A thriving cannabis crop is built upon a healthy root system. If you're growing in stone wool, you’re already way ahead of the pack. But how can stone wool growers maximize their advantage? Here are three time-honored tips from seasoned growers that can transform the health of your root zone.

Get Smart About Water Content (WC)

The obvious challenge facing growers who want to evaluate root health directly is that all the action down below is invariably hidden inside growing media! However, with GroSens sensors, you’ve got permanent eyes on the engines of your cultivation operation.

Insert a few GroSens sensors at different depths in your stone wool blocks. Then, use the e-Gro app to set up alerts for when things get too wet and automate irrigations to prevent your stone wool from becoming too dry. Remember, proper dry-back is important, especially over the respiration phase (dark period). GroSens allows you to dial this in with pinpoint accuracy.

Remember, when it comes to irrigation, guesswork is for amateurs. With real-time data, you'll nail that sweet spot between access to moisture and air. Your plants will thank you with healthier roots and bigger yields.

Spread the Love (and Water) Evenly

To truly unleash the potential of cannabis cultivation in stone wool blocks, there’s really no substitute for a professional drip irrigation system complete with pressure-compensated emitters. Be sure to place your dripper stakes strategically. Typically, a four or six inch stone wool block will require at least two dripper stakes, positioned diametrically opposite from each other, equal distant between the main stem and the edge of the block.

Dripper stakes are subject to salt and particulate build-up over time. This can lead to blockages or impaired flow, throwing off your water distribution. Professional growers periodically use drip line cleaning products to their nutrient solution to mitigate the risk of blockages caused by mineral precipitate and organic debris.

Using Beneficial Microbes for Root Health

If you’re one of those growers who think beneficial microbes only work in soil—think again! You can introduce beneficial biology into the root zone to enhance nutrient uptake, improve root health, and increase resistance to diseases. For a deeper dive into how microbes interact with stone wool, check out The GroShow podcast episode with MIIM Horticulture, where we explore the science and benefits of microbial activity in soilless substrates.

You can’t apply mycorrhizal fungi too soon in the growing process. Endomycorrhizae (arbuscular mycorrhizae) are most commonly used for cannabis and form a symbiotic relationship with plant roots, increasing nutrient and water absorption, enhancing root growth, and improving plant resilience to stress.

Also, try Bacillus subtilis and Bacillus amyloliquefaciens. These beneficial bacteria produce enzymes that help decompose organic matter, enhance nutrient availability, and provide protection against root pathogens.

Trichoderma (Trichoderma harzianum, Trichoderma virens) compete with harmful fungi so that they are effectively ‘crowded out.’ They also enhance root growth and nutrient uptake.

Apply beneficial microbes when transplanting seedlings or cuttings into stone wool blocks. Dust the root zone or dip the roots in a microbial solution before placing them into the stone wool. Alternatively, mix microbial products into the initial watering solution.

Re-apply microbial products every 2-4 weeks throughout the growing cycle to maintain a healthy population in the root zone. Increase the frequency of application during periods of plant stress, such as high temperatures, drought conditions, or after pest and disease outbreaks.