Dr. Grow: Get to the root of your lawn; fertilizer and aeration are key to establishing a healthy lawn

There seems to be a lot of confusion when it comes to selecting fertilizers to apply to your cool-season lawn in the fall. Now's a good time to clear the air.

Lawn grasses are fertilized to establish a good root system in the turf. A good root system will produce lush, thick, green turf. A poor root system will result in a thin lawn, weed infestation and possibly disease problems.

So how do you get a good root system under your turf? The proper user of fertilizer and aeration will give you that.

If you have seeded your lawn this fall with cool-season grasses, you should have used a new lawn starter fertilizer at that time. Fertilizer like 9-13-7 is lower in nitrogen, the first number, than it is in phosphorus, the middle number.

New lawn starter is used because new seedlings need a lot of phosphorus in order to establish their new root systems. The nitrogen level is reduced because too much nitrogen at the time of seeding may inhibit seed germination.

Once your new lawn is established, you need to fertilize in September or October with a high-nitrogen lawn fertilizer, such as 28-4-4. You should use this same fertilizer if you did not seed in the fall.

High-nitrogen fertilizers are used in the fall because cool season grasses are growing rapidly. They need a lot of nutrients during this growth spurt. In the fall the soils are still warm, but the air temperature is beginning to cool off. Therefore, grass plants put most of their energy in producing roots in the fall. This is just what you want to produce a good turf.

Next, in November or early December and six to eight weeks after the first application, you should apply winterizer fertilizer, such as a 10-5-14, to your cool season lawn. This fertilizer has plenty of nitrogen to continue promoting root development throughout the winter (cool-season grasses produce roots throughout the winter months unless the temperatures are extremely cold).

In addition to nitrogen, the winterizer has a high concentration of potassium, the third number. Potassium is known to reduce plant shock resulting from environmental stresses, such as extremely cold winter temperatures.

I am recommending fertilizers that are specifically formulated for turfgrasses. I am often asked why someone couldn't use ammonium nitrate or 12-12-12. Both of these fertilizers are okay, but you should realize that the nitrogen source in both of these fertilizers is one that rapidly releases into the soil. The nitrogen staying power is limited.

Fertilizers that are specifically formulated for turfgrasses usually have urea as part of their nitrogen source. Urea releases nitrogen more slowly. Therefore, nutrients will be available to grass plants over a longer period of time. That results in steady growth of turfgrasses.

If you do this, you'll be proud of your lawn next spring.