At Ecothrive, we’ve been perfecting the AutoPot Tray2Grow system in conjunction with Grassroots Living Soil Beds, aiming to refine and enhance our methods for cultivating plants in living soil using an automated sub-irrigation system. Through extensive trials, controlled experiments and valuable feedback from the grower community, we've gathered insights to help you optimise your Tray2Grow setup.
This guide shares our best practices for maximising plant health and yields using the system.
The Science Behind Sub-Irrigation with AutoPot Tray2Grow and Living Soils
The AutoPot Tray2Grow system utilises sub-irrigation, where water is drawn up through a capillary mat beneath the soil. This allows plants to absorb water as needed, eliminating the need for manual watering and closely mimicking natural water uptake. However, managing this system requires attention to specific nuances to prevent issues such as over-saturation or waterlogging, which can negatively impact plant health.
One key lesson we’ve learned through our trials is that leaving the AquaValve open continuously can result in low soil tension, causing the soil to remain at its maximum water-holding capacity. This can restrict root oxygenation, disrupt nutrient uptake and may cause plants to exhibit a "stretching" response, especially during late vegetative and early flowering stages. Such conditions often lead to hormonal imbalances, where insufficient root function skews the balance between auxins and gibberellins, causing excessive vertical growth at the expense of structural strength.
In indoor environments, this elongation can produce "leggy" plants, which are harder to light evenly and more prone to weak stems and mechanical stress. To avoid this, we recommend allowing the soil to saturate with the AquaValve before turning it off, letting the soil dry back slightly to encourage deeper root growth and prevent excessive stretch.
Moisture Management and Soil Tension
Managing soil moisture is crucial for maintaining plant health. Overly moist soil creates anaerobic conditions, inhibiting root respiration and microbial activity, while overly dry soil stresses the plants and limits nutrient uptake.
By using a soil tensiometer, such as the Blumat Digital or Irrometer, growers can measure soil tension to maintain the optimal moisture balance. We suggest letting soil tension rise to 60–80 mbar in the bottom thrid of the bed before reactivating the AquaValve for ideal plant growth. During the transition and early flowering phase, allowing the soil tension to rise to 100-120 mbar can help prevent excessive stretch and encourage good flower set.
Note - when allowing higher dry backs up to 120mbar, ensure the capillary mat is still wicking water when you switch the valve back on. If the bed continues to dry even when water is in the tray, add more water to the tray until the water level reaches the bottom of the bed. This will thoroughly re-wet the capillary mat.
Testing Living Soil: Eco-Life and Ecothrive Living Soil in the Tray2Grow System
We have tested both Eco-Life and our Ecothrive Living Soil in the Tray2Grow system over multiple growing cycles. Sub-irrigation with living soils presents a unique challenge in maintaining consistent moisture levels while promoting adequate aeration. During our trials, we experimented with different levels of soil aeration, measuring root development, soil porosity and microbial activity.
Initially, we concentrated aeration materials at the bottom of the bed, but this method did not improve overall soil structure. Instead, incorporating aeration materials throughout the soil mix yielded better results. Proper aeration is essential for ensuring sufficient oxygen reaches the roots, facilitating both root and microbial health.
Optimal Soil Aeration Blends: Experiment Results
Our most recent trials tested three distinct aeration blends:
- Standard formulation (Ecothrive Living Soil)
- 34% aeration by volume
- 50% aeration by volume
Through this testing, we found the 34% aeration blend struck the perfect balance between moisture retention and aeration, promoting compact, healthy growth with no signs of nutrient deficiencies or water stress. This formulation produced the highest yields at final harvest, supporting the theory that 34% aeration ensures optimal gas exchange while providing sufficient water retention.
How to Amend Living Soil for Optimal Sub-Irrigation
For the best aeration ratio, we recommend mixing 5 litres of pumice per 40 litre bag of Ecothrive Living Soil. Pumice, a lightweight volcanic rock, enhances soil structure by creating air pockets, increasing oxygen availability to roots and beneficial microbes. If pumice is unavailable, perlite or similar materials can be used, though pumice has been proven most effective in balancing water and air retention. To maximise results, integrate the pumice evenly throughout the soil mix rather than layering it at the bottom of the bed.
With our Tray2Grow Kit, we provide the extra 10 litres of pumice necessary to add the extra aeration to 2 x 40L bags of Ecothrive Living Soil.
The Importance of Soil Moisture Management in Sub-Irrigation Systems
Maintaining the right moisture levels is crucial for plant health and soil microbiology in sub-irrigation setups. Contrary to popular belief, more water doesn’t always mean better growth. Our trials showed that finding the balance between water availability and aeration is vital. Allowing the soil to dry slightly before turning the AquaValve back on prevents waterlogged conditions, and results in healthier root development and overall plant vigour.
One of the best tools you can use to manage soil moisture is a soil tensiometer, such as the Blumat Digital or Irrometer. In a sub-irrigation system like the Autopot Tray2Grow, when the valve is open and water is in the tray, the tensiometer typically reads around 20-30 millibar, which indicates field capacity — the point where soil holds the maximum water without being waterlogged.
Periodically, we recommend closing the valve and allowing the soil tension to rise to around 60-120 millibar. This drying back is important for promoting healthy soil biology, as it ensures the microbes cycling nutrients aren’t kept in overly saturated conditions. Continually growing at field capacity can also lead to stretchy growth and poor flower set, as plants tend to elongate in overly moist environments. By balancing moisture levels, you create an optimal environment for both plant roots and soil biology.
Environmental Conditions
Having a good growing environment is arguably the most important consideration when growing plants indoors. Ensuring the plants are transpiring well and actively taking up water from the soil is very important. If you have moderate or cool growing conditions, the plants won't take up much water. This can lead to a very slow water turnover in the soil, particularly if you have a bed with a large volume of soil at a high moisture content.
It is therefore very important when growing with a Tray2Grow that you have a good environment generating a healthy transpiration rate. See our VPD article here for more information.
Fine-Tuning the System: Feedback and Continuous Improvement
Thanks to feedback from growers who have used the Tray2Grow system in various conditions, we’ve been able to refine our recommendations. Collaborative efforts have helped optimise the aeration mix to balance moisture retention and oxygenation, reducing the incidence of overstretching and improving overall plant productivity.
Key Takeaways: Summary of Best Practices for the Tray2Grow System
To summarise, here are the key steps for optimising your Tray2Grow system with living soil:
- Irrigation Management: Avoid keeping the AquaValve open continuously. Allow the soil to dry back to 60-120 mbar on a tensiometer to prevent overstretching and weak growth.
- Aeration: Use a soil blend with 34% aeration by volume. Add 5 litres of pumice per 40L bag of Ecothrive Living Soil for optimal soil structure and mix the aeration materials evenly throughout.
- Soil Tensiometer: Regularly monitor soil tension with a tensiometer to maintain the ideal moisture balance and determine when to open or close the AquaValve.
- Drying Phase: Allow the soil to dry back to an optimal level before reactivating the AquaValve. This prevents waterlogged conditions and promotes healthy root development.
We’re always here to help you refine your growing techniques. Don’t hesitate to reach out if you have questions or need support with your system.
Happy growing!
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