When fertilizing plants, consider the 4Rs of nutrient management: the right kind of fertilizer applied in the right amount, at the right time of year, and in the right location where it can be taken up by plants. The right kind of fertilizer refers to how quickly or slowly nitrogen is available to plants. It also refers to what nutrients are already available to plants based on soil test results. Ideally, choose a fertilizer based on soil test results to apply the nutrients that are lacking or absent in the soil. For more information, HGIC 1230, Choosing a Fertilizer. Apply the right amount of fertilizer based on soil test results and fertilizer label instructions to avoid applying too much fertilizer, which can harm or kill plants, or too little fertilizer, which may not satisfy the needs of the plants.
The fertilizer should be applied at the right time—when the plants are actively growing and can absorb the fertilizer and not before a heavy downpour when rainfall will cause the nutrients to either leach down into the soil away from the roots or cause it to runoff and escape from the site. Fertilizer should also be applied in the right place: in the root zone area of plants where the nutrients can be absorbed by plants.
When fertilizer is applied and not taken up or absorbed by plants, it may contaminate the environment. Nutrients, notably nitrogen and phosphorus, markedly reduce water quality. Nitrate is the form of nitrogen that is not held by clay or sand particles, so it can leach down through the soil and contaminate groundwater. It can also wash across the soil surface in runoff and contaminate surface waters.
Phosphorus, on the other hand, is held tightly or adsorbed by soil particles. When soils erode and flow offsite, they carry the attached phosphorus particles with them. When these soil particles spill into water bodies, the excessive levels of phosphates lead to nutrient imbalances. In fact, high levels of nitrates and phosphates lead to nutrient imbalances in lakes and streams and cause algal blooms that deplete oxygen levels and harm aquatic life.
When applying fertilizers to satisfy the nutritional needs of your plants, follow these best management practices to maintain plant health and protect water quality and aquatic life.
- Test your soil each year when growing annual crops, such as bedding plants and vegetables or fruiting plants. Established lawns and landscapes can be tested every 2 to 3 years. Soil samples can be submitted to any Cooperative Extension office. Alternatively, a prepaid soil sample mailer kit can be ordered from the Clemson University Agricultural Service Laboratory or picked up at any county Extension office. This postage prepaid mailer kit can be mailed to the Agricultural Service Lab from home.
- Apply recommended fertilizers based on the results of a soil test. Apply only the nutrients in the amounts recommended by soil test results.
- Maintain an appropriate soil pH as determined by a soil test. The pH (acidity or alkalinity) of the soil affects the availability of nutrients applied to your plant or that are already present in the soil. See HGIC 1230, Choosing a fertilizer, for More Information.
- Read, understand, and follow the fertilizer label instructions. See HGIC 1228, Reading a Fertilizer Label, for more information.
- Apply the correct amount of fertilizer at the right time of year to improve the uptake of nutrients and avoid injuring your plants. Calibrate your fertilizer spreader to apply the right amount of fertilizer to your plants. For more information, see HGIC 1657, Calibrating Spreaders.
- Do not fertilize plants during droughts: water is necessary for nutrient uptake and to support growth initiated by the fertilizer application. Avoid harming your plants by delaying the application when normal rainfall returns.
- Near bodies of water, create and maintain a vegetated buffer: a fertilizer- and pesticide-free zone that absorbs any nutrients and prevents them from contaminating water bodies. For more information, see HGIC 1855, Shorescaping freshwater shorelines, and HGIC 1876, Maintaining your freshwater shoreline.
- When heavy rainfall is expected, postpone fertilization to prevent losses due to leaching and runoff.
- Avoid applying fertilizer to hard, impervious surfaces, such as sidewalks, patios, driveways, and streets. Sweep up any fertilizer that falls on these surfaces and return it to landscaped areas or back in the bag.
References and Further Reading
- 4Rs of Nutrient Stewardship: Economically, Environmentally & Socially Sustainable Crop Nutrition. May 5, 2022. Accessed <https://nutrientstewardship.org/4rs/>.
- Comeau, E. S. 2020. Protecting water quality with vegetated buffers. May 5, 2022. Accessed <https://hgic.clemson.edu/protecting-water-quality-with-vegetated-buffers/>.
- Huffman, R., L. Roth, R. G. Burroughs, and B. Polomski. 2004. Designing a shoreline buffer, p. 77-98. In: L. Roth (ed.). Life at the Water’s Edge: A ShorelineResident’sGuide to Natural Lakeshore and Streamside Buffers for Water Quality Protection in South Carolina, Clemson University Public Service Publishing. WQL 24.
- Polomski, B., R. Huffman, L. Roth, and W. C. Stringer. 2004. Establishing and maintaining shoreline buffer vegetation, p. 101-122. In: L. Roth (ed.). Life at the Water’s Edge. WQL 24.
- Pachota, S., K. Giacalone, K. Counts, and A. Dabbs. 2014. Principle 7: Be wise when you fertilize. In The Carolina Yardstick Workbook, p. 22-23. May 5, 2022. Accessed <https://www.clemson.edu/extension/carolinayards/>.
- Clemson University Cooperative Extension Water Resources Team. Water Quality Challenges in Stormwater Ponds. May 20, 2022. Accessed <https://www.clemson.edu/extension/water/stormwater-ponds/problem-solving/water-quality/index.html>.
Originally published 03/23