Secrets of the Pros: 24 Cannabis Cultivation Tips

From HVAC and harvesting to pruning and pest control, six expert growers share their advice

by Omar Sacirbey

Life isn’t easy for marijuana growers these days.

Cannabis cultivation is becoming ruthlessly competitive in some markets, while falling wholesale prices and an increased focus by regulators on pesticide use are creating new challenges and long-term concerns. And then, of course, there are the common day-to-day hurdles that come with running an agriculture business, such as weather fluctuations, pest problems and the possibility of equipment failure.

Given that growers already face numerous obstacles that threaten their incomes, it’s important to counter potential losses with gains in other areas, such as efficiency, yields and quality.

Marijuana Business Magazine interviewed six top commercial cannabis cultivators from around North America to get their tips for growing high-quality marijuana and keeping expenses under control. These growers cultivate indoors, outdoors and/or in greenhouses. Some are large operators with facilities well over 100,000 square feet in size, and others are craft growers. Between them, they have decades of experience and their tips have withstood the test of time.

The lineup:

  • Alecia Weisman, Legion of Bloom
  • Matt Sampson, North Coast Growers
  • Jesce Horton, Panacea Valley Gardens
  • Jeannette VanderMarel, Green Organic Dutchman
  • Shane McKee, Shango Premium Cannabis
  • John Andrle, L’Eagle Services

These experts shared their insights into six key areas of growing: heating, ventilation and cooling (HVAC); lighting; watering; nutrients and supplements; pruning, and harvesting.

We boiled down their advice to two dozen top tips to help other growers and cultivation companies refine and improve their methods.

Heating & Cooling

McKee: Protect your investment and income with redundancy

As a longtime cultivator, McKee knows it’s inevitable that air conditioning units will fail.

“It doesn’t matter what brand. We use high-end equipment and they all fail, they all have problems,” he said.

So McKee’s biggest priority is having a failproof system.

His advice for cultivation sites with hundreds of thousands of dollars in a grow room: Don’t rely on just one large air conditioning or dehumidification unit. If it goes down, all the plants in the room could be lost.

Instead, it’s better to have multiple units in a single room so that if one air conditioner experiences problems, the room will still have cool air from the others.

“For me its flexibility and redundancy,” McKee said. “If I lose my air conditioning I don’t want to lose all my air conditioning, I only want to lose a small portion of it, so we have multiple units.”

Sampson: Use variable refrigerant volume technology to circulate only the cold air your environment needs

Sampson swears by air conditioning units from Daiken, a Massachusetts company that invented variable refrigerant volume (VRV) technology in 1982. Units that use VRV circulate only the minimum amount of cold air needed to reach the desired temperature, helping cut down on power bills.

Sampson said his company can now cool the same space for 25%-50% of what it would cost before switching to the VRV technology.

“We paid more up front so we can be operationally cost efficient in the long run,” Sampson said.

Horton: Consider desiccant technology – which is more expensive up front, but the payback is quick

Horton prefers desiccant dehumidification technology over refrigerant-based dehumidifiers, and he believes this is where most HVAC technology is starting to go. Desiccant is a type of chemical that absorbs moisture but can also release it when heated. It often comes as a wheel with descant-coated flutes that can be placed on a wall. When it spins, it absorbs wet air.

The technology costs 50%-80% more than a regular dehumidifying and air conditioning setup, Horton said, but the payback period is pretty fast because the cost of electricity is lower.

“It’s effective, and it also provides many efficient energy benefits and lets you recycle heat from your growing space,” Horton said.

McKee: Zone your units so plants are never exposed to excess light heat

It’s also important that air conditioners distribute air throughout a room. For example, if a room has four air conditioners, avoid having each unit responsible for one quarter of the space. If a unit fails, the grow lights will overheat and damage the plants in that section of the room.

The best strategy is to distribute air from all the units through the whole room via ducts. That way, when one unit fails, all the plants will continue to receive cooled air from the other units.

For added protection against cooking your plants in the event of an air conditioning unit failure, McKee’s facility has an automated dimmer that will lower the lights.

Weisman: Light deprivation curtains can help with HVAC, too

During the summer months when Weisman needs light deprivation curtains for her Legion of Bloom greenhouse, she goes with triple-layered breathable tarps.

These tarps not only block the sun when needed, but they also have an important environmental function by allowing air to flow freely in the greenhouse and reducing the risk of mold and trapping too much humidity.

She estimated a 50-foot by 30-foot tarp costs about $4,000, while a tarp for a hundred-foot greenhouse costs about $7,000.

Lighting

Horton: Sometimes less is more

Conventional wisdom says more lighting means more trichome production, larger flowers, better yields and an overall better grow.

That’s not always true. In fact, Horton said many strains thrive with less light.

“I’ve gotten better production out of OGs with 600-watt lights versus 1,000-watt lights,” said Horton, who used 1,000-watt lights for all his plants before switching over to 600-watt lights for most of his plants.

If you use too much light, what happens?

“You see lots of light stress,” Horton said. “From light stress, you’ll see plants that don’t finish as fast as you would like. Some plants get really leafy, or not dense because they’re stretching out.”

You can also identify light stress from leaves that are droopy instead of reaching up toward the lights.

Since making the switch to 600-watt bulbs, Horton said his strains have seen much healthier growth, and plants “finish when they should.”

“The vast majority of our strains don’t want thousand-watt lights. They prefer something with lighter demands,” Horton said.

Weisman: Ease your plants into natural light

Outdoor growers often like to start their plants indoors or in a greenhouse so the plants can get 24 hours of light (possible with supplemental lighting). But when they transfer those plants outside, problems can arise. The plants might get, say, only 15 hours of light and could face cooler temperatures. As a result, the plants can be tricked into thinking it’s time to go into flower mode, prematurely.

This situation can be avoided. Instead of immediately going from 24 hours to 15-16 hours of light, Weisman recommends a gradual transition. This can be accomplished by reducing lighting by 30 minutes per day inside until you’re at the equivalent level of light the plants will receive outside.

Similarly, if you’re vegging your plants indoors, you want to give them some brief exposure to light by taking them outside and putting them in the shade for a couple of hours every day. That way, the plants get some indirect UV rays and “harden up” a bit before they go outside full time, Weisman said.

“We do that because it’s easy to sun damage or bleach your plant; this is especially true in the higher elevations,” Weisman said. “If you go from inside to high UV, your plants are probably going to bleach.”

Sampson & McKee: Take steps to keep your grow rooms from overheating

While strategically zoning your air conditioners is one way to prevent your grow rooms from overheating, another important backstop is having lights that can react to an air conditioning failure. For example, Sampson of North Coast Growers likes the Gavita e-series, a widely used brand in both greenhouse and indoor grows. They have an auto dim feature and an auto shutoff if something happens with your HVAC gear.

“There are situations where you have HVAC shut down and then the lights cook the plants – it happens. This technology prevents that from ever happening,” Sampson said. “It doesn’t take long to cook a room. Your plants can survive a couple of days without the lighting, but they can’t survive more than a few hours if the room is past 90 or 100 degrees.”

Shango’s McKee agrees.

He uses multiple high-temperature light sensors because if one fails – which happens often – and you don’t have a backup, your plants will get cooked.

“We’ve had those sensors fail and not catch it. We’ve lost substantial revenue due to that,” McKee said.

Watering

Weisman: Give your roots a chance to dry

Weisman of Legion of Bloom prefers doing a few big waterings rather than a little one every day.

The problem with watering every day is that the soil never has a chance to completely dry, so it’s always moist or wet – which leads to root rot. It also makes it harder for the roots to uptake nutrients because they are already saturated.

“When you water every day, your plants never have a chance to dry out,” Weisman said.

When Weisman does water, she prefers to do it in between nutrient feedings, which cleanses the roots of any nutrient residue left over from the feedings.

“By doing this, you promote a very clean root environment, and that encourages nutrient uptake,” Weisman said.

VanderMarel: Tame the unpredictability of your well water

Wells are nice to have for a source of water. But one of their quirks is a large amount of variation in the amount of nutrients – calcium, magnesium, etc. – the water is carrying from the well. This makes it hard to achieve consistent nutrient levels, which makes for inconsistent results.

VanderMarel of Green Organic Dutchman deals with that problem by putting the water through reverse osmosis – removing any kind of extra particles from it – and then adding the desired blend of nutrients to the water.

To ensure that consistent amounts of nutrients are being added, VanderMarel uses dosing equipment to measure the amount of nutrients and then measures the water with an electrical conductivity (EC) meter, which gives growers a read on the amount of nutrients present. That eliminates inconsistency tied to the amount of nutrients in the water.

Sampson: Invest in a pump

In his facility, Sampson keeps a few thousand-gallon tanks of water in one spot. The tanks have pumps that can handle 80 gallons of water per minute and feed into holding tanks in the other vegetation and flower rooms. In turn, the tanks in those rooms feed into drip irrigation systems.

Before erecting this watering system, Sampson’s team spent hours a day filling the tanks with hoses. Sampson then decided to implement his current system, investing $25,000-$30,000.

The result? It’s reduced the amount of man hours spent on watering from eight or more a day to just 30 minutes, Sampson estimated.

“You don’t want to be paying anyone any amount of money to hold a hose and watch a tank fill,” Sampson said. “If you can make sure that flow is as fast as it can be, that is worth quite a bit of money over the long run.”

Nutrients and Supplements

VanderMarel: Add some organic nutrients directly to the soil

Organic phosphorous comes as what VanderMarel describes as a ground-up, powdery mineral. She tried to feed it through her stan-dard irrigation system, but the minerals weren’t fine enough and kept clogging the lines.

So now, VanderMarel adds the organic phosphorous directly to the soil.

Her company buys a pre-blended soil mix that includes most of the nutrients VanderMarel wants in her soil anyways, so she doesn’t have to add many nutrients. She also believes nutrients are more effective when they are premixed into the soil rather dissolved in water and then added.

Magnesium, molybdenum and zinc are other trace minerals that are better off going straight into the soil, she said.

“They’re all trace materials that are needed to grow good plants, but they’re much easier to blend into the soil then have them in a fertilizer mix,” she said.

Weisman: Foliar feeding is an easy way to nourish plants whose roots may still be saturated

During vegetation, Weisman ideally feeds her plants once per week. But if it’s a cooler week and the plants don’t dry up so fast, she will also do a foliar feed – spraying food on the leaves. That way, even though the roots may not have dried out, you can still feed the plants through the leaves and avoid risking root rot by oversoaking the roots.

During the bloom phase, they feed more aggressively – every five days – but stop feeding altogether about three weeks before harvest.

Andrle: Don’t rely too heavily on nutrients

Used properly, nutrients can lead to healthier, stronger plants. But don’t deceive yourself into thinking that nutrients will make your crop great. For plants, potassium, nitrogen and phosphorous are not as necessary as CO2 and light.

If your plant is having problems, the solution probably isn’t more nutrients. More likely, the problem will probably be in the environment, such as too high of a temperature, or salinity, which can cause the plant to “lock out” nutrients.

Rather than following the exact instructions for how much nutrient they use, Andrle of L’Eagle recommends that growers go underneath the recommended amount and see if their plants do better with less.

“One of my favorite tests was in 2013 when we grew plants without any nutrients in the flowering stage and the end result made shockingly little difference,” Andrle said.

Weisman: Avoid ammonium nitrates, and complement nutrients with compost

Legion of Bloom’s Weisman uses a proprietary blend of organic nutrients, including a fish powder nutrient that she likes for foliar feeding. She follows up those feedings by giving her plants a compost tea that contains five different sources of compost or humus to provide the highest possible microbial diversity to the soil.

“Once those microbes enter the soil in the presence of nutrients, they increase nutrient uptake,” Weisman said.

Pruning

Horton: Study how your plants react to being topped

Different strains react differently to being pruned, as well as to the different methods of pruning, namely topping – cutting more off the top of the main stalk – and FIMing (FIM is an acronym for “F**K I missed) – cutting less off.

Cultivators must study and note how their plants react to being pruned and record the outcomes. If the plant sprouts its new branches quickly, that means it likes being pruned and can handle regular and frequent pruning. If the reaction time is slow, it means the plant takes time to recover from being cut, and it doesn’t like being pruned, so prune cautiously.

Weisman: Prune frequently

“We like to prune often,” Weisman said.

For example, let’s say you have an 8-inch plant in an intermediate five-gallon soil pot that is getting into the vegetation stage. That plant will start with one stalk, but if it’s healthy enough and has several nodes, you can “pinch” – or cut – the stock down at least one node to 6 inches. When that stalk is cut, it releases two more branches that become the main stalks. From there, after it grows a couple more nodes, you pinch another node, so that every couple of nodes, you have a new branch.

“That creates a nice, broad bushy look,” she said.

After Weisman tops a plant, she gives it a week or two, sometimes three weeks, to see how it grows. If it’s looking tall and lanky, you want to get rid of that look.

VanderMarel: The Screen of Green method will let your best buds rise to the top

The Screen of Green method stress-trains the plants to grow surrounded on the sides and tops by a wire screen. This trains the plants to grow at a flat canopy, Green Organic Dutchman’s VanderMarel said. The leaves at the bottom don’t add much to the plant, so all those are removed. VanderMarel uses a flat screen to get an even canopy crop and ensure the flowering buds can come through the screen.

“It also keeps it very clean and neat,” she said. And because VanderMarel’s crew works with cloned plants, they essentially grow to the same heights, “so you have a nice even, consistent crop,” she added.

They don’t allow any of the lower leaves or branches grow, instead preferring to let the flowers grow on the top branches.

Weisman: Sativas can handle more cutting

Sativas can handle more cutting because it’s a more stretchy variety than indicas. This characteristic means the plants are physically better suited to handle a cut. But because many or most plants nowadays are hybrids, it’s hard to make generalizations or forecast how an individual plant might react. Rather, you must observe and pay attention to your plant, Weisman said.

Preventing Pests, Mold and Mildew

Sampson: Raise the dehumidifiers at night

When plants are in their flowering stage, they give off moisture during their night cycle, which raises humidity levels in the room. And more humidity increases the likelihood of pests, mold or mildew being introduced to your grow room. Knowing that, growers must increase the work rate of their dehumidifiers at night to reduce the added humidity, Sampson said.

Andrle: Harvest your rooms completely so they can be cleaned

Harvesting in complete cycles allows for proper hygiene maintenance of a cultivation facility while harvesting perpetually does not, according to Andrle.

Even though cyclical harvesting makes trimming more difficult, Andrle said, it is still worth it over time because it allows you to clean and disinfect in the form of less problems.

“While imperative that flower rooms must be full of plants 365 days per year in order to be operating at 100%, if ours is full 355 days (and being cleaned the other 10, and L’Eagle is operating at 97.2% instead), we’re OK with it as we save time and money the rest of the year not dealing with the same pest and disease issues that plague everyone else,” Andrle said.

Harvest

Weisman: Take a close look at the trichomes

Have a small microscope on hand. You don’t need a tabletop scientific microscope, but there are smaller handheld microscopes that are 100x or 60x that you can buy at your hydro store that enable you to look at your buds and see the milkiness of the trichomes.

If your trichomes become a little amber, then they’re ready. You don’t want them to be clear – that means it’s too early – and you don’t want them to become too amber, which means they’re overready.

VanderMarel: Keep your harvesting tools sanitary

As a craft grower who harvests every week or two, VanderMarel said keeping the harvesting tools super clean is vital. How does her company do it? It has a microbiologist on staff who swabs and tests all the tools for contaminants before they are used for trimming. And those tools don’t leave the harvesting part of the facility; they don’t go into any other room.

If you use a clipper in the cultivation area, where it’s exposed to bacteria that occur naturally in the soil, you don’t want those same clippers or that bacteria touching your final product.

“We don’t want to risk contaminated tools touching the final product,” VanderMarel said.

Sampson: Don’t wait too long to harvest

Many people harvest way too late, which can leave your product overripe or smelling like cut grass. North Coast’s Sampson likes to harvest a little earlier in terms of trichome color. After harvesting, Sampson dries the plants upside down in a cool, dark, room for a couple of weeks and then dry trims. That makes for better trichomes and more terpenes.