Fall fertilization can be beneficial in the landscape if you follow some simple guidelines. The following is more information.
In turf, a second or third fall fertilizer application is often recommended with moderate amounts of Nitrogen (N), low phosphorus (P), and moderate to high rates of potassium (K), of course depending on soil test results for P and K. Timing of this application can affect turf performance. October applications can promote continued top growth and excess N at this time can reduce winter hardiness. If applying fertilizer in October, use modest N rates. A later fertilizer application at the end of November, can help root systems continue to grow and keep turf greener, longer into December. However, excess N at this time may be subject to leaching losses so limit soluble N fertilizers to modest rates that roots can utilize. Fertilizers with higher percentage of temperature dependent slow release N are very appropriate for fall applications. Potassium is important for improved wintering over and P is important for root growth so added P and K can be beneficial in the fall if soil levels are not high (based on a soil test).
Most other landscape plants require little or no fall fertilization if they are in the middle of fertilized lawns or in well maintained long-term established mulched beds with high organic matter. However, new landscapes, plantings in poor (low organic matter) soils, or landscapes that have been under stress may need additional fertilization. Woody landscape plants and some perennials continue root growth until soils are at freezing temperatures so fertilization using materials with low to moderate N, some P, and higher K levels can be beneficial to winter performance. Root growth will be improved and bud health can also be enhanced. However, excess N in the fall can promote bud break and new growth, or continued shoot growth in some plants, leading to increased winter damage.
Gordon Johnson, Extension Agriculture Agent, UD, Kent County