Insects are cold-blooded, so their activity is directly tied to temperature. As the weather warms, their metabolism speeds up, they come out of dormancy, and breeding cycles kick into gear.
The most effective time to start is in the spring, before pest populations build to noticeable levels. This is typically late April through mid-May in most of New Hampshire.
Scents like citronella, eucalyptus, lavender, and peppermint can deter mosquitoes at close range, but none of them provide reliable, lasting protection on their own.
Mosquitoes breed in standing water, and properties near lakes, ponds, and wetlands sit closer to larger breeding populations and the persistent humidity mosquitoes need to thrive.
Smoke from a bonfire can deter mosquitoes in the immediate area, but only in areas where the smoke is highly concentrated and where you will likely not want to sit for long.