Late fall fertilizing has two purposes. It continues the strengthening of the root system right through December. But, as it gets colder, the microbial action in the soil slows down, so some of that late application just sits there until the soil warms up again in the spring. Those stored goodies serve to help the grass green up in the spring without giving it a huge nitrogen hit that comes with that early spring application.

During September and October, turf grass begins to slow down on the growth of its foliage, while directing nutrients to developing new roots and storing carbohydrates in the existing roots. Building up the root system is essential to having a healthy turf year-round.

At first, a lot of the improvement in your lawn will be dramatic, as you see recovery from summer damage.

But don't stop there.

The real improvement comes with the second feeding in late fall. This second fall feeding helps to lock in the early fall gains in turf vitality and carry them forward into next spring. This late-fall winterizing gives your grass everything it needs to prepare for winter. The roots will absorb and store these vital nutrients. The grass will continue underground root development until the ground freezes solid. Once spring arrives, the grass plant will quickly tap this stored-up nutrition to stimulate growth and burst into a vibrant, deep green lawn. In fact, a lawn fed twice in the fall will be the first to green up in spring.

The first thing to understand about fertilizer is the formula, which is represented by three numbers.

• The first number represents nitrogen, which promotes lawn blade and foliage growth. The nitrogen source is an important factor as well when choosing a turf fertilizer. Some sources release their nitrogen quickly, while others release it slower resulting in longer, more even feeding.
  
  
• The second number stands for phosphorus, which helps root growth.
  
  
• The third number is potassium, which promotes cell function and absorption of trace elements.

Nitrogen:
Nitrogen is absorbed by the plants in the greatest quantity. It is necessary for rapid growth and promotes deep green leaves and stems. Nitrogen will not fix itself to the soil, and if unused by the plants, will percolate past the root zone with watering and rains, and must continually be replaced..

Phosphorus:
Phosphorus is essential in all phases of plant growth, but is particularly associated with early maturity, the formation of seeds and fruit, increased root growth, and disease resistance. Phosphorus stays in the soil until it is used by the plant, usually requiring fewer applications than nitrogen, and its effectiveness is enhanced by adding organic matter. Additional phosphorus is recommended for early season plantings, as availability is lowest in cool weather.

Potassium:
Plants take large amounts of this nutrient, almost as much in some cases as nitrogen. It contributes to the overall vigor of the plant, building strong stems and leaves, helping to overcome the effect of heavy foot traffic or adverse weather. Potassium levels in many intermountain area soils are naturally high, but become depleted as plants use it, and in heavily irrigated areas, such as lawns and gardens.

Your lawn needs 16 different elements to survive. Most of them are already provided to the lawn from the soil and natural surroundings. However, three primary elements - nitrogen, phosphorus, and potassium - need to be added to your lawn in the form of fertilizer. You will commonly see these elements reflected in numbers such as 12-6-6, 24-5-11, etc.. These numbers tend to reside below the package labels and titles to tell you the total weight (amount) of each of the elements that is contained in each bag. the first number tells you the percentage of nitrogen present, the second the percentage of phosphorus, and the third is percentage of potassium. In some bags, you may see a zero reflected such as 0-0-9 which tells you that there is no nitrogen or phosphorus present, but only potassium. This is commonly seen in mixtures of pre-emergence, winterizer, and weed control fertilizers. The three numbers represent the weighted total of each element per bag. For example, a 100 pound bag of 30-10-10 has a ratio of 3:1:1, where 30 percent of the 100 pound bag, or 30 pounds is nitrogen, 10 percent - or 10 pounds is phosphorus, and 10 percent - or 10 pounds is potassium. The additional 50 pounds are filler ingredients often used to help distribute or time-release the product. These various element combinations help create the optimal blend for each purpose.