The successful use of fertilizer relies heavily on the proper management of water, which acts as the vehicle for nutrient delivery to the plant. Fertilization introduces nutrient salts into the soil, and these compounds must be dissolved in a liquid solution before they can be absorbed by roots. Water is necessary for both the physical solubilization of the fertilizer and its transport into the soil profile. The precise timing of watering is not a universal rule; it changes significantly based on whether the nutrients are applied in a solid granular form or as a pre-dissolved liquid solution.
Watering Instructions for Granular Fertilizers
Granular fertilizers, which look like small pellets, are designed to be activated by moisture. Immediate application of water after spreading these dry products is necessary to initiate the process where the outer shell of the granules begins to dissolve and release the concentrated nutrients into the soil. If the granules sit on the surface without moisture, the nutrients remain locked up and unavailable to the plant roots.
A deep, thorough watering is better than a light sprinkle, as the goal is to move the dissolved nutrients off the plant foliage and down into the root zone. The water helps to uniformly disperse the fertilizer compounds throughout the soil, preventing concentrated pockets of salts from forming near the root crowns. This immediate and deep saturation also helps prevent the high salt concentration from drawing moisture out of the plant tissue, which causes chemical burn.
For typical lawn applications, soaking the area until the soil is moist a few inches deep is a good guideline. This process can often take 45 minutes to an hour of watering.
Watering Instructions for Liquid Fertilizers
Liquid fertilizers, applied as a solution or diluted spray, require a different approach to watering because the nutrients are already dissolved. The general recommendation is to ensure the soil is already moist before the fertilizer solution is introduced. This practice, known as pre-watering, protects the plant’s root system and optimizes nutrient uptake.
Applying a concentrated liquid solution to dry soil can be detrimental because the lack of moisture increases the concentration of salts directly contacting the roots. Pre-watering hydrates the roots and surrounding soil, which helps dilute the fertilizer solution as it is applied, minimizing the risk of osmotic stress.
After the liquid fertilizer has been applied, avoid overhead watering for a few hours. This allows the nutrients time to be fully absorbed before they might be washed away.
Consequences of Mistimed Watering
Ignoring the correct timing for watering after fertilization often leads to fertilizer burn, a form of chemical dehydration. Fertilizers contain various salts, and when these salts become highly concentrated in the soil solution, they reverse the natural process of osmosis. The high salt content draws moisture out of the plant cells instead of the roots drawing water from the soil, effectively scorching the tissue.
Visual signs of fertilizer burn include the browning or yellowing of leaf tips and margins. In severe cases, particularly with granular products that are not immediately watered in, the roots themselves can turn brown and cease growth.
Another consequence of mistimed watering is nutrient runoff. This occurs if a granular product is left too long without water and is then washed away by heavy rain or excessive irrigation. Similarly, applying too much water immediately after a liquid application can cause nutrients to leach below the root zone, making them inaccessible to the plant.
Environmental Variables Affecting the Schedule
External conditions introduce nuance to the standard watering guidelines, requiring adjustments to the application schedule. Soil composition is a major factor, as sandy soils drain water quickly and retain less moisture than clay soils.
In sandy soil, nutrients are more likely to leach out, so lighter, more frequent watering is needed to keep the fertilizer in the root zone. Conversely, clay soil holds moisture well but has a slower infiltration rate, meaning water must be applied slowly to prevent runoff.
Temperature and humidity also significantly affect the risk of fertilizer burn and the necessity of immediate watering. High temperatures, especially those exceeding 85 to 90 degrees Fahrenheit, increase a plant’s heat stress and susceptibility to damage from fertilizer salts.
Under these conditions, the need for immediate and thorough watering of granular products is heightened to quickly dilute the salts and prevent dehydration. If rain is forecast shortly after a granular application, the initial activation watering can be delayed or skipped entirely, allowing nature to carry out the necessary dissolution.