The Teros 12 Sensor, SOLUS Spot Meter App and EC
Learning about EC
Electrical conductivity is a measurement of salt levels in plant growing mediums like soil, coco coir or rockwool. Adding nutrients to your soil increases electrical activity. Adding water washes out the salts. EC is one of three measurements the SOLUS displays.
Teros 12 Sensor Measurements
-water content %
-temperature F
-electrical conductivity ds/m
For predictable high yielding results these variables must be managed carefully.
Why EC Matters
Avoiding the Guess Game
Maintaining healthy plants can be a guessing game that can result in lower quality crops.
Its difficult to know the best time to water and feed plants.
It can take years of experience with one crop to know by looking at a plant whether or not it is healthy.
Note: As you read about the SOLUS you'll find our personal experience in italics.
EC and Water Content Sensors
The Teros 12 EC ds/m Sensor.
SOLUS App displays EC which it reads from the Teros 12 sensor placed in your grow medium.
AROYA SOLUS with the Teros 12 Sensor
SOLUS App WC and EC Display
SOLUS App
SOLUS App Download links (phone only)
Choosing Betwen Soil/Soiless Mediums
Growing mediums and the Teros 12
First Hand Experience
We have a test garden in our Seattle showroom. We've been using the Teros 12 and SOLUS app to grow a dozen cherry tomato plants (we're limited in this location). We've used the same grow strategies cannabis growers use in large scale gardens.
Forever Green Indoors Test Garden Videos and Ads
Using the Teros 12 For Cannabis Growing
Why runoff or solution EC are not the same as grow medium EC
Bulk EC versus Pore EC
Bulk EC
EC measured in solution or runoff is measured using a different sensor than the Teros 12. This measurement is called Bulk EC. The Teros cannot be used to measure EC outside of the growing medium.
We recommend that you have a sensor for Bulk EC as well.
Pore EC
The Teros 12 sensor measures EC levels using a Pore Water calibrated measurement in ds/m, a measurement in growing mediums.
Ds/m and ms/cm measurements are equivalent and can be compared 1:1 to each other. Even though each sensor is different.
Bulk EC levels will be higher when nutrients levels are being raised to reach the ideal balance in the grow medium.
EC Levels In Cannabis Growing
Ideal EC levels in soil/soiless cannabis growing are generally as follows;
The study of EC and WC levels in cannabis is evolving. These are currently the safe zone however we know of gardeners who are experimenting with higher levels during the generative (flowering) phase as they learn how to steer certain strains to maximum crop yield potential.
Starts/Clones
- EC levels for seedlings and young veg plants is around .5-.8 ds/m. Stay at this level until the plants develope 6-8 leaf sets and are fully rooted.
Veg
- Increse to 1.1-1.5 ds/m through vegitative phase.
Flowering
- Boost the EC level to 2.0-2.5 ds/m through flowering.
Pre-Flush
- 1.8- 2.2 ds/m through to flush after which point EC measurements are not necessary.
EC levels for growing cannabis plants
courtesy of Cannabis Business Times
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When To Measure EC
Minimum Water Content
The Teros 12 sensor is most accuate when water content (WC) is above 17%. Levels below 17% confuse the sensor as salts build up around the stainless steel prongs.
Water content in grow mediums below 20% would be extremally low and unhealthy for the plants.
We've experimented with letting rockwood and coco moisture levels go below 20%. They weigh practically nothing, dipping a finger in feels completely dry. And it is nearly impossible to resaturate them to 50% with drip irrigation. If the levels go this low the plant is likely not going to make it.
Maximum Water Content
Choosing the maximum water content level depends on the grow medium's ability to hold water which is shown in the chart below.
Rockwool and Coco Coir have similar moisture content holding ability.
Both are fully saturated at 60% WC and will dry back to about 30%. It is very difficult to get either back to the 60% saturation level with drip irrigation.
When to check WC Levels
Measuring WC helps set watering intervals and amounts. We recommend a low threshold of 35% water content and then re-watering.
We leave the Teros 12 sensor in the same grow container and take readings every hour at two hours after watering to watch the water content move towards 35%. When it does we program the drip system for this length of time, and adjust the minutes of watering.
2 hours dryback + amount of time to dry to 35% = the weekly watering interval.
We keep an eye on the plants with additional WC readings towards the end of the week and if they are stripping the medium of water we increase the minutes of water from our emitters.
The upper threshold depends on the medium, and generally we aim for 45-50% with coco or rockwool before stopping the watering and starting the dry-back.
When to check EC Levels
Generally it is best to check EC between one and two hours after the last watering schedule as the medium will no longer be draining off and the EC level will be stable and the most accurate.
Water / Feed Schedule Setting
After several weeks of mutiple readings per day we program our auto-drip irrigation system to reach 45-50% WC.
Our garden has a dozen 3 gallon pots with a pair of emitters at .5 gph.
We look at the EC levels 1-2 hours later (it does not change much in that time). Then we adjust the fertigation injectors up or down based on the plant phase EC target.
Remember that if you measure EC when WC is below 20% you will not have an accurate number so disregard EC at very low water content levels. And also at fully saturated levels.
Bring the level back to the upper WC threshold and dry-back before measureing EC. Then adjust feeding as required to maintain the EC target.
Flood versus Pluse Watering
EC and WC targets remain the same for either type of watering strategy.
Pulse watering becomes necessary with larger plants to keep the grow medium from drying out too far which is unrecoverable.
Crop Steering - Managing Plant Stress For Yield
This is a topic for another post. Crop steering tactics are used together with pulse watering and feeding schedules to intentionally stress the plant. Cycling between low minimum water levels results in a competitive growth response in the plant which improves yield.