Source:
growweedeasy
Outdoors, you have less options to reduce heat during a heat wave, but you can monitor your local weather via weather forecasts.
It is possible to partially shield your plants when you know the temperature is going to get hot. You can also adjust your watering schedule to make sure plants at least have plenty of water.
Some things to try when you know the weather outside is going to be hot or dry:
- water plants in the evening or early morning to help prevent water evaporation during the hottest hours
- keep roots cool – for example by putting your potted plant in a ceramic pot to help insulate the roots from the sun. I’ve also heard of growers digging a hole in the ground to place their potted plant inside, because the ground is usually cooler than the air when the temperature gets high
- kelp extract for roots – provide a small amount of liquid fertilizer that contains seaweed kelp extract(can help protect against heat stress)
- increase shade to reduce the heat experienced by plants – you can use an old sheet or other cloth as a short-term solution or get a professionally made “Sun Shade Sail” which is made particularly to create shade outdoors. It’s important to remember that giving plants shade for more than a few days will make them less “hardened” to the sun, and you may need to reintroduce full sunlight back slowly to prevent them from getting shocked from the light intensity
- move potted plants – luckily with potted plants, it’s usually easier to move them out of direct sunlight during a heat wave
- take extra good care of heat-stressed plants – when cannabis plants appear heat-stressed, try to baby them as best you can, and offer shade during the hottest days.
Fungus Gnats
A fungus gnat infestation on your cannabis plants can cause all sorts of strange problems – often they look like overwatering, pH problems or nutrient deficiencies. The more fungus gnats you have, the more likely you’ll see damaged leaves and reduced growth rates.
Since fungus gnats are almost always caused by overwatering and too-wet topsoil conditions, some of these symptoms may be caused by too-wet soil. In any case, when you see fungus gnats, it means there’s a problem in your setup that needs to be addressed.
I attached a picture of both symptoms
Heat 
Fungus Gnat 
