KC Gardens

September is the time to fertilize your lawn: Here’s a guide

September is the best time to apply needed nutrients to bluegrass and tall fescue lawns.
September is the best time to apply needed nutrients to bluegrass and tall fescue lawns.

It’s dinnertime for area bluegrass and tall fescue lawns. Just as we need certain vitamins and minerals to be healthy, turfgrass needs nutrients for healthy growth and development.

September is the best time to apply these needed nutrients. After a summer of growth under our ever-changing conditions, our lawns are hungry, and this meal will help rebuild the roots and crowns so that a dense lawn of our dreams will reappear.

Nitrogen, the first number listed on a bag of fertilizer, helps thicken the stand and encourages development of a healthy root system. A strong root system is the foundation of a nice lawn. Cooler temperatures, fall rains and the nutrients help the lawn recover from stressful summer conditions.

November is the next most important time to fertilize. The timing of this application should be around the final mowing of the season, normally mid-month. This enables the lawn to green up earlier in the spring, without encouraging the excessive shoot growth that often accompanies early spring applications.

Choosing the right type of fertilizer is important. Bags of fertilizers will always have three numbers displayed that stand for the percentage of nitrogen, phosphorus and potassium contained. Examples of fertilizers to apply in the fall would be such numbers as 30-0-0, 27-3-3 or 25-5-5.

Nitrogen fertilizer, the first number, is the most important nutrient, as it is needed and used in the greatest quantities by the turf. Vigorously growing lawns use more than is available in the soil, so it must be replenished on a regular basis.

Phosphorus, the second number listed on the bag, is needed for growth of roots and shoots. Adequate quantities are often present in the soils of established grass. Potassium, the third number listed, is essential for the overall health, stress resistance and cold hardiness of lawns. Like phosphorus, it is usually found naturally in the soils.

Applications of fertilizers containing phosphorus and potassium are not recommended unless a soil test indicates the need. A starter type fertilizer, one higher in phosphorus, can be applied when overseeding to help encourage quick establishment of the new seed.

This emphasis on fall fertilization may conflict with some that promote spring applications. Cool-season lawns experience a flush of shoot growth in the spring. Applying fertilizer before this flush is over can cause the grass to grow too fast. The rapid growth exhausts the plant’s food stock and leaves it with few reserves for the stressful summer ahead. Therefore, it is best to wait until the flush is over, usually in early May, before making any spring applications.

Remember, for fertilizer to become activated it must be watered into the soil either by natural rainfall or irrigation.

Lastly, be sure to sweep or blow all fertilizer pellets back onto the lawn. Pellets that land on hard surfaces quickly wash into our water supply, leading to impaired water quality.

Dennis Patton is a Johnson County Extension horticulture agent. To get your gardening questions answered by him, go to kcgardens.kansascity.com.