When to Use 20-20-20 Fertilizer? | How to Use Triple 20

When it comes to any new gardening project, whether that’s laying new turf, setting up an allotment, or digging a border, it’s important that your soil is as fertile as possible so that plants get the best start.

In an ideal world, your soil will have been cultivated with a ton of well-aged compost and manure to really boost the nutrient count way before any planting takes place. And if that’s something you’ve been able to do then good on you, amazing job!

But what happens if you didn’t have the time, money, or resources to get ahead of the game? Are there any alternative options when it comes to enhancing the soil once you have started planting? Thankfully, there is something you can do and it’s as easy as reading on.

I find that when it comes to revitalizing soil that is otherwise infertile and tired, a 20-20-20 fertilizer is a great option. Made up of 20% nitrogen, 20% phosphorus, and 20% potassium, its generous macronutrient ratios are a surefire way of getting a big bang for your buck.

Then, after just one or two applications, follow up with a soil test and adjust your fertilizing needs accordingly.

Understanding 20-20-20 Fertilizer Labels?

With such a vast array of choices available, deciding which is the best fertilizer can be daunting and also time-consuming. At the end of the day, you just want soil that is enriched with nutrients and brings benefits to your plants and you don’t want it to cost a fortune. The good news is that can be easy to achieve, provided you understand the labeling. 

Fertilizer manufacturers have an obligation to state on their packaging exactly how much nitrogen, phosphorus, and potassium their products contain. They also tend to provide a list of other micronutrient ingredients and details of any fillers used (if any). This includes any trace elements such as zinc, boron, copper, calcium, and magnesium that can support plant health.

If you are still wondering about all this talk of NPK ratios and exactly what the numbers associated with it mean for your plants, then read on.

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N-P-K Ratio

On every fertilizer label, you will see three numbers that are separated by dashes. This represents the fertilizer’s N-P-K ratio, and it corresponds with the amount of nitrogen, phosphorus, and potassium contained within. So for example, a 20-20-20 NPK simply means 20% nitrogen, 20% phosphorus, and 20% potassium.

Every plant needs these three macronutrients in order to function ranging from cell formation, photosynthesis, nutrient distribution, and absorption of water and oxygen to flower and fruit production. The exact amount needed varies from one plant species to another and also depends on how nutrient-dense the soil is.


Plants need Nitrogen to fuel the production of chlorophyll. This in turn encourages the growth of healthy foliage and is what provides foliage its green color. It also ensures that photosynthesized energy is available to convert starches and carbohydrates into food. 

In addition, nitrogen provides energy to the proteins and enzymes that regulate water and nutrient absorption and distribution through the plant. High nitrogen fertilizer is the preferred option where foliage growth is the main objective of the plant – such as for lawns, non-flowering trees and shrubs, and leafy green vegetables.


Phosphorus is the driving force behind photosynthesis in plants. During this process, plants utilise phosphorus to help with the conversion of starches and carbohydrates into food once they have produced sufficient chlorophyll.

Plants also use this beneficial macronutrient to help with the production of buds, that eventutally become flowers and fruit. 

its work

The work of phosphorus begin at a cellular level, helping to construct cell-based proteins and enzymes that nitrogen then uses to absorb and regulate water, oxygen and nutrients.


Potassium increases a plant’s resiliance against diseases and drought by equiping them with the ability to conserve moisture. It is also required if you are looking to harvest a bumper crop of well-formed vining edibles such as zuchini, melon, squash and tomatoes.

In addition, potassium activates the proteins and enzymes that were developed with the help of nitrogen and phosphorous as well as having responsibility for enabling water, nutrients, and photosynthesized food to circulate throughout your plants.

Fertilizer Type

There are four main fertilizer application types available, depending on your preferences and specific needs. These fall into the following categories: 

  • Fast-Acting – These are available in liquid or water-soluble formulas and provide your plants with immediate access to nutrients. Expect plants to show signs of increased growth and improvement in health in as little as 5-7 days. Regular applications are required as these formulas are either quickly washed away or absorbed. Great for heavy-feeding plants.
  • Slow-Release – Heavily concentrated granular or powder formulations that provide the soil with a continuous stream of nutrients for between 4 weeks to 3 months. A great option if a gentler approach is required, or if you don’t have time to keep re-applying.
  • Organic – The ingredient list for these non-synthetic fertilizers is made up of ingredients that contain naturally occurring amounts of nitrogen, phosphorus, and potassium and are either well-rotted plant-based matter or animal bi-products such as fish, blood, and bone meal.
  • Inorganic – Manufactured using a blend of minerals and synthetic chemicals. These fertilizers – whilst very effective for plant growth and health – are usually highly regulated due to the potential for water source and soil contamination, plus hazards to people, pets, and wildlife.

Liquid Concentrate

Liquid concentrates can either be bought as ready-to-use formulas or will need to be diluted with water prior to application. Most manufacturers recommend pouring the formula over the soil near the base of your plants although some formulas can be administered directly onto the foliage and used as a foliar spray. 

Nutrients are then immediately absorbed either by the roots or the leaves and stems and carried to the plant’s root system. 

Liquid feeds are cost-effective but, can easily be over-used and over-applied so caution is advised to avoid over-feeding which can lead to root burn.

Water Soluble Powder

These are powdered formulas that can either be sprinkled directly into the soil around the base of trees, shrubs, and plants or diluted in water before watering into the soil or used as a foliar spray. They are the most cost-effective method of fertilizing your plants because a little goes a long way.

Another cost-effective method but one I’d recommend for fertilizing larger plots such as in orchards or farms due to the quantities they cover. They are fine to use for smaller spaces but bear in mind, you’ll have plenty left over for next time and so they will need to be stored in line with the manufacturer’s recommendations.

They also carry a risk of leaf or root scorching if used too often or in quantities that exceed the manufacturer’s recommendations.

Slow-Release Granules

Granules offer a slow-release fertilizing option. They provide consistent, yet gradual nourishment for plants for between four weeks to nine months – depending on the brand used. Nutrients are released by the microorganisms that live in the soil and you can expect to see results within a couple of weeks.

Granules can be cast around the base of trees, shrubs, and plants either by hand or using a spreader. Once applied, watering-in activates the release of nutrients.

This type of fertilizer poses less risk of leaching into nearby water sources. Plus, there is less risk of root burn with these plants since the release of nutrients is gradual rather than instantaneous.

Fertilizer Spikes

Spikes are a pre-measured, slow-release fertilizer option and are either loved or loathed by gardeners. The major benefits of using them are their convenience, ease of use, and lasting effects. Simply calculate how many spikes you need for the area you want to fertilize, and press them into the soil around your plants.

The negatives of using spikes are their cost, the quantities you’ll need, and also the potential damage they can cause to the root system of your plants. They can also be tricky to push into hard ground so using them in loamy soil works best.

The spikes rely on the microorganisms in the soil to break down over time and depending on the brand you buy, can last from between 4 weeks to 3 months on average.

Any leftover spikes can then be stored mess-free until you need them again.

What is Triple 20 Fertilizer Used For?

If you want to increase plant success and fertility in poor soil then opt for a 20-20-20 fertilizer. They can also be used for plants grown in hanging baskets where the risk of heavy leaching can occur.  

When used in the right setting, a 20-20-20 NPK will stimulate vibrant color and healthy foliage growth along with assisting with the development of buds and later fruits and flowers. In addition, your plants will be better protected against the risk of disease and damage caused by extreme weather conditions.

I don’t recommend using a 20-20-20 NPK fertilizer on an ongoing basis, especially for plants grown in the ground. Using too often or too much can lead to a build-up of salt in the soil. Excessive amounts of sodium can prevent plants from functioning effectively and prevents them from being unable to absorb water and oxygen.

I suggest using it at full strength for one or two applications where the soil is extremely lacking in nutrients. If you have any triple 20 left over, use it in half measures or as a diluted formula thereafter.

Why Use a Balanced Fertilizer?

Many outdoor plants require more of one macronutrient than another. But, when planted in poor soil, the infusion of a balanced fertilizer will provide the kind of nutrient-rich environment that plants need for healthy growth. 

Indoor plants benefit from a balanced fertilizer due to more frequent watering and the inevitable leaching of vital nutrients from the soil. An equal NPK will keep the growing medium fertile enough to keep them happy.

How and When to Use 20-20-20 Fertilizer

The usage of a 20-20-20 fertilizer depends on the product you buy, the quality of your soil, and the type of plant that needs fertilizing.

When planting new trees in nutrient-deficient soil, I like to add a handful of triple 20 granules to a freshly dug planting hole. I find this helps roots get established more quickly and encourages new growth. 

In new garden beds, I like to work slow-release 20-20-20 fertilizer granules into the top few inches of soil before planting. Alternatively, if plants are already in situ, it’s a good idea to apply a water-soluble option, to boast soil nutrients.

For my vegetable plot, I find that applying a triple 20 NPK just after transplanting leafy greens promotes an abundant harvest.

Here’s a more thorough rundown of when I use this type of heavily concentrated NPK fertilizer:

Trees and Shrubs

Apply triple 20 fertilizer for a month or two after planting young evergreen trees and shrubs. This will encourage roots to become established quicker and help to produce healthy foliage that greens up faster and grows more robustly.

An increase in soil fertility for a triple 20 feed can also ensure larger specimens develop resistance against the browning of foliage that is caused by extreme temperatures. In addition, your trees will be better equipped to retain moisture that can then be used in times of drought.

Once established, perennial evergreens typically don’t require any further fertilizing. But, if loss of foliage or discoloration occurs out of season, a good soil test should be conducted to reveal what nutrient is lacking and needs to be added to the soil.

Fruit Trees

Fruiting trees and shrubs typically need more of one macronutrient than another at different times. So a triple 20 may not be suitable for them, in the long term. This includes

Trees that produce berries, stone fruits, and citrus typically benefit from higher quantities of phosphorous and potassium (depending on the species and time of year) and therefore using a 20-20-20 fertilizer in the long term is not ideal.

However, if you are planting young fruit trees in nutrient-depleted soil, then mixing a couple of scoops of slow-release granules into the soil you use to back-fill the planting hole will encourage their root system to get established.


Producing masses of vivid, summer color takes a lot of energy so it is no wonder that many varieties of ornamental flowering plants are heavy feeders.

Applying a slow-release 20-20-20 fertilizer to ground-based flowering plants at the start of the growing season will provide them with access to vital macronutrients and ensure strengthened roots plus that all important bud and flower development.

I don’t recommend continued use throughout the season, however. Instead, dilute your 20-20-20 fertilizer by at least half or switch to a phosphorous-rich fertilizer as the season progresses.

The University of Michigan advises against fertilizing flowering perennials from late summer onwards as this can force new growth too late in the season. This additional growth will be too tender to harden off and can lead to damage caused by freezing temperatures.

Vegetable Gardens

All vegetables require the three primary macronutrients at some point during their various growth stages and many can perform well with the type of balanced nutrients that a triple 20 fertilizer can provide – especially when planted in nutrient-poor soil. However, climbers like tomatoes, squash, and melons require higher amounts of phosphorus and potassium once buds set.

In 2017, a biological research study, published on researchgate.net, focused on the effects of a 20-20-20 NPK on white radish plants. The results demonstrated that high levels of nitrogen stimulated large leaf growth, which maximized photosynthesis and root growth. Equal proportions of phosphorus and potassium harnessed the energy acquired through photosynthesis and funneled it toward large radishes and a much higher yield.

These results suggest clear benefits not only for radishes but all root vegetables, as they metabolize and utilize nutrients in a similar manner.

For other vegetable varieties, it’s often beneficial to start out with 20-20-20 NPK, just after transplanting. Especially if you’re working with poor soil. Then, switching to a lower nitrogen NPK once buds set. Leafy greens prefer the opposite, higher nitrogen and lower phosphate and potassium.


Just like outdoor varieties, your indoor plants and trees need the right ratio of nutrients to form strong roots and healthy foliage. Extra 20-20-20 fertilizer can be diluted down to a 10-10-10 to give your indoor greenery all the nutrients they need. 

Flowering plants like African violets, begonias, and bromeliads use phosphorus to form lots of lovely flowers. Nitrogen for vibrant foliage and potassium for the circulation of nutrients and water. So, these do well with a 7-9-5 NPK.

I prefer to take a more modest approach when feeding houseplants and if triple 20 is the only fertilizer you have then I advise diluting the formula by half or even down to a quarter measure to avoid root burn or leaf scorching as this can ultimately be detrimental to plant health.

Lawn and Grass

It’s certainly true that turf grass does need all three macronutrients:

Nitrogen for vibrant color and resilience to footfall

Phosphorus for root strength and to encourage thick foliage growth

Potassium protects against diseases and improves water absorption and circulation – especially in times of drought.

It is not necessarily the case that your lawn will need it in equal measure and the easiest way to know what NPK your lawn needs is to do a soil test prior to starting any kind of fertilization schedule.

20-20-20 Fertilizer FAQ’s