercial options which can be replicated at home for a fraction of the price for a technically minded individual.
My setup is a low-cost thin client, running home assistant as my automation base, and I use an MQTT broker to receive all my sensor data over the network, store my data in an influxDB instance, and display data with Home Assistant and Grafana dashboards. My automations are also done via Home Assistant, but Node Red and other options can be utilized as well.
I intend to keep linking all open source projects and resources relating to steering as I find them. Currently working on a Home Assistant steering setup which I intend to share, once it becomes scalable and more easily adaptable.
Here are some examples of my yaml automations for home assistant. Pump on and off functions for p1/p2, and several others to keep helper variables updated
pwEC template sensor yaml for home assistant, coco calibration. Using the calibration code from Kroma and Dr. Hernendez.
Killerherts' HA NodeRed github is a well fleshed out example of using node red in home assistant for steering tasks
Splore's github dedicated to home assistant steering.
Grodan's steering irrigation plan guide is very handy
For a more to the point guide ccheck out Dankemshunter's steering program it lays it all out very well.
Low cost EC & moisture meter DIY guide by Dr. Daniel Fernandez. Comparable to the arroyo teros-12 for a fraction of the cost. There is also
Kroma's THC-S github with code and more information about the THC-s sensor.
Gitpud's github with code for THC-s sensor more suited to rockwool instead of coir, and added MQTT functionality..
ESPHome example code for the WinComTop THC-S sensor from aliexpress. May still need additional temp compensation to get accurate readings.
Crop steering excel spreed sheet to helpp dial in shot sizes and timings and such.