To protect cannabis plants from the heat, keep them watered without drowning the roots, keep the root zone cool and give them shade when the sun is brutal. Heat-stressed weed plants tend to droop and wilt. Sometimes only the edges of the leaves curl up, or the leaf tips roll up or down like a taco, and a stressed plant may stop growing altogether until the weather cools off.
The good news: there are a few simple things you can do to protect your plants and help them ride out a heat wave.

1- Never let your plants dry out: this is one of the most important preventive steps, so make sure they're always watered. Plants drink a lot in the heat, and if they dry out they can die almost overnight. Keeping enough water available helps them stay as healthy as possible.

2- Don't overwater: it's easy to overwater in the heat because warm water holds less oxygen. Overwatering and drooping are really symptoms of roots getting plenty of water but not enough oxygen. So while you don't want the plant to dry out, don't soak the soil every day either, or the roots won't get any air. Making sure your soil drains well (for example, mixing about 30% perlite into your potting mix) will help prevent overwatering symptoms.

3- Keep the roots cool: plants with cool roots handle heat much better. If you're growing in a container, keep the roots cooler by putting some kind of barrier between the sun and the outside of the pot. For example, set your container inside a bigger one. Another idea is to dig a hole in the ground and drop the container into it. Both tricks keep the sides of the pot from baking in direct sunlight. Don't set containers directly on ceramic tiles or other surfaces that get really hot in the sun. Bigger containers help too, because the extra soil acts as a buffer for the roots.

4- Give them shade: when your plant is sitting in direct sun and the heat is intense, your best move is to bring it indoors or into the shade if you can. If there's no shade available, some growers stretch shade cloth over the top of their plants on the hottest summer days.

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