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Article: Does fertiliser destroy corten steel and galvanised steel?

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Does fertiliser destroy corten steel and galvanised steel?

Spring not only brings longer days and warmer weather, it's also the time to give your garden the boost it needs to ensure lush growth and beautiful flowers. One of the most important factors for a beautiful and healthy garden is fertiliser.

When you have a raised bed or planter made of corten steel or galvanised steel, it makes sense to consider whether fertiliser will damage the steel.

After all, certain types of fertiliser can potentially damage corten steel and galvanised steel. This is because fertilisers can accelerate the corrosion process in the metals - especially if they contain high levels of salts. This is especially true in humid environments or when the fertiliser is in direct contact with the metal for a long period of time. Read below how fertiliser can affect the two types of steel:

Corten steel

Corten steel is known for its ability to form a protective rust layer that prevents further corrosion. This rust layer protects against the elements. The chemicals found in fertilisers can interfere with the formation of the rust layer or even penetrate it and cause corrosion. This is especially the case if the fertiliser is rich in nitrates or ammonium salts.

Galvanised steel

Galvanised steel is steel coated with a layer of zinc to protect it from corrosion. Although the zinc layer provides good protection, aggressive chemicals, such as those in fertilisers, can attack the zinc layer and accelerate corrosion. This is because some of the chemicals in fertilisers can react chemically with zinc to form compounds that don't protect the steel as effectively.


To protect the corten steel and galvanised steel from potential damage from fertiliser, it is important to:

  1. Use organic fertiliser
    Organic fertilisers contain natural nutrients and microorganisms that are not only beneficial to plants, but also less likely to cause damage to raised beds or planter structures. Therefore, organic fertiliser is a gentler choice that helps maintain the longevity and appearance of raised beds.
  2. Avoid direct contact
    Avoid direct contact between the fertiliser and the metal. When spreading the fertiliser, make sure it doesn't hit the steel or lay directly on the steel.
  3. Cleaning
    Clean metal surfaces that have been hit by fertiliser.
  4. Good drainage
    Ensuring that the soil is well-drained and that there is no water standing in the planter or raised bed will help prevent the build-up of chemicals from the fertiliser.

By taking these precautions, you can help extend the life of corten steel and galvanised steel - even if you use fertiliser.

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