Canadian consultant Rob Smallman says greenhouse growing is tough but fun.

Smallman, of  Avitas Consulting and the Global Cannabis Exchange Canada / Portugal, recently participated in the Cheeba webinar on South African medical cannabis  which looked at the country’s strategic options. Although he is a firm proponent of EU-GMP certified growing, he’s cut his teeth on greenhouse cultivation while Director of Cultivation & Post-Harvest at Curaleaf International’s Portuguese facility.

Here he shares his thoughts with MMJ Daily in an interview published in September 2023.

“We had a lot of 40-degree weather in Portugal this year” says cannabis consultant Rob Smallman.

“We use a fog system to keep the temperatures in the greenhouse down. Usually, we can keep the temperature in the greenhouse around the same as it is outside, but sometimes the inside temperature even reaches 45 degrees.

Now that the days are luckily cooler again, humidity has taken its place, we have to deal with lots of rain and humidity levels of around 80-90%, which isn’t good for the plants either.

“Growing in a greenhouse, you’re constantly faced with such challenges.”

Air movement and genetics

As the company is growing cannabis in a greenhouse that was originally designed for vegetables, they have been on a journey to figure out how to best adapt the environment to cannabis.

“For cannabis, a positive airflow greenhouse works the best. That’s why we’re still adding to the air movement and ventilation, especially for the heat as well,” says Smallman. “Now that the humidity is a problem, air movement continues to be a major focus.

We don’t have dehumidifiers or air conditioners, but we use ventilation to play with the air.” The company also uses radiant heating that is put on the floor throughout the canopy of the plants.

“Even in the summer, we heat up that area so that it dries the area up with radiant heating. It’s a nice solution that helps quite a bit.”

Still, such high temperatures can make growers quite nervous. “Therefore, you have to rely on the right genetics. If you don’t have the right genetics, you will run into mould problems, foxtails, and airy flowers,” he says. That’s why the company is in the midst of trialing 10 different genetics, with another 90 coming in.

“We’re constantly upgrading and seeing what works in our temperatures.

This is especially necessary when growing cannabis in a greenhouse, as it is the most difficult way of growing cannabis, in my opinion. Once an indoor facility is properly set up, you just have to hit a button, and all the parameters are perfect at all times.

Outdoor growers have the air movement, which prevents the humidity issues that greenhouse growers have to deal with. Greenhouse growing is tough, but it is a fun challenge,” says Smallman.

So, how did the plants react to the heat? Not all genetics enjoyed the summer weather, he replies.

“Some new genetics we tried out didn’t like the heat at all, while some other genetics loved it, and there were no issues. That’s where we weed out the weak and keep the good ones, constantly cycling that until we have a nice library that can handle our conditions.”

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