The question of whether to fertilize in the winter generally leans toward no, but specific exceptions exist based on plant type and local climate. This practice, sometimes called dormant feeding or winterizing, requires precise timing to be effective and avoid negative consequences. Understanding a plant’s winter physiology and the environmental risks of misapplication are key to making an informed decision.
Understanding Plant Dormancy and Nutrient Uptake
Most plants in temperate climates enter dormancy, a biological strategy to survive cold temperatures and reduced sunlight. Triggered by shorter day lengths and cooler air temperatures, this process causes a dramatic physiological slowdown. Plant metabolic activity, including photosynthesis and respiration, decreases significantly as enzymes function less efficiently in the cold.
Deciduous plants stop sending energy to above-ground growth, instead storing carbohydrates in their roots and crowns for winter survival. Since growth has largely ceased, the plant’s need for water and nutrient uptake is drastically reduced. Applying fertilizer to a deeply dormant plant is inefficient because the nutrients cannot be absorbed.
The most important factor determining nutrient absorption is soil temperature, not air temperature. Root growth is significantly impaired when soil temperatures drop below 10°C. When the ground is frozen solid, nutrient uptake stops because roots cannot absorb immobilized water.
Specific Scenarios That Require Winter Feeding
The primary exception to avoiding winter fertilization is the late-fall application for cool-season turfgrasses, often termed “winterizing.” This timing is specific to grasses like Kentucky bluegrass and fescue, which remain metabolically active later into the fall. The goal is to apply fertilizer after the grass blades stop growing but while the soil is still warm enough for root absorption.
This late-fall feeding stimulates root growth and carbohydrate storage in the crown, which are crucial for winter hardiness. This stored energy enhances the grass’s ability to survive the cold and provides the fuel needed for rapid, early green-up in the spring. A water-soluble, quick-release nitrogen source is often preferred for this purpose. It is rapidly taken up before the ground freezes, unlike slow-release formulas that rely on microbial activity minimal in cold soil.
Fertilizing evergreens and woody ornamentals is another scenario, though the timing is late-fall, not deep winter. In mild climates or for stressed plants, a slow-release fertilizer can be applied in late summer or fall. The product feeds the roots through the late season, helping the plant build reserves for winter. Applying nitrogen later than recommended risks stimulating tender new growth that cannot “harden off,” making it susceptible to winter injury and dieback.
Environmental Hazards of Misapplied Winter Fertilization
Applying fertilizer when the ground is frozen, saturated, or when plants are dormant poses a significant risk of nutrient pollution. Dormant plants cannot absorb the nutrients, leaving soluble nitrogen and phosphorus compounds exposed on the soil surface. When the ground is frozen, water cannot infiltrate the soil, causing rain or snowmelt to become surface runoff.
This runoff carries excess nutrients directly into storm drains and waterways. This nutrient-rich flow leads to eutrophication, fueling excessive algae growth. The decomposition of these algae blooms consumes dissolved oxygen, creating hypoxic zones or “dead zones” that cause large-scale fish die-offs.
Another hazard is fertilizer burn, which occurs when fertilizer salts accumulate at high concentrations. An excess of these salts can chemically draw water out of the plant’s roots, a process called reverse osmosis. This dehydrates the dormant roots, causing damage and potentially killing the plant.