Benzelsanswered grow question 4y ago Not too much if its only temp weather...and if its 60% or less then it wont affect growth much at all, but the risk of mold will be quite a bit higher, get a fan, air flow is the best defense against humidity...even if its 70% humidity if the air is moving fast enough then mold wont be an issue, its when there is still moist air that you get issues fast. If you have a fan turn the speed up. Even if plants are gently swaying in the breeze, its fine. Better that than mold right? Air flow will be your weapon here to fight humidity if you cant run AC. Move that air and you will be ok.