Cool Season Turf fertilizing strategies

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Most lawn grasses grown in New England — Kentucky bluegrass, perennial ryegrass and fescues — are cool-season grasses. They grow best in spring and fall.

The roots of cool-season grasses grow best between 55 F and 65 F. Shoots grow best between 67 F and 75 F. In early spring, even before the grass starts to green up, the roots break dormancy and begin growing.
The combination of long days, cool temperatures and usually adequate moisture produces a flush of growth in the spring. This sometimes makes it challenging just to keep up with mowing. In a normal year, 60 percent of grass growth comes during 6 weeks in spring.

Spring is a good time to get the lawn off to a good start, but over fertilizing a healthy lawn at this time just promotes excessive top-growth (and mowing chores) at the expense of root growth. This lush, succulent growth encouraged by early spring fertilization makes the plant more susceptible to insects and diseases. Plants with smaller roots are also more vulnerable to drought later in the season.

As temperatures warm during summer, growth slows down and lawns require mowing less frequently. This is known as summer dormancy. Roots can be damaged when temperatures are above 85 F. During this “summer slump,” warm-season weeds such as crabgrass and spurge can thrive because they are more competitive in warm weather.

The combination of warm temperatures and lack of moisture can cause cool-season grasses to go dormant and turn brown during dry summers. This is a very natural occurrence with cool season grasses. In most cases, the grasses haven’t died. They will green up and grow again in fall when cool weather returns and soil moisture is replenished.

Fall is the best time to fertilize lawns because the nutrients primarily support root growth. They help the plants build up reserves to get through the winter and green up in spring.

An ideal time to apply your last application, (commonly called a winterizer application) is about 2 weeks after your last mowing when the lawn goes into winter dormancy. Apply 1 pound of nitrogen per 1,000 square feet. This is one of the only times I would recommend an immediately available nitrogen source (quick release nitrogen).

Don’t over fertilize, and avoid early spring applications.

Just like people, lawns need a balanced diet, too. If you feed them too much, too little or the wrong kind of fertilizer, they won’t be healthy. With lawns, when you fertilize is just as critical.

Be sure to test your soil and adjust pH, if needed. Lawns should have a slightly acid pH, between 6.0 and 7.0. If your soil tests fall outside of this range, follow instructions for adding lime or sulfur to bring pH into this range. Rarely will you have to apply sulfur in New England as soils tend to be acidic.

Focus on fall. If phosphorus and potassium levels are adequate in the soil, nitrogen (N) is the most important nutrient for grass growth. Understanding how grass grows is important when making decisions about how much and when to apply nitrogen fertilizer.

For lawns properly fertilized the previous fall, a full application of fertilizer (1# N per 1000 sq ft) can sometimes be put off as late as Memorial Day.

Research shows that early spring applications do not really enhance spring green-up compared with late-fall applications, and the risk for later problems like disease, is far greater.

Applying a low analysis organic fertilizer, or a product like Solu-cal is a much better choice in the spring. Neither will promote excess top-growth (or clippings), and both will greatly benefit the turf and the soil. Using these products in early spring will actually help reduce summer stress and disease pressure later on.

At least 50-60 percent of the nitrogen applied to New England lawns should come between the middle of August and November for healthy green turf in spring.

Lawns that did not receive fall fertilizer applications or have suffered from winter injury may benefit from earlier spring nitrogen applications. But wait until soil temperatures have warmed to at least 55 F before applying.

Water it in. Water your lawn with a quarter to a half inch after spreading fertilizer to get the material into the ground where it can be used by plants.

Consider the source. If you are using synthetic lawn fertilizers throughout the season, use products that contain at least 40% total slow-release nitrogen. Slow-release N becomes available to the plant over a period of time depending on soil moisture, temperature and microbial activity.

Their are many different slow release N choices. The cheapest (and least consistent) is Sulfur coated urea or SCU. Other types (and more predictable) are polymers, methylene ureas and IBDU . These types tend to last longer and release more predictably. The balance of the Nitrogen in the bag is water soluble nitrogen, which is readily available for plant uptake.

In addition to supplying N over a longer period of time, slow-release nitrogen sources have a lower risk of burning plants and a lower potential to leach out of the soil. The tradeoff is that higher quality slow-release N is usually a little more expensive. The few extra pennies up front will save you much more later on. Don’t trip over a dollar, trying to save a nickel.

Natural organic fertilizers supply nitrogen in complex organic forms that are not immediately available to plants. Most require warm, moist soils for microbial activity to release the N over a period of time. Natural organic fertilizers are well-suited for applications during warm summer months when the potential for burning plants with higher-salt synthetic fertilizers is higher.

Lawns grown on mostly sandy soils should rely more on higher quality slow-release nitrogen to reduce the possibility of N leaching out of the root zone. Incorporating high quality organic fertilizers not only provides the turf essential nutrients, but the soil also. If you fertilize with a “ground up” approach, the turf will benefit greatly.

Consider different needs. High-traffic areas usually require more fertilizer than low-traffic areas. Different species of grass have different needs, too. Kentucky bluegrass, for example, requires more nitrogen than fine leaf fescues.

If bluegrass doesn’t get enough N, it is less competitive against weeds and pests. If fine leaf fescues (which normally grow slowly) get too much N, they produce lush, weak growth that is susceptible to pests.

Apply with care. The whole idea is to get the right product on the lawn at the right time. Lawn care is all about timing. I can probably be more successful using low quality products at the right time, than using the highest quality products at the wrong time. Neither is an ideal situation and should be avoided. If you can scrape by using low quality fertilizers at the right time, imagine what can happen when you use high quality products.

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2 responses to “Cool Season Turf fertilizing strategies

  1. This article is very practical and informative – good stuff! I like how this person explains the thought behind the recommendations. Very useful.

  2. Glad you found it helpful….thats why I write it

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