Beards Grow Faster During Summer!
For two simple reasons that might not be too obvious but they are 100% accurate and the reason why you are in fact more manly when it's hot out.
1. Increased Activity
Those scientific wizards in lab coats have proved several times over that when you are more active your body produces more testosterone. Now we can connect the dots from the, people are more generally more active in the summer. There are some rare cases where you have a great life and snowboard all day during the winter but that's an exception to the rule. We've all seen those lovely ladies at the gym who have tried their hand at using male hormones... testosterone increases body & beard hair!
2. Increased Blood Flow
This one is a little more obvious but any organ in your body that receives more blood flow becomes more active. The biggest organ in your body is no exception (that's your skin if you got lost or got distracted by my awesome writing style and started day dreaming about us playing poker.) as blood flow increase so does the ability for your capillaries to expand.
In conclusion, yes beards do in fact naturally rock harder & grow more in the summer.