When to use 10-20-10 Fertilizer? | How to Use it

If you have 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 powder. 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 needed for plants to thrive.

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

N-P-K Ratio

In total 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.

So for a 10-20-10 fertilizer, by weight, this ratio equates to:

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

Higher numbers mean higher concentrations, so this particular blend is heavy on phosphorus.

Nitrogen 

Protein production requires nitrogen. Low nitrogen levels cause lower leaf yellowing, and too much can kill the plant.

When this fertilizer is properly balanced, nitrogen makes up 10% by weight. To calculate how much nitrogen is in a 10lb bag, multiply 10 x 0.10 = 1. In a 10lb bag, there is 1lb of nitrogen.

Phosphorus

Phosphorus, often known as phosphate, aids photosynthesis and helps plants efficiently use and store energy. Low phosphorus levels in the soil can cause stunted growth and issues producing flowers or fruit.

Phosphorus is the most plentiful element in this particular formula. It makes up 20% by weight. To calculate how much phosphorus is in a 10lb bag, multiply 10 x 0.20 = 2. In a 10lb bag of this formulated mix, there is 2lb of phosphorus.

Potassium

Potassium gives plants strength to resist disease, wilting from extreme temperatures, and fortifies the root system. Similar to nitrogen, low potassium levels can cause leaf yellowing as well.

In this mixture, potassium makes up 10% by weight. 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. 

Testing Soil

Whatever you’re planting, soil testing is important to the health of your next yield. Profiling your soil allows you to better evaluate what nutrients your plants require during the growing season and analyze the success of nutrient management approaches. You’ll also save money by avoiding the distribution of fertilizer that isn’t needed.

Typically, it’s best to test your soil for pH and nutrient density after harvest and before fall fertilizer treatments, when it 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 bias your results.

What is 10-20-10 Fertilizer Used For?

Gardeners looking to stimulate root growth can benefit from a complete 10-20-10 fertilizer with twice as much phosphorus levels as nitrogen and potassium. Here’s a look at that in closer detail.

10-20-10 Fertilizer for 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 be sufficient to help establish a strong and healthy root system without causing root burn.

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

Because plants have various nutritional requirements, multiple formulations are available. 

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 your lawn or for houseplants. 

A 10-20-10 fertilizer has double the amount of phosphorus compared to the nitrogen and potassium in the blend. 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 7-10 pounds per 1000 square feet of your established lawn at the start of the growing season to get root growth underway. For the remainder of the season and into the fall and in winter, switch to a fertilizer with a lower ratio of phosphorus.

New Seeded Lawns

Before laying down sod or seeding soil, apply fertilizer at 10 lbs per 1000 square feet. This will help to establish a root system for your lawn.

Trees and Shrubs

Apply 1/2 lb of surface fertilizer per inch of the trunk’s diameter under the tree limbs. This surface fertilizer method should be repeated in early spring and late summer.

Fertilizer is more effective for trees if a deep application is done. Make holes 3-4 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.

Houseplants

Flowering houseplants do best with high phosphorous concentrations in fertilizer, so 10-20-10 is perfect to stimulate growth and encourage flowering during the growing season. 

Always make sure to check the packaging for application instructions, as it is possible to over-fertilize houseplants and avoid using them when your house plant is in winter dormancy.

Flowers

Flower applications need a more careful technique to avoid disturbing the roots. Before planting, apply 1 lb 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 1 lb of fertilizer per 100 square feet of topsoil and mix gently every 3-4 months. Make sure to water in any application of fertilizer.

Vegetable Gardens

Apply 15 pounds per 1000 square feet to flowering vegetable plants such as tomatoes, squash, and pumpkin. This can be mixed and watered before seeding. 

After 4-5 weeks, repeat the application by spreading 5-7 lbs per 1000 square feet of garden vegetables:

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

Fertilizer Type

You can pick from a range of 10-20-10 fertilizer types based on delivery method and reapplication time 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 pot. 

This type of fertilizer delivers nutrients to the roots and foliage of plants quickly and 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 wither into the base of a plant pot or onto nearby paths, surrounding plants, or – more seriously – into nearby water sources.

Water Soluble Powder

A water-soluble powder needs to be mixed into the water before being applied to plants via a watering can. 

These 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 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 concentrate as they continue working for between 4 weeks and 3 months.

Fertilizer Spikes

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

They are best used in small areas like houseplants or small trees and plants in the yard because larger species require more spikes and 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 they are mess-free. They do need to be placed equally apart and away from roots to avoid fertilizer burn.

10-20-10 Fertilizer FAQs

In Review

10-20-10 fertilizers are effective at supplying nutrients to your garden, trees, flowers, and houseplants. This combination offers a wide range of applications, making it appropriate for usage at all stages of plant development.