How large of a heating system (boiler, furnace, heater) do I need to heat my greenhouse? Although the calculations can get complex, especially if more than one glazing or building material is used, they can be simplified to give a meaningful estimate. The information that is needed to make the calculation is the surface area of the greenhouse, the glazing material, the desired maximum night temperature and the average coldest outdoor temperature during the winter. The two major ways heat is lost is by conduction and infiltration.

Heat loss by conduction

Most heat loss occurs by conduction with the addition of a small amount from convection and radiation. These usually occur simultaneously from the surface of the greenhouse. This component of heat loss can be calculated from the equation:

Conductive heat loss = SA x U x TD

SA is the glazed surface of the greenhouse exposed to the cold. Calculate this by adding the areas (length x width) of the roof, sidewalls and endwalls.

U-factor represents the overall heat transfer coefficient of the glazing (Btu/hr – sq ft-° F). It includes a small value for the convection and radiation component. Typical value for greenhouses with a single layer of glass, polycarbonate or polyethylene is 1.15. Use 0.7 for double poly and 0.6 for double wall polycarbonate or acrylic.

TD is the temperature difference (maximum inside night temperature - winter design temperature) (° F). A good inside night temperature is usually 70° F as this provides heat for melting snow. Winter design temperatures can be found in the following reference: bit.ly/degreedesigntemp

Heat loss from Inflation

The other major source of heat loss can be from infiltration — the exchange of warm inside air with that from outside. This exchange occurs through cracks around doors, vents and shutters, from cracked or slipped glass and from air escaping up the chimney. This component of heat loss can be estimated by the equasion:

Infiltration heat loss = 0.02 x V x C x TD

V represents the volume of the greenhouse calculated by multiplying the floor area by the average height resulting in cubic feet.

C stands for the number of air changes per hour. Use 0.5 to 1 for a new greenhouse, 1.5 for a well-maintained glass house and 2 to 3 for a poorly maintained glasshouse. Add 10 to 15% to these values if the greenhouse is located in a windy area.

TD represents the same value used in the previous equation, which is the difference in temperature (°F) between the maximum inside night temperature - winter design temperature.

Adding the conductive and infiltration heat losses together will give the total heat loss. The heating system you install should have an output rating equal or greater than the total heat loss. Consider installing two smaller units for greater efficiency and for safety.

The author is an agricultural engineer, an emeritus extension professor at the University of Connecticut and a regular contributor to Greenhouse Management. He is an author, consultant and certified technical service provider doing greenhouse energy audits for USDA grant programs in New England. jbartok@rcn.com

It’s not every day that a whole new revenue stream opens up for greenhouse growers. But in recent years, as cannabis has become legal for various uses across North America, growers are experimenting with the crop. And some are seeing some serious success.

In this issue, we explore the various ways this could be good news for those who choose to get involved in the cannabis industry. Some are choosing to rent out space for hemp production, which you can read more about here. Others, like ColorPoint (one of the largest greenhouses in the U.S.) are jumping into the cannabis industry. Brothers Art and Ken VanWingerden are switching the operation to 100% hemp production. You can read more about that here.

But many are still wary of the crop. I recently visited a greenhouse that was experimenting in cannabis production but was unable to discuss their future plans. And another grower I spoke to said they’re starting production, but was unable to provide any details. It seems as though many are starting to dip a toe into the market to see what they can do. They want to be prepared to make hard decisions about their production space when the right time comes.

According to exclusive research from our sister magazine, Cannabis Business Times, greenhouse production of cannabis is rising, increasing 4% from 2016 to today. And who knows where the market will go from there?

As more and more states legalize hemp and marijuana production — and as the market continues to grow — it’s becoming an increasingly attractive prospect. But it’s also one that requires a lot of leg work and due diligence.

No matter what decision your operation makes, there’s plenty the two industries can learn from each other. As growers forge a path in the constantly changing cannabis market, they’ll face challenges and opportunities that could provide new perspectives on traditional greenhouse operations.

Whether it’s new technology, new methods or new solutions to old problems, it will be exciting to see what happens next.

Photo © gunuXOX | Adobe Stock

Facing competition from big box stores and cheaper imports — amidst shifting markets, unpredictable weather and inflating costs — greenhouse operators Brian Wheat and Bob Aykens are rethinking their business models. Both fourth-generation business owners, they’ve watched their predecessors adapt over time, but their families would have never guessed that their greenhouses would one day be filled with cannabis.

“One of the key lessons my father always told me is that diversification is key,” says Aykens, who owns Memorial Florists and Greenhouses in Appleton, Wisconsin, with his sister. “We’ve been around since 1923 because we’ve diversified from growing cut flowers to growing chrysanthemums and annuals, and now this is the next step.”

But learning how to grow a new plant can be a risky business fraught with trial and error — especially in the highly regulated cannabis industry. That’s why Wheat and Aykens decided to lease greenhouse space to hemp production, rather than entering the market themselves.

“Our greenhouses were in such disrepair and we were only generating income from three months out of the year, but we didn’t want to sell the land,” says Wheat, CEO and owner of Lafayette Florist, Gift Shop and Garden Center in Lafayette, Colorado. “Leasing seemed like a better option, because at least you’re pulling in rent money, generating some cashflow year-round.”

That doesn’t mean leasing to hemp is easy money. For every opportunity, there are obstacles to overcome, so Wheat and Aykens shared their advice for renting greenhouse space to cannabis.

Vetting partners

“For the last six years, people have been calling me about cannabis,” says Wheat, a master gardener and member of the Society of American Florists. “I wasn’t going to grow marijuana in my greenhouse — for security purposes, for reputation purposes, for a lot of different reasons. It just wasn’t the right fit for our family retail business in small downtown Lafayette.”

Then, Wheat started taking CBD oil for joint problems. Once he learned the difference between marijuana (which contains psychoactive THC) and hemp (which produces CBD), he recognized the crop’s potential. So, he was intrigued when a representative from Front Range Biosciences walked in one day and asked Wheat to meet with Jonathan Vaught, the company’s co-founder and CEO, about leasing some greenhouse space for hemp production.

Other hemp growers offered Wheat a percentage of profits after processing — and although those six-digit numbers were enticing, the uncertainties of sharecropping posed too many risks. Wheat wanted regular rent payments, but when he calculated his costs, the price even shocked him. However, Vaught understood greenhouse operating expenses, as he was already renting facilities across the country. Plus, Wheat’s business — located just two miles from FRB’s lab — offered a prime location, so Vaught even offered to renovate the space to meet his operation’s standards.

“We agreed on the length of the lease and the price per square foot — which, across the country, goes anywhere from $4 per square foot for a greenhouse that might need a lot of repair, all the way up to $10 per square foot if the greenhouse is in great condition,” says Wheat, who couldn’t share specific details, but emphasized that Vaught has been a wonderful partner.

Although rent payments and renovations sweetened the deal, these decisions should be based on due diligence, not just dollars.

“Right now, in the cannabis world, people are willing to invest significant money to retrofit a structure if it’s faster than building a new one,” Vaught says. “But beware of the hype. Vet your tenants and get to know them; make sure they’ve got strong financial models and business plans behind them. It’s a long-term deal, kind of like a marriage, so you don’t want to jump into it overnight. If you do your due diligence, you’ll be able to weed out the ones that aren’t going to be sustainable partnerships.”

Sharing space

Vaught’s renovations to Wheat’s greenhouse included new lighting, environmental controls and security systems with locks and cameras — which ended up benefitting the rest of Wheat’s business.

“Now I can see what’s going on and control the boiler, the air conditioning and the vents from my phone, even when I’m not there,” Wheat says.

But inviting another business into your greenhouse requires careful consideration. When Wheat called his mother to share the news of his tenants — which initially included two other hemp growers in addition to FRB — her first comment was, “You don’t have enough bathrooms.” Six months later, Wheat realized she was right.

Although FRB only brought in six employees, Wheat’s other hemp tenants had as many as 75 people on the property, in addition to Wheat’s 26 employees — which strained the parking situation, the break room capacity and the facility’s four restrooms.

Splitting up energy costs was an even bigger hurdle, since Lafayette Florist only has a single utility meter.

“I had to sit down with the tenants and say, ‘If you aren’t going to put in your own meter so we know exactly how much gas, water and electricity you used, you’ll have to agree with our assessment,’” Wheat says. “People can get angry about their share of energy costs, so you better come up with a plan before you go down this path.”

Educating the community

When Wheat started leasing to FRB, an elderly customer who’d been shopping with him for several decades quickly shared her disapproval.

“She poked me in the chest and said, ‘You sold out to the devil’s cabbage,’” he recalls. “She was mad because she couldn’t go into the greenhouses where we used to keep 20,000 geraniums. I tried to explain that we’re helping our family business survive. I could have sold the land and bulldozed the greenhouses, but I didn’t do that.”

Overall, the pushback from customers has been minimal, because Wheat made deliberate efforts to educate the community about the new crop on his property and why he decided to lease space to hemp production.

“It’s vital for anybody who’s thinking about doing this to be totally open and honest with your employees and your customers, because if you’re secretive, then they think you’re hiding something,” says Wheat, who crafted an explanation letter (available at here).

Early on, Wheat also met with the city manager and chief of police to preempt any concerns. They asked him to install shade curtains to mitigate night-time lighting that might bother the neighbors. In terms of regulatory requirements, FRB held the necessary hemp licenses, which reduces the burden for their greenhouse landlords.

Aykens agrees that transparency is key. “You have two options: You can keep it quiet or be vocal about it,” he says. “We got ahold of the media and hosted a hemp lunch-and-learn, and it created a huge buzz in the community. The key was educating the consumer that hemp does not have THC. That took away a lot of the stigma.”

Memorial Florists used to grow 60% of its plant material, so when Aykens began entertaining this idea, he met with key growers who supplied the rest to ask if they could make up the difference. That means “customers haven’t seen a difference in quality,” he says. “Instead of having hundreds of each variety of coleus, we’ve got maybe 20 on-hand at a time.”

If customers balk at the limited selection, Wheat offers to pick up special orders from growers. “We’ll go that extra mile because we don’t want our hemp rental business negatively impacting our customers,” he says.

Profiting from opportunity

For Aykens, the hardest part has been adjusting to the change of scenery in greenhouses once filled with colorful blooms, that have now become seas of hemp green.

“I’m used to walking in our growing facility and seeing color,” he says nostalgically. “But we’re in business because we need to be profitable. We need to make sure that the people who work for us have good jobs, and that means we’ve got to have a good bottom line.”

Thanks to hemp, he’s now seeing green in more ways than one. “We’ve become more profitable as a company and our bottom line has changed substantially because of it,” he says.

Of course, operators must weigh the pros and cons that hemp rental can have on their facilities and their reputation. For vexed greenhouse owners like Wheat, year-round leasing “helps cashflow in slow retail times” by generating income from structures that sat empty.

“If you operate with the right amount of caution, it can be incredibly lucrative,” Vaught says. “There’s a good opportunity to monetize your property through the right partnerships.”

The author is a freelance writer based in Cleveland. She is a frequent contributor to GIE Media horticulture publications.

While the national cannabis market has changed drastically since 2012, when Washington state and Colorado first legalized adult-use cannabis sales, at least one thing hasn’t changed: The industry is very much still amidst a significant boom, with no signs of slowing.

According to the most recent State of the Industry report from our sister magazine, Cannabis Business Times, greenhouse production is trending upward, increasing 4% from 2016 to today. But cannabis cultivators are shifting away from indoor/warehouse operations. Indoor operations once were a standard for cannabis production: 80% of research participants reported growing indoors in 2016, the first year of this study. That number has dropped by 21 percentage points during the past three years — with 59% of cultivators reporting growing indoors this year.

The number of growers who cultivate in greenhouses seems to be on a slight rise compared to prior years: 38% of 2019 research participants stated they grow in a greenhouse, up four percentage points from 2016.

And cultivators are planning to expand in the coming years. This year, 85% of cultivators studied indicated plans to expand their operation’s square footage for growing cannabis. In 2018 and 2017, that figure was 77% and in 2016, 71% of participants indicated any expansion plans.

In 2017, the average square footage that cultivators said they planned to add in the next two years was 22,300 sq. ft. In 2018, that figure increased to 27,400 sq. ft. This year, the average is 39,700 sq. ft., growing by 12,300 sq. ft. compared with the previous year and by nearly 18,000 sq. ft. compared to 2017.

In addition, nearly a quarter of participants (23%) plan to add 80,000 sq. ft. or more for growing cannabis in the next two years.