How Long Does Granular Fertilizer Last?

  • By: CarlBroadbent
  • Time to read: 5 min.
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Fertilizing your plants is one of the key factors to maintaining a healthy lawn or garden.

Before buying the biggest bag of granular fertilizer you can find, you should ask how long does granular fertilizer lasts?

This is a loaded question and it can be asking three different things. Granular fertilizer doesn’t decompose, so it has no expiry and can be kept indefinitely as long as it is stored correctly. This means you can buy it in bulk, and apply it when you need it every 2-6 weeks. 

How Long Can You Store Granular Fertilizer?

You can store fertilizer until you empty the bag.

Granular fertilizer is made from elements that don’t break down, which means it doesn’t have an expiry date. 

How Long Can You Store Granular Fertilizer?
Granular fertilizer expiry date

That is if you store it correctly. If you leave granular fertilizer sitting outside, or leave it open, the product can go to waste. 

Ammonium nitrate is a cost-effective way of adding Nitrogen to the fertilizer, but it is extremely reactive if ignited.

It could be something as simple as a stray ember from a bonfire that could result in the bag of fertilizer exploding. 

Granular fertilizer is also prone to clumping if there is any moisture in the air. If your fertilizer clumps, it won’t become ineffective, but you might find it difficult to use. 

To use the fertilizer after it has clumped, you will need to break the granules apart again.

Many gardeners have found that a hammer is the most effective way to separate the clumps. 

Here are some tips to keep your fertilizer in its best condition:

  • Keep the product in the original bag, and keep the bag in a sealed plastic or metal container
  • Keep in a cool, dry place (garage or shed)
  • Keep out of sunlight

How Long Will Granular Fertilizer Feed Plants?

This will depend on whether you have a synthetic fertilizer or an organic fertilizer. 

Synthetic fertilizers are designed and manufactured to break down quickly to have an instant effect on your lawn.

Use Lawn Fertilizer
Lawn fertilizer

Not only will the synthetic granules break down faster, but the plants will absorb the nutrients faster since they are available. 

This type of fertilizer can release nutrients for a few weeks and will need to be reapplied every 2-4 weeks during your plant’s growing season. 

Organic granular fertilizer on the other hand takes a lot longer to break down. Think of it as compost, it takes a while for the natural process for organic material to break down. 

Organic fertilizer usually takes six weeks to break down in your soil, but it can feed your plants for a few months or even a few years.

You can fertilize your lawn every 6-8 weeks with granular fertilizer, but be careful not to add too much that causes your roots to burn! 

Wait! Root burn? What’s that?

Root burn is the side effect of over-fertilizing. It is tempting to keep adding fertilizer when you see your plants doing well, so nobody will blame you for accidental over-fertilizing. 


Be Careful: If you notice the lower leaves are starting to yellow or wilt, the leaf tips are turning brown, and there hasn’t been much growth, it is likely you have over-fertilized.  


How Many Applications Can You Get From a Bag of Granular Fertilizer?

The short answer is the bag will tell you how many times you can fertilize with that one bag. 

Before you go shopping for fertilizer, measure the area you want to fertilize.

A 5,000 square foot lawn is going to need a lot more fertilizer than a 100 square foot garden. 

It will also depend on what you are fertilizing.

Lawns, flowers, vegetables, shrubs, and trees all need different amounts of fertilizer with different ratios of nitrogen, phosphorus, and potassium. 

Lawns, for example, need 1lbs of nitrogen per 1,000 square feet.

A bag of lawn fertilizer will tell you how many square feet it will cover, and if you know the area of your lawn, you can figure out how many applications you can get out of the bag. 

Is it Worth Paying for Lawn Care?
Lawn care tips

The average U.S. lawn size is about 10,000 square feet. There are a handful of states where the lawn size average is over 50,000 square feet and quite a few have 10,000 square feet or less. 


What to Expect: Most bags of fertilizer you can buy in stores cover around 15,000 square feet, so you’ll go through 2 bags every 2 months or so. 


Final Thoughts

You won’t need to worry about buying too much fertilizer.

As long as you store the fertilizer in a sealed container, inside, and out of any sunlight, you can use it for as long as you have it. 

That’s great for a small garden or specialty plant fertilizers if you don’t need to use a lot, but you will probably find you won’t need to store lawn fertilizer for very long before you need to apply it again. 

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