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Climate Control: Pros and Cons

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Keeping our plants happy can be a daunting task, especially without knowing what it is that actually allows them to thrive.

What Type of Environment Do I Need?

When trying to determine the ideal climate for your plants, always look at seed packs or on seed bank websites, to determine the exact environmental needs. Most of our favorite plants thrive with temperatures between 65 and 77 degrees and with humidity levels of anywhere between 40% and 65%. Most seasoned gardeners allow the humidity level to near 60% while their plants vegetate, and lower the humidity during the flowering period, down to 40% by the final weeks. Plants grown within these parameters have fewer pest and mold issues, so stay within the lines folks!

Now that we’re clear on which climate is best for your favorite plants, let’s talk about the ways gardeners set their gardens up to provide that climate.

How Do I Get That Climate?

Lights are hot and plants respire (sweat), so lowering both the temperature and humidity is usually the goal, but every climate and season can present their own obstacles. There are two main camps when it comes to climate control: sealed room and exhaustive. Both require differing amounts of tinkering and provide differing amounts of success.

Exhaustive Rooms

An exhaustive room evacuates the air from the room and sucks in air from a different location, typically outside. Usually exhaustive rooms use air-cooled lights that efficiently suck heat away from the room and the plant canopy, without using much electricity or requiring much investment. 

When sizing a fan for a room, please consider that a fan can be slowed down or put on a timer, but the only way to move more air is to buy a bigger fan, so buy the right fan or even the next size up (if you are thinking about expanding). 

Here’s what works for most gardeners:  Anything that is 400w or less, needs a 4” exhaust fan to keep the temperature in check. A single 600w or 1000w can usually be serviced well by a 6”. When cooling more than two 1000w lights in a row, consider getting 8” reflectors and using an 8” fan. 

Reducing the ductwork from 8” to 6” impedes airflow. Air cooled rooms are also at the mercy of the elements. When it becomes 90 degrees outside, there is no way to suck in air and lower the temperature to 75 degrees. If it is very humid outside, humid air will be invited into the garden too. For most of the year here in the Northwest, the exhaustive or air-cooled room works pretty well. The exhaust fan usually has to get slowed down in the winter and in the summer, well, maybe think about paying for a sealed room.

Sealed Rooms

A properly set up sealed room provides the most consistent conditions for growing regardless of the season. 

A sealed room requires an  air conditioner (which cools and de-humidifies), a  dehumidifier (because the A/C only runs when the lights are on) and something to introduce CO2 into the room. None of these items are inexpensive, but the no-hassle harvest in the middle of a heatwave is priceless. 

To properly size an air conditioner to the room, plan on a minimum of 6000 btu (British thermal unit) of cooling per 1000w lamp that is not air cooled and 4000 btu of cooling per air cooled 1000w. 

If a dehumidifier needs to run 24 hours a day to keep the humidity in check, plan for enough btu to cool that too. We already have an article on sizing a dehumidifier, so check out that article next:  How to Properly Size a Dehumidifier to a Garden

CO2 is what plants breathe, so get ready to provide that too. CO2 tanks do not emit extra heat or humidity so I recommend using tanks. There are also burners out there that burn either LP or NG and emit a ton of heat. The more burners in a single unit, the quicker the room can fill with CO2.

Which Climate is Best for Me?

Choosing which style of climate control best fits your garden is up to you. If you like knowing what is typical, just for reference of course, here’s what’s up. 

Around the west side of the Cascades, gardens with 4 or less 1000w in the flower room use air cooling. They pull their hair out from May until late September but you get what you pay for. Once a gardener has committed to setting up a large room or warehouse, A/C is the way to go. Yes, it costs more, but inconsistent yields or quality can ruin a grower’s reputation or even their business entirely, so choose wisely and grow with confidence!


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