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Guide to Fertilising

It’s not always easy knowing what and when to feed your plants. In containers, plants require a bit of extra fertilising oomph during their peak flowering period because their roots can’t go beyond the pot they are in. Composts in containers will feed the plants for a while but they can become depleted of nutrients, especially if the plant is romping away and growing well.

So, here’s a refresher of a few basics to help you care for your plants and get a joyous display throughout the year. We’ll cover:

  • Why fertilise?
  • What’s in a fertiliser?
  • Which fertiliser to use for each plant?
  • How often to feed plants?
  • How to fertilise while looking after the planet?

Why fertilise?

Fertiliser is just food for plants. Remember being told to eat your greens to grow big and strong? It’s the same for plants – if you want more flowers, taller growth, and brighter colours, then you need to fertilise.

What’s in a fertiliser?

Most fertilisers contain three main nutrients: nitrogen, phosphorus and potassium (NPK). They also commonly contain trace elements and micro-nutrients needed by plants, such as iron, manganese and zinc. 

At Muddy Trowel, we think you can’t go far wrong with liquid tomato feed or seaweed extract to feed your plants. However, there are lots of alternatives and here’s a bit of background on why different nutrients matter.

Which fertiliser to use for each plant?

First of all, familiarise yourself with your plant. Look at it and ask yourself:

Is beautiful foliage its star attraction and has it got wonderful lush leaves? Examples of plants like this are hosta, fern, heuchera, fatsia. If the answer is yes, then you need more nitrogen in the feed for the leaves and stems to flourish (indicated with an N on the feed label).

Is it a young, small plant that needs to do a bit more growing and develop its roots and shoots? If the answer is yes, then your plant will benefit from feeds that contain phosphorus (indicated with a P on the feed label). This is a nutrient that influences the way minerals travel in plants and contributes to the development of healthy roots and shoots.

Are there lots of buds or flowers on the plant? Examples of plants like this are fuschias, penstemons, geums, violas, cosmos, geraniums, delphiniums, salvias (the list goes on!). If the answer is yes, then these plants will benefit from feeds that are higher in potassium (indicated with a K on the feed label). Your plants will concentrate their energy on producing flowers, that will stay open for longer. If it’s a plant that produces fruit, then potassium is also key for the development of those fruits. For a long and colourful flowering season, potassium is your plant’s friend.

Basic multi-purpose fertilisers

General soluble feed

Soluble multi-purpose mass-produced fertilisers offer the holy trinity of nutrients (NPK) in ratios that will focus your plants efforts on flowering and leaf growth. They need to be diluted with water according to the instructions on the packaging and applied directly on to the soil around your plants every couple of weeks during their peak growing and flowering period.

In our Muddy Trowel shop, you can find two litres of EcoGro Bloomer Fertiliser which is made entirely from plant residues, is completely organic and perfect for flowering plants to keep them at peak performance.


Fertilisers that are hugely popular are slow release granules or pellets that can be sprinkled onto compost or even tabs or cones that you can push into the compost. 

Slow release feeds (sometimes called continuous release but they aren’t quite the same) have a balance of nitrogen, phosphorus and potassium that most plants will thrive on. 

They take the hard work away from you and are low maintenance because you can apply the feed and it can last an entire season (make sure you check the instructions on the packet on how long they last). All you need to manage is watering and deadheading.

Tomato feed

Tomato feed tends to have potassium as the highest proportion of nutrients, then nitrogen and finally phosphorus. This makes it a great all-rounder liquid feed for most plants, not just your tomatoes and vegetables.

Tomato feed will need to be diluted with water according to the instructions on the bottle and applied every couple of weeks.


Concentrated seaweed extract is often used in the production of tomato feed. As well as containing the all-important potassium (highest proportion), nitrogen (second highest) and phosphorus, it contains loads of trace elements and micro-nutrients that your plants will absolutely thrive on. 

Once diluted (according to the instructions on the bottle), it can either be applied every couple of weeks to the soil around your plants, which helps the soil retain water due to the natural alginates in the seaweed, or directly to the plant leaves as a tonic that will get absorbed by the leaves.

Blood, fish and bone

Blood, fish and bone feed is made from exactly those components and provides a very even balance across the nitrogen, phosphorus and potassium nutrients needed by plants. This means it’s excellent for root, shoot, leaf and flower development and is normally sprinkled into the soil around plants (avoid sprinkling on the plant stems and leaves) every 6 weeks from when the plant is planted up, right the way through the growing and flowering season.

Advanced options

Suphate of potash

Sulphate of potash is a potent potassium-based feed, specifically for use when your plants are in bud and can be applied as a dilution or as granules sprinkled on the surface of the soil. This is one really powerful feed for flowering plants and creating masses of blooms to maintain their peak performance.

Chicken manure

Chicken manure that is dried and formed into pellets is a feed that is high in nitrogen and great for sprinkling on the soil around established plants to encourage leaf growth. The pellets provide the important NPK (with the emphasis on the nitrogen) as well as the all-important trace elements and micro-nutrients plants need. The pellets are also a great soil conditioner in that they add fibre and organic matter to the soil, helping to keep it light and aerated as well as helping to retain moisture when you have watered.

One thing to note, chicken pellets are neutral to alkaline and so acid-loving plants like azaleas, camellias, heathers and rhododendrons won’t respond well to this feed.

How often to feed plants?

As a general principle, fertilise regularly in the growing season (Mar-Sep for most plants). Frequency depends on the type of fertiliser used: every few weeks for liquid feed and less frequently for other types. Follow the advice given by the specific fertiliser you have and feel free to message us if you have any questions.

How to fertilise while looking after the planet?

At Muddy Trowel, we love nature, plants and wildlife and we always look for alternative methods and materials to help you enjoy your plants and outdoor spaces with minimal impact on the environment.

This is why we want to suggest a few alternatives to the mass produced fertilisers you can buy and point you towards smaller producers who have fully embraced sustainability and organic ingredients in their products. These are just as effective as the big brands and their eco-credentials make them well worth a try.


Based in Cumbria, this family business make fertilisers using by-products of common agricultural practices that are entirely plant based. In our Muddy Trowel Shop you can find two litres of EcoGro Bloomer Fertiliser which is perfect for most plants to keep them at peak performance.


Based in Norfolk, PlantGrow is created from harvested and shredded farm crops, that go through an anaerobic digestion process to produce natural, chemical free fertiliser.

Natural Grower

Based in Leicestershire and are approved by the Soil Association, Organic Farmers and the Vegan Society. They use the by-products of biogas production to generate petrochemical free natural fertilisers.


Got a bit of garden space and fancy making your own fertiliser that your plants will love? 

Comfrey is a wonder plant which is not only grown for its pollinator friendly flowers, but because it can be used to make the most effective liquid fertiliser for flowering plants and fruits.

Nettles, whilst viewed as a weed can be put to good use and used as a nitrogen rich fertiliser for foliage plants and encouraging leafy growth.

Follow the step by step guide on the Garden Organic charity website to make your home brews, and wear a clothes peg on the nose or get a tight fitting lid for the container you use, because it gets smelly!

Learn more