• Weed and Grass City Ordinance 10.06 

LEAVES -- WHAT CAN YOU DO?
  
Mulch Them In Place/Mow Them 
Leaves are rich in carbon, phosphorus, and potassium - all essential nutrients needed by plants including turf grasses (Wisconsin Department of Natural Resources). Simply mow your leaves along with the grass during fall, and let the small leaf pieces filter down among the grass blades. Make sure grass is exposed to the sun after the tree leaves have been mulched.  
 
The following guidance is taken from the Department of Horticulture - Michigan State University Green Tips sheet on Mulching Tree Leaves Into Lawns.

• Leave your mower set to the same height you use to mow your lawn
• Use a rotary mower that pulverizes the leaves
• Mow when the leaves are dry
• Make sure that mower blades are sharp and use a slow movement with the mower to help grind the leaves finer
• 3-4 passes may be required to chop leaves fine enough so that they filter through the turf and expose grass leaves to sunlight; i.e. make sure that pulverized leaves do not cover the grass blades completely
• Ground leaves should settle into the turf in a day or two, especially with rain
• It is best to mow tree leaves regularly, not letting them lie more than 3-4 days

Although additional nitrogen has not shown any major benefit, the Department of Horticulture - Michigan State University suggests applying 1/2 pound of nitrogen per 1,000 square feet in addition to the normal fall fertilization in order to speed tree leaf decomposition