When a Fertilizer Hardens: What To Do?

Last updated on October 25th, 2023 at 01:11 pm

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You open a bag or container of fertilizer in the spring and it’s a disaster! The fertilizer has set (hardened). Is it still usable?


When a Fertilizer Hardens: What To Do?

You’ll notice that there is no expiration date on most fertilizers because they are made of minerals and minerals don’t break down. Simply take a hammer or pestle (a simple piece of wood can be used) and grind your fertilizer into a powder again.

Theoretically, liquid organic fertilizers could decompose and some manufacturers give an expiration date of 8 to 10 years after manufacture. In fact, if they do break down, it is to be reduced to minerals… and therefore, they are still useful to plants. However, solid particles can eventually settle on the walls or the bottom of the container. Simply shake the container to mix the deposits with the liquid.

When fertilizer hardens, it can be due to exposure to moisture, humidity, or improper storage. Fertilizer that has clumped or hardened can still be usable with some effort and proper handling. Here’s what to do when your fertilizer has hardened:

1. Break Up the Clumps:

Use a garden tool like a shovel, hoe, or trowel to break up the hardened fertilizer into smaller pieces. The goal is to restore it to a granular or powder-like consistency.

2. Sieve or Sift the Fertilizer:

Pass the broken-up fertilizer through a fine mesh sieve or a sifter to separate the clumps from the smaller particles. This step helps ensure that you have a more uniform and usable product.

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3. Store Properly:

To prevent future hardening, store your fertilizer in a cool, dry place. Airtight containers or resealable bags can help keep moisture out. Avoid leaving the fertilizer exposed to the elements or humidity.

4. Use a Fertilizer Spreader:

If your fertilizer remains slightly clumped, using a fertilizer spreader can help disperse it evenly across your garden. The spinning mechanism of the spreader can break up clumps as it distributes the fertilizer.

5. Rehydrate Slow-Release Fertilizers:

Some slow-release fertilizers may become hard due to moisture exposure. For these types of fertilizers, you can try rehydrating them by misting them with water while breaking up the clumps. Be cautious not to over-wet the fertilizer.

6. Follow Label Instructions:

Pay attention to the manufacturer’s instructions on the fertilizer label. It may provide guidance on how to handle hardened fertilizer or whether it’s still suitable for use.

7. Use a Chelating Agent (Optional):

In some cases, adding a chelating agent like citric acid can help loosen clumps in the fertilizer. This is a more advanced step and should be done with caution, as adding too much citric acid can affect the fertilizer’s composition.

8. Test It First:

Before applying the reconstituted fertilizer to your entire garden or lawn, do a small test application to ensure that it spreads evenly and doesn’t harm your plants. This helps avoid over-fertilizing or causing fertilizer burn.

9. Replace if Necessary:

If the fertilizer has hardened to the extent that it cannot be effectively broken up or if it has been exposed to moisture for an extended period, it may be best to replace it with fresh fertilizer to ensure your plants receive the nutrients they need.

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Properly storing your fertilizer in the first place is the best way to prevent it from hardening. Regularly inspect your fertilizer storage area to ensure it remains dry and well-sealed. When you follow these steps and take care of your fertilizer, you can make the most of your gardening investment and provide your plants with the nutrients they require for healthy growth.

Fertilizers combined with herbicides

Herbicide fertilizers are still widely distributed, especially in the United States.
The exception to the rule is for “weed and feed” fertilizers, which are fertilizers that are combined with herbicides. Usually, these products have an expiration date of 3 or 4 years, but it is the herbicide that loses its effectiveness, not the fertilizer.

Note that fertilizers containing synthetic herbicides have been banned in Canada and in many other countries, at least for consumers. Only fertilizers containing organic herbicides, such as corn gluten, remain on the market, and there is no expiration date for these. Reduce these powdered herbicide fertilizers if they harden off.

To prevent hardening

Fertilizers harden in contact with moisture. Much of this hardening can be prevented by keeping them in the house in the winter (in a shed, there is often condensation when temperatures drop in the winter). Or, you can attach a bag or two of silica gel to the inside of the container to absorb excess moisture.


  • James Jones

    Meet James Jones, a passionate gardening writer whose words bloom with the wisdom of an experienced horticulturist. With a deep-rooted love for all things green, James has dedicated his life to sharing the art and science of gardening with the world. James's words have found their way into countless publications, and his gardening insights have inspired a new generation of green thumbs. His commitment to sustainability and environmental stewardship shines through in every article he crafts.

    https://www.linkedin.com/in/james-jones-436784297/ gardeninguru@outlook.com Jones James
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