Hemp: Hype and Hyphae

Heady Vermont is happy to welcome to another great new guest columnist, Matthew Lavallee!

It’s an exciting time in Vermont. The hemp and CBD scene is exploding, and eager gardeners are anticipating exercising their newly found right to cultivate cannabis. Vermonters are hanging lights, constructing greenhouses, prepping soils, and making seed or clone arrangements, as they put into motion research and planning. The fever is palpable in the local grow stores, where clients line up to ask a full gamut of cannabis questions. Setting up for the vegetative growth phase is crucial. Two quick examples: the creation of a healthy root/zone and atmospheric environment both provide the foundations upon which the flowers will stack.

Soil is a complex matrix teeming with microbial life. Many microbes are symbionts – organisms living within a host community –  which feed and protect the plant.  Amending the soil with compost, manures, kelp, worm castings and other natural complements are the best way to renew and feed these microbe populations. The permaculture approach is to sustain and build the soil over time using natural processes. Adding organic matter also improves the overall soil profile, texture, and tillage. Soil amendments are a good start, but further fertilization will likely be required before the season is complete. Some organic commercial soils claim 3 months’ worth of fertilizer in the mix.

The texture of the soil determines its porosity, permeability to air/water, or aeration/drainage and water retention. Cannabis plants like a wet/dryback cycle. Drying back promotes the growth of fine feeder roots characteristic of a healthy rhizosphere, or root-zone. A plant will often appear healthiest right before it tips the balance into being too dry and losing turgidity (swollenness) in the leaves, thriving in the balance. The soil’s texture is the key to this balance. All potting soils for containers are amended to improve aeration and drainage using various substrates. Perlite, vermiculite, coco fiber and peat are particularly good texture modifiers. Note – our experts say that the most common problem in the garden is overwatering.

The first experiment in an introductory soils class is to determine soil texture by sedimentation. A soil sample is submerged in a glass jar filled with water and a pinch of dishwasher detergent. Upon shaking, the largest particles of sand settle the fastest. Silt stacks in the middle, fine clay particles settle last with the organic layer floating on top. Each layer will be a slightly different color and the volume of each can be visually calculated to determine the composition. With a little work, even sandy and clay soils can be productive.

Beneficial microbes are the best defense against many plant diseases. Trichoderma is a genus of common soil fungus that is an effective biofungicide. It colonizes real estate which could otherwise become populated by pathogens, preventing damping off and root rot. The mycorrhizae of several soil fungi live in and on the roots forming a symbiotic relationship with plants. The fungus is fed sugars produced by the plant, and in turn, the plant has the surface area available for nutrient uptake effectively doubled by the entwined fungal hyphae. There are a wide variety of mycorrhizal inoculants available on the market and lots of pre-packaged soils come pre-inoculated. Plants may need only be inoculated once with these beneficial microbes for the populations to colonize for the life of the plant.

Vegetation booms in a warm humid environment. Growth rate is directly proportional to transpiration or the plants ability to exchange gases. Good airflow is imperative for maximum transpiration.  Problems can develop if the air is not constantly moving. Vapor pressure deficit (VPD) is the most accurate environmental measurement of a plants prospective transpiration. It is essentially the drying capacity of the air at a given temperature/humidity. Low VPD corresponds with high vascular output and plants ability to transpire most effectively.

With all the hype about hemp and cannabis, I’m hoping this article provides you, the beginning grower, with important information to cultivate your own cannabis plants and help us elevate the state of cannabis here in Vermont and nationally.

Matt Lavallee – A Brief Bio

I moved to Northern California in 2003 to attend Humboldt State University where I got a degree in biology and went on to do grad work in genetics, sampling extremophiles living in boiling springs lake at Mt. Lassen national park for phylogenic analysis.

In California the green gold rush was on. Prices and demand were high, as product was being hustled down to dispensaries in hungry LA markets and across the country. California Prop 215 allowed me to grow up to 99 plants in Humboldt county with a physician’s recommendation. I did so for over a decade.

With a construction background I had a lot of side work building grow rooms and wiring 240V boxes to hot water heater timers to double the number of lights per circuit. I got to know horticultural products by going to tradeshows and familiarizing myself with the plethora of garden shops that flourish on the west coast. Through my network I was fortunate to work with more than a handful of growers on the farms that line the hills in the emerald triangle.

Since moving back to Vermont I worked as a cultivator at Champlain Valley Dispensary for two years and am excited to be cultivating hemp this year under the Island CBD license. Legal cultivation is a joy that I have known for 15 years. I am excited to see the public get the chance to take the flower back and look forward to helping others maximize this experience.