Brunnings All Purpose NPK, what it is and when to use it

March 25, 2025

Brunnings All Purpose NPK Fertiliser is a granular general feed, and NPK is not a brand name or a technology, it's just the three letters for the three nutrients plants use most of, so it's worth knowing what they actually do before you buy anything.

What the three letters mean

N is nitrogen and it drives leaf and stem growth, which is why lawn foods are heavy on it and why too much of it gives you a big green plant with no flowers on it. P is phosphorus and it goes into roots and into flowering and fruiting. K is potassium and it's the one behind flower quality, fruit and general toughness, so a plant short of potassium tends to look soft and cop every bit of stress that comes along. Every bag of fertiliser you pick up is some ratio of those, plus whatever trace elements the maker has put in.

An all purpose product means the ratio is fairly even, so it isn't pushed hard in any one direction. That's the point of it. It's the bag you reach for when you've got a mixed bed or some pots, or you just want to feed something and you don't want to stand in the aisle working out which specialist product applies.

Where it suits

Pots, indoors and out, are the obvious one, because potting mix runs out of nutrients faster than anybody expects and a plant in a pot has nowhere else to get them from. Beyond that it's fine on flower beds, on shrubs and on most ordinary garden plants. It's a granular product rather than a liquid, so it feeds over a longer stretch than something you water on, and that suits the way most people actually garden, which is in bursts rather than on a schedule.

The plants to keep it away from

Australian natives, and particularly the Proteaceae, so banksias, grevilleas, hakeas and waratahs. Those plants came off phosphorus poor soils and they're very efficient at taking up what phosphorus there is, so an ordinary balanced fertiliser hands them more than they can cope with. You get blackened leaf tips and then dieback, and sometimes you lose the plant altogether. It's slow enough that most people never link the two. Natives get a low phosphorus product instead, which is a different bag and it's in the same aisle.

Using it without overdoing it

Go off the rate on the bag rather than a handful. Fertiliser is one of the few things in a garden where more is genuinely worse, and burnt roots are much harder to fix than a slightly hungry plant.
Spread it out over the root zone rather than in a heap next to the stem.
Water it in afterwards, every time. Granules sitting dry against foliage are what causes burn.
Feed when a plant is actually growing. Feeding something dormant or heat stressed does nothing useful and can do harm.
If a plant looks sick, work out why before you feed it, because a plant that's waterlogged or sitting in the wrong spot does not have a nutrient problem.

Shop related products

Brunnings All Purpose NPK Fertiliser 500g. The small pack, which is enough for pots and a small bed.
Brunnings Organic+ All Purpose Plant Food 2.5kg. The organic based version, if you'd rather feed the soil as well as the plant.
Neutrog Seamungus 500g. Seaweed and manure pellets, low analysis and hard to overdo.
Brunnings Blood & Bone Based Fertiliser 2.5kg. Slower again, and worth knowing it is not one for natives either.

Did you know we also keep the All Purpose NPK in the bigger 3kg on the shelf in the shop, and that size is not available to buy through the website, so give us a ring on (08) 8536 4333 and we'll check what's there.

The whole fertiliser run sits in our garden centre, and if you tell us what you're feeding we'll point you at the right bag rather than the biggest one.