Fall fertilization of cool-season lawns such as Kentucky bluegrass is a common and recommended practice for Colorado. When watering is not restricted, fall fertilization increases turf quality during the fall and following spring and promotes healthy fall and spring rooting. Watering restrictions and cutoffs create situations where this practice should be modified or not practiced at all. Note: Buffalograss, blue grama, zoysiagrass, and bermudagrass should not be fertilized with nitrogen after Sept. 1st. (However fall K and Fe applications are beneficial to those lawns)
Green (no watering restrictions), actively growing lawns should be fertilized according to the normal fall lawn fertilization schedule. Watering (1/2 inch) just afterfertilization will provide the greatest benefit to the lawn. Additional watering will increase fall benefits while early water cutoffs will postpone the appearance of some benefits until spring.
What about lawns where water applications have been restricted to the point that lawn quality is poor (spotty brown and green) and early water cutoffs are expected? Fall fertilization can benefit these lawns if the fertilizer is applied and watered-in before the watering cutoff. In these cases, most of the fertilization benefits will be seen in spring.
Fall fertilization of dormant (brown) lawns, especially those that have been dormant (brown) a month or more, will provide little or no benefit this fall (although spring green-up of dormant, still-living bluegrass lawns will be enhanced.).Some tall fescue and other lawns that have been brown for 2-3 months may be partially or totally dead or will die during the winter. If there is a reasonable certainty that the lawn is dormant but still alive, an application of slowly available fertilizer may provide spring benefits.
For more information, see the following Colorado State Extension fact sheet(s).
For more information, see the following Planttalk Colorado™script(s).