The Geography Of Indoor Growing

“Indoors, YOU are Mother Nature!”

I first read these inspiring (and somewhat daunting) words in a now antique guide to indoor gardening. This well-thumbed, early growers’ manual sported a black and white photo of its author, his back characteristically turned towards the camera as he regarded his magnificent indoor garden. The vibe was that you could grow ‘anything’ you wanted indoors despite the weather outside.

Since then, my idealistic notion of a discrete indoor garden has collided with the reality of running them in different parts of the world. I have erected grow tents and constructed grow rooms around the UK, USA, Canada, Portugal, and France. The primary thing I’ve learned during this time is that what can work for one indoor grower simply won’t cut it for another—and the fundamental differentiating factor is geography.

Unless you’re growing in a subterranean bunker hundreds of feet below the surface, your indoor growing environment will be inexorably subject to your geographical location. Think of the outside world as your indoor grow room’s ‘base climate’. It’s the foundation upon which you must build your indoor growing environment.

English Garden

As an indoor grower, I had it easy in Britain. For a nation that loves to discuss the weather, it’s pretty unremarkable. It seldom gets extremely hot or cold, and the humidity remains moderate throughout the year. As such, installing an air conditioner or dehumidifier never occurred to me. Instead, I just vented the hell out of my rooms with the biggest extraction fans my neighborhood was willing to collectively ignore and hoped for the best. The primary purpose of air exchange was to mitigate the inevitable increase in air temperature generated by old-school HPS and metal halide lamps.

Mercifully, I only ran small rooms. Air exchange was a three-for-one deal, though—exhausting the hot air from near the ceiling of my grow room and replacing it with cooler, fresh air drawn from an adjacent room also helped to regulate humidity and maintain atmospheric carbon dioxide levels.

O Canada

Things changed on Vancouver Island, BC. My grow rooms expanded in size, and the wattage of my lights increased from 600W to 1000W. The winters were much colder, and the summers much hotter (or was it that wooden buildings provided less insulation than the brick I was used to?). Also, I needed to tackle humidity head-on with a chunky dehumidifier (when it rains in a place for nine months straight, there’s little point trying to regulate humidity with air exchange alone). It wasn’t all bad news, though. Electricity was much cheaper than in the UK, and the tap water was so pure I thought my Bluelab EC truncheon was broken (it wasn’t—it’s still going strong to this day! I’d never known such pure water to come out of a tap)!

Growing in a French Wine Cellar

When I eventually settled in the south of France, near the Mediterranean coast, a whole new Dunning-Krueger rollercoaster ride began. The mild winters were very welcome. The hot summers were a bit of a shock, though—I’d never experienced heat above 110°F (43°C)! Fortunately, my grow room was safely ensconced in an old wine cellar carved into the rock 300 years earlier. The house above was constructed of stone walls over three feet wide at their base. I’d never known insulation like it. But now I have another problem—aridity! The cacti and succulents growing at the side of the road paid testimony to the fact that only specialist plants can survive year-round here. The dry air wreaked havoc on my seedlings, forcing them to over-transpire, leading to stress and nutrient toxicities like I’d never seen before. I countered this by switching to soilless potting mixes to control the available nutrition more carefully and conservatively.

Meanwhile, I invested in a humidifier and connected it to my reverse osmosis water purifier. The water coming off the Pyrenees was the hardest I’d ever encountered—pushing 0.7 mS or even 0.8 mS (350 – 400 PPM) out of the tap. First, I had to pass it through a water softener, then through RO. I then had to visit three grow stores before I found some Calmag for sale!

Being so well-insulated and having switched to LED grow lights by this time, I was amazed that I still had to heat my grow room in May! The increased air temperature meant that my nutrient solution also started to warm—so my final investment was an aquarium chiller (so much for energy efficiency). Ultimately, I decided to invest in side lighting to increase my daytime air temperatures as it pained me to run a heater in my grow room at 25°C outside.

Seal the Deal

I bit the bullet and sealed my grow room—something friends in BC had been encouraging me to do for years. By generating my own supplemental carbon dioxide and running a powerful dehumidifier, I could harness the heat produced by my lights rather than vent it away. It was also much easier to retain some of that transpired or generated humidity in my grow room—so crucial in those early vegetative days.

Lessons Learned

I’ve learned many lessons over the years. The first one is: never trust a generic ‘my way or the highway’ grow guide! Always take into account the author’s location. Also, if you plan to grow indoors year-round, you may need to change tack a little with the seasons. For example, NFT tanks work well in a cooler winter grow room, but in summer, you could be better off filling some pots with media and giving your roots extra insulation.

Finally, always consider the implications of the precise location of your grow. An attic indoor garden in the UK may suffer from bigger temperature extremes than a basement grow room in Spain. Don’t make choices that limit your wiggle room further down the line. If high air temperatures are a recurring issue and an AC unit is out of the question, you can still mitigate any attendant issues by using larger containers and soilless media (so you can dial down nutrient strength and provide roots with plenty of insulation).

Investing in a nutrient chiller is also highly recommended for growers in warmer climates. It’s incredible what the aerial parts of plants can tolerate if their roots are nice and chill!