Since at least the 1600s, farmers and scientists have experimented with hydroponic cultivation and all sorts of substrate alternatives to everyday soil. But it wasn’t until 1969—the same year as the moon landing—that Grodan introduced stone wool to horticulture and changed the way the agricultural industry approaches large-scale commercial hydroponics.  

And everything we’ve learned over the past 50-plus years is now shaping modern cannabis crop steering techniques. The result: maximized yields, efficient use of water, nutrients, and other resources, and accurate long-term planning capabilities. 

The 6-Phase Model for Fruits and Vegetables 

Since the 1970s, Grodan has worked in partnership with commercial growers to maximize the potential of stone wool. This hygienic, hydrophilic, soilless substrate was first adopted by European cucumber and tomato growers.  

The substrate made its way into greenhouses and indoor cultivation spaces worldwide, readily adopted by tomato, pepper, cucumber, and berry farmers, as well as the floriculture sector. To help these specialized growers make the most of stone wool substrate, in the early 2000s, Grodan developed the 6-Phase Model that details how to produce hydroponic crops efficiently from seed to harvest. 

The 6-Phase Model takes a straightforward approach with a set of irrigation strategy guidelines based on crop type and slab type for steering plants through each period of growth. This results in better yields, higher-quality produce, and more efficient and precise use of growing inputs. Grodan’s methodology has gone on to influence cultivation data collection and documentation for food producers worldwide.  Crop-specific models continue to evolve as agricultural research and technology advance each year. 

That oft-imitated, never fully replicated model is exactly what inspired Grodan to develop a cannabis-specific version of this ag-science classic for a new era of commercial cultivation.  

The 5-Phase Model for Cannabis Cultivation 

Grodan’s 5-Phase Model, specific to steering hydroponic cannabis, is being further developed and tested through a series of 16-week trials conducted at the preeminent Netherlands research station at Wageningen University. Grodan also has an in-house team of cannabis cultivation experts dedicated to new product R&D, as well as educational initiatives like the new phase-based model.  

So, what’s the big difference between hydroponic vegetable cultivation and commercial cannabis? Why do tomatoes need different growing guidelines than the genetically and morphologically diverse array of commercially produced Cannabis varieties?  

This is what our in-house and academic research partners have determined: 

Five Phases, From Roots Down to Harvest 

With cannabis, growers must first establish a robust, strong rootzone to support a healthy structured, flower-laden plant. The Grodan 5-Phase Model for Cannabis guides growers through the best practices for root development, vegetative growth, and all other aspects of plant care from the moment clones or seedlings are ready for a stone wool block or slab through harvest. 

The 5-Phase Model takes the essential elements of crop steering and systematizes them, so growers have an easy roadmap to follow from rooting their first clone to harvesting their last cannabis plant. Knowing when, how, and just how much to stress plants and manipulate them into producing desirable cultivar-specific characteristics used to take a lot of trial and error for growers. The 5-Phase Model details what a cannabis plant’s needs are through its rooting, vegetative, and flowering periods. 

With other, longer-cycle hydroponic crops, including those grown in uniform substrates like stone wool, growers typically want as much root development as possible as early as possible to support the plant through many months of growth and simultaneous fruiting. With cannabis, however, a shorter vegetative growing cycle is preferable, and plants are encouraged to root and define their canopy as easily as possible. 

In the early stages, when the cannabis plant is tasked with root development and vegetative growth, the goal is to develop the plant structure and swiftly expand the total leaf area as well as root volume. All the water, temperature, and irrigation parameters recommended during this phase will enable the plant to absorb a maximum amount of light and nutrients over its lifespan. Large dry downs in the substrate are beneficial during the generative phase when cultivators are trying to manipulate their plants’ size and shape before flowering. This is less the case in fruit and vegetable cultivation, where growers are simultaneously trying to manage vegetative growth and fruiting for a much longer production cycle.  

To initiate bud formation on the cannabis plant, adjustments to the photoperiod and nutrient supply are introduced to encourage the plant to transition from vegetative growth to flower initiation. This requires careful rootzone management to ensure the roots stay active and healthy as the plant transitions more of its energy to full flower development, allowing the buds to fill in and swell. It’s during this critical phase that water and nutrient uptake must be monitored carefully, as well as the amount of light, air, and carbon dioxide penetrating the plants’ dense canopy. 

Carefully managed irrigation is crucial to see the flowers through maturation, as are sufficient support structures to keep the plants rooted and upright—particularly for taller, thinner cultivars. Rootzone management is also a focus for cultivators during this time, particularly to ensure internal energy is maintained as the plant focuses on flowering.  

The final phase calls for dry backing—a regimented dry-back period with a reduction of irrigation and fertilizer application to prevent flowers from developing mold and requiring excess curing time all while encouraging proper ripening and maturation. This stage also involves monitoring electrical conductivity (EC) and titrating the fertilizer inputs to avoid excess nutrient accumulation ahead of the final harvest, especially as the sensing crop’s fertilizer demand slows dramatically. 

Cultivators can benefit from the 5-Phase Model not only by improving yields and making the growth process more consistent but also by reducing labor and other inputs. When growers know precisely how much water and fertilizer to introduce at different phases of plant development—combined with other technological advances like automation—resource utilization drops.  

It’s an important moment for cannabis agriculture when this crop finally gets its due with researchers and commercial cultivation specialists. As technology for commercial cannabis cultivation progresses, it’s exciting to see education initiatives and resources follow suit. And we at Grodan couldn’t be more proud to support growers everywhere—yesterday, today, and tomorrow. 

Learn more about cannabis crop steering on Grodan’s blog.