Timing and Choosing Pre-emergent Weed Preventers, Spring and Fall
Pre-emergents (weed preventers) are applied to the landscape to prevent seeds from germinating.
The key is the timing. Pre-emergent herbicides MUST be applied BEFORE weed seeds germinate.
In general, to get good summer weed control in Atlanta you should apply a pre-emergent on March 1.
For winter weeds (annual bluegrass, henbit or chickweed) the apply date is September 15.
If you want specifics: Weed scientists use soil temperatures to determine the trigger point for their application of pre-emergence herbicide.
Crabgrass seeds germinate when spring soil temperatures tend upwards from 55 degrees F.
Annual bluegrass starts germinating in late summer or fall as soil temperatures fall below 70°F.
The University of Georgia College of Agricultural and Environmental Sciences oversees a network of 50 weather stations across Georgia. Click here to chart your own soil temperatures.
Pre-emergents for lawns. Some prevent both grassy weeds and broadleaf weeds:
Pre-emergents for Ornamental Beds (not lawns)
Pre-emergents for Ornamental Beds and Vegetables
PRE- and POST-emergent combo products for lawns
REMEMBER: Read all herbicide labels thoroughly to be sure the product can be used on your particular turfgrass and that it controls the weed(s) you are trying to manage.
And also keep in mind that hand-pulling weeds is often good enough if done early enough.