Cooling a Greenhouse in Summer: Beat the Heat When It's 95°+ Outside

A greenhouse needs the right setup to stay productive once temperatures climb into the 90s.

This is the question I've been getting more than any other in my Friday emails lately, so I figured it was time to put together a real answer. With temperatures climbing into the 90s (and the inside of an unventilated greenhouse running even hotter), a lot of growers are watching their plants wilt and wondering if they made a mistake investing in a greenhouse at all.

You didn't. A greenhouse that's set up right will actually help you get through summer better than growing outdoors, not worse. The heat problem almost always comes down to one thing: airflow. Once you fix that, everything else gets a lot easier.

Here's what's actually happening inside your greenhouse on a hot day, and what we recommend to keep it from cooking your crops.

What Makes Cooling a Greenhouse in Summer So Difficult

A greenhouse is built to trap heat and sunlight — that's the whole point in spring and fall. The problem is that the same poly film that holds in warmth during a cool morning will keep holding in heat all afternoon too, with nowhere for it to go. On a 95° day with no airflow, it's common for the inside of a greenhouse to climb to 120°F or higher. That kind of heat stress shows up fast: wilting, blossom drop, scorched leaves, and stalled-out fruit set on tomatoes and peppers.

The fix isn't one single product. It's a combination of shade, airflow, and smart end-wall design, and most of it can be built right into your greenhouse setup from the start.

1. Roll-Up Sides: The Best Passive Cooling You Can Build In

Roll-up sides let you crank open the entire wall for instant cross-breeze.

If I had to pick the single most useful upgrade for summer heat, it's roll-up side walls. They let you crank up the entire side wall of your greenhouse or high tunnel and let a cross-breeze move straight through, which does more to cool things down than almost anything else you can add.

The reduced-gear crank we offer with our roll up side walls makes it easy to operate by hand, no electricity required, so it works even if your power goes out or you don't want to run a motorized vent system. It also doubles as a backup if you do have an automated ventilation setup and it ever goes down.

One thing growers ask us about a lot this time of year: we always recommend ordering roll-up sides at the same time as your greenhouse or high tunnel kit, since they're built to match your specific frame and it keeps everything simple to install. It is possible to add them to a greenhouse you already own, but it's a more involved retrofit and typically costs more than adding them at the time of your original order. If you're dealing with a greenhouse that's struggling through this summer without them, it's worth reaching out to us for a quote on adding roll-up sides now, or planning ahead so they're built in from the start next time.

2. Exhaust Systems: Active Cooling When Passive Airflow Isn't Enough

Exhaust shutters and double doors work together to keep air moving through the structure.

Roll-up sides are great for passive, no-electricity airflow, but on the hottest days, or in greenhouses that are tightly built for season extension, you may need something more active. That's where an exhaust system comes in.

We size every exhaust fan and shutter combination so that it gives your greenhouse a full air turnover once per minute, no matter what size building you have. We've already done the math on fan size versus square footage, so you don't have to guess at CFM ratings or oversize (and overpay for) your system. You just tell us your greenhouse dimensions and we'll get you the right setup.

Exhaust systems can be ordered as a standalone add-on for an existing greenhouse, or they come included with our All Inclusive Kits, which bundle the properly-sized exhaust fan and shutters right in with your structure, shade cloth, ground cover, and thermostat. If you're ordering a new greenhouse and know summer heat is going to be a factor where you're growing, going with an All Inclusive package is usually the simplest way to make sure cooling is handled from day one.

3. Shade Cloth: Cut the Intensity of the Sun

Even with great airflow, direct summer sun can be more than your plants need. That's where shade cloth comes in. Our most common is a 50% reduced knit black shade cloth, which cuts down on light intensity and heat buildup without leaving your plants in the dark. It resists mold and mildew, breathes well so air still moves through it, and is easy to size for any of our kit widths.

We get into more detail on choosing the right size and how shade cloth interacts with greenhouse temperature in our earlier post, The Power of Shade Cloth, if you want to go deeper on that one.

4. Open Up Your End Walls

If you built your greenhouse with double doors on both ends rather than solid walls, summer is when that decision really pays off. Open doors on both ends, combined with rolled-up sides, create a real cross-breeze instead of just letting hot air sit. If your end walls are solid, even propping doors open during the hottest part of the day makes a noticeable difference.

This is one of the reasons we leave end wall design flexible on our kits. Growers in hot climates tend to lean toward double doors specifically because of how much it helps with summer airflow.

5. Watering and Timing Adjustments

Ventilation handles the air, but how and when you water matters too. Watering early in the morning, before the heat of the day sets in, gives your plants time to take up moisture before they're under stress. Avoid watering in the late afternoon heat, since wet soil combined with high temps can actually encourage root issues and fungal problems.

Misting or damp gravel pathways can also help on the worst days, since evaporative cooling brings down the ambient temperature inside the structure a few degrees.

Watering early in the day keeps plants hydrated before the afternoon heat sets in.

6. Plan for Next Summer Now

If this summer has been a struggle, the best time to fix it is actually before fall planting, not next June. A lot of growers reach out to us in July and August wishing they'd added roll-up sides, an exhaust system, or planned for double-door end walls when they first ordered their kit. Getting that figured out now means you're set up and ready well before next year's heat hits, instead of scrambling again.

Whether you're starting from scratch with a Fully Braced Kit or adding a ventilation system upgrade to a greenhouse or high tunnel kit, we're happy to walk through what setup makes the most sense for your climate and growing goals.

Final Thoughts

Summer heat is genuinely one of the toughest stretches for any greenhouse grower, but it's also one of the most fixable problems out there. Airflow, shade, and a little timing on your watering schedule go a long way, and the right setup means you're not fighting your greenhouse all season — you're working with it.

If you've got questions about cooling down your current setup, or you're thinking ahead to ordering a kit with summer ventilation built in from the start, give us a call. We answer our own phones, and we're always happy to talk through what's worked for our own greenhouse and for the thousands of growers we've helped get set up over the years.

Stay cool out there, and happy growing!