When is it Best to Fertilize Cool Season Grass?

In the parts of the country with cool or cold winters, yard care activities might not be possible or needed during those months. For cool season grasses that will endure those cooler temperatures, maintenance will feel like preparation for and recovery from winter.

Like many plants, the period of most active growth is spring and fall. Cool season grass goes dormant in the summer and winter, so your fertilization schedule for those grasses will be focused within the transitional months.

Cool Season Grasses

Cool season grasses grow in spring and fall and go dormant in winter and summer. These include Tall Fescue, Kentucky Bluegrass, and Perennial Ryegrass, which sprout and thrive when temperatures are in the 60s and 70s.

These grasses grow hearty blades that are better able to stand the cold winter months, whereas they can’t tolerate the heat of summer.

Testing Your Soil Profile

Before fertilizing your soil, you should perform a soil test to see which nutrients it may need more or less of. Some people test their soil once a year, in spring or fall, to avoid taking corrective steps several years apart.

In some areas of the country, soils may be naturally low in one or another mineral. When grass grows, it takes nutrients from the earth to build its structure, so over time, you have to supplement these in the soil for a healthy lawn.

More than likely, if you’re following your schedule, fertilizing to give your lawn a regular boost of nutrients will keep it in normal balance. However, if it has been an especially wet year with flooding and/or high growth, your soil may be more depleted than usual.

Soil Fertility

Soil Fertility

Performing a DIY soil test, or having it done by a local university extension office, will help you know about the conditions of the growing environment for your lawn. These tests check the pH level (which measures acidity) and the main elemental minerals available in the soil (listed on grass fertilizer formulas as N-P-K: nitrogen, phosphorus, and potassium).

The pH level measures the acidity of the soil. PH stands for “potential for Hydrogen,” where the more Hydrogen ions present means a higher acidity and a lower level of biotic activity. Alkalizing minerals like lime and potash may need to be added to make the soil more hospitable when the soil is too acidic.

Phosphorus in the soil contributes to good root growth, while potassium helps the plant’s cellular structure retain water.

For mature grass with strong root systems, nitrogen is the favored nutrient, a fundamental part of chlorophyll, which makes the grass green, and the photosynthesis process makes the sugar that gives the grass energy to grow.

How Often Should You Fertilize Cool Season Grass?

Cool season grass should be fertilized three times a year:

  • In early spring, when new grass is growing
  • In late spring, for summer dormancy
  • In early fall, for winter dormancy, before the ground begins to frost and freeze

Your Cool Season Grass Maintenance Calendar

Healthy Lawn

Keeping an annual schedule will help you be sure to maintain lush turf in every season. Not only will this help you keep in tune with the seasonal changes and growth patterns of the grass, keeping track of the quality condition of the lawn will help you know what to look out for, what’s normal for your yard, and when the last time was that you performed one or another task, as well as how it went.

Since yard care is about growth and managing growth, fertilization is just one of several activities necessary to keep your lawn in excellent-looking condition. Care activities like soil preparation and mowing need to be done in coordination with fertilization, planting, weed killer application, and watering.

In nature, timing is everything, so you want to keep on schedule for the best results.

Soil Aeration

Low-tilling and lawn aeration are ways to keep your topsoil in top quality. Soil gets compacted over time, decreasing its ability to hold air and water and leaving less space for roots to grow.

Soil aeration is best in the fall when new grass growth can establish itself before a winter of dormancy to be ready for its spring revival.

Planting Seeds

Planting seed for cool season grasses is best done in early fall and early spring, giving several weeks for the grass to establish itself before dormancy in the hot and cold months. Overseeding or planting seeds to fill in an already grown yard, is best done in the fall after aerating the lawn.

This gives the new grass a season of rest between its new root growth and the upcoming spring season of blade growth.


As stated above, cool-season grasses should be fertilized in spring and fall. To get the greenest lawn with the densest coverage for any lawn’s particular characteristics, fertilizers come in many different forms and interact with the grass in different ways.

Synthetic fertilizers are man-made nutrient isolates, meaning they are the pure form of the element. These are part of a fertilizer formula that provides quickly accessible nutrients for immediate use by the plant. These should be applied in the spring and fall because they are directly available to growing roots and grass.

Organic fertilizers are formulas that use natural ingredients like manure, compost, and other animal or vegetable materials. Since these need time to be broken down by the soil’s biotic activity to be available, they should be applied in the summer. The nutrients will be slowly released over the following year.

When Should Nitrogen Fertilizer Be Applied To Cool Season Lawns?

Nitrogen Fertilizer

Nitrogen should be added in the fall since growth in the summer of warm-season grasses will use up a lot of the soil’s nitrogen for their blades and to keep them green. In fall, fertilizing with nitrogen will provide the cool season grass with a fresh supply of nutrients to grow its blades and prepare for the winter dormancy.

Nitrogen-rich fertilizers may also be known as “grass food” since they focus on blade health and appearance.

What About Phosphorus And Potassium?

Potassium will be included with many different fertilizers since it contributes to cell-wall strength and moisture retention. Applying phosphorus outside of germination periods, however, can block plants from absorbing nitrogen. It is used primarily in starter fertilizers since it is essential for root development.

Weed Prevention

Your fertilization program will keep your lawn green and growing, so keeping the growth of unwanted plants under control is as crucial to the health of the lawn as providing it with nutrients. One of the first steps of the spring or fall season, even before fertilizing, is to attend to any weeds you see.

Be on the lookout in early spring and late summer/early fall, when weeds may pop up. If you don’t catch the weeds before you fertilize, you may encourage growth of those and your grass.

Using a pre-emergent herbicide will target weed roots while not disturbing your grass’ root system. A post-emergent herbicide targets the leaves and stalks of weeds, killing its root system for lack of photosynthesis. It’s recommended to wait about a week after herbicide application to put down fertilizer.


Mowing before putting down fertilizer can help the product reach the soil better. Once applied, fertilizer needs a day or two to soak into the ground. After laying down the fertilizer, watering the grass will help the dirt and the roots absorb it. Get the soil moist and wait a couple of days before applying fertilizer.

Raking For Thatch And Lawn Buildup

Thatch And Lawn Buildup

Like with mowing, clearing the soil’s surface before putting down fertilizer will help it be absorbed by the ground better. Post-mow is also a good time to rake for thatch: the buildup of dry, dead grass and other yard litter.

Fertilizer can get caught in dense thatch, which also blocks sunlight from reaching the base of the grass’ blades, suppressing the growth you’re trying to encourage.


Cool season grasses tend to require more water than warm-season grass, which is better adapted to dry conditions. Tall Fescue has deep roots and is more tolerant of drier soil, but  Kentucky Bluegrass and Perennial Ryegrass will go dormant during a drought.

Cool season grasses are used to the precipitation of spring and fall, so if there is less rain than usual, keep an eye on the soil moisture level and provide extra water as necessary.

Should I Fertilize Cool Season Grass In The Summer?

Cool season grass doesn’t need to be fertilized in the summer since it isn’t a period of growth for that grass type. A little extra nitrogen from your summer fertilizing might not hurt, but too much phosphorus or potassium may be absorbed by the cool season grass’ roots, which are in an energy-saving state and stress the dormant plant.

Warm season grasses share their growth period with cool season ones in spring, but while cool season grass goes dormant, warm season grasses like Bermuda or Zoysia will thrive during summer. Warm-season grass fertilization in the summertime is generally primarily nitrogen for blade color and density.

Cool season grass roots may be stressed during hot, dry soil conditions and can benefit from a little of the nitrogen fertilizer that the active warm season grass will mostly absorb.