DEF As Fertilizer: Not A Good Choice

DEF is urea mixed with water. Urea fertilizer is made of the same compounds, so in theory, it can be applied to lawns or gardens, but it is not recommended. DEF is designed to be added to large truck engines and is not approved to be used in field applications.  

There are quite a few other reasons that you may not want to use DEF on your lawn or garden. 

Urea fertilizer, which is a granular fertilizer that is pure urea has an NPK ratio of 46-0-0. It is pure nitrogen fertilizer. 

DEF is made of about 30% urea and the rest of the product is water, so it is an incredibly inefficient way to add nitrogen to your plants. 

DEF is a bit easier to store than granular urea. The solution can be stored for about a year but then it is recommended that it be discarded.

Urea is a granulated product and it is recommended that it be stored in low humidity for no longer than 6 months. 

Urea fertilizer is much more affordable and potent than DEF which is diluted urea.   

DEF As Fertilizer: Not A Good Choice

Can you use Diesel Exhaust Fluid as Fertilizer?

Diesel Exhaust Fluid is often abbreviated DEF. This is an additive that is added to large truck engines to change the composition of the exhaust produced by these trucks. 

DEF’s main ingredient is Urea, a popular fertilizer that is used in industrial agriculture. 

DEF is about 67% water, so it is not a good source of nitrogen for your lawn or garden. 

When considering using DEF as fertilizer you should do the math to understand the incredible difference in nitrogen concentration in each of these two products. 

Urea contains a little less than half a pound of nitrogen per pound of urea. DEF contains about a quarter pound of nitrogen per gallon. 

This makes urea the much more affordable choice. 

It is also important to note that DEF is manufactured to use as a fuel additive and it is not regulated for use in lawn and garden applications. 

Urea is manufactured as a fertilizer and food-grade urea is safe for use on edible crops. 

Is It Dangerous To Use DEF As Fertilizer?

DEF is made of urea and deionized water, so the ingredients appear to be harmless for lawn and garden use. 

However, DEF is not subject to inspection by the FDA and it is not required that they list all the ingredients in the product. 

DEF must be in a strict specific gravity as it passes over sensors in truck engines so the ingredients must be fairly pure, but the addition of other compounds is not outside the realm of possibility. 

While DEF is likely a simple solution of urea and water it is not regulated in the same way as food products. 

Urea is becoming a more expensive compound as most of the urea used in America is imported. This could impact the purity of some DEF on the market. 

Urea is not the only way to add nitrogen to the soil, there are several other nitrogen fertilizers available for purchase. 

Coffee grounds, compost, and other organic matter are also great choices for nitrogen amendment. It is even possible to use human urine to fertilize your garden. 

How Much Nitrogen is in DEF? 

The main argument against using DEF as fertilizer is that DEF is mostly water, around 67%. So when you are applying DEF you are applying only 30% nitrogen. 

At the time of writing 50 pounds of Urea is about $75 while 10 gallons of DEF is $78 and remember most of the DEF is water. 

50 pounds of Urea contains 23 pounds of nitrogen while 10 gallons of DEF contains 2.6 pounds of nitrogen.

When applying nitrogen to your lawn or soil be sure to test soil regularly to ensure you have a fairly balanced NPK ratio in your soil.  

Why Use Urea in Your Garden

Gardeners who have asked the question, “Can I use DEF in my garden?” are looking for a way to add nitrogen to their lawn or garden. 

Urea is a very inexpensive lawn and garden fertilizer. It is produced on a large scale globally and 90% of the produced urea is used in agriculture. 

This product is easy to transport and easy to use in industrial agriculture.

Urea is a low-cost way to amend soil that is lacking nitrogen. Lawns and some vegetables can benefit from supplemental nitrogen application. 

The best way to gauge the nitrogen needed is to understand the plants you are growing. 

Heavy feeders are plants that require a lot of nitrogen, beets are one example. Soil should be amended before and after growing heavy feeding crops. 

If your plants are showing signs of nitrogen deficiency like poor, stunted growth, light-colored leaves, or abnormal leaf formation, then you should add nitrogen well away from leaves. 

This type of fertilization is called side dressing when the fertilizer is added parallel to the crops being fed. 

Nitrogen on its own can cause leaf burns, and many nitrogen fertilizers are acidic and can cause damage to leaves. 

Be sure to test your soil before adding any nitrogen products as they can often increase soil acidity which can be harmful to many plants. 

Nitrogen Fertilizer To Use Instead of DEF 

Urea is often chosen as a cheap fertilizer to add nitrogen to lawns and gardens, but if it is not available you can safely use low-cost nitrogen fertilizers. 

Human Urine

Recent government studies have shown that gardeners can safely use their own urine to add nitrogen to the soil in their garden. 

Urine should be added to plants well away from leaves to prevent nitrogen burning. 

If possible check the PH of the mixture to avoid over-acidifying the soil. 

Coffee Grounds

Coffee grounds are often considered kitchen waste and it can be collected and added to compost piles, but the coffee grounds can be used alone to create a liquid fertilizer. 

To create a concentrated liquid nitrogen fertilizer collect coffee grounds in a large bucket and add water. 

This liquid can be used as a nitrogen-rich fertilizer. 

Coffee can be very acidic, so when possible check the PH before applying and apply well away from leaves to prevent burning. 

Blood Meal

Blood Meal is a good organic nitrogen fertilizer that is available at most big box stores. The NPK ratio is 12-0-0 and it also contributes other minerals to the soil. 

It is a slow-release fertilizer that remains in the soil for 1 to 4 months. 

While it is not as affordable as Urea fertilizers it has the added benefit of repelling some garden pests. 

It is known to repel squirrels and rabbits for many gardeners. 

Using DEF as Fertilizer

While a cursory look at the ingredients in DEF may seem like an appropriate fertilizer for lawns and gardens, however, it is not an efficient fertilizer and it is not regulated for use on lawns or in gardens. 

Urea, the main ingredient in DEF, is readily available for use as fertilizer at a much lower price. 

Urea in its pure form has an NPK ratio of 46-0-0 and is still one of the most affordable nitrogen fertilizers. 

DEF is only about 30% urea and the rest is water, so it is not an efficient way to enrich your soil and feed your plants. 

DEF is not regulated for use in agriculture and urea is more tightly regulated. This makes it a safer option for lawn and garden use.