The answer to whether you should water before fertilizing plants is almost always yes. Water is the medium that facilitates the entire process of feeding a plant, directly influencing nutrient uptake efficiency and overall plant health. A slightly moist environment ensures the plant is physiologically prepared to absorb nutrients and minimizes the risk of damage from concentrated fertilizer compounds.
Why Soil Moisture is Crucial for Nutrient Absorption
Water serves as the essential solvent and transport vehicle for nutrients within the soil and into the plant roots. Most nutrients, especially those from granular fertilizers, must first dissolve into the soil solution before a plant can use them, as roots cannot absorb solid fertilizer particles directly.
The movement of these dissolved nutrients to the root surface occurs primarily through two mechanisms: mass flow and diffusion. Mass flow is the movement of nutrients carried along with the bulk flow of water as the plant draws moisture into its roots. This process is responsible for the majority of nitrogen, calcium, and sulfur uptake. Diffusion involves the movement of nutrient ions from an area of higher concentration in the soil solution to a lower concentration near the root surface, which is important for less mobile nutrients like phosphorus and potassium. Both mechanisms rely heavily on sufficient soil water to keep nutrients mobile and accessible; when the soil is dry, movement stops, preventing nutrient uptake.
The Dangers of Fertilizing Dry Soil
Applying fertilizer to dry soil significantly increases the potential for “fertilizer burn” or “salt burn.” This damaging effect occurs because most fertilizers, particularly synthetic granular types, are composed of soluble salts. When applied to dry soil, these salts remain highly concentrated in the root zone, drastically altering the soil’s osmotic balance.
Normally, water moves into the root because the solute concentration is lower in the soil solution than inside the root cell. However, a high concentration of fertilizer salts reverses this osmotic gradient. This causes water to be drawn out of the plant roots and into the surrounding soil to dilute the high salt concentration. The plant effectively dehydrates itself, resulting in cellular damage, scorched leaves, and wilting. Properly moistening the soil beforehand ensures there is enough water to immediately dissolve and dilute the fertilizer salts, maintaining a favorable osmotic environment.
Follow-Up Watering and Exceptions
A light follow-up watering immediately after applying granular fertilizer is also beneficial. This post-application moisture washes any residual fertilizer granules off the plant foliage and further dissolves the nutrients into the soil. Moving the fertilizer down into the root zone prevents granules from sitting on the surface, where they could cause contact burn or be lost to runoff.
The main exception to the pre-watering rule involves liquid fertilizers and foliar feeds. Since liquid fertilizers are already dissolved in water, the risk of severe salt burn is significantly reduced. Foliar feeds are sprayed directly onto the leaves, bypassing the soil and roots entirely. Even with these applications, the underlying soil should not be completely dry, as a water-stressed plant is less capable of utilizing applied nutrients. For most granular applications, the best practice is to ensure the soil is evenly moist, apply the fertilizer, and then follow up with enough water to settle the product without causing waterlogging.