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Feeding Plants 101

Now we are in mid-July our gardens should be flourishing! Daily jobs will be deadheading the dahlias, cutting back early perennials, watching out for pests and weeding before unwanted friends take to seed. However, there's one important job - and that's task of feeding our plants.

The great importance in feeding plants is that those who don't receive enough nutrients will be stunted from reaching their full potential. This can be through a) reduced overall plant growth, b) underwhelming flowering or c) disappointing crop yields.

Feeding plants is particularly important with container gardening. Unlike our garden boarders who receive a steady supply of nutrients from healthy top soil (decomposing plants, leaves, insects, and twigs) plants grown in pots receive only what's in the growing medium.

Bagged composts are purchased with nutrients blended into the medium. But as time goes on these nutrients are absorbed by the roots or washed away.

At some point, almost certainly sooner than you may expect, these lost nutrients need restoring. To give you an idea, Melcourt specifies that their SylvaGrow Multipurpose Compost contains 'balanced nutrients sufficient for the first 4 - 6 weeks of growth'. That means after the initial 4- 6 weeks, you will need to begin replacing lost nutrients!

So to provide you with a brief understanding of the major nutrients, the forms and the applications available - here is a beginner-friendly article to get you on the right tracks.

The 3 Major Nutrients

Nitrogen (N)

Nitrogen is a plant nutrient responsible for leafy growth. This is important as plants use their leaves to photosynthesise (think of their leaves as solar panels - converting sunlight into energy). A deficiency in Nitrogen will lead to smaller leaves or yellowing of the leaves.

Phosphorous (P)

Phosphorous is a major plant nutrient responsible for healthy roots and development. A deficiency in Phosphorous will lead to smaller plants and dull colour.

Potassium (K)

Potassium will help your plants to grow deeper and stronger roots assisting with flowering, fruiting and general hardiness. A deficiency in Potassium will lead to Yellow or purple leaf-tints with browning at the leaf edge and poor yields.

A helpful saying is 'Up, Down and All Around.' Nitrogen helps what's above, Phosphorous helps what's below and Potassium helps general health.

Ratios Explained

When it comes to purchasing feeds, packaging and online descriptions will reference a 3-part ratio. This important ratio informs us what a particular feed targets and will follow the order listed above, N:P:K (Nitrogen : Phosphate : Potassium).

A ratio of 15:15:15 indicates a balanced fertiliser containing an equal amount of each nutrient and a ratio of 10:12:24 indicates a fertiliser containing a higher amount of potassium - meaning that feed is designed to target flowering and fruiting (don't forget, N:P:K!).

For example, Levington Tomorite (a tomato feed based on improving crops) has a ratio of 4-3-8... whilst Vitax's Organic Bonemeal (a concentrated feed based on root development) has a ratio of 3.5-20-0.


Occasionally labels will refer to Potassium (K) as potash or pot-ash. Traditionally potash was produced through the process of burning wood in pots (pot... ash.... get it?). Basically charcoal. However, that practice is no longer used on a large-scale and Potash is now mainly derived from mineral sources.

The reason why some manufacturers reference Potash over Potassium (K) is because Potash naturally contains Potassium (K). However, just because a lot of Potash is now sourced through minerals does not mean you cannot find organic sources (hardwood charcoal and kelp are two).

Organic Vs. Inorganic

(The great debate!)

Organic fertilisers

These are derived from natural sources. Organic products are known to be slower acting due to larger molecules needing to break down - so it's a good idea to plan the use of these into your gardening routine. Organic gardening is a whole different topic and discussion however the basic principle is that you're feeding the soil to improve its structure and quality and in return feeding the plants. Common organic ingredients are seaweed, blood, bone meal, comfrey and manure.

Inorganic fertilisers

These are derived from synthetic (man-made) or mineral sources. Inorganic (or chemical) fertilisers are usually more concentrated than organic fertilisers meaning they are faster acting. Common inorganic fertilisers are Growmore, Miracle-Gro, Sulphate of Ammonia, Sulphate of Potash and Tomorite.

Organic gardening is the winner in my books! Yes, you will likely pay more for an organic fertiliser than an inorganic fertiliser *but* you wouldn't eat a junk food diet - so why should your plants... particularly if you consume what you grow!

Forms of Organic Fertilisers

To give you a hand, here are the main options we find in the UK.

Blood fish and bone - A balanced feed with elements of all major nutrients. Blood is high in nitrogen, fish contains Potassium, and bone (as below) contains phosphorite for root growth. Similar to bonemeal - a coarse powder to be used as a top dressing and watered in.

Bonemeal - bones that have been crushed down as a by-product of the meat industry. A slow-release coarse powder, high in phosphate, that is ideal for use when planting at the start of the season or using as a top dressing for established plants.

Liquid seaweed (and comfrey) - a concentrated liquid made from seaweed or comfrey that is then diluted down for watering on. Both sources are great for a quick burst of nutrients and will also contain micro-nutrients. Little and often they say.

Calcified seaweed - crushed and dried seaweed with added calcium. A sort of chalky-granular, general use feed that can also improve soil structure as the calcium breaks down. Not good for ericaceous plants because of the lime content.

Manure Pellets - manure that has been dried and compressed into more user-friendly pellets. A steady slow-release all-round feed that also helps to improve soil quality as it breaks down.


With all of this information above, here are some handy tips.

  • Feed little and often, starting in Spring and finishing right at the end of Summer.

  • When applying fertilisers to the soil around plant roots, make sure that the soil is moist. Fertilisers are less effective in dry soil and when dry may actually damage the roots of your plants.

  • Don’t feed plants that are poorly from root damage or drought. Water first, possibly move into shade to give them a break, then wait for them to pick up.

  • Water after feeding to distribute fertilizer evenly around the roots however too much water may dilute the fertiliser.

  • Read manufacturers instructions and follow their directions. You may be tempted, but overfeeding can actually be harmful for your plants.

Happy gardening!

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