Before fertilizing, conduct a soil test. Soil samples should be around six inches deep, and they should be collected from about eight to 10 areas throughout the yard. These samples will tell you the soil’s pH, which will let you know what nutrients are present and which will need to be added back in. You can buy a testing kit at your garden center, or send your sample to the Soil Testing Laboratory at the University of Minnesota.
After testing your soil and determining the correct amendments to make to your soil, you can apply fertilizer to your lawn. Follow the directions carefully and do not use too much! Check the forecast before you start. Avoid fertilizing your lawn before heavy rainfall to prevent runoff. Not only is fertilizer runoff bad for water systems, if your fertilizer washes away there will be no nutrients left for your lawn!
While the chemistry can be a little intimidating, fertilizing your lawn in the fall is one of the best things you can do to encourage healthy growth and overwintering.
More information
UMN Extension Lawn Care Calendar
UMN Extension Fertilizing Lawns