How Soon Can You Fertilize New Grass?

New grass requires nutrients as soon as it starts growing. This is true of grass grown from seed and from grass grown from plants in the form of sprigs, plugs or sod. Newly planted grass needs different nutrients than an established lawn, so the fertilizer application when planting will be different than the first time you fertilize newly planted, actively growing grass.

Apply a "starter fertilizer" when you're preparing the lawn before planting. Nitrogen (N) and phosphorous (P) are the most important nutrients for new grass, so look for a fertilizer with an N-P-K ratio that has the three numbers the same -- known as a balanced fertilizer -- or is higher in the first two numbers. The fertilizer should also include potassium (K), but the amount need not be high.

For a standard starter fertilizer with an N-P-K ratio of 24-25-4, apply at a rate of 3.27 pounds per 1,000 square feet. The best way to do this is to use a broadcast or rotary spreader. Always check the rates on the bag as they vary among brands. Lawn fertilizer packaging will include instructions on which setting to use on a spreader.

Using a fertilizer spreader helps ensure the fertilizer is evenly spread across the lawn so you don't get "burned" patches. It also helps reduce waste and keeps the fertilizer on the lawn, rather than on pathways or in gardens around the lawn.

Apply starter fertilizers to the lawn right before planting plugs, sprigs or sod. Lightly water the soil after fertilizing, then water it again after the grass is in place.

If you're sowing seed, apply fertilizer at seeding time or two weeks after sowing seed. Water lightly after seeding, and continue to water the seeds and plants at least twice a day to keep the soil moist until the grass is actively growing.

Never use "weed and feed" fertilizers when planting a new lawn. They are not properly formulated for new grass plants, and the herbicides can kill grass seedlings.

Starter fertilizers release nutrients slowly, and they will supply nutrients until the grass is established and growing. Begin applying regular lawn fertilizer once the grass has a good root system and is actively growing. This means you'll start fertilizing four to eight weeks after planting. The exact time frame depends on how fast the grass grows and whether you started from seed, which will take longer to establish, or from sod or sprigs, which establish faster.

Mature lawns need more nitrogen and less phosphorous than newly planted lawns. For a dry lawn food with an N-P-K ratio of 32-0-4, apply at a rate of 2.5 pounds per 1,000 square feet. As with other lawn food, the fertilizer packaging will include spreader settings for easy application.