By: Tony Koski, Extension Turf Specialist

Fall fertilization of cool-season lawns is a common and recommended practice for Colorado lawns. Under normal growing conditions (when irrigation is not restricted or prohibited), fall fertilization increases turf quality during the fall and following spring and promotes healthy fall and spring rooting. However, watering restrictions and cutoffs imposed due to the current drought may create situations where this practice should be modified or not practiced at all. Most lawn areas will fall into one of the following categories.

Lawns regularly irrigated with well water, effluent/wastewater, non-potable water, or in communities WITHOUT current or anticipated watering cutoffs

• Green, actively growing lawns should follow normal fall lawn fertilization scheduling (refer to CSU Fact Sheet 7.202 Lawn Care,
• Only actively growing bluegrass, ryegrass, and fescue lawns should be fertilized in the fall
• Buffalograss, blue grama, zoysiagrass, and bermudagrass lawns should NOT be fertilized after September 1
• Fertilizers consisting of a mixture of quickly (at least 50%) and slowly available nitrogen are effective for fall fertilizing, as are those products consisting of 100% quickly available nitrogen
• While nitrogen (N) is the most important fertilizer nutrient for fall fertilization, it can be beneficial to use a fertilizer that also contains phosphorus (P) and potassium (K), as well as iron (Fe)
• Irrigation (1/2 inch of water) should be provided at the time of fertilizer application to provide the greatest benefit to the lawn; ongoing fall watering will increase the beneficial effects of fall fertilization

Lawns where watering is currently allowed (2-3 days/week; circle/diamond/square programs), but it is anticipated that irrigation will be prohibited in the fall

• Fall fertilization can benefit these lawns if the fertilizer is applied and watered-in before fall watering cutoff occurs
• Recommendations described above should be followed on these lawns

Lawns where watering is restricted to the point that current lawn color is poor (spotty brown and green) and growth is minimal and watering will be prohibited in the fall

• Where lawn watering regulations severely restrict the amount of water applied to lawns, fall fertilization may not provide visible benefit to the lawn during the current fall period
• Fall fertilization of these lawns may provide benefits (better rooting and earlier green up) next spring
• Fertilizer types described above can be used, but effectiveness will be limited by the amount of irrigation water that can be applied this fall (and by the amount of fall and winter precipitation)

Lawns that are completely dormant (brown), and where lawn watering is prohibited

• Fall fertilization of already dormant lawns, especially those that have been dormant for a month or more, may provide little or no benefit
• Depending on turf species and previous health, lawns that have been dormant for 2-3 months may be partially or totally dead (or will die during the winter)
• If there is reasonable certainty that the lawn is dormant (but still alive), an application of slowly available fertilizer (natural organic products, sulfur-, plastic-, or resin-coated fertilizers, or ureaform-based fertilizers) may provide benefits during the spring
• Urea and ammonium-based fertilizers should not be applied to lawns where supplemental irrigation is unavailable; application of these fertilizer types to dry lawns/soil will be largely ineffective