Welcome to part 2 of decoding garden jargon so that you can use your initiative and common sense to help you grow great veges and attractive ornamentals instead of being 'blinded' by science and having to rely on the 'experts' for advice and garden products. Today we're demystifying "NPK", those three letters you so often see on the back of bags of fertilizer and compost-mix. In fact, after you read what's below, you may never have to buy a bag of either again!
NPK stands for 'nitrogen, phosphorus, and potassium', three essential goodies our gardens can't do without.
Nitrogen (N) is a nutrient (think 'plant food') that helps plants grow and keeps them looking green. If you have plants with sickly yellow-looking leaves, it's very likely that they're not getting their fill of nitrogen. How do you give them some? Adding animal manure to the garden is one way (some kinds of manure can go on the garden straight away and some kinds need to sit around for a few months first). A few handfuls of dried blood on the garden is another way to serve up nitrogen (this may sound gross but if you buy dried blood from a garden centre it will be in a powdery form). If you don't want to depend on animals for nitrogen, you can grow some nitrogen-fixing plants (plants that are good at collecting nitrogen out of the air) and then dig them into your soil.
Phosphorus (P) is a nutrient that helps plants use other nutrients in the soil. You'll know if you're missing it because your plants will be miserably small when they should be large. They'll have stunted little flowers – or no flowers at all! And the whole plant may have a nasty bright green or purplish tinge to it. But if that's the case, don't despair. Throw on some bone meal (ground bone) or rock phosphate dust (which you probably will have to buy from a garden centre). Piling on the compost will help, too because compost assists plants in using the phosphate that's already in the soil.
Potassium (K) is a naturally occurring all-round tonic that encourages good plant health. It helps plants to grow faster and stronger, use water better, fight off disease, resist pests, and produce a good harvest. You seriously don't want to be without it in your garden but if you are, you may notice your plants' leaves look a little yellow round the edges and have some nasty brown spots on them. If you're a do-it-yourself-er and don't want to rush to the garden centre for a bag of general fertilizer, add potassium to the soil by piling on the sea weed and letting it rot down, sprinkling round a few handfuls of wood ash, and heaping on the compost. If you're in a hurry for potassium, make seaweed and comfrey-leaf soup (comfrey is rich in potassium) by steeping the two in a drum of water and then watering the liquid directly onto your plants.
Now that you have the 'science' of NPK under your belt, I hope you'll enjoy the very hands-on experience of delivering it to your garden. It's a load more fun, and a lot cheaper, than ladling it out of a plastic sack!