Nitrogen is the key to green growth in your lawn, and fall is the perfect time to fill in dead lawn areas. Learn what to do to maintain healthy grass.

Last week, we looked at what we can do to bring lawns back from a disastrous summer. Heat and drought coupled with crabgrass and nutsedge, mixed with a few diseases, may have left our lawns in an undesirable condition.

Aerating and seeding are two options. Aerating will loosen the soil and allow turf roots to grow, leading to more top growth. Seeding is a quicker way to establish new grass to fill in dead and dying areas.

Of course, once you get the dead grass out and kill the crabgrass and related weeds, you need to work up the soil so the seeds will root and grow faster. And if you don’t want to wait, once the soil is worked, you can just lay sod. Instant gratification: the American way!

The other magic bullet is fertilizer.

The first couple of weeks in September are ideal for fertilizing cool season grasses, such as Kentucky bluegrass, ryegrasses and fescues. (If you have Zoysia, you can skip the rest of this column and go clean the underside of the mower.)

For our lawns, nitrogen is key to green growth. While phosphorus and potassium have their uses, especially with rooting and increasing the overall hardiness of the turf, studies have shown that most of our lawns have more than enough phosphorus and potassium.

 Nitrogen encourages new shoots, or tillers, and all the leaves that we constantly mow as the grass keeps growing.

Nitrogen has a direct relationship with available moisture and temperature.

First, grass plants won’t produce a lot of shoots until the air temperature starts declining, particularly in the evening. Days in the 90s aren’t the best for getting cool season grasses to produce new growth, no matter how much nitrogen you put down.

On the other hand, if the day temperatures are in the 80s and the night thermometer reads in the 50s or 60s, the grass starts going to town.

In the fall, the ground temperature is still too warm for root growth. However, since our goal in September and October is to generate top growth, and we’ll wait for November for the roots to catch up, using fertilizer now won’t have any direct effect on roots.

The other aspect is water.

Without moisture, granular fertilizers just sit on the soil surface, waiting for water to break them down so the roots can absorb the nutrients. Liquid fertilizers dry on the grass blades unless given moisture. September tends to bring moisture, although not as much as the spring months.

There are two ways you can look at the moisture and nitrogen.

First, you can decide to help nature along and turn on your own irrigation system. After applying the fertilizer, make sure to water at least 45 to 60 minutes to get the nitrogen down to the root zone. Excess watering may be beneficial for roots penetrating the soil deeper, but it may leach the nitrogen past the root zone.

Or you can keep an eye on the weather forecast and, when rain is predicted, you can apply the fertilizer beforehand.

Granular fertilizer really isn’t going anywhere. This means if you apply and wait and wait, the fertilizer will still will be present when the rain does fall.

Liquid fertilizers are harder to move the longer they dry on grass plants. So, if you go the liquid route, it’s probably better to plan on watering right after the application.

Next, the amount.

Too much fertilizer will burn the roots, and then the top dies. Too little and you will see hardly any new growth.

The ideal amount is about a pound of actual nitrogen per 1,000 square feet of turf. Math comes into the equation here and it can be sticky, what with “actual” nitrogen and figuring out the area in square feet. Throw in the fertilizer spreader setting and then you can send yourself to the fermented beverages.

In light of such, fertilizer companies have packaged their products so you don’t really need to do much math, other than having a rough idea of how large your yard is. (If you don’t know that, contact a sixth-grader who should be able to multiply the length by the width and give you a number.)

Make sure your fertilizer spread is not rusty and the hopper drains smoothly. Make several passes over an area instead of trying to dump everything in one pass.

Consider setting the spreader on the lowest possible setting that allows the fertilizer to drop out, and then walk over the area a couple of times.

Turn on the sprinkler, have a relaxing drink and wait for the grass to respond in a week or two.

Finally, as mentioned earlier, clean the underside of the mower from any caked-on grass clippings. While you’re down there, sharpen the blades, which cuts down on the spread of diseases and gives the lawn a nice, tailored trim.