The answer to 'when to weed control' is that the best time to control weeds in your lawn or garden is in the spring and fall. This is when weeds are actively growing and are most susceptible to weed control treatments. In the spring, apply a pre-emergent herbicide to prevent annual weeds from germinating. Then in the fall, use a post-emergent herbicide to target any weeds that have already sprouted.
It's important to time your weed control applications correctly to get the best results. Pre-emergent herbicides need to be applied before weeds germinate, typically 4-6 weeks before your average last spring frost date. Post-emergent herbicides work best when weeds are young and actively growing, usually in the fall when temperatures are cooler.