By Veronica Castillo

Ask cultivators about growing cannabis outdoors in hot and humid places like Florida and the Caribbean, and many say quality cannabis can’t be grown in climates like that because of mold concerns and infections. And yet, many cultivators not only do grow in places like this but also want to know how to grow under the sun despite the humidity. I travel around Florida and there are plants everywhere. Florida is a Spanish word that means “flowery” or “covered with flowers.” So while many say it can’t be done, I look around and wonder why. All I see is an abundance of greenery. 

Veronica Castillo with GramCo.’s Mike Dukes at the nursery. Photo by @Robinpartonpate, Green Point CMO

I interviewed Mike Dukes, Director of Agriculture Operations at GramCo., a central-Florida based cannabis company, cultivating cannabis under the Florida sun. Mike has cultivated indoor, outdoor, hydroponic, nursery, and traditional row crop farming for 20+ years in Colorado, Florida, Colombia, and South America in regions 4 to 11b on the USDA hardiness zones. 

Many say that outdoor cannabis cultivation in places like Florida won’t produce great cannabis/hemp. As a cultivator of over 20+ years, cultivating outdoors in Florida; how do you respond to that? 

It’s definitely not true that good-quality cannabis can’t be grown outside. Florida has abundant sunlight, and that’s an important natural element needed to grow healthy plants outdoors. No matter where you cultivate, you’ll be paying close attention to the aspects that can create a challenge in the growth of the plant, whether it’s managing the moisture levels or keeping an eye out for pests. Use diligent practices to combat climatic conditions. My recipe to success has been a good integrated pest management plan, strong genes, and the application of a regional knowledge.

Florida’s hot days hit 100 degrees with ease. What would you say are the biggest challenges on days like this? 

On days with excessive heat, plants need more water as the hot environment can dehydrate them quickly. The staff, who are outdoors in the heat all day, also need to stay hydrated. With that temperature, a covered grow house can reach dangerously hot temperatures in excess of 120. Staff will need more hydration breaks, sunsafe equipment, and shaded areas for breaks. The plants won’t make it if the people who grow them aren’t taken care of too. We match our labor with our temperatures so the more labor-intensive jobs and time-consuming tasks in the greenhouse are done early in the morning. This leaves the rest of the day for less labor intensive work in the extreme heat. 

With the heat, the number one thing is cuticle temperature. We monitor that over almost everything other than soil moisture content. In a greenhouse or shade house, we’re able to manipulate different elements of the climate. We don’t have that luxury outdoors. That’s not to say that plants are not strong and resilient and don’t want to survive; they do. 

We utilize shade curtains in the summer and clear plastic for our hoops in the winter to let in more light, as well as many nursery productions to mitigate cuticle temperature raising. With heat comes abiotic stress. There are things that can be used to mitigate that stress as far as fertilizer/nutrients, correct media/aggregate, and air movement. In regions 8, 9, 10, and 11, for any structures that have plants we utilize HAF fans (horizontal airflow fans) that create a sheet of wind correctly spaced apart, and pushes all the hot air directly off of our plant cuticles, and brings in fresh air 24 hours a day in a nursery. 

Veronica Castill. Photo by @Robinpartonpate, Green Point CMO

Silica can also be added to reduce abiotic stress. We have a strict spray regiment that aids in not only reducing abiotic stress but mitigation of pest/pathogen which helps a lot in the summer months. The army worms, caterpillars, various mites, and aphids are abundant in the warmer months.

Break down silica and outdoor cannabis plants.

I think silicas are very misunderstood. They are mainly used to reduce abiotic stress. It’s absorbed foliarly very fast and they can be further gated or sprayed. Basically, silica reduces the stress from drought or heat or soil compaction. I’ve seen it work with a lot of different applications. Silica basically adds strength to the cell. When the cell is stronger, it has a better chance of diffusing nutrients and water through the plant. There are many forms of silica, but I think the point that needs to be taken away from this conversation is that it has to be available to the plant — something like monosilicic acid (MSA) or orthosilicic acid (OSA). This is the most broken down form that is the most readily available. 

Also, anything with spraying or fertilizing any plants is all about pH. You have to get your pH correct before application or else it’s virtually useless, and can honestly do more harm than good.

Would you say that there are major differences between using silica for indoor grow vs outdoor? 

The only difference between the silica indoors and outdoors is going to be the application rate indoors is more fine-tuned. When outside, we do something that’s known as spoon-feeding where we give very small amounts quite frequently, and we monitor how much is going into our pots / growing media and coming out of our pots so we can gauge what the feed needs to be on a given set of irrigations.

What are the signs of a plant overdosed on silica?

Too much silica can prevent nutrient or fertilizer uptake. It’s rare to see an overuse of silica, but with overusing it, you can create the inability to uptake other nutrients/compounds. Ultimately, you can grow anywhere so long as you become extremely familiar with your region.

How hot is too hot for flowering? 

There isn’t a “too hot.” It’s more about the size of the plant when it gets into the heat stress. If it’s a small plant, you may lose the whole plant. If it’s bigger and stronger, it’s chances of survival are better. The plant could still be alive, but may not produce the same amount of oil. It’s like a baby that gets sick with a fever. It may get better, but it’s not functioning at full capacity.

How can you identify heat stress? 

An early stage of heat stress is canoeing, when both sides of the leaf turn completely up. The second stage of heat stress is when the leaf turns down and is crisp. 

How do you deal with heat stress indoors? 

HVAC helps us mitigate this. Sometimes we use evaporative heat cooling towers. 

 Can plants recover from heat damage?

The plant may look like it’s fine, but the plants may not produce the optimal amount. It depends on how badly the plant was damaged.