When to Use 19-19-19 Fertilizer? | How to Use Triple 19

When starting a new garden border, vegetable bed, or laying new sod, your soil is going to need to be as fertile as possible. Not only for all those new plantings to survive, but also to thrive.

If you amend your soil with well-aged compost, manure, and other organic compounds to increase its fertility, prior to planting, that’s great!

If not, that’s perfectly ok too but you are likely going to need to give plants a helping hand with a balanced fertilizer and one that provides a high concentration of N-P-K.

The nutrient ratio in a 19-19-19 fertilizer is pretty simple. 19% nitrogen, 19% phosphorus, and 19% potassium. Which is near twice as much of each as in a standard 10-10-10 fertilizer. Making it the perfect choice to revitalize tired and infertile soil.

Then, once a soil test confirms that your soil is up to par, a 19-19-19 fertilizer can easily be diluted down to a 10-10-10 for continued use on lawns, garden beds, and vegetables. Not to mention, houseplants. 

Understanding 19-19-19 Fertilizer Labels

With so many NPK fertilizer options to choose from, deciding on the best one may seem tedious. Especially when all you want to do is to grow healthy plants.

No need to panic! With just a little knowledge, it can be easy to match a fertilizer to your plant goals just by understanding the fertilizer labels. 

Most fertilizers state their NPK ratio right on the label. On the back of the container should be an ingredients list and this will provide you with details of what’s been included to make the product.

The list starts with details of the macronutrients or NPK. Then all the secondary micronutrients are listed. This is followed by trace elements and any included fillers. But, what exactly is an NPK ratio? 

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N-P-K Ratio 

Every fertilizer label reflects three numbers, separated by dashes. This is its N-P-K ratio, indicating the fertilizer’s proportions of nitrogen, phosphorus, and potassium.

For example, a 19-19-19 fertilizer NPK has 19% nitrogen, 19% phosphorus and 19% potassium. Every plant requires these three elements in order to thrive. Just in different proportions or NPK ratios.

Each of these macronutrients plays a vital role in cell formation, photosynthesis, nutrient distribution, and flower and fruit production. 


Nitrogen is what plants rely on to fuel the proteins and enzymes that they use to absorb and regulate water and nutrients effectively. It also fuels the production of chlorophyll and ensures that photosynthesized energy is available to convert starches and carbohydrates into food.

Another important and most visible function of nitrogen is that it gives plants their lush, green leaves. High-nitrogen fertilizers are most commonly used when foliage is the primary focus. For example, in lawn care, and for non-flowering plants.


Phosphorus is the macronutrient that supports the creation of flowers and fruit and plays a vital role in assisting with the construction of the proteins and enzymes that nitrogen then uses to absorb and regulate water and nutrients throughout plants.

Additionally, when it comes to the process of photosynthesis, phosphorus plays a starring role in triggering the energy captured in the production of chlorophyll, into becoming converted into food from starches and carbohydrates.


Potassium is required to assist plants with the effective circulation of water, nutrients, and photosynthesized food.

In addition, it helps plants to be more resilient to extreme weather conditions (i.e. severe frost and drought) and serves to protect plants against diseases.

High potassium fertilizers are used to help plants produce well-formed fruit in a bountiful supply and are especially recommended for vining edibles such as melons and tomatoes.

Uses for Triple 19 Fertilizer

Use a triple 19 fertilizer when you want to increase fertility in poor soil. This will help to improve nutrient uptake in plants.

You can also use it to compensate for the leaching that occurs when plants are grown in hanging baskets or pots.

For in-ground plantings, a 19-19-19 NPK should only be used at full strength for a short time usually just before planting or at the start of the planting season. All subsequent applications should either be a diluted version or a feed with a lower NPK such as 8-8-8 fertilizer – whatever is better suited to the needs of specific plants. 

Why Use a Balanced Fertilizer? 

When planted in poor soil, a balanced fertilizer can provide even nutrient availability that then promotes healthy growth. 

A balanced, 19-19-19 fertilizer is a good option to use for potted plants. The relatively high NPK ratio can help to offset the leaching of nutrients caused by frequent watering. Essentially, the equal NPK will keep the growing medium fertile enough to keep potted plants happy. 

Fertilizer Type 

The type of fertilizer you choose will dictate how it needs to be applied, how quickly it will deliver nutrients to the soil, and how readily it can be made available for plants to absorb.

For example, the nutrients in quick-release or fast-acting formulas are available for plants to absorb instantly. Whereas, slow-release granules need moisture and soil microbes to break them down which can take upwards of one week before they can be absorbed by plants.

Once you have decided if it’s slow-release or fast-acting that your plants need, you’ll then need to choose whether you want to use an organic or non-organic fertilizer type.

Organic fertilizers are derived from plant matter and animal bi-products including kelp, seaweed, fish emulsion, blood, feather, and bone meal. In most cases, ingredients will be used because they contain naturally occurring macro or micronutrients. For example, fish emulsion is a natural source of nitrogen and bonemeal is a natural source of phosphorous.

Non-organic fertilizers are mass-produced using synthetic chemicals and tend to produce better results. Synthetic fertilizers tend to get bad press however, due to the potential risks they pose to people, animals, other plants, and our water sources if not used correctly.

    Liquid Concentrate 

    Liquid concentrate fertilizers are fast-acting. Once watered into the soil around plants or over foliage, plants will start absorbing the nutrient-loaded formula straight away. You can expect to see results in just a few days.

    You can buy liquid fertilizers either as a concentrate that will need to be diluted in water or as a ready-to-use formula. The latter is more convenient and less messy, but they also tend to be more expensive.

    Fast-acting liquid formulas need to be re-applied frequently for two main reasons. Firstly they are absorbed quickly but also because they can easily be washed away. They also carry the risk of contaminating local water sources due to run-off.

    I recommend using fast-acting fertilizers for heavy-feeding plants that need regular fertilizing. Alternatively, use them for potted or hanging basket plants where water is prone to leaching out and thus vital nutrients are lost.

    Water Soluble Powder 

    Similar to liquid concentrates, powder fertilizers are fast acting and need to be diluted in water before application. Most gardeners refer to this as a ‘fertilizer tea’ that can be watered directly into the soil or used as a foliar spray.  

    Water-soluble powders offer excellent value for money when it comes to fertilizing and any leftovers will store well thanks to their extensive shelf life.

    These also carry a risk of root or leaf burn if used excessively or in concentrated amounts. Make sure to carefully read the manufacturer’s instructions before using. 

    Slow-Release Granules 

    Slow-release fertilizers are purchased in the form of nutrient-packed granules. These granules need to be broken down by moisture and micro-organisms in the soil before nutrients can be released and then absorbed by plants via their roots.

    This process takes time and depending on the brand, nutrients can remain in the soil – waiting to be absorbed – from 4 weeks up to 6 months. This means that fewer applications are required compared to fast-acting liquids. Results will be visible around 2 weeks after application.

    I use slow-release fertilizers when my soil has been depleted of nutrients. It can be added to the soil before planting starts, used as a side-dressing for edible vegetables, or sprinkled around trees, shrubs, or lawns from the start of and throughout the growing season.

    Granules are far less likely to cause root burn and because granules remain in the soil rather than leaching, they pose considerably less risk to water source contamination.

    Fertilizer Spikes 

    Spikes are a compacted version of granules. They offer slow-release fertilizing and need to be activated by moisture and microbes in the soil before their nutrients are available for plants to absorb. On the plus side, they are convenient and mess-free, and only a few applications are required per year for your growing plants.

    The perceived downsides of spikes are firstly their cost since you’ll need several spikes if you have anything more than one houseplant to feed.

    They also receive criticism for causing damage to plant roots when they are inserted into the soil. Damage can also be caused due to the concentration of fertilizer that becomes present in one area as opposed to the even distribution you get from applying granules or liquids.

    How and When to Use

    A 19-19-19 fertilizer can be applied as a liquid when watering or by spreading slow-release granules. In container gardens, fertilizer spikes can be very effective. 

    When planting new saplings in poor soil, a handful of triple 19 granules, in the hole prior to planting, will encourage faster establishment and new growth. 

    In borders, working granules into the top few inches of soil or applying a water-soluble option, just after planting, will provide plants with a great start. 

    With vegetables, applying a triple 19 just after transplanting will promote an abundant harvest. 

    Trees and Shrubs 

    Use a triple 19 fertilizer in the 3rd and 4th months after planting trees and shrubs. Once established, these typically don’t require any further fertilizing. If symptoms occur, a soil test can reveal any deficiencies. 

    Fruit Trees 

    If you’re planting fruit trees in poor soil, a handful of dry 19-19-19 granules added to the planting hole, in spring, will also help these get established quickly. 

    Fruit tree fertilizers tend to contain more of one macronutrient than another. So a triple 19 may not be suitable for them, in the long term.


    Ornamentals need consistent nutrition to produce lots of summer color. In less-than-fertile soil, a triple 19 NPK can ensure this and help accelerate plant maturity. 

    If you already benefit from rich, fertile soil, select a feed with a lower N-P-K rating such as a Triple 10 fertilizer, or better still, select a phosphorous-rich fertilizer as this will support the growth of more plentiful and larger flowers, as well as healthy stems, leaves, and roots. 

    Vegetable Gardens 

    If you’re stuck with poor soil, it’s beneficial to mix 19-19-19 NPK slow-release granules into the soil before planting, with another application just after transplanting. 

    Fertilizers for tomatoes, and other vining edible plants such as squash, and melons contain more phosphorus and potassium than nitrogen and should be used once buds are set.

    Green, leafy veggies, on the other hand, thrive when side-dressed with a much lower NPK and ideally one with more nitrogen to encourage that all-important foliage growth.


    A 19-19-19 fertilizer is typically too high for houseplants. It would need to be significantly watered down. A triple 8 NPK (or a 10-10-10 for nutrient-deficient soil) will support their needs without over-fertilizing.

    Bloomers like bromeliads, need more phosphorus to form flowers and do well with a 7-9-5 NPK. 

    Lawn and Grass 

    Feed for lawns and native grasses need phosphorus to grow thick and lush. Yet, they also need a high nitrogen fertilizer to maintain a tough, vibrant structure. 

    If a soil test has revealed nutrient-poor soil beneath your grass, a 19-19-19 NPK would infuse your soil with enough nutrients to support a healthy lawn.  

    19-19-19 Fertilizer for Garden FAQ’s