Black Hen

N is used by the plant mostly for making lots of leaves and stems. It seems strange to think about leaves and stems being protein, and mostly it's not protein humans can use well, but if you look at cows, they are almost all meat, and they eat leaves and stems (they have 4 stomachs so they can do this; we aren't as good at being vegetarian as we only have the one stomach).

P is mostly for growing roots.

K is mostly for growing fruits and seeds.

All kinds of plants need all three. Plants like lettuce, Swiss chard and kale need mostly nitrogen though, since we mostly want their leaves. Carrots, beets and turnip need more phosphorous. Tomatoes, beans, peas and peppers need more potassium.

If you give a plant too much of the wrong fertilizer, it can screw up. For example, tomatoes given lots of nitrogen will grow 10, even 12 foot tall. But they won't make many tomatoes because all the plant energy is used up growing leaves and stems instead of fruiting. Giving a lettuce crop too much K means it will try to fruit instead of growing leaves; this is called bolting and it makes the leaves bitter.

JBK wrote:But would using the 5-3-2 be that big of a difference for a fruit crop? Would it matter that much using 5 instead of 2?