When to Use 20-10-20 Fertilizer | General Purpose

Fertilizer products are used to provide measured nutrition to your houseplants, flower beds, gardens, trees, and shrubs. But not all fertilizers are suitable for all applications. 

This article covers everything you need to know about 20-10-20 fertilizer. From what it is, what it’s suitable for, how to use it, and where to buy it.

Understanding 20-10-20 Fertilizer Label

Some specialty fertilizers are labeled for a specific type of plant (orchid food, for example). But in the absence of specific labeling for a particular tree or plant, most other fertilizers are labeled with three numbers. 

These number labels, such as 20-10-20, 14-14-14, etc., identify the quantity of the primary nutrients found in the fertilizer. 

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N-P-K Ratio

N-P-K stands for nitrogen, phosphorus, and potassium. These are the primary nutrients that plants need to survive and thrive. The three numbers in the N-P-K ratio describe the total percentage ratio of each nutrient in the fertilizer. 

20-10-20 fertilizer, for example, contains 20 percent nitrogen, 10 percent phosphorus, and 20 percent potassium. You’ll notice those three numbers add up to only 50 percent. The remaining 50 percent of the fertilizer volume comprises other micronutrients, inactive ingredients, and fillers.

Compare those numbers to another fertilizer, such as 10-5-10, which is 10 percent nitrogen, 5 percent phosphorus, and 10 percent potassium. The nutrients’ ratios to one another are the same, but they’re only half as concentrated compared to the 20-10-20 fertilizer.

All plants need all three nutrients to thrive, and most require supplementation through fertilizer of some sort, especially if soil and growing conditions are anything less than completely favorable. 

How much of each nutrient they need will depend a lot on the type of plant, soil nutrition, as well as weather, and water conditions. What’s more, it is possible to give them too much.

Here’s everything you need to know about nitrogen, phosphorus, and potassium and how they can help (or hurt) certain plants. It is aimed to help you decide and understand what fertilizer ratio is best for your garden.


Nitrogen is responsible for producing proteins, and amino acids, and supporting the process of chlorophyll production and photosynthesis in plants. 

It’s also necessary for plant cell formation. Nitrogen deficiency in plants leads to stunted growth, early leaf death, and a sickly yellowish-green coloration. 

On the other hand, too much nitrogen can cause nitrogen toxicity in plants. Symptoms of nitrogen toxicity include cupped, claw-like leaves, unusually dark green foliage, and slow growth. Leaves may turn yellow, get crispy, and die.


Phosphorus is responsible for metabolism, protein synthesis, and cell formation in plants. This nutrient is absorbed only through the roots of the plant. Lack of phosphorus can cause plants to produce smaller, unusually dark leaves, lack root growth, and reduced bud and shoot growth.

Too much phosphorus is not a problem in itself, but it can cause other nutrient deficiencies. Excess phosphorus interferes with a plant’s ability to absorb iron and zinc, leading to a deficiency in these nutrients. 

Iron deficiency causes the leaf tissue to turn yellow while the veins stay green. Zinc deficiency causes plant tissue to bleach. These symptoms in plants could suggest an underlying issue with excess phosphorus.


Potassium is responsible for enzyme activity and water regulation in plants. In particular, potassium helps plants retain water and resist wilting on hot, dry days. It also helps to build resilience against pests and diseases and damage in freezing temperatures.

The primary sign of potassium deficiency in plants is a tendency to wilt, even in mild temperatures, but especially in the heat.

Like phosphorus, potassium itself is not harmful to plants. However, excess potassium can make it difficult for plants to absorb nitrogen, calcium, and magnesium, causing deficiencies in other nutrients.

What is 20-10-20 Fertilizer Used On?

20-10-20 fertilizer is great for trees, especially fruit trees, and other hardy, leafy shrubs. However, the nutrient ratio in 20-10-20 fertilizer is less useful for flower gardens and houseplants, which usually need either more prosperity to help with bud development or more balanced nutrition respectively.

Identifying any soil deficiencies by using a soil test kit is always a good place to start before you begin planting or using any form of fertilizer. The test results will help you understand any nutrient shortfall or pH imbalance that can then be corrected either by fertilizer or soil amendments.

Here’s more on what you should know about using 20-10-20 fertilizer in and around your yard or garden.

Trees and Shrubs

The high nitrogen ratio in 20-10-20 fertilizer is excellent for keeping the foliage of trees and woody shrubs looking healthy and growing well. These plants consume more nitrogen than others, and therefore this nutrient needs to be replenished regularly. 

On the other hand, they don’t consume a lot of phosphorus, so the lower level of this nutrient in 20-10-20 fertilizer reduces the risk of other deficiencies caused by too much phosphorus in the soil.

Fruit Trees

Potassium is essential to the production of big, healthy fruit that is disease and pest free, so the high potassium level in 20-10-20 fertilizer is ideal for fruit trees, especially apple, cherry, pear, and prune.

Flower Borders

Generally speaking, most flowers respond well to a balanced fertilizer. 20-10-20 fertilizer may benefit a flower border that’s significantly deficient in nitrogen and potassium but stick to a more balanced 14-14-14 Fertilizer or similar for flowers unless you’re aware of a deficiency.

Vegetable Gardens

Non-flowering vegetables like sweet corn and leafy greens thrive on fertilizers with higher nitrogen levels, such as 20-10-10. 

However, as with fruit trees, producing large, colorful fruiting vegetables requires a healthy dose of potassium that can be found in 20-10-20 fertilizers.


The ratio between the nutrients in 20-10-20 fertilizers (high nitrogen and potassium, low phosphorus) is suitable for most houseplants, but it’s likely too concentrated. Go with something less concentrated like 1-1-1 or even a diluted 10-10-10 fertilizer for more delicate potted indoor plants.

Lawn and Grass

The high nitrogen levels in 20-10-20 fertilizer make plants greener, which is excellent for grasses. This fertilizer is a good choice when feeding lawns and grasses in the Fall as the added potassium will help protect against winter frosts and help build resilience during dormancy against pests and diseases.

When fertilizing lawns and grasses in springtime, opt for higher nitrogen and higher phosphorous fertilizer. This will encourage healthy growth both in the blades of grass and the roots as well as add vibrancy and color to your lawn.

How and When to Use 20-10-20 Fertilizer

There’s a lot of guidance that recommends using certain fertilizers for specific plants on a regular schedule or at a particular time of year. But the only real way to know how to supplement your garden is to have your soil tested.

A soil test will give you an accurate representation of the nutrient levels in your soil, so you’ll know how to treat and feed your plants. If your soil’s nitrogen and potassium levels are lower than the phosphorus level, 20-10-20 fertilizer can get them back in alignment.

You can buy at-home soil testing kits for basic information about your soil’s nitrogen, phosphorus, and potassium levels. Or, for more detailed information and guidance, contact your local agricultural cooperative extension

The United States Department of Agriculture (USDA) partners with local colleges to offer agricultural information and services to residents and farmers for free. They can test your soil and give you detailed information on any specific gardening requirements and specifications in your region.

Can You Use Too Much 20-10-20 Fertilizer?

Yes, you can use too much 20-10-20 fertilizer. 20-10-20 fertilizer has a higher concentration of nitrogen and potassium than phosphorus. Using more than the recommended amount of 20-10-20 fertilizer can cause nitrogen and potassium to build up in the soil.

Excess nitrogen can lead to nitrogen toxicity, inhibiting plant growth and increasing leaf death. Too much potassium, while not itself toxic to plants, can cause a deficiency in other essential nutrients, such as nitrogen, calcium, and magnesium.

If in doubt about quantities and measurements, always refer to the manufacturer’s instructions and never exceed the recommended dosage. Using too much fertilizer can lead to root and leaf burn.

Fertilizer Types

Synthetic fertilizers (as opposed to organic fertilizers like manure and compost) come in several forms, each with advantages and disadvantages. 

Some distribute nutrients more evenly but can be inconvenient to apply. Others are easy to apply but may result in uneven coverage. Here’s what you need to know about the different types of fertilizer products that are currently available to buy.

Liquid Concentrate

As the name suggests, liquid concentrate is a concentrated fertilizer in liquid form that must be diluted in water according to the product instructions before application. 

Liquid concentrate fertilizers saturate the soil around the plant roots, making the nutrients easier and more quickly absorbed compared to dry fertilizer products.

Liquid concentrate fertilizer is easy to apply to small houseplants and garden plots. Applying liquid fertilizer to larger gardens and farms generally requires specialized equipment such as a hose attachment, which can be costly.

The disadvantage of liquids is the potential runoff that can occur by leakage into water supplies causing contamination to local water sources. 

Water-Soluble Powder

Water-soluble powder fertilizers are highly concentrated fertilizers that also need to be diluted in water according to the product directions before application. 

Once diluted, water-soluble powder fertilizers behave the same as liquid concentrate fertilizers, with the same advantages and disadvantages.

Slow-Release Granules

Slow-release granules are a dry fertilizer that you can spread over the soil’s surface or gently mix in. Often, they need to be activated with water in order for them to start breaking down in the soil. 

Full absorption into the soil and through the roots of plants can take anything from 4 weeks to 3 months depending on specific product types.

Granules are easy to spread over large gardens and lawns using a spreader that broadcasts products evenly. For larger plots broadcasting can be done by hand albeit usually less evenly.   

The downside of granules is that the mixture can sometimes separate in the bag or spreader, causing an improper balance of nutrients. This can lead to a nutrient deficiency on the one hand and “hot spots,” or highly concentrated fertilizer zones that can cause fertilizer burn, on the other.

Fertilizer Spikes

Fertilizer spikes are molded fertilizer stakes that you can push into the soil. They provide a slow release of fertilizer into the surrounding area and work in a similar way to granules. 

This is a simple, one-step solution for trees, shrubs, and potted plants. They are convenient, mess-free, and odorless.

Fertilizer spikes are usually less effective in garden plots, flower beds, and larger plots. Because they concentrate all the fertilizer in one spot, only the roots directly in contact with the spike will absorb the nutrients. 

20-10-20 General Purpose Fertilizer FAQs

Here’s one additional question you might have about buying and using 20-10-20 fertilizer.

Final Thoughts

20-10-20 fertilizer gives your soil an all-around boost of nutrients, with an extra dose of nitrogen and phosphorus. 

While 20-10-20 fertilizer is generally good for fruit trees, vegetable gardens, and grasses in Autumn, have your soil tested to determine what it needs. Bear in mind that you can give your plants too much of a good thing when it comes to fertilizer.