Garden And Gardener

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Which fertiliser for what?

by Sarah - March 28th, 2010.
Filed under: General Gardening. Tagged as: , .

What’s in fertliser? It’s nitrogen, phosphorus, and potassium and is normally shown by a ratio of numbers. Potassium is sometimes described as Potash.
Concentrate as it’s a bit complicated due to Scientists having to use letters for elements!

NPK – Nitrogen (N) Phosphorus (P) and Potassium (K).

General Fertiliser is usually 7:7:7 (or 15:15:15)
which gives the same percentage of nitrogen, phosphorus, and potassium
The remaining % of the fertilizer is comprised of inert matter. A liquid fertiliser that needs diluting should have higher percentages of NPK.

How can you tell which ratios do what?
Nitrogen promotes top growth – the leaves
Phosphorus promotes good roots – underground
Potassium benefits the whole plant – everything

Natural blood meal has an N-P-K ratio of 13-0-0
Comfrey has 8:3:20

Recommended ratios for different things:
10-20-20 for vegetables;
6-10-4 for flowers
29-3-4 for lawns. (Because the top growth is very important on a lawn)

Potato is a potassium-hungry plant so you need to look for a high end number!
Potato ratio could be 7-5-12
Tomato varies according to type of feed but one is 7-12-12

Don’t forget though it’s not always as simple as adding a man made fertiliser. Adding a bulk material like well rotted compost or horse manure also increases the organic matter in the soil making it healthier for plants and worms! The organic matter also holds the water better stopping your soil from drying out as quickly.

Next time you want to buy fertiliser ask yourself if you’re buying the right one. Look at the NPK ratio on the container.