grow media water management

It’s just water, right??

Cultivating healthy, vibrant cannabis requires attention to numerous inputs. Commercial cultivations expend considerable amounts of capital to supply light, nutrition, and environmental management, but the most inexpensive input is frequently overlooked and under managed. Grow media water must be managed so that plants can assimilate nutrients and so that the conditions for beneficial soil microbial colonies are supported. Different growing medias can have a wide variety of characteristics. From growing in straight perlite to the rich soil of an old growth forest, the unique characteristics of each media must be considered since the water volume and interval are drastically different for different media.

Cultivating with soilless media

Commercial greenhouses the world over are largely run using soilless media.  Examples of soilless media include peat, coco, perlite, and rockwool. The benefits of soilless medias for commercial greenhouses are numerous. Soilless media is largely chemically inert so that it is easy to have precise control over the nutrient solution the roots are absorbing. Soilless media, particularly perlite and rockwool, have a pore structure that provide maximum oxygen penetration into the root zone. These porous oxygen rich soilless medias are almost impossible to overwater, so they are well suited for massive cultivations that cannot afford the labor required to spoon-feed more dense and complicated media.  The flip side to the ease of soilless media is that they can only hold so much nutrient solution. This can have devastating repercussions if an irrigation pump or valve fails and goes unnoticed.

Growing in native soil

On the other end of the spectrum from soilless media is using native soil and cultivating in the ground. Native soils are generally dense and heavy and comprised of a combination of sand, silt and clay.  Sand makes up the largest particles and clay makes up the smallest particles. Spaces between the particles allow water and oxygen to make their way into the root zone. Pore space can be increased by fostering a healthy soil microbial community. Soil microbes glue particles together to create a soil structure that with time, and increased microbial diversity, creates a considerably larger surface area than the mere inert particles that make up the mineral component of soil. Increasingly diverse pore space allows the storage of water, nutrient and oxygen in the soil. The size of microbial community is largely based on the availability of organic matter and the presence of adequate soil water, so water management takes on a regenerative aspect in how microbial pore space is encouraged. The complex systems of pores that make up microbial capillary action can be easily disturbed by tillage, which is why trying to grow a plant in soil dug from the ground in a container is so difficult. To properly manage the water in a soil both the particle size and the health of the microbial community must be considered. A healthy living soil rich in organic matter and minerally balanced can provide all the nutrition a plant needs and has access to deep reserves of water through complex capillary action. Living microbial soils are complex and balanced systems that when properly managed can buffer the extreme environmental swings of outdoor cultivations far better than the light and porous soilless media.

Which is best?

The best grow media depends on your environment and your particular cultivation goals. Porous soilless media, like rockwool, are a great choice for controlled environment indoor grow rooms because it effortlessly keeps oxygen in the rootzone even during frequent irrigations making proper media water management easy even by untrained hands. Living soils rich in water and nutrient buffering capacity have advantages for the unpredictable swings of environment experienced in outdoor farming. Different goals demanding very different media.

About the Author

Scott Sirles, co-founder and president, is a cultivation expert and agronomist who has been growing both indoors and outdoors for more than 20 years. What sets Scott apart from other cultivation experts is his appreciation of permaculture concepts that help businesses design systems to maximize useful connections between components, and thereby reduce the waste of time and energy resources. Scott has had diverse experience in agronomy, pest management, farm layout, greenhouse design, irrigation, organic soil, hydroponic systems, lighting, environmental systems, and progressive agriculture technology. Scott earned a Bachelor of Arts in Environmental Design with an emphasis on Architecture from the University of Colorado in Boulder and currently lives in Denver.