It is some what strain dependent but in general the plants growth will slow once you start getting up around 95+. Most stop growing completely once it hits over 100 in my experience. Some strains handle it better though and will keep chugging along. Doing greenhouses in Cali in the summer can be a bitch - it really helps if you can open up the sides and have some fans going.
Here's an easy way to figure out if the heat is affecting your growth:
Take height measurements of some of the plants. Come back 5-7 days later and measure the same plants again - this will show you how fast they are growing. If the temps are getting too hot for them to grow, you will see this on your height measurements. This technique can also be very helpful for spotting issues before the show visual symptoms on the plant. If one or all of your plants suddenly experiences a big decrease in growth compared to previous weeks you know something is up.
