When To Use 10-20-10 Fertilizer? | How To Use It

If you’ve recently visited the lawn and garden section of your favorite home improvement store, you have likely seen a range of fertilizers, including liquid, granules, sticks, and powders. Numbers on packaging represent nutrient ratios, but how do you know which one to pick?

Read on to learn when and how to apply the versatile 10-20-10 fertilizer to your plants, trees, and grass.

Understanding 10-20-10 Fertilizer Labels

Plants require a higher concentration of nitrogen, phosphorus, and potassium compared to other soil nutrients. These three elements are known as macronutrients and are essential for plants to thrive.

Nitrogen encourages leafy development, phosphorus aids in root production and reproductive processes, and potassium encourages growth and stress tolerance. 

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N-P-K Ratio

According to The Fertilizer Institute, plants require 17 nutrients to thrive and reproduce. But the significance of the primary macronutrients means that almost all fertilizers will include them. 

On fertilizer labels, these nutrients are shown as an N-P-K ratio. The figures in this ratio explain their relative quantities as a percentage by weight.

In a 10-20-10 fertilizer, the macronutrient content by weight is:

  • 10% Nitrogen (N)
  • 20% Phosphorus (P)
  • 10% Potassium (K)

Fertilizer with an N-P-K ratio of 10-20-10 contains twice as much phosphorus in total than nitrogen or potassium.


Plants need sufficient nitrogen for healthy protein production. Low nitrogen levels cause issues like leaf yellowing. At the same time, too much nitrogen can be deadly.

In a fertilizer labeled 10-20-10, nitrogen makes up 10% of the total formula.

To calculate how much nitrogen is in a 10lb bag of 10-20-10, multiply 10 x 0.10 = 1. In a 10lb bag of this fertilizer, there is 1lb of nitrogen.


Phosphorus, often known as phosphate, aids in photosynthesis and helps plants use and store energy. Low phosphorus levels in the soil can cause stunted growth and interfere with flower and fruit development.

Phosphorus is the most plentiful element in a 10-20-10 fertilizer formula. It makes up 20% of the total formula by weight.

To calculate how much phosphorus is in a 10lb bag, multiply 10 x 0.20 = 2. In a 10lb bag of this type of fertilizer, there is 2lb of phosphorus.


Potassium gives plants the strength to resist disease, extreme temperatures, and drought. It also plays a key role in root system health. Similarly to nitrogen, low potassium levels may cause leaf yellowing.

In a 10-20-10 fertilizer, potassium makes up 10% of the total weight.

As with nitrogen, to calculate how much potassium is in a 10lb bag, multiply 10 x 0.10 = 1. In a 10lb bag of fertilizer, there is 1lb of potassium. 

Conducting a Soil Test

Regardless of what you’re planting, soil testing is key to the success of your garden. Analyzing the soil composition allows you to better calculate what nutrients your plants require during the growing season and determine the success of future nutrient management strategies. You’ll also save money and protect your garden health by avoiding the use of fertilizer that isn’t needed.

It’s usually best to test your soil pH and nutrient levels after harvest but before any fall fertilizer applications. This is when the average garden is most depleted of nutrients. To get the most accurate comparison of your soil, test at the same time each year. 

Avoid soil testing near old feedlots, homesteads, ponds, and within 50 feet of gravel roads, since these sites may throw off your results.

What Is 10-20-10 Fertilizer Used For?

Gardeners looking to stimulate root growth can often benefit from using a 10-20-10 fertilizer. There are also a number of plants that benefit from high-phosphorus fertilizers in general, such as fruit trees and flowering annuals.

Using 10-20-10 Fertilizer On Seedlings

Seedlings have enough energy to produce the first set of leaves. Once the second set of ‘true’ leaves appears, a 10-20-10 fertilizer mix can be diluted with water and used at half-strength. 

This will aid in establishing a strong and healthy root system without causing root burn.

10-20-10 vs 10-10-10 Fertilizer

Nitrogen, phosphorus, and potassium are all present in equal proportions in a 10-10-10 fertilizer ratio. These fertilizers have a balanced nutritional profile and can be appropriate for anything from your lawn to your houseplants. 

Meanwhile, a 10-20-10 fertilizer has double the amount of phosphorus compared to a 10-10-10 formula. Since phosphorous aids in the production of fruits and flowers and also supports root development, a 10-20-10 fertilizer is better suited for your garden than your lawn. 

How and When To Use 10-20-10 Fertilizer

Depending on what you’re fertilizing, you’ll need to apply the mix in different ways. Before applying any fertilizer, always read the directions.

Lawn and Grass

Use a broadcast fertilizer and water in 7 to 10 pounds of fertilizer per 1,000 square feet of established lawn at the start of the growing season to jump-start root growth. For the remainder of the season and into the fall and winter, switch to a fertilizer with a lower ratio of phosphorus.

New Seeded Lawns

Before laying down sod or seeding soil, apply fertilizer at a rate of 10lb per 1,000 square feet. This will help to establish a root system for your lawn early on.

Trees and Shrubs

Apply ½ lb of fertilizer per inch of trunk diameter under the tree limbs. This application should be repeated in early spring and late summer.

Fertilizer is most effective for trees when worked deep into the soil. Make holes 3 to 4 feet apart around the circumference of the tree and pour ½ cup into each hole. This method of application should only be done in the spring. Again, this is to benefit the root system.


Flowering houseplants do best with high-phosphorous fertilizer, so a 10-20-10 ratio is perfect for stimulating growth and encouraging flowers during the growing season. 

Always make sure to check the packaging for application instructions, as it is possible to over-fertilize houseplants. Avoid using fertilizer when your houseplant is in winter dormancy.


Flower fertilizer applications need a more careful approach to avoid disturbing the roots. Before planting, apply 1lb of fertilizer per 100 square feet and mix it well into the soil. 

A high-phosphorus fertilizer is perfect for when flowers are established. Apply 1lb of fertilizer per 100 square feet of topsoil and mix gently every 3 to 4 months. Make sure to water in any application of fertilizer.

Vegetable Gardens

Apply 15lb per 1,000 square feet to flowering vegetable plants such as tomatoes, squash, and pumpkins. The initial application can be mixed and distributed before the season starts.

After 4 to 5 weeks, repeat the application by spreading 5 to 7lb per 1,000 square feet of garden vegetables:

  • Apply fertilizer with a broadcaster to high-nitrogen plants like potatoes, corn, or onions.
  • Apply fertilizer directly to the soil and mix it in when feeding tomatoes, squash, or beans.

Fertilizer Types

You can pick from a range of 10-20-10 fertilizers with various delivery methods and reapplication times, depending on what suits your needs and gardening style best.

Liquid Concentrate

Liquid concentrate fertilizer can either be purchased as a ready-mixed formula or as a concentrate that must be diluted in water before application. Apply it directly to the soil through a hose sprayer or a watering can. 

This type of fertilizer delivers nutrients to the roots and foliage of plants quickly. It requires regular applications to maintain the effects. 

Liquid concentrate is great for use on outdoor plants as well as houseplants although it is prone to run-off. This is where excess liquid is not absorbed and can seep away onto nearby paths, surrounding plants, or – more seriously – into nearby water sources.

Water-Soluble Powder

A water-soluble powder needs to be mixed into water before being applied to plants via a watering can. I’ve also seen hose-end sprayer systems that are compatible with powdered fertilizer.

Powders tend to be more cost-effective when compared to liquids but the outcome is similar. — i.e., they get to work quickly but need applying more often and can be prone to run-off. 

Slow-Release Granules

Slow-release granules are often the most cost-effective method of fertilizing. They are easy to apply – either by hand or with a broadcast spreader — and they break down over time.

Typically, they can take a week to produce any apparent benefits since they are slow-release. But they require less frequent applications than liquid concentrates as they continue working for up to 8 months.

Fertilizer Spikes

Fertilizer spikes eliminate the need to store and measure fertilizer. You simply press them down into damp soil and, as they decompose, nutrients are released into the surrounding area. 

They are best used in small areas like pots or around small trees. Larger plants require more spikes, so they tend to weigh in at the more expensive end of fertilizing. 

The good news is that they can last for between 1 and 3 months and are mess-free. They do need to be placed equally apart and kept away from roots to prevent fertilizer burn.

High-Phosphorus Fertilizer FAQs