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Fertilisers – Part One

We’ve looked at how and why we might want to improve the condition of our soil. This time we’re going to start to look at how we might choose to feed our seeds and plants and to maintain their health.

Fertilisers help plants grow. If the plant is a fast grower then the more fertiliser we apply then the happier the plant will be. If your soil is healthy then it might not always be absolutely necessary to add fertilisers, but if you do then your plants should produce a much more impressive show of flowers or higher yields of fruit or veg.

Fertilisers also help keep your plants in tip top condition. If your plants have yellowing leaves then it may well be a sign of a nutrient deficiency. A quick dose of the correct fertiliser, applied in the correct way, should see them return to good health.

Healthy soil structure (and the correct pH for the plants that you are growing) is just as important as adding fertiliser if we are going to be successful in maintaining healthy plants. Soil structure that has been improved through the addition of manure and compost, and where the soil has been manually worked to break it down to create space for air and water between the individual particles is also vitally important.

So what are fertilisers?

Well we don’t need to have a qualification in chemistry to understand this – even if they are often referred to by their chemical symbols!

All fertilisers will usually contain a source of plant nutrients in either a chemical or organic form. Some might contain major plant nutrients, which some of our plants might need a lot of. Some will contain something that is referred to as a trace element, which plants only need in tiny amounts.

Most fertilisers are based on the three major plant nutrients:

Nitrogen (N): For plants that produce green leafy growth – like cabbages and other brassicas.

Phosphorus (P): For healthy root and shoot growth.

Potassium (K): For plants that produce flowers and fruit – like tomatoes and apples.

If you buy your fertilisers then their N:P:K ratio should be clearly stated. As an example if the ratio is stated as 20:20:20 then this would indicate a balanced, all-purpose fertiliser. If however the ratio is 10:12:24 then this would indicate a fertiliser with a higher potassium content. This would be good for plants that produce flowers – like roses.

How are they made?

Fertilisers are either man-made – inorganic - or are naturally found in plants or animals – organic!

Inorganic fertilisers: These are synthetic, artificial forms of plant nutrients or naturally occurring mined minerals. They are usually more concentrated and act faster than organic fertilisers. Popular examples include Growmore, Miracle-Gro and Tomorite.

Organic fertilisers: These originate from plant or animal sources and contain plant nutrients in organic form. They tend to be slower acting, as the molecules are larger than those found in inorganic fertilisers and these have to be broken down before the nutrients within them are released for the plant to use. Examples of organic fertilisers include seaweed, fish blood & bone, poultry manure pellets and liquid comfrey or nettle feeds.

The potatoes in the foreground were planted at the same time as those in the background. The only difference being that those in the foreground had our special homemade seaweed fertiliser.

We use seaweed at the allotment. Every Autumn we take a trip to the Dorset or Hebridean coast where we gather kelp that has been washed ashore after a storm. We then put it in to a butt and cover it with rainwater. Six months on we have our own liquid seaweed fertiliser that we then dilute and use to water our plants. As the photo shows our vegetables love it!

Seaweed after 6 months in the water butt making a nice kelp tea. All nutrients taken out with what's left waiting for the compost bin.

Next time we’ll talk about the different types of fertiliser and how they can best be applied.

Do get in touch if you would like to know more, either through my facebook page, at or on 07734 365028.


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