Cultivation Corner with Olivia Sobelman: Beat the heat in your indoor grow this summer

Cultivation Corner with Olivia Sobelman: Beat the heat in your indoor grow this summer


With summer comes the very fun and exciting outdoor season, but indoor growers can start to see major issues with heat in their grow environments. There are a lot of low-cost ways to bring the heat down until the winter rolls back around.

There are Pros to high heat environments, the biggest one being that plants respond incredibly well when CO2 is added to the room. Whether it’s added by a CO2 burner, canisters, or fungus (Exhale) bags, these methods can increase vigor and yield by 20%.  I can go on and on about the benefits of CO2 in a grow environment but will re-address it in a later article that will expand on advanced growing techniques and dialing in your environment. That being said, your room can healthily run low to mid 80’s when you add CO2 to your environment, so if you have higher heat and want to give that a try, it’s a great opportunity to use the heat to your advantage.

Because LED lights run at a lower wattage and are ultimately less hot because of it. Switching to or starting out with these LED lights will give you the best chance of reducing your heat output during the summer months.

When your plants flower or are forming buds in high heat environments, especially humid ones like Missouri, you will start to see a lack of bud density in your final product. The plant forms this way to allow air to pass through the buds in an attempt to cool off and lessen the possibility of bud rot. Your plants may also suffer from root issues from mold that can quicly cause nutrient lockout or even plant death. High temps and humidity also create a breeding ground for pests and mildew that can become problematic at around 50+% humidity. That being said, if temperatures run a little higher than normal and you don’t have humidity issues, even if the bud structure changes with the heat, the quality won’t suffer much at all. An often-overlooked factor can be where and how you store your reservoir as well. Try to keep water temperatures in the mid 60’s – low 70’s to help prevent root issues.

Whether you are in a grow room or a grow tent, the first and most effective way to mitigate heat is to change your light cycle to start coming on during the nighttime hours and shutting off during the daytime. My husband and I start programming our lights to come on at around 8:00 PM and shut off at 8:00 AM and that allows us to go in and water our plants before bed and check on the girls in the morning if we get up early enough. Any variation of this timeline is still better than trying to keep the lights on all day during the peak of summer.

Early signs of heat stress and curling

The same can also be used to try and beat the heat during your Vegetative stage as well, sometimes I run lights for 24 hours a day, sometimes I switch to 18/6. During the summer if you turn your lights off during the hottest part of the day you’ll save a little money on electricity and keep your plants cooler. Right now, ours are off from 11:00 AM – 5:00 PM. Your room can run hotter in the vegetative state, the plants are naturally used to it because they are usually growing outdoors in 100-degree weather. It is fine for them to grow indoors in the mid 80’s without damage, but any hotter and you’ll see some burning and heat stress on the leaves, and an increased likelihood of bugs and powdery mildew.

There are treatments, organic and otherwise, that can push back mildews and soil-borne pests, so it’s not the end of the road if you come across it. It’s just the nature of the beast this time of year.

Venting out your heat with an inline fan can dramatically help with heat and humidity issues. You can opt to have it on all the time, which is fine unless you are trying to supplement CO2 in your environment. If that is the case then the fan will simply remove the CO2 from your room which will minimize its effectiveness. Another option is to purchase a fan with a built-in controller that senses the heat and humidity and kicks on when you program it to so that it only works and flushes out the air when you needed. If you already have a fan and aren’t looking to replace it, you can purchase these controllers separately and they just plug right into any fan, inline or otherwise.


Heat and humidity can be problematic if you’re running more than one light and if you have single or double-ended hoods instead of LED fixtures. A slightly more costly way to cool down a room is to, of course, install an air conditioner. For the price, a window unit is always my go-to. A general rule of thumb is for 2500 BTU per light fixture, but that can vary depending on what brand or output of light you are running. Air conditioners have the added bonus of dehumidifying your room, the only pitfall is that smell can leak through the unit, which is much less of an issue now for many people. There are portable standing units that are available but because they themselves put off heat, you’ll need to get a higher BTU unit. This helps to offset the heat that radiates from the unit.

Severe stress and curling exhibited on leaves

That helps segue into another low-cost trick. If it’s at all possible, move any mechanical device in your tent and set it up outside of the tent. If you have a fan hanging inside your tent and blowing out, place it outside your tent and have it pulling from your tent and blowing outside or into another room. The same can apply to stand-alone or detachable ballasts, etc. If you are running ducting, switch it out for insulated ducting. All these little fixes that may each only reduce the temperature by a degree all add up to a much more manageable grow space.

Know that you’re not in it alone! Even though fighting nature is all but impossible, try these methods and take it in stride. It’s a challenging time of year for indoor gardening, but absolutely worth it.




Olivia Sobelman has been a cannabis grower for 10 years and was part of a team that won the US Cannabis Cup Awards three times. Sobelman and her husband, Tyler, own and operate The Grow Depot Hydroponics Store in Mid-Missouri. Fast becoming “The Plant Doctors,” The Sobelmans’ mission to educate and destigmatize cannabis is at the root of their business. Grow depot offers access to free consultations for patients and growers, both in-person and by phone, to diagnose and mend many issues in the garden. Visit Grow Depot for grower tutorials, past articles, and to learn more about the services they offer and their contributions to the cannabis community.