Who else has wondered if the best time to fertilize your lawn is before or after it rains? I certainly have. Here’s what I found when I looked into this common lawn care question.
It’s best to fertilize your lawn after it rains rather than before a significant rainfall. This is mainly because rainfall can transport nutrients away from your turf grass. Lawn fertilizers are often highly soluble in water, leading to environmental pollution following rainfall events (not to mention a waste of money for the homeowner!).
There are quite a few reasons that it’s better to fertilize your turf grass right after it rains instead of right before it rains. Read on to learn more about aligning your lawn fertilizer application with the weather forecast.
Fertilizer loss due to rainfall
Fertilizer loss due to rainfall is a common issue with all water-soluble fertilizers, but it can be particularly troublesome with lawn fertilizers. This is because lawn fertilizers are formulated to contain higher amounts of nitrogen than other blends. Water-soluble nitrogen quickly washes through soil, and can mean that your lawn never gets the benefit of the nitrogen you’ve purchased.
Rainfall itself also helps to bring usable nutrients from the soil itself into the rhizosphere of the turf grass. This is particularly true in new lawns with fresh soil and in seasons when the soil is warming or has been recently warmed. It is quite possible that the rainfall itself will supply the lawn with adequate nutrients for growth. This is one reason the best time to fertilize the lawn is after, not before, the rain.
“With excessive fertilizer applications, crop nutrient efficiency declines and farmers obtain diminishing financial returns.”
Mineral Nutrition of Plants: Principles and Perspectives, by Emanuel Epstein and Arnold J. Bloom
“Don’t pour nitrogen down the drain; avoid fertilizing right before a big rain or irrigation.”
Building Soil: A Down-to-Earth Approach: Natural Solutions for Better Gardens & Yards, by Elizabeth Murphy
“In crop plants subject to excessive fertilization, photosynthetic capacity ceases to increase with additional leaf nitrogen.”
Mineral Nutrition of Plants: Principles and Perspectives, by Emanuel Epstein and Arnold J. Bloom
Groundwater pollution from fertilizing before rainfall
Leaching of fertilizer nutrients such as nitrogen leads to pollution of the soil in the surrounding environment. The rainfall carries the nutrients down through the root zone of the grass and away through the soil beyond your lawn.
While nitrogen is an important nutrient for plants, so is the natural balance of nutrients in the natural ecosystem. Disrupting the naturally-occurring ratios of nutrients can upset the way the ecosystem functions.
“Since nitrogen leaches through the soil easily, water runoff containing this surplus nitrogen can end up polluting the groundwater or nearby lakes and streams.”
The Lawn Bible: How to Keep It Green, Groomed, and Growing Every Season of the Year, by David R. Mellor, Fenway Park’s Master Groundskeeper
Surface water pollution from fertilizing before rainfall
Surface water pollution of creeks, rivers, lakes, and oceans is an increasingly visible problem. While soil and groundwater pollution isn’t very visible, it’s hard not to notice giant algae bloom at the beach. Lawn fertilizer ingredients like nitrogen and phosphorus are key contributors to this problem. Fertilizing the lawn before it rains (rather than after) worsens the effect.
Eutrophication of aquatic environments with synthetic fertilizer has become such a problem in some areas that it has created “dead zones” – areas where oxygen levels in the water become too low to support the life in the ecosystem. This pollution is one of the main reasons that the best time to fertilize the lawn is after forecasted rainfall has finished, rather than before it rains.
“Phosphorus is a component of most fertilizers that helps plants to grow. When too much is applied or is applied at the wrong time—such as right before it rains—most of it is washed away and ends up in the local waterways. This type of pollution is called nonpoint source pollution. It causes eutrophication (a reduction of dissolved oxygen in water bodies caused by an increase of minerals and organic nutrients) of rivers and lakes. This reduced level of oxygen in water ends up suffocating fish.”
Why is phosphorus, a component of lawn fertilizer, bad for the environment?, Chicago Botanic Garden
“More and more nitrogen keeps pouring into waterways, unleashing algal blooms and creating dead zones. To prevent the problem from worsening, scientists warn, the world must drastically cut back on synthetic fertilizers and double the efficiency of the nitrogen used on farms.”
Can the World Find Solutions to the Nitrogen Pollution Crisis?, Yale School of the Environment, by Fred Pearce
Lawn fertilizers that are ok to apply before rainfall
As issues like marine eutrophication and groundwater contamination become more well-known, there have been changes in the types of lawn fertilizer available. Some states and countries have regulated residential lawn fertilizers that contain potassium (meaning that the middle number in the NPK ratio is zero). Some have been formulated so a large percentage of the nitrogen is slow-release (not water-soluble).
Look for a slow-release, organically-sourced lawn fertilizer to lessen the potential negative effects of lawn fertilizer and maximize the return on your financial investment. My favorite lawn fertilizer is a 1″-thick top-dressing of homemade compost! There are also a variety of high-quality organic lawn fertilizers available. Be sure to read and follow the directions for the fertilizer you choose.
Seasonal considerations for lawn fertilizer application timing
Northern lawns (bluegrass, fescue) are generally fertilized in early spring and early fall, right before their most active periods of growth. Southern lawns (Bermuda grass, zoysia) are generally fed in late spring and summertime.
While the directions for fertilizers vary, it’s generally best to apply fertilizer to a dry lawn so that only a small amount of fertilizer sticks to the grass blades. A light watering – more like a surficial washing – of the lawn after applying the fertilizer is a controlled method to get the fertilizer off the blades and into the soil.
“Fertilizing will be most beneficial before the period of active growth of your grass. For cool season grasses, this is usually in the spring and fall. Warm season grasses will benefit from a feeding in the late spring through the summer.”
The Lawn Bible: How to Keep It Green, Groomed, and Growing Every Season of the Year, by David R. Mellor, Fenway Park’s Master Groundskeeper
“Soil nutrients become scarcer toward the middle of the growing season when (1) plants are larger and require greater amounts of nutrients to sustain growth, (2) microbes, stimulated by the input of organic carbon from roots, acquire a larger portion of the nutrients released from soil organic matter or inorganic substrate, thus competing with growing roots and (3) competition from roots of other plants also intensifies.”
Mineral Nutrition of Plants: Principles and Perspectives, by Emanuel Epstein and Arnold J. Bloom
“The best time of day to fertilizer is when the grass is dry. Fertilize the lawn, then water it to knock the fertilizer off the blades of grass and activate it into the soil. Don’t fertilize on wet grass – as the grass dries, the fertilizer left on the blades can actually burn the grass in the hot sun.”
The Lawn Bible: How to Keep It Green, Groomed, and Growing Every Season of the Year, by David R. Mellor, Fenway Park’s Master Groundskeeper
