For Cool Season Lawns
Mowing the lawn for winter
You may have read some recommendations to mow the grass shorter before winter. If you subscribe to that school of thought, then be sure to maintain the rule of thumb of not removing more than one third of the grass blade at a time.
I don’t personally believe it is necessary to mow shorter for winter and advise against it. The reason is preparation for that all-important last fertilizer application of the year. You know you don’t have to mow the lawn anymore when the effort does not return results. That is, of course, provided you maintained the same mowing height up to now and didn’t adjust the mower to a different setting.
Lowering the height at the last mowing requires the grass blades to concentrate resources on repairing the tip, resources that would normally be reserved for the following spring. As long as your grass is properly maintained, your usual mowing height of 3 inches or somewhat higher will not prove detrimental or surrender the lawn to disease or winter injury. If you normally maintain at 4 inches or higher, then mowing shorter might be a good idea since the taller blades will more easily lay down and yield to matting.
The fall time of year brings cooler temperatures and sometimes torrential rains but without rainfall, your lawn still needs irrigation. You don’t want to allow that the grass enters winter lacking adequate moisture. In those final days it photosynthesizes, moisture continues to help it convert carbon to carbohydrates. Even though you might not think you need to irrigate, ample moisture prevents desiccation and wards off attack from the snow mold or blight pathogens. On the other hand, too much water can actually encourage disease. The cooler temperatures means there is less moisture lost to transpiration so in the absence of weekly rain, perhaps reduce irrigation from one inch per week to half an inch as it gets colder. Following irrigation (or rainfall) to water in the winterizing fertilizer application, you likely won’t have to irrigate for the rest of the year.
Remove leaves and other debris
It’s a good idea to mulch fallen leaves throughout the season because, like the grass blades, leaves are a valuable source of nutrients and organic matter. But, if there are a lot of leaves, you may consider removing some and leaving some to mulch so as not to smother the grass. Remove whole leaves and any other debris from the lawn, which includes water hoses and children’s toys so the grass goes into winter free of obstruction from sunlight.
The thatch layer is safe haven for various diseases. Spores like to hide and multiply in the thatch layer because oxygen cannot penetrate. You don’t want the grass to go into winter suffocating by heavy thatch layer of much more than a half inch, or you could invite problems like snow mold disease or others. If you missed the prime opportunity for aerating or dethatching earlier in the fall or previous spring, there are liquid dethatching products on the market you may want to consider.
Take full advantage of ideal time for carbohydrate accumulation
Late fall is when cooler temperatures begin to control above-ground activity. This is the best time to apply the winterizing fertilizer application because top growth ceases and you don’t have to mow the lawn anymore, yet the grass is still green. You get more carbohydrate storage during this time because it is not mowed and because top growth has slowed, but the roots are still growing.
Until the ground freezes, the roots beneath the soil are still growing and able to take up nutrients from fertilizer even though the grass above ground stopped growing. It is how the grass plants utilize these nutrients that is most important in late fall.
Photosynthesis is the process the grass plants use to manufacture its own food. It uses energy from the sun, nutrients from fertilizer, and moisture to convert carbon dioxide into foodstuffs. That food is in the form of carbohydrates.
Because the grass is still green, you know it is still photosynthesizing, which means it is using the sun’s energy and still managing moisture and nutrients from fertilizer.
When you mow the grass, much of the plant’s energy is directed at repairing the tips for re-growth. When top growth ceases during late fall and you no longer have to mow the lawn, the grass plants are able to conserve those resources.
Now that the grass no longer needs to use the food for growth above ground or for re-growth to repair mowed leaf blades, the grass plant requires less energy to sustain itself. Excess production of carbohydrates is transcolated into the storage organs of the plant and kept in reserve until needed. These stored reserves are used for growth and greenup the following spring. Also, the grass stays green longer into winter and may not turn brown at all during winter dormancy.
The exact timing of this application will vary by location and can range between mid-October and late November, depending on where you live. Once the soil freezes, the roots are no longer growing and the grass plants no longer photosynthesize, so timing should be at least two weeks before you expect freezing. You don’t have to worry about missing your window of opportunity because fertilizing late is better than applying it too early. If applied too early, the fertilizer will cause upper shoot growth, which can be stressful and render the grass vulnerable. It is easier to judge by the time you no longer have to mow.
Which fertilizer to use
The brand or name of fertilizer you use is less important than choosing the right type of fertilizer. Some companies call their late fall product “Winterizer” that often contains high amounts of nitrogen and potassium. Former school of thought is that a high rate of potassium is needed in late fall to aid in winter hardiness. Current school of thought is that grass really cannot absorb more potassium than it needs. Popular belief is that adequate amounts is provided during regular fertilizer applications through the year to promote disease resistance, strengthen plant walls, prevent water loss, improve drought resistance, and protect against cold weather. Therefore, excess potassium is leached through the soil.
However, you do want high nitrogen, and it is best in quick release form, such as urea or one that contains a 60-70 percent quick-release nitrogen component. Coated urea is not suggested, as those are normally time-release products. If you prefer to use organics, then choose a quick-release source, such as blood meal or other.
Late fall is also the best time to control broadleaf weeds. Application of a selective herbicide at this time will help control the winter crop, as well as help prevent broadleaf weeds the following spring and summer. Be sure to check labels for temperature limitations.
Other helpful information
If you have any questions or comments, please feel free to post them on the forum.