Keep your lawn or garden healthy before it goes into a period of winter dormancy with an application of fertilizer in the late fall. This is the time when cool-season grasses recover from summer stresses, such as drought, heat, and disease and turfgrass can begin to store carbohydrate reserves in the stems, rhizomes, and stolons. These carbohydrate reserves help grass resist winter injury and disease, as well as serve as a source of energy for root and shoot growth the following spring. Late-fall fertilization will also provide better winter color, enhanced spring green-up, and increased rooting. Additionally, a mild feeding of ornamental garden beds or vegetable gardens can also replenish soil that has been heavily depleted by growing plants over the season.
When to Fertilize
The exact timing to fertilize varies based on weather conditions and climate zone; however, the final fertilizer application should be done sometime in November in most regions. This is the point when the grass has stopped growing or has slowed down to the point of not needing to be mowed. If fertilizer is applied too early while grass or garden plants are vigorously growing, it can invite winter injury and snow mold the following spring. However, do not wait until the ground freezes or apply fertilizer over snow or ice.
How Much Fertilizer to Apply
Nitrogen is the most important nutrient for a fall fertilizer. A recommended dose for lawns is 1 pound of soluble nitrogen for every 1000 square feet or 1 1/2 to 2 pounds of slow-release nitrogen for every 1,000 square feet.
Choosing the Right Mixture
A complete fertilizer with a high ratio of both nitrogen and potassium (K) is essential for enhanced rooting, cold hardiness, disease resistance, and wear tolerance. An ideal fall fertilizer blend has a nitrogen to phosphorus to potassium (N:P:K) ratio of 24-4-12 with isobutylidene diurea (IBDU). In this formulation, a small amount of nitrogen is immediately available to the plant, while the rest is in slow-release form, allowing it to slowly break down and provide an extended feeding to the grass. Be wary of applying a fertilizer with too much phosphorus (P), as the run-off can damage to rivers and streams.
For flower and vegetable gardens, a mild fertilizer feeding in the fall will replenish the soil and prepare it for a quicker green-up when planting begins the following spring. Gardens do better with this approach than with a heavy dose of fertilizer in the early spring.
It's possible to over-fertilize your yard and garden. Too much nitrogen can be as damaging to plants as too little, and using natural sources of nutrients, such as compost on the garden or mulching lawn clippings rather than bagging them, can replace some of the traditional chemical fertilizer applications. One late- to mid-summer feeding of a lawn, followed by a light fall feeding, produces a better lawn than the old recommendation for three or four major feedings for each growing season, as championed by fertilizer manufacturers.
Flower or vegetable gardens similarly can thrive with fewer fertilizer applications than once believed, especially if they are properly amended with compost and other natural organic materials. Most gardens do well with one feeding shortly after planting and one as the growing season concludes. However, plants that produce large quantities of vegetables or large, plentiful flowers may need more.
Manuel, John. Nutrient Pollution: A Persistent Threat To Waterways. Environmental Health Perspectives, 122,11,A304-9, 2014, doi:10.1289/ehp.122-A304
Too Much Fertilizer Is Not A Good Thing! North Carolina State University Cooperative Extension.