5 ‘Green-Thumb’ Innovations Marijuana Gardening Will Unleash


epa02310452 A worker tends to cannabis plants at a growing facility for the Tikun Olam company near the northern Israeli town of Safed on 31 August 2010. In conjunction with Israel's Health Ministry, the company currently distributes cannabis or Marijuana for medicinal purposes to over 1,800 people to help relieve pain caused by various health conditions.  EPA/ABIR SULTAN ISRAEL OUT


Canada has been leading the legalization of cannabis in North America since it legalized medical marijuana in 2014.  This has triggered new agricultural innovation in Canada.  Now Canada is considering ending prohibition for adult-use cannabis.  But a key issue is protecting youth from substance abuse. Last week Canada’s new Prime Minister was asked, "When can Canadians expect you to legalize pot if you're elected?" Justin Trudeau responded that his government is committed to ending the former Prime Minister’s "failed approach on marijuana that he said makes it easier for young people to get their hands on the drug than beer or cigarettes”.


This is the same issue being debated here in Vermont as our Legislature considers legalizing cannabis for adult-use (it already is legal for medicinal use).  Dr. Harry Chen, the VT Commissioner of Public Health noted: "Our smoking rate in teenagers is probably about 13 percent. Our marijuana rate is about 37 percent. One is regulated, one is illegal. I think there's, if you do it right, there's ample room for improvement."


Four other states plus Washington DC have already legalized cannabis through citizen initiatives and more states will do this in the next year.  VT may be the first to regulate and tax adult-use cannabis through legislative action. Most of the state-level initiatives allow home cultivation of marijuana and a recent article about the Canadian legalization effort noted: “If home cultivation is not allowed, then cannabis is not truly legalized in Canada. Canadians must have at least as much right to grow their own cannabis as they do to brew their own beer and wine.”


Last month I reported on a national survey that indicated 24.5 million home gardeners would grow marijuana if it were legal to do so.  What might the affect of legal marijuana gardening have on home horticulture?  I think it could be huge, as big as suburbanization and lawns, as big as patios and container gardening, as big as drought and xeriscaping.  But probably not as big as climate change and related gardening challenges!


Let’s look at areas where illegal marijuana growing has advanced horticulture practices and how ending marijuana prohibition might affect home gardening innovation and success.  But first, I have some biases informed by 35 years of supporting the local, sustainable food movement through Gardener’s Supply and the Intervale Center.  These biases include: growing in living soil is better (for plants and us) than growing in ‘chemical soups’, mimicking nature with organic solutions is better than fighting nature, and the most successful gardening always embraces low-energy and water-smart ways to grow.


Overall, because commercial and home cultivation of cannabis has been illegal in the US, and in most states it still is, the approach to growing this crop has been intensive in terms of space, technology and inputs.  So, this high-profit crop already has been spawning horticulture innovation for decades.  As more states legalize there will be new partnerships with experienced growers, universities, extensions services and new legal businesses, unlocking more innovation.


Here are 5 areas we will see more horticultural innovation stimulated by legal cannabis home cultivation:


1. Plant-specific organic soils and fertilizers for intensive gardening success

Like with a human diet, where whole foods derived from natural sources and eaten in moderation is best, the same is true for plants.  Plant health and yields are best when grown in healthy soil and avoiding too little or too much nutrients. The highest quality commercial cannabis is grown organically in containers and raised beds.


Growing in living soil is easier and more forgiving than in hydroponic systems, which require constant nutrient testing and adjustment.  Success starts with the soil mix and ideally it uses an organic compost base.  There is an art to creating fertile living compost, full of microscopic organisms that “digest” organic matter and make nutrients accessible to plants.  The best compost “recipes” include carefully balanced inputs such as nitrogen, carbon and moisture, which support healthy microbes to thrive.  The compost helps soil life buffer the disease and pest stresses of intensive growing, providing both NPK and needed micronutrients. 


As intensively grown plants move from vegetative growth to flowering and fruiting their nutrient needs change, whether tomatoes or cannabis.  Again, the best solution for the home grower is a balanced organic fertilizer with NPK and micronutrients attuned to the needs of the crop.  As growing cannabis is openly researched it will become clear how different varieties and strains benefit from individualized formulated soils and fertilizers. This ‘designer fertilization, could be liquid, granular or “spikes” that will provide a localized, nutrient rich growing pocket. Plant roots will only take what they need preventing nutrient overload or lock out.


A secret used by Vermont craft cannabis growers is to add molasses or maple syrup during the last weeks of flowering, both rich in nutrients and a carbohydrate source to feed soil microorganisms, boosting soil structure, moisture retention, and adding a bit of sugar allowing the plant to focus on bud production.  This can increase yields and add sweet flavor by stimulating terpene production.


2. Light makes the difference.  Cannabis plants have two life stages: vegetative and flowering. Whether from sunlight or grow lights, light is basically food for plants, creating plant energy through photosynthesis.


Vegetative growth begins when seeds first sprout. Indoor growers give their cannabis plants 18-24 hours of light a day during the vegetative stage normally using compact fluorescent lights (CFLs) or fluorescent tube grow lights postioned very close to plants. Relatively weak fluorescent lights do not perform well during flowering when greater light intensity is needed.


High Intensity Discharge (HID) lights have historically included Metal Halide (MH) and High Pressure Sodium (HPS) lamps, but now also include the latest generation of Light Emitting Plasma (LEP) and Light Emitting Ceramic (LEC) fixtures. All of these HID lights are more expensive to buy and especially to operate than fluorescent fixtures. But their light intensity is needed for indoor flowering and can also be used during the vegetative stage.


Light-emitting diodes (LED) grow lights are the third option and they work well with vegetative growth.  However, performance varies widely by manufacturer. LEDs have many advantages over both fluorescent and HID lights sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching, plus their light spectrum can be closer to sunlight. The need for temperature control in the grow room and lower electric bills has motivated the shift to LED lights in some of the best commercial growing operations.  With continued R&D LEDs will eventually replace other grow lights for indoor gardening success.


To initiate flowering in cannabis, buds will begin to form indoors when the light cycle is reduced to 12 hours a day, and the other 12 hours marijuana plants are kept in total darkness.  This is difficult to do for outdoor growing, where cannabis cultivation basically can be guided by best practices from tomato growing.


3.) Prune like a tomato, ‘espalier’ like a pear.

Tomatoes are determinate or indeterminate. Determinate tomatoes usually require no pruning. Indeterminate tomatoes perform best if pruned so more plant energy goes to flowering and fruiting rather than more leaves and stems. Cannabis plants behave more like indeterminate tomatoes where pruning is the best way to get maximum yield in small spaces.


Healthy cannabis plants usually form one of two typical growth patterns – a “Christmas tree” shape with one central terminal bud on the tallest stem and smaller terminal buds forming around the plant.  The alternative is a “candelabra” shape where the lower arms form more of an even canopy. Either shape can be aided by pruning. As with pinching off new growth stems from indeterminate tomatoes, manipulating cannabis plants to form more terminal bugs can increase your yields without investing in more nutrients or better lights. Generally, wider cannabis plants with many terminal buds perform better because the light available to leaves is maximized.


Many commercial growers start by “topping” the tallest terminal bud to break the dominance of the central stem and trigger lateral growth.  Then, like espaliering for fruit trees, plant productivity can increase by bending and manipulating stems. Indoors, low-stress training increases leaf exposure to grow lights, capturing more available light while reducing heat stress.


There are various approaches to this, including “low-stress training”, which entails forcing plants to grow wide and bushy by bending down and training the growth tips to grow laterally rather than topping them. The “Screen of green” method uses a horizontal mesh or screen to keep many terminal buds growing at uniform height. “Sea of green” forces more younger plants, packed tightly together in smaller pots, into earlier flowering at about the same height maintaining the central stem and bud but trimming away lower stems. There will be many productively gains in the future as the best ways are discovered to coax more productivity by training and pruning various strains of cannabis.


4. Micro-climates matter.

While cannabis is began as a weed before centuries of hybridization, any time you grow intensively in small spaces there are increased risks to plant heath.  Managing temperature and humidity to achieve a healthy indoor growing environment is crucial to the health of your plants, as well as to your final yields and potency (cannabinoid content). When the temperature (and to a lesser extent the humidity) is too high or too low, your plants will not grow properly and yields and potency (cannabinoid content) will decline.


Indoors, cannabis plants generally prefer temperatures in the 70-85°F range during the day when lights are on. When lights are off (or at night), cannabis plants are happy with slightly cooler temps. If it feels too hot or too cold for you in your grow area for you it’s probably too hot or too cold for your cannabis plants as well.


Colder temperatures reduce photosynthesis and slow growth.  Plants are also more vulnerable to mold with cold temperatures because humidity tends to increase. Indoor plants can be more susceptible to cold than outdoor grown plants where winds blow and conditions vary.


While cannabis plants don't usually die from the heat, too hot temps will cause plants to grow much more slowly. During flowering temperatures above 90°F will not only slow down bud growth, but can reduce the potency of the buds. Pests and diseases also intensify in the heat, including spider mites, white powdery mildew (especially with high humidity), nutrient burn (from increased water transpiration), and wilting due to root oxygen deprivation.

Innovation will emerge from new “controlled environment agriculture” with scalable computer-controlled software and hardware that optimize temperature, humidity, lights, water, fertilization and CO2.  Greenhouses will become more efficient and be powered by renewable energy, with the capacity for multiple harvests per season thanks to automated light deprivation covers.


Smaller growing spaces, including grow tents and integrated raised bed systems, will help home growers achieve optimum temperature and humidity with proper venting. These tents can expose plants to the greatest concentration of light thanks to interiors covered in highly reflective materials. They also can keep light out during the flowering stage and can help contain odor with the aid of carbon filtration.


The right soil containers can also be critical.  Fabric pots help prune roots by exposing roots to dry conditions at the edges of the container, driving roots back to the moist soil.  Containers can be self-watering to help achieve optimum moisture, conserve water and nutrients and make it possible for you to ignore your containers for days at a time.


5. New strain development will be more about wellness than getting “stoned”.

Cannabis strains available today produce higher yields and are more potent than strains even a decade ago. Strain potency, yields, and ease of growth have been improving steadily over the last several decades as growers around the world are constantly breeding new strains and improving on old favorites.


In the past 2-3 decades breeding interest in cannabis has been focused on high levels of THC, the psychoactive cannabinoid that can produce a euphoric effect in the recreational user.  The THC craze caused breeders and growers to focus on boosting THC levels. This resulted in cannabidiol (CDB) and other cannabinoids with clear health benefits to almost be bred out of most strains of marijuana.


More recently medicinal cannabis breeding projects in Israel, Europe and the US have been responsible for the resurgence of interest in CBD. CBD research has shown that this cannabinoid has significant medical benefits, but does not make people feel “stoned” and can actually counteract the affect of THC. The fact that CBD-rich cannabis is non-psychoactive makes it an appealing option for patients looking for relief from inflammation, pain, anxiety, psychosis, seizures and spasms without disconcerting feelings of lethargy or feeling “high”.


New scientific and clinical medical cannabis research emphasizes CBD’s potential as a treatment for a wider range of conditions, including alcohol and opioid addiction, arthritis, diabetes, MS, chronic pain, schizophrenia, PTSD, depression, epilepsy, and other neurological disorders. CBD has demonstrable brain-protective effects, and its anti-cancer properties are currently being investigated at several medical research centers in the United States and elsewhere.



This is the new frontier of cannabis strain development.  It offers an expanding realm of health benefits and new opportunities for home gardeners to “grow their own health revolution”.

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