Fertilizer storage mistakes – experts reveal 7 missteps that can ruin this temperamental gardening essential

Fertilizer helps plants grow strong and healthy. Whether you're growing a luscious lawn or prize-winning roses, fertilizer can take your garden game to the next level.

However, fertilizer can be dangerous. Some can irritate your skin, and they're poisonous if ingested, so you need to store them out of reach of kids and pets. On top of that, fertilizer is a little temperamental, and storing it incorrectly can make it lose all its effectiveness.

I spoke to gardening and fertilisation experts about the common fertilizer storage mistakes they see amateur gardeners fall into again and again - and how you can avoid them.

1. Never store fertilizer in sunlight

Firstly, you should never store fertilizer in sunlight. This is usually a problem when gardeners keep fertilizer in a greenhouse. It makes sense to keep fertilizer around when potting plants or to keep it near tools, but sunlight can damage fertilizer.

The UV rays in sunlight can break down the compounds in nitrogen, potassium, and iron-based fertilizers. This makes them much less effective, hampering your plants' growth and health.

Keeping fertilizer in the sun is also a fire risk. The heat of the sun can cause spontaneous combustion that could start a fire in your greenhouse or shed.

Instead, keep your fertilizer somewhere dark, like an insulated garage or basement.

2. Don't store fertilizer near water

Another fertilizer storage mistake is to keep your fertilizer near water and moisture. Water can make granule fertilizer unusable.

Garden expert Jimmy Patterson says 'Storing fertilizer in a moisture-rich environment is a huge but yet common mistake. Most slow-release fertilizers are coated to help aid in slowing the release of nutrients. This coating is made to be water soluble. As moisture seeps into a fertilizer container, this coating may begin to breakdown, and the urea and other fertilizer components may begin to melt and create residues. If allowed to dry again, this can cause the bag of granules to link together, forming a solid block and making it very difficult to spread without breaking it up.'

While fertilizer can be damaged by water, it can also cause huge harm to local water sources. Storing fertilizer close to rivers and wells can lead to fertilizer leaking into water supplies. Gardener Jen Jerman explains 'A leak could cause algae blooms if there is a high phosphorous content and enough fertilizer leaking into that water source.' These algae blooms deplete the oxygen level in water, killing fish and making water undrinkable.

Keeping fertilizer in a sealed tub in a garage or basement is one of the best ways of preventing it from contaminating local water sources. You don't need anything fancy - a simple airtight tote like this from The Container Store will keep your fertilizer safe.

Jimmy Patterson

Jimmy Patterson is the founder and president of TruScape LLC, a leading provider of residential and commercial landscape maintenance and construction services based in Greensburg, Pennsylvania

Jen Jarman

Jen is an expert landscaper and Fertilization Manager at Drost Landscape.

3. Don't leave fertilizer near a heat source

Just as keeping fertilizer in the sun can cause fires, so can keeping it near heat sources like heat ducts and boilers. Some people keep their fertilizer in their basement to keep it out of the sun and moisture but store it too close to their boiler or furnace.

Nursery expert Tammy Sons explains 'Heat sources can quicken the pace on fertilizers decomposing and ruining, as well as causing it to release toxic fumes.'

Gardener Jen Jerman agrees and says 'Keep fertilizer away from heat sources, as they sometimes create a combustion reaction.'

Tammy Sons

Tammy Sons is a horticulture plant expert, garden writer, and educator. Tammy is the CEO and founder of TN Nursery, a thriving online plant nursery based in Altamont, Tennessee. She is also a prolific writer, sharing her knowledge through articles on various gardening topics, including plant care, sustainable landscaping, and the latest trends in horticulture.

4. Don't leave fertilizer in the cold

But while it's a mistake to heat up fertilizer, keeping it too cold is another common error, particularly in winter. While you should never fertilize in freezing weather, the cold can damage fertilizer in itself.

The first reason for this is obvious. Jen Jerman says 'Storing liquid fertilizers in the cold can cause them to freeze.' This makes the fertilizer unusable until it thaws back into liquid.

But even if it thaws, you may find that the fertilizer becomes less effective. Freezing can cause the chemicals in liquid fertilizers to separate, making the fertilizer ineffective. Freeze-thaw cycles can cause moisture to gather on fertilizer granules, which can make the fertilizer clumpy and hard to use.

Tammy Sons says 'Places that are too cold can kill off the plant-aiding chemicals and cause it to become clumpy and ineffective,'

5. Don't keep fertilizer on the floor

Nor should you keep fertilizer on the floor. Floors - especially in utility rooms like garages and basements - gather moisture from muddy shoes. As we covered above, this moisture can make your fertilizer ineffective.

Fertilizer on the floor is easy to kick over by accident, which can cause a spill that can be very hard to clean.

Keeping fertilizer on the floor is also a mistake because it puts fertilizer at the right level for kids and pets to access. Keeping fertilizer in a storage tub is the best way to ensure curious kids or pets don't open the fertilizer and hurt themselves.

6. Be careful with fertilizer on wood shelves

Wood shelves can be a poor choice for storing fertilizer. It seems like they should be a good choice, because wood isn't conductive and won't heat up the fertilizer.

However, wood, particularly the MDF used in inexpensive shelving, can hold a surprising amount of moisture that can degrade your fertilizer. Tammy Sons warns 'Wood shelves can store moisture that can seep into the fertilizer and ruin it.'

Instead, keep your fertilizer in a plastic tub on a metal wire shelf unit like this from Walmart.

7. Don't store incompatible fertilizers next to each other

Finally, make sure to keep different fertilizers separate. Mixing up fertilizers can make them less effective, but it can also be a big safety risk. Tammy Sons says 'If you store incompatible fertilizers next to each other, they can react to one another and release dangerous fumes, even starting fires.'

However, this is solved by keeping different fertilizers in different tubs. Jen Jarm says 'Try to keep incompatible fertilizers in impermeable containers so that a chemical reaction would not occur or keep them separate. '

You don't need to rely on chemical fertilizers, however. Some of the best fertilizers for a vegetable garden are homemade tomato fertilizers made from nettle tea and coffee grounds, and you can also make DIY rose fertilizers. On top of that, making a composter can provide organic compost from kitchen and garden scraps, bringing the benefits of chemical fertilizers without the worries.