Handling Old Fertilizer: Disposal and Reuse

By: Ken Wilson

Hidden deep in the back of most garages is an open bag of fertilizer that has been there for years. When the day finally arrives to do a spring clean, it can be confusing to know what to do with the relic from the past. Of course, it would be great if it could be used, but what if it has been quietly evolving into a bomb while in storage?

Most old fertilizers can last a very long time if stored correctly. If it must be discarded, the ingredients dictate the method of disposal required. Organic blends can be composted. Chemical mixes containing nitrogen or phosphorus must go to a household hazardous waste disposal site.

If you are wondering what to do with old fertilizer, you are not alone. Let’s find out if the dusty bags of plant food in the back corner of your garage can breathe new life into your garden or if they will be the kiss of death for your plants.

How to Safely Dispose of Fertilizers

Getting rid of old plant food can be tricky. Since some fertilizers are considered hazardous waste, they should not be included with your regular garbage for collection.

The way to safely dispose of unwanted fertilizer depends entirely on the ingredients of the liquid or mixture. Organic varieties can be added to your compost pile. They can even be included with your regular household waste.

The challenge arises when you have old chemical fertilizers that contain large amounts of nitrogen, potassium, or phosphorus. In small doses, these can work miracles in your garden to supercharge your plants to grow. In large quantities, they can contaminate groundwater and kill wildlife or fish that come into contact with it.

What to Do with Old Fertilizer

There is no single best solution to dispose of old fertilizer safely. Factors like what kind it is, how much you need to get rid of, and what condition it is in all play a role. However, by knowing your options, you can make the decision that will work best for your situation.

Here are six ways to dispose of old fertilizer:

1. Give it away.

When stored properly, most plant food can last indefinitely. If you have leftovers that are in good condition that you no longer need, ask your local community group if anyone may be interested in taking it off your hands.

2. Use household hazardous waste collection days.

Check if your neighborhood has regular household hazardous waste collection dates. Several communities have annual or biannual dates when the local waste disposal company comes by specifically to collect hazardous waste. This is the perfect time to responsibly and safely dispose of any unwanted chemical fertilizer you have.

3. Ask your garden supply store to take it.

Not all garden supply stores will take it, but many do, especially if the fertilizer is in good condition and still in its original bag. They may even give you store credit, so it is well worth trying.

Do not try this if the fertilizer has moisture damage or the bag makes the mixture unidentifiable. However, you could still ask if they would be willing to dispose of it for you. Some centers may have a hazardous waste disposal plan and be able to include your old collection.

4. Check for disposal instructions on the bottle or bag.

Many fertilizer companies include a help number on the bag that you can phone for advice about the product. The manufacturer may be able to guide you regarding how best to dispose of their product.

5. Contact a lawn service to dispose of old lawn fertilizer.

Chemical lawn fertilizers are one of the most common types that require disposal. Your local lawn care service may offer a collection service of old lawn products or be able to advise on the safest way to dispose of it.

6. Drop it off at local hazardous waste collection site.

Be careful when transporting old fertilizer, as the dust can become airborne, and even the fumes can be harmful if inhaled. Double-seal the contents into a heavy-duty trash bag and tie it closed before transporting it.

Does Fertilizer Expire?

They may no longer look fresh and new, but the old bags or open bottles of liquid fertilizer in the back of your garden shed may not need to be thrown away. Many of these products, like household cleaners, can last indefinitely if stored in protected areas.

Before disposing of old plant food, it is worthwhile checking if it can still be used. You may be surprised, and using what you already have means you will save money for more plants!

Since fertilizer promotes growth and good health in plants, it is easy to think of it as having a short shelf life. But unlike something like milk that can go bad quickly, most plant foods are better categorized with things like household cleaning products and can be stored for very long periods.

Some products, especially organic varieties, may degrade slightly over time but are still OK to use. Organic fertilizer should only be discarded if it smells rancid (not including fish emulsion products that always smell terrible!) or if you can see visible fungus or mold.

Let’s find out how long the various types of fertilizers can last:

Synthetic Granular

If stored correctly, it can last indefinitely. If it has clumped because of moisture, wear a mask and crumble it. It is still OK to use.

Organic Granular

One to five years. Some mixtures containing microbes may last slightly shorter than others, but disposing of organic products is never a problem. It is safe to add it to your compost pile.

Liquid Synthetic

Can last indefinitely. Some products show a best-before or expiry date on the container, but if stored correctly, they can last for many years.

That being said, never store liquid plant food in areas where it can freeze in winter, as it can change the composition of the mixture. It can also decrease the effectiveness of some of the components. Always thoroughly shake liquid fertilizers before using them to mix ingredients that may have settled on the bottom.

Weed and Feed Lawn Care Products

One to four years. Lawn dressings often also contain herbicides, which often lose their efficacy faster than the nutrient component of the mixtures. So, while the herbicides in an old fertilizer mix may no longer be effective, the nutrient part may still be good to spread on your lawn.

Final Thoughts

Disposing of old fertilizers responsibly is essential to prevent any environmental damage these concentrated plant foods could cause. The solution used to dispose of old garden dressings should be determined by the mixture’s ingredients. Before getting rid of opened bags or bottles from a few seasons ago, first check if they can be reused.

About the author 

Ken Wilson

Long time career in the home services industry from remodeling to patio construction. Currently residing to in SWFL and active contributor to multiple home & garden publications.