Hosts Michael Williamson and Anders Peterson speak with Jon Jirikovec, Crop Specialist at Grodan, about substrate management, irrigation strategy, and cannabis cultivation.

Grodan manufactures stone wool (Rockwool) for hydroponic and soilless cultivation, offering high control and steerability for growers.

Jon shares his journey from retail cannabis work in 2013 to his current role supporting growers across North America.
Grodan emphasizes listening to customer feedback and conducting research with institutes like WUR and CRIC to refine techniques.

The team discusses crop steering and irrigation phases (P1, P2, P3) and how they’ve evolved in cannabis compared to vegetables.

Rockwool offers better control and water efficiency than coco, though it requires more precision; it’s easier to rewet and adjust EC.

Substrate sizing is critical; under-sizing can lead to overly vegetative growth and poor-quality flower (e.g., more C buds).

Transitioning from HPS to LEDs often requires adjustments in substrate volume to avoid over-drying and improve irrigation control.

Case studies show that even novice growers can succeed with Rockwool when supported with tools, data, and proper guidance.

Slab systems offer more forgiveness and better resaturation uniformity than blocks, making them ideal for newer cultivators or limited environments.

Labor efficiency and facility design (e.g., racking height and accessibility) play a key role in productivity and plant health.
Rockwool systems reduce labor and mess compared to cocoa/soil systems, making post-harvest cleanup easier and faster.

There's a trend toward more sustainable, low-EC, low-runoff irrigation strategies to conserve water and nutrients.

Growers in water-restricted regions (e.g., U.S. Virgin Islands) may benefit from Rockwool due to its water efficiency.
The importance of environmental control (e.g., VPD, leaf surface temps) in syncing with substrate performance was emphasized.

Discussion of water circularity systems (e.g., True Zero Corp) that reclaim runoff and reduce operational costs.

Greenhouse vs. indoor production: each has advantages; multi-tier greenhouse cultivation is less common but may suit tight spaces.

Harvest and cleanup timing impacts microbial loads and crop quality; separate these steps to reduce contamination risks.

Transitioning to bulking phase should be based on crop observations (e.g., end of stretch), not arbitrary timelines.
Removing fan leaves too early can lead to foxtailing due to hormonal stress; timing and gradual EC changes are key.

Crop steering is a spectrum, not a binary approach—subtle adjustments help maintain plant health and yield.
Under-canopy lighting improves consistency in A/B grade flower but is not always necessary with good canopy and lighting strategy.

Common Rockwool mistakes include letting blocks dry too much before irrigation and using undersized substrates.
Substrate strategy should align with veg time, plant count limits, and business goals.
Discussion teases future episodes on “synganic” growing—blending salt-based fertigation with organic additives for better terpene expression.

Grodan is exploring microbial steering and root-zone microbiome strategies for added performance.