Applying fertilizer can be tricky. You want to apply the nutrients your plants need without applying more than necessary. And that means you need to choose the right type of fertilizer.
The trouble is that hundreds of different fertilizers are out there, and it can be difficult to know when to use one versus the other.
In this article, I’m going to cover 0-20-20 fertilizer. When you’re done reading, you’ll know when and how to apply this fertilizer.
A 0-20-20 fertilizer contains 0% nitrogen, 20% phosphorus as phosphate (P₂O₅), and 20% potassium as potash (K₂O) by weight. It’s important to note that these 0-20-20 numbers only refer to the amount of nitrogen, phosphorus, and potassium—they do not tell us anything about other nutrients the fertilizer may contain.
Want to know more about the NPK ratio and what it means? Then head on over to our article on fertilizer numbers.
As mentioned above, a 0-20-20 fertilizer won’t supply any nitrogen, but it will supply equal amounts of phosphorus and potassium.
If you know anything about plants, you probably know that plants need a lot of nitrogen to thrive. This element is a major component of chlorophyll, enzymes, and structural proteins, which means it’s essential for completing photosynthesis, building plant tissue, and fending against disease.
So, why would you want to supply a fertilizer without any nitrogen? Well, the soil might already contain enough nitrogen, or plants may not need nitrogen.
Let’s look at the first example: nitrogen-rich soil. While fertilizer is one way to apply nitrogen to the soil, it’s not the only way. The roots of legumes like peas, beans, clover, and vetch harbor bacteria called rhizobia.
The rhizobia capture gaseous nitrogen (N₂) from the air and convert it into ammonia (NH₃). Plants can then take up this form of nitrogen and use it to build tissues and complete essential processes.
That means if you plant a cover crop of clover or peas or planted beans in an area of your garden, the soil might be rich in nitrogen. In this case, you may need to apply phosphorus and potassium but not nitrogen. And that’s where 0-20-20 fertilizer comes in.
Then there’s the second example: plants don’t need nitrogen. This may occur in the fall when plants are getting ready to enter dormancy.
In this instance, plants may not need nitrogen since it helps with vegetative growth. However, they may benefit from potassium and phosphorus to help them deal with colder temperatures as well as diseases and pests.
As mentioned above, you’ll only want to apply 0-20-20 fertilizer when the soil already contains nitrogen or your plants don’t need nitrogen. Most plants will perform better during the growing season if you apply a balanced fertilizer like 12-12-12 or 19-19-19.
With that said, here’s how to apply 0-20-20 fertilizer to various types of plants.
If you’re planting a mixed vegetable garden, I always recommend taking a soil test before fertilizing. This can give you an understanding of the nutrients already present in the soil, allowing you to apply the nutrients your soil needs while not applying the nutrients it doesn’t.
A soil test also allows you to determine the soil pH, which impacts whether or not nutrients are available to plants.
If your soil test indicates that your soil has lots of nitrogen but needs phosphorus and potassium, it may be beneficial to apply a 0-20-20 fertilizer. However, you should only apply this fertilizer if your soil needs equal, or near equal, amounts of phosphorus and potassium.
If you don’t take a soil test, you can use past land use practices to determine whether or not 0-20-20 would be an appropriate fertilizer to apply. Leguminous cover crops like clover, winter peas, and hairy vetch will add nitrogen to the soil and make it unnecessary to apply nitrogen fertilizer.
Therefore, if you’ve just mowed, crimped, or otherwise killed a leguminous cover crop, you may want to apply a 0-20-20 fertilizer.
If you’ve decided that it makes sense to apply a nitrogen-free fertilizer, you’ll want to use your soil test recommendations to determine how much 0-20-20 to apply. If you don’t take a soil test, you can start by applying two pounds of 0-20-20 fertilizer per 1,000 square feet.
The best time to apply this fertilizer is in the spring before you plant vegetables. Use your hands or a fertilizer spreader to evenly broadcast the fertilizer across the soil surface. If possible, apply the fertilizer shortly before it rains or irrigate after application.
Read here to know more information about fertilizing vegetable gardens.
I do not recommend applying 0-20-20 fertilizer to lawns. That’s because grasses benefit from a fertilizer that’s high in nitrogen and free from phosphorus.
You may hear some people say that 0-20-20 is a good fertilizer to winterize your lawn, but this isn’t the case. Even in the winter, lawns do not require the large amount of phosphorus that a 0-20-20 fertilizer supplies.
The best option for winterizing your lawn depends on the type of grass you’re growing. Cool-season grasses can benefit from a fertilizer with an NPK ratio similar to 30-0-4, and cool-season grasses will do better with a product with an NPK ratio of 8-0-20.
Most houseplants are sensitive to the high level of nutrients found in 0-20-20 fertilizers. Additionally, houseplants benefit from a fertilizer with nitrogen. Therefore, I don’t recommend you apply this fertilizer to houseplants.
A better option for houseplants is a fertilizer with an NPK ratio of 1-1-1 or 2-2-2.
Like with the above examples, you should only apply 0-20-20 fertilizer to trees and shrubs if the soil has sufficient nitrogen but lacks phosphorus and potassium.
This may occur if you plant a leguminous cover crop like red clover or hairy vetch around your woody plants. As these legumes grow, they partner with rhizobia to capture nitrogen from the atmosphere and convert it into a form that plants can take up.
While the legumes will use some of the nitrogen, the remainder will be released into the soil where other plants (like trees and shrubs) can take it up.
If you determine that your soil contains enough nitrogen for your trees and shrubs, the next step is to figure out how much 0-20-20 you should apply. The best way to do this is to take a soil taste and then look at the results.
However, if you’d like to forgo a soil test, you can follow some basic recommendations. Apply between two and three pounds of 0-20-20 fertilizer for every 1,000 square feet of trees and/or shrubs.
And remember that the roots of these woody plants extend outward at least as wide as the plants’ canopies. That means that while a single tree’s trunk may only cover five square feet, its root system may extend over hundreds of square feet!
As for the time to fertilize, it depends. You can fertilize newly planted trees and shrubs once a year in the spring. However, more established plants may only require fertilizer every two to three years.
To reiterate, legumes like clover can produce their own nitrogen due to their relationship with rhizobia. That means you typically do not need to apply nitrogen fertilizer to clover.
However, if you want to grow a lush clover stand for livestock or wildlife, you should still fertilize your clover crop with a nitrogen-free fertilizer. One such product is a 0-20-20 fertilizer.
The best time to apply a 0-20-20 fertilizer to clover is before or during seed planting. One application at this time is sufficient.
Application rates will vary depending on the amount of potassium and phosphorus already present in the soil. However, you can expect to apply between 100 and 200 pounds of 0-20-20 fertilizer per acre of clover.
The best way to evenly broadcast the fertilizer is to use a spreader.
I’ll start by stating that 0-20-20 isn’t a common type of fertilizer. It’s not as easy to find as fertilizers with NPK ratios like 20-20-20 or 20-0-0. That’s because it’s rare that you’ll need to apply this much phosphorus and potassium without adding any nitrogen.
With that said, the 0-20-20 products you find will typically be synthetic granular fertilizers.
Synthetic means that the products are synthesized in a laboratory rather than made from naturally occurring materials. Granular refers to the fact that the product is made up of tiny granules.
Typically, these granules will dissolve and release nutrients into the soil shortly after they become wet.
This fertilizer supplies plants with 20% phosphorus, 20% potassium, and 0% nitrogen. It is available in a 50-pound bag and is produced in the United States.
Since this is a granular product, the best way to apply it is with a fertilizer spreader. However, if you are only fertilizing a small area, you can broadcast the product using your hands.
While you may hear people say it’s good to apply a 0-20-20 fertilizer as winter arrives, this isn’t the case. Most plants do not require fertilization in the late fall and winter.
If you decide your plants need a boost of fertilizer during the late fall, applying a fertilizer with an NPK ratio similar to 5-10-10 is better.
Yes! If you can’t find a premixed 0-20-20 fertilizer, you can combine phosphorus and potassium fertilizers to form a 0-20-20 fertilizer. For example, combining equal parts 0-40-0 and 0-0-40 fertilizer will allow you to form a 0-20-20 fertilizer.
No, a 0-20-20 fertilizer does not contain nitrogen. However, it does contain phosphorus and potassium.
Since 0-20-20 fertilizer isn’t a commonly used product, it isn’t always easy to find online. However, you may be able to find it for sale at Ag Care Products.
As you’ve read, 0-20-20 isn’t the best type of fertilizer for every application. Often, plants can benefit from a nitrogen-rich fertilizer or a product with a different NPK ratio.