February 2025: Fertilisers Made Simple
5th February 2025
Way back in the mists of time, when I was a young man acquiring my first allotment, I soon became totally confused about fertilisers. In those days, it was common to purchase individual constituents—both organic and non-organic—and mix your own fertiliser compounds. Nowadays, it has become the norm to buy ready-made mixes.
Fertilisers were, and still are, a massive subject. So, I researched the whole topic from multiple sources and compiled a ‘reference bible’ that I could understand and follow—one that I still use to this day.
It starts something like this:
“FEED THE SOIL, NOT THE PLANT”
If you only remember that from this factsheet, I’ll be content. More details to follow.
Categories of Fertilisers
I separated the many types of fertilisers into distinct groups as follows:
Two Main Groups: Organic and Non-Organic
- Organic fertilisers consist of only natural ingredients, for example, Fish, Blood & Bone.
- Non-organic fertilisers contain at least some chemicals, for example, ‘Growmore’.
Both of these groups are further divided into Single and Compound Fertilisers.
- Single fertilisers consist of just one ingredient, such as ‘Dried Blood’, and are used to correct a specific deficiency. In this case, an insufficiency of nitrogen for growing vegetables that require higher nitrogen levels.
- Compound fertilisers consist of more than one ingredient, such as Fish, Blood & Bone, which is a general-purpose feed containing nitrogen phosphorus, and potassium.
All these fertilisers are available in granular/pellet form, or as liquid formulations—either ready-to-use (e.g. tomato feed) or mixed with water (e.g. ‘Miracle-Gro’ or homemade comfrey tea).
Understanding NPK
All fertilisers are quantified chemically using a system called NPK, which refers to:
- NITROGEN (N) – Essential for leafy plants like brassicas and rhubarb. Apply in spring, especially after a very wet winter.
- PHOSPHORUS (P) – Supports root development in root crops and perennials. Can be applied any time of year; the particle size controls the release rate.
- POTASSIUM (K) – Enhances colour, speeds up maturity, and promotes flowering (for example if you need to hurry up a flowering plant for a show!).
The amount of Nitrogen, Phosphorus, and Potassium in a fertiliser is expressed as its NPK ratio. For example, Fish, Blood & Bone has an NPK of 3-9-3. These numbers indicate the percentage of nitrogen (N), phosphorus (P), and potassium (K) in the fertiliser. These three nutrients are essential for plant growth and are known as macronutrients.
Additional micronutrients may also be added, such as Boron (B), Chloride (Cl), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Nickel (Ni), and Zinc (Zn).
More commonly a selection of these are packed as ‘Trace Elements’, and denoted on packaging as ‘+T.E.’s ‘and Magnesiumdenoted as ‘+ Mg’. For example ‘Vitax Q4’.
You will find the addition of Trace Elements to a fertiliser ups the price quite a bit but they are very beneficial to your plants. You pays your money and takes your choice.
A ‘Fertiliser on Tour’ Tale
All this talk of fertiliser finds me sat here with a broad grin, chuckling away. It goes back 39 years and the memory never fades.
My son Miles was 10 years old and I felt it was time we had a Father & Son event. Well, a chat about the birds and the bees was due you see. I suppose social media beats dads to it these days.
It had to be a tough test as he had been an insulin dependant diabetic since he was 4 years old and I wanted to demonstrate that he could physically do what all other boys could.
So we only chose to walk the 78 mile long Dales Way didn’t we? I suppose it was handy because at the time we lived just a few hundred yards down river from the Old Bridge in Ilkley where it starts.
I bought a couple of cheap notebooks from Woolworths so that we could each make a daily record of our journey and off we went. 2 days walking, one day rest, two days walking, one day rest and the final day walking to the finish at Bowness. My wife and daughter joined us on our rest days and at the finish.
Fortune favours the brave they say. And it did by golly.
During the second day we were happily chatting away when Miles exclaimed, “What are they doing Dad?” pointing to a cow being mounted by a bull. I looked skywards and mouthed thank you and proceeded to tell my son how babies are made. I would give him information in bite-size chunks, let it sink in and wait for the inevitable questions before proceeding with further detail.
I had just explained how the man’s sperm fertilises the woman’s egg and waited patiently during an extended pause and then he asked,
“Dad, have you got any fertiliser left?”
I immediately struck my best macho-man pose and growled down at him, “The hell I have son!”
Well, I mean, “Have I got.. ..” I was only 37 for goodness sake!
We both continued the rest of the walk with a spring in our step. The two journals were written up every evening and to this day sit on the coffee table at my side of the settee facilitating occasional read throughs and a smile every time I come to that word- ‘fertiliser.’
Which reminds me, I have gone off piste.
So, how do we best put these fertilisers to use – horticulturally. Near the beginning I wrote,
Feeding the Soil
As mentioned earlier:
“FEED THE SOIL, NOT THE PLANT.”
Well worth repeating.
Feeding plants after planting has its place, but it should supplement, not replace, soil preparation before planting
- Autumn: I dig trenches for my sweet pea and dahlia beds, adding a decent layer of well-rotted manure or garden compost in the bottom before backfilling. I also spread manure or a 2” layer of compost over the remaining beds—except those intended for root vegetables like carrots and parsnips. The plan is to finish by mid-winter. Spent mushroom compost is a good alternative (around £90 per large builder’s bag from builder’s merchants).
- Spring (two weeks before planting): I rake in Fish, Blood & Bone fertiliser for root vegetable beds and apply potato fertiliser to my potato beds. Fruit trees and bushes receive a general-purpose fertiliser in early spring.
- Brassica beds: I apply a light dusting of lime in spring. If no manure is used, lime can be applied in Autumn—but never both together.
Supplementary Feeding
By early spring, all my beds are fully loaded, reducing the need for additional feeding during the growing season. However, some plants may need extra nutrients, especially if grown for show or if they are very hungry plants (e.g. tomatoes, squashes, dahlias, and potted plants).
The Keighley Horticultural Society/Keighley Trading Hut has prepared an excellent Product Information Table listing fertilisers, their applications, and suitable plants. They have kindly given me permission to email copies of it to anyone interested. If you’d like a copy, email me at ramonkporter@gmail.com, and I’ll send you the table along with a list of available fertilisers. Please refer to the table before purchasing and applying fertilisers.
Liquid Feeding
- Apply liquid feeds to the soil, avoiding excessive splashing on leaves.
- On dull days, a foliar spray feed can give plants a quick boost—apply to the undersides of leaves for better absorption. I use a sprayer with a lance and an adjustable nozzle which makes under leaf spraying much easier.
- My go-to liquid fertilisers are Chempak soluble feeds:
- No. 2 (High Nitrogen)
- No. 3 (Balanced)
- No. 4 (High Potash)
- No. 8 (Low Nitrogen)
An alternative is Vitax Vitafeeds, They do the same job and can be bought relatively cheaply from allotment shops.
Homemade Fertilisers
I also use home-made fertilisers, two in particular:
Nettle
Add about 1kg (2 lb) nettles to 10 litres (2 gal) of water, leave for about two weeks and use at a dilution rate of 10:1.
Comfrey
Add 1kg comfrey leaves to 15 litres (3 gal) of water and leave for six weeks in a sealed container then use undiluted.
These are quite a bit weaker than the commercial fertiliser but can be used with gay abandon, and they work! Be warned, both of these stink to high heaven in the making of but that can be got round by making a concentrate if you have access to copious quantities of leaves or by storing the buckets/bins closer to your neighbour’s allotment than yours!
Put a hole on the centre of a tall bucket. After a wet spell to ensure the plants are turgid, cram the bucket with as many leaves, exclude stalks, as possible. Put a large stone on top, but do not add water. Put a lid on top and place the bucket out of the rain and over a receptacle that will catch the dark liquid that oozes out of the leaves This liquid does not stink. Dilute to a pale straw colour. Alternatively use a barrel/bin with a drain tap and mix comfrey, nettles, lawn mowings, even groundsel. Bocking 14 variety of Comfrey is sterile so does not set seed and take over your garden/allotment and is rich in potassium, Nettles have more nitrogen content. How perfect is that?
I hope all the above gives you a basic understanding, so we’ll wrap it there.
Next Month: Pest Control
Until then,
Keep fertilising, keep healthy, keep smiling, and keep sowing.
Best Wishes,
Ramon 07594 456292
Plot 21 Silsden Road site