All gardeners want to see healthy plants growing in their garden. When plants don’t grow as we had hoped for, the most commonly made mistake is to apply fertilizers even when the plants don’t need them. Over-fertilization of plants can kill them. However, when the problem is identified in time, there are steps you can take to revive them. The following information will help you determine if you’ve over-fertilized your plants and, if so, how to help the plants recover and avoid related problems in the future.
Symptoms of over-fertilization (fertilizer burn)
- Yellowed and wilted leaves
- Browning leaf margins and tips
- Rotting roots (browned or blackened limps)
- A slowing down of growth or no growth
- A sudden death of seedlings
- Leaf drop
- White crusty soil surface around the plant
- Sudden plant growth without a sufficient root system to supply enough water and nutrient to the plant, causing a reduction in flower and fruit production
- Plant stress, making them susceptible to diseases and insect attacks, particularly sap-feeding insects
In this video you can see examples of over-fertilized tomatoes:
Causes of over-fertilization
- Too much or a too high concentration of soluble fertilizer added at once
- Multiple applications of soluble fertilizers without proper leaching
- Too much use of slow release fertilizers
- Improper combination of slow release and soluble fertilizer
- Insufficient drainage of the soil
- Adding fertilizer to insufficiently humid soil
- Repotting plants from a high fertilization environment into a less humid soil without first leaching the fertilizer
How to resolve over-fertilization
Step One: Get rid of any visible fertilizer
Begin by removing any fertilizer that you see around the plant base. If the fertilizer is a powder, and you see it laid out on top of the plant or on the topsoil, make sure to dispose of it. This will help prevent your plant from any further overfeeding. Similar to this, if you see that the fertilizer salts have formed a white crust, eliminate that as well.
Step Two: Flush the soil with water
Rain or irrigation won’t be able to remove naturally the excess fertilizer, but instead, the salt levels will increase through evaporation. Too much salt will raise the pH level of the soil and will prevent the plant to absorb necessary nutrients. That’s why this step is crucial because it will help move the fertilizer far away from the plant’s root system, ultimately preventing any additional over-fertilization from occurring. This will also allow the plant’s roots to start healing from what it went through. As a general guideline for flushing (leaching) out soluble salts from the top foot of soil, apply 6 inches of water to leach about 50% of the salts; apply 12 inches to leach about 80% of the salts.
For Pots Or Containers apply the following amounts of water:
- 6″ of water applied will reduce salts by 1/2
- 12″ of water will reduce salts by 4/5
- 24″ of water will reduce salts by 9/10
Step Three: Eliminate damaged leaves
Grab a pair of scissors and begin cutting off any leaves that you notice look burned. In this case, they will have brown spots on them. Also, remove any leaves that are wilted or have an irregular shape. Even if you are able to save your plant that has been over-fertilized, there is no hope for these leaves. They have already been damaged and cannot be revived at all. Getting rid of these leaves is important to ensure that your plant gets healthier. Actually, if you keep them on your plant, it may become infested with pests.
Step Four: Don’t fertilize your plant
If your plant has been over-fertilized, the last thing you want to do is give it more fertilizer. Wait until the plant looks healthy again, which typically occurs within 3 to 4 weeks. You have to give your plant and its roots time to recover from the strain of being over-fertilized.
Step Five: Replace top soil or transplant your plant in a new pot
To help the plants recovery, replace the top layer of the soil around the plant with a not-nutrient rich soil. For plants in pots, it could be beneficial to transferring your plant into another pot with new soil to help both the plant itself and the roots to heal.
Preventing over-fertilization
Have your soil tested. It is very important that you’re sure your plant need supplemental nutrient before applying fertilizer. It could be good to have your soil tested before applying fertilizer or other nutrient-adding components such as manure or compost to know the actual levels of nutrients in the soil. You can send the soil to a local lab who knows the local soil best or buy an affordable test kit, that can be found here. Don’t add fertilizer or compost unless the test results indicate that the soil needs certain nutrients.
Improve the soil. Instead of using fertilizer, in certain cases, it might be better to improve the soil. Home-made or store-bought organic compost, cured manure, decomposed leaves or bone meal emulsions could be a safer way to improve the soil.
Use organic fertilizers. If you’re sure you need to use a fertilizer, use a natural, organic brand because they release the nutrient more slowly. They’re also less concentrated than non-organic commercial fertilizers and this will decrease the risk of plant and soil damage.
Sufficiently dilute liquid fertilizers. Always add enough water to liquid fertilizer, add more than indicated on the package to be on the safer side.
Be careful when combining fertilizers. Never combine a slow release fertilizer together with a soluble fertilizer.
Limit use of slow-release fertilizers. Slow releasing fertilizer needs to be used sparingly unless you’re absolutely sure of the proper necessary amount.
Here’s an interesting video showing a natural alternative to fertilizer:
Additional Resources:
- Corrective Measures and Management of Over-Fertilized Soils [UMassAmherst]
- Over-fertilization of Potted Plants [University of Pennsylvania]
- The Perils of Over-Fertilizing Plants and Trees
