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NPK: Understanding The Secret To Healthy Plants

28th May

Ensuring the health of our plants is a universal goal for gardeners, yet the information on fertiliser packaging can often leave us scratching our heads!

Read on to find out what NPK is and how key nutrients affect your plants.

What is NPK?

Six different key elements, known as macronutrients, form the building blocks of plant life.

Plants obtain Carbon, Oxygen, and Hydrogen from air or water, while they usually derive the remaining three macronutrients, Nitrogen, Phosphorous, and Potassium, from the soil.

The term NPK indicates the ratio of each of these elements in a particular fertiliser product.

Understanding the function of each nutrient helps you choose the right product for cultivating a thriving garden.

N – Nitrogen is one of the most commonly found elements within plants and it plays a key role in chlorophyll molecules and promotes lush green leaf and shoot growth.

P – Phosphorous is essential for plant maturation, serving a central role in ATP, the primary energy source for plants. It stimulates root branching, improving water and nutrient uptake.

K – Potassium supports all cell growth and aids in Nitrogen uptake. Plants demand high levels of Potassium during fruiting and flowering stages due to its influence on sugar metabolism.


Plants need more Nitrogen, Phosphorus and Potassium than any other plant nutrients, but many other micronutrient elements are needed in smaller quantities and will usually be present in sufficient levels to stop any deficiencies within complete fertiliser products.

Why do you need to feed plants?

Fertilisers are used to supply nutrients to your plants, maximising the growth which they can produce. They are even more beneficial for annual plants or those which are faster-growing.

Supplemental nutrients can be applied to deal with plant deficiencies or to enhance low nutrient compost.

Peat-free compost is very much here to stay for UK gardeners. Plants can grow just as well without the use of peat, but their needs will be different.

Many peat-free composts contain low nutrient substrates such as coir. This means that supplementary nutrients are often needed earlier in the season.

Regularly feeding container plants is also important to maximize their growth, as water can easily wash away the nutrients in the soil.

Types of NPK fertilisers

NPK numbers relate to the ratios of the 3 nutrients. A higher number signifies a greater concentration of nutrients.

Different feeds for different needs

Nitrogen is crucial for leafy green growth, so is arguably the most important for all-round plant health. Ratios of these nutrients can differ depending on a plant’s specific needs.

For example, tomatoes and greenhouse crops may require more potassium for fruiting stages so an organic feed such as Maximato with an NPK of 4-2-6, would be beneficial.

Conversely, an ideal feed for grass should be higher in nitrogen, but not so high that it can cause lawn burn. These targeted feeds will build stronger, healthier lawns.

Greenkeeper’s secret, with an NPK of 3.5-2-2  is one such product and comes with an easy-to-use hose-end sprayer.

Choosing an all-rounder organic fertiliser such as Allgrow, with an NPK of 6-2-4 is the simplest way to tackle feeding your garden. It provides a balanced mix of nutrients suitable for a variety of plants, from roses to bay trees to pumpkins.

What does organic mean?

Organic feeds are derived from natural plant or animal sources such as seaweed, manure or bonemeal while inorganic are man-made or derived from mined minerals.

Both types will contain Nitrogen, Phosphorous and Potassium though inorganic tend to be more highly concentrated. Organic certification is a strict process to ensure all materials are uncontaminated by inorganic sources.

How to use NPK fertiliser

Broadly speaking, fertilizers can be divided into two categories based on their usage: slow-release granular or solid feeds and readily available liquid feeds.

Solid Feeds

Slow-release feeds such as chicken manure pellets or inorganic coated granules can be mixed into the soil to evenly distribute nutrients.

Alternatively, feeds like digestate or well-rotted manure can be top-dressed to act as mulch. These slow-release options may take anywhere from months to years to fully release their nutrients.

Liquid Feeds

Liquid feeds are available as dissolvable granules or pre-mixed liquids. You can apply these feeds in two ways: spray them directly onto leaves as a foliar spray or water them onto the soil around the plant.

Foliar spraying enables plants to quickly receive and utilize nutrients, especially in cases of deficiency, although plants absorb less this way. Watering feeds onto the soil allows plants to absorb nutrients through their roots and use them quickly.

Take precautions to avoid letting the feed contact the leaves in bright, sunny weather to prevent scorching.


To learn more read our how to feed your plants blog.

How to make a DIY liquid nettle feed

If you have an overgrowth of nettles in your garden or allotment, why not try making a DIY nettle feed? (Beware of the stingers!)

(1) Collect the Nettles: Using gloves, gather enough nettles to fill your container.

(2) Chop the Nettles: Cut the foliage and stems into smaller pieces.

(3) Add Water: Pour enough water into the container to cover the plant material.

(4) Weigh Down the Nettles: Place a large stone on top of the nettles to keep them submerged.

(5) Let It Ferment: Allow the leaves to rot in the water for up to 6 weeks. After this period, discard the solids into your compost heap.

(6) Use the Liquid Feed: Dilute the liquid feed at a 1:5 ratio (one part nettle feed to five parts water) for a natural fertiliser.


But if you can’t wait, check out our feeds range!

Related Products

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  • Envii Maximato organic tomato plant feed New in

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    Organic liquid tomato plant feed with added seaweed, calcium and magnesium
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  • Envii Greenkeeper’s Secret

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  • Seafeed Xtra 1L Front - Organic Gardening Products

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About the author

Rachel Greenhill

Rachel is our resident Doctor, Plant Doctor that is. She is a certified gardening lover with a Ph.D. in plant science and a published scientific author. When she’s not testing and developing new envii products, you’ll find her managing the envii social media and writing one of our next best blogs. 

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