It is my understanding that winter fertilizer is best applied when the frost creates a crunch when walking on the lawn. Supposedly, the plant uses the high amount of potassium in the winter fertilizer to set a better plant for the spring.
I recently bought a new home with sandy loam soil. Since sandy soil does not retain fertilizer as well as a clay loam, is it more efficacious to apply winter fertilizer just as the grass starts to green rather than in the beginning of winter when a large percentage will be washed through the sand?
In Ontario it is recommended to fertilize twice in the fall. The first application should be made in early fall (from mid-August to mid-September) which will give lawns that are damaged by summer droughts or pests a boost so they can recover. Usually the temperatures are cooler, there is more rain plus there is additional moisture from morning dew. All of this helps turf plants grow and take up the additional nutrients. A second application should be made when the turf has stopped growing but is still green, usually in mid- to late October. This allows the roots to grow and store nutrients so that in the spring the lawn will green up sooner. Lawns with a better root system, will resist summer drought damage better as well. You can read more at the Ontario Ministry of Agriculture, Food and Rural Affairs webpage. It is not necessary to purchase specialized “fall” fertilizer for these applications. You can use the same fertilizers you might already have used in the spring.
You mention that you have sandy soil which makes watering and fertilizing lawns a little more challenging since water will leach out more quickly and take fertilizers with it. There are a couple of things you can do to help with this problem. The first is to top dress your lawn once a year with ¼ – ½ inch of compost or high quality top soil to improve the soil texture and its water holding capacity. The second thing you can do is use a slow release fertilizer so that the nutrients are less likely to wash through the soil and into the water table.