Zone 4 encompasses a large part of the north central United States as well as a portion of northern New England. If you live in zone 4, you will be growing a cool season grass. Proper lawn care is essential in this zone since it is prone to long, harsh winters with extended periods of snow cover. Poorly maintained lawns will be prone to weed infestations and grass that fails to thrive.
Rake your entire lawn with a steel rake once it dries out in the spring. After being covered in snow all winter, your grass will be matted down. A thorough raking will let sunlight and warmth reach the ground and will also remove dead grass plants. This will allow the healthy grass a chance to get a jump start.
Fertilize in the spring after growth resumes with a 1/2 lb. of nitrogen per 1000 square feet. Use a broadcast spreader to evenly spread the fertilizer over the entire lawn. Walking parallel paths will ensure total coverage.
Apply corn gluten meal at a rate of 20 lbs. per 1000 square feet as a pre-emergence herbicide for crabgrass and dandelions. Apply when forsythia are in bloom, as this plant blooms almost exactly when crabgrass or dandelions will begin germinating.
Mow your grass with your lawn mower on its highest possible setting all summer. Long grass blades have more area to photosynthesize and they will also shade out weeds. Mow every five to seven days throughout the entire growing season so that you don't remove more than one-third of the grass blade in each mowing.
Water your grass so that it receives 1 inch of water per week. This water should be delivered over one to two waterings per week. Set a pan out in the lawn and use this as a guide to see how long it takes your sprinklers to deliver 1 inch of water.