Can You Mix Fertilizers? Everything You Need To Know


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Mixing and making your own fertilizer combinations might seem intimidating. Perhaps you are concerned about finding the right combinations for your fertilizing needs. Maybe you are worried about mixing caustic and dangerous chemicals.  

You can mix fertilizers if you follow a few basic guidelines. By finding the right balance of nutrients and testing the soil, you can ensure optimal plant growth. Always verify fertilizers are compatible with each other, as some components can cause adverse chemical reactions when mixed. 

In this article, we’ll explore everything you need to know about mixing fertilizers, including soil testing, the importance of ratios, safety, and mixing fertilizers. We’ll also take a closer look at the benefits and dangers of mixing fertilizers, the best types of fertilizers for mixing, and the nutrients needed for healthy plant growth. 

Benefits of Mixing Inorganic Fertilizers 

Benefits of mixing to make your fertilizer include saving money and flexibility to create the right blend for your horticultural needs. You can mix the fertilizers if they are composed of similar materials and types, such as combining a kind of granular with another granular, and then spread or spraying them together over your plants.

Let’s consider a mixing example. You’ve bought several types of inorganic fertilizers. One is designed to treat your lawn, and the other is homegrown tomatoes. You wonder if you can mix them and spread fertilizer all in one trip. 

First, check if the lawn fertilizer has a pesticide in it. If it does, it’s likely to harm or kill your vegetation. And, you may not want to worry about ingesting it from any fruit you grow. If it doesn’t, then you can mix the two fertilizers.

Consider the following: The lawn fertilizer contains a 30-10-20 ratio, and the tomato is 15-30-15. Using equal amounts of the two fertilizers, add the correlating numbers together for each nutrient and divide by 2 to determine your total nutrient ratios if mixed. It would look like this:

Lawn FertilizerTomato FertilizerTotal % in Mixture
Nitrogen301518%
Phosphorus103020%
Potassium201517.5%

The ratio that you get as the final total is the crucial factor to consider. You must determine if the final percentage will provide the appropriate nutrient balance for healthy plants.

Consider what you are trying to accomplish by mixing. Nitrogen promotes the growth of the leaves and stems for plants such as lettuce and cabbage. Phosphorus is used for flowering, which leads to fruit production. Potassium benefits the whole plant, especially the roots and flowers.

Your local gardening store or county extension can help you determine good ratios to use as well. As a general rule, certain types of plants benefit from the following ratios:

Type of Plant:Ratio Proportions:
Lawn/Grass4-1-2; 4-1-3, 3-1-2
Tomatoes/Peppers, Flowering/Fruiting1-2-1; 1-3-2
General Use (if flowers and leaves don’t need support)1-1-1

Mixing Organic With Non-Organic Fertilizers

Gardeners may desire to use organic alternatives for their fertilization needs. Again, you may need to reach out to your local gardening center or county extension to inquire if these are safe to mix with inorganic.

Keep in mind, you may not be able to determine the exact nutrient ratio in organic fertilizer. Therefore, when mixing it with a store-bought and premeasured fertilizer, it’s easy to accidentally give your plants too much of something.

If you decide to mix, use caution when doing so, and keep an eye on your plants to see if they’re thriving. If using organic alone, be sure to spread it evenly over the garden. Use 20-30 lbs (9-13.6 kg) for every 100 square feet (9.29 square meters) and work it into the soil.

The Dangers of Mixing Fertilizers

Some components of fertilizers are not compatible with mixing due to chemical reactions and solubility, including even in organic ones. 

There are charts and information that can be accessed to help you make good mixing decisions. For example, if a fertilizer contains ammonium nitrate, it can ignite a fire if mixed with flammable materials. It’s important to only mix materials together that are safe for you and the environment.

Best Types of Fertilizers for Mixing 

Novice and expert gardeners alike can find the best fertilizer for the needs of specific plants. Knowing which are best will help these plants grow sufficiently to be healthy and vibrant. Some different options and nutrients will impact the overall health of your plants.

Fertilizers can come in several forms, such as liquid, powdered, granular, and molded solids. 

Granular fertilizers are easy to spread on top of the soil and soak in the garden over time, releasing nutrients into the ground.

Liquid fertilizers are diluted with water and can easily be applied to plants with a hose attachment.  

Powdered forms of fertilizers can be sprinkled and spread by hand. Water is then poured on it to ensure absorption.

Molded solids are an innovative way to add fertilizer to plants. These often are a hard form; they will break apart over time when water is added. For example, fertilizer “spikes” can be placed next to the plant, as found on Amazon.com, called Tree & Shrub Fertilizer Plant Food Spikes (also available here on Walmart.com). These organic-based spikes, made with molasses, can be hammered in providing nitrogen, phosphorus, and potassium to trees, evergreen, and shrubs.

Inorganic Fertilizers

Inorganic fertilizers contain the proper nutrients within the chemical components of the fertilizer. In particular, options such as the Osmocote Smart-Release Plant Food Flower & Vegetable (available on Amazon.com, or here on Walmart.com) are good for those looking for quick and successful short-term growth. Sprinkle this on your perennials to feed them for up to four months for strong root development, flavorful vegetables, and colorful blooms.

Organic Fertilizers

Organic fertilizers are made with natural and organic materials such as compost, manure, and plant and animal products. This is a common choice as it’s easy to make your own at home. The raw materials provide many nutrients to plants and help build-up the health of the soil over time. 

However, exact nutrient percentages may not be available or even measurable, and this fertilizer will work more slowly. 

If you can’t make your own organic fertilizer, I recommend Liqui-Dirt Nano Powder All-Purpose Organic Complete Plant Food (available on Amazon.com) for indoor and outdoor plants. This product uses organic materials such as poultry litter, rabbit manure, bat guano, and gypsum. It makes 50 gallons (227.3 liters) worth of liquid fertilizer, and each gallon has 128 applications.

Nitrogen Fertilizers

Nitrogen is processed and cycled by living organisms naturally. Green plants and algae consume nitrates from the soil to build up DNA, RNA, and amino acids.  

Nitrogen processed chemically with hydrogen to make ammonia is used with fertilizer to promote growth, vibrant colors, and increased crop yields for your plants. In particular, nitrogen benefits plants during the middle stages of their lifespan to grow large and produce more leaves. Both inorganic and organic fertilizers will have nitrogen in them.

A lack of nitrogen causes lower leaves to be yellow, and the whole plant will turn light green. For more information about fertilizers high in Nitrogen check out my article here.

Phosphate Fertilizers

Phosphorus is essential for all living things, and it is a backbone of DNA and RNA and responsible for energy transfer in cells.

Phosphorus is a nutrient that plants need throughout their entire growth cycle for healthy fruit and vibrant blooms. This element will help strengthen both the stems and root systems of plants. Since phosphorus is both long-lasting and slow-acting, it’s a good idea to put it in the soil before planting.

A deficiency in phosphorus will present poor flowering, fruiting, and stunted growth.

Potassium Fertilizers

Potassium is another essential nutrient for all living things. It is found in all cells and is vital for balancing fluids and electrolytes.

Plants get potassium or “potash” directly from the soil and can be in all of their cells. In the agriculture industry, harvesting depletes potassium from the soil, making it necessary to use fertilizers to add it back in for future crops. Potassium will encourage deep and strong roots and is protective if the plant lacks other nutrients.

Potassium is also essential for photosynthesis and can slow down infectious plant diseases. This fertilizer should be placed near the root system of the plant. If it does not have enough potassium, the plant’s leaves may turn yellow or brown, falling off over time if there is a deficiency.

It’s important to note that nutrients and fertilizer may not be the problem if plants are healthy yet still growing incorrectly. It’s important to investigate the matter, as this could be due to a number of reasons, including:

  • The soil is poorly draining
  • Plants have improper shade and lighting
  • Weeds or tree roots are competing for nutrients

For more information about fertilizers high in Potassium check out my article here.

Preparing Proper Ratios for Mixing Fertilizers

Before beginning, gather all tools and materials for mixing, including buckets, a water source, something to stir the mixture, and a measuring cup or scale. In case of spills and for proper air ventilation, mixing and preparation should be done outside and away from pets and children.  

Also, be sure to read any of the safety precautions listed on the packaging. It’s recommended to wear protective gloves and eyewear. When done, store remaining fertilizer away from pets and children in a sealed container or bag and clean tools used with care according to package instructions.

Photo 240856076 | © Anatol1973 | Dreamstime.com

Find the Right Balance of Nutrient Ratios

Know what your plants’ needs are. You may need to research this or refer to the label on the plant or seeds you bought.

A complete fertilizer has all three nutrients denoted on the packaging by numbers. This fertilizer analysis indicates the percent of nutrients always in this order: nitrogen – phosphorus – potassium. 

For example, a bag of 10-20-10 fertilizer weighing 100 lbs (45.35 kg) has 10 lbs (4.53 kg) of nitrogen, 20 lbs (9.07 kg) of phosphorus, and 10 lbs (4.53 kg) of potassium, with the nutrients totalling 40 lbs(18.14 kg). The remaining 60 lbs (27.21 kg) is made of filler materials, like sand, rice hulls, or perlite. 

Gardeners will find that good fertilizer for their growing needs should have twice as much phosphorus as nitrogen or potassium. These are easy to find and may list ratios 10-20-10 or 12-24-12. Soils may already have enough potassium, but a slight increase in their lifecycle should be okay.

It’s important to look at the cost of purchased fertilizer and the price per pound of the nutrients. Notably, bulk containers and higher analysis fertilizers are generally cheaper. 

For example, there’s no cost difference between a 10-20-10 and a 5-10-5 mix for a 50 lb (22.67 kg) bag of fertilizer, however, the 10-20-10 has double the amount of nutrients.

Test the Soil To Verify It’s Good for Your Plants To Grow In

Test your soil every two years or so. Ask your local gardening store or county extension where and how to get your sample tested. Testing soil in midwinter, if possible in your climate, can help you prepare for spring planting.

Testing is an excellent way to discover what your soil already has and what you might need to grow healthy plants. Collect a moist soil sample by digging about 6 inches (15.24 cm) in the ground. Collect samples from several locations and mix it all together in a large container. Remove about ½ pint of this soil mixture for testing.

If you decide not to test the soil, you can use 2 lbs (0.9 kg) for sandy soil and 3 lbs (1.36 kg) for clay-based soil of 10-20-10 fertilizer for every 100 square feet (9.29 square meter) of garden space. 

Two cups of fertilizer will weigh about 1 pound (0.45 kg); however, keep the ratios in mind. 2 lbs (0.9 kg) of a 5-10-5 fertilizer will supply upwards of 1 ib (0.45 kg) of nitrogen in a 10-20-10 fertilizer. You want to make sure you’re still giving your plants the right and proper amount of nutrients.

Final Thoughts

Novice and master gardeners can help give their plants soil for them to thrive in with the right kind of fertilizer. In general, most fertilizers are okay to mix but do so with informed caution in mind. When plants have the right blend of nutrients, they can grow beautiful blooms, healthy fruits and vegetables, and eye-pleasing vegetation for all to enjoy.

Lars

I am always happy to share all my knowledge about how to keep your garden in good condition and make it special.

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