Pests in December
Houseplants: Inspect regularly for pests on indoor plants. Keep in mind that plant-specific temperature, light, and humidity are key to ensuring that indoor plants thrive. See Houseplants
Mulch/compost - Renew mulch to conserve water and discourage weeds. Use fallen leaves to provide the carbon ingredient needed for successful composting and also to make a good mulch.
See Backyard Composting & Landscape Mulches

Landscape and garden pests: Continue monitoring and treat as needed. While cooler weather generally means fewer pests, some populations actually increase at this time of year.
Insect Management in the Home Garden