Tuesday, October 20, 2009
This November, turf managers and homeowners will be making late fall fertilizer applications with the hopes of improving turf vigor, color, and recovery from winter injury next spring. The main purpose of late fall fertilization is to enhance spring green-up without the excessive growth that often accompanies early spring fertilization. This green-up often will last into mid spring, so an early spring fertilizer application is not needed. A fertilizer application in mid to late spring is usually required to sustain turf color and growth into the summer months.
Research has shown that late fall fertilizer applications do not force as much leaf growth in spring as equal amounts of early spring nitrogen fertilizer, thus carbohydrates are not exhausted as quickly. Carbohydrates help turf tolerate environmental stress and recover from disease injury during spring and summer. The result is a slight advantage to the turf in the form of better heat and drought tolerance and recovery potential.
One reported advantage of late fall fertilization is increased root growth during late fall and winter. The theory is that roots are still growing at a time when shoot growth has ceased, thus allowing the roots to make full use of the fertilizer. However, root growth is very slow at this time of year, and if the soil is frozen, roots do not grow at all. Consequently, the benefit of increased root growth in response to fall fertilization is questionable.
Late fall fertilization should take place when foliar growth stops (or slows to the point that turf no longer needs to be mowed), grass is still green, and before the soil freezes. In Indiana, this period usually occurs around Thanksgiving. Application timing may vary from year to year depending on weather conditions.
Late fall fertilizer applications can be put down on most lawns at rates of 1 to 1.5 lb of nitrogen/1000 sq ft. Just about any source of nitrogen can be used for late fall fertilization, but slow-release sources may be a better choice than soluble sources on sandy soils because of reduced potential for leaching. Nitrogen fertilizer should never be applied to frozen soil due to the increased chance of nutrient runoff. Although application timing is not as critical with phosphorus and potassium as it is with nitrogen, these elements can benefit turf when applied in late fall. Application rates for phosphorus and potassium should be determined according to soil test recommendations. There is no need to apply either of these nutrients if they are present in the soil at sufficient levels.