Gardening – What is NPK And What To Do With NPK

Shopping for better plant’s showing or better veg production, you’ll often come across products with these strange numbers on the packet. Before those numbers, there are the letters NPK.


They tell you the ingredients’ ratio in that packet 10 parts Nitrogen, 20 parts Phosphorous & 10 parts K for Potassium or Potash. These numbers change depending on what strength & purpose the product is designed to be used on.  For example Carrots might be NPK 0-10-10 & Roses – NPK 6-12-6 to add to that information you must also read on the box how the product should be used – sprinkled, added to water etc and the spread of it’s use per metre or yard.

If you don’t want to pay the high price of buying these each & every year you can buy the raw materials in bulk, this what I do, and then I spoon the required amounts for a square metre into an old jam jar, putting the names of the plants & the time of year the contents should be used in the garden. If you were to buy in granular form, say 20k of each of the three compounds in 2023 it would cost around £50 in total. 10k of Growmore (a well-known brand) would cost about £20.). Growmore is NPK 7-7-7, but our bulk product would be 5 times stronger or even more. Your money would buy to £200 worth of 7-7-7 fertilizer or even more. But in general, what you will find it you will only need to supplement one or maybe two of the given compounds to get much better results. Of course this depends on the soil of your garden and the balance of that soil. In an even balanced soil or growing pot for example, Tomatoes need Phosphate early on in the growing season, then when in flower they’ll need more phosphate plus the same amount of Sulphate boost. Finally, when in fruit they want an even amount of NPK

Here’s more information on what plants need. Remember to always follow the per square mitre rules for each. . Going back to our first NPK ten parts N, 20 Parts P & 10 parts K (these could be spoons, cups etc) The total weight x the usage state will give you the total area your filled jam jar can be used on. It’s likely the jar will last for many years, so keep in sealed in a dry place.

Ammonium Sulphate | NPK 21-0-0 /35g msq – N leafy growth – spring and early summer
Phosphate | N.P.K 0-46-0 / 20/30gms msq – P Root development – Autumn
Sulphate of Potash/Potassium Sulphate N.P.K 0-0-50 / 30-50g msq – K – flowers and fruit – Summer

Spuds – 2-2-3
Toms – Small plants 3-15-0. Flowering 6-24-24 Fruiting 18-18-21
Peas, Peppers, Beetroot – 5-10-10.
Carrots – 0-10-10.
Cabbage, Parsnip – 1-1-1
Lettuce – 1-2-4
Onions – 15-15-30
Celeriac – 10-52-10

Roses – 6-12-6
General Flowering plants like Cosmos, Carnations,Lilly- 3-1-2
Clematis – 5-10-5
Fuchsia – 2-1-1
Mums – 6-2-4


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