How to Save Money on Fertiliser When Prices Are Up

If you’re trying to save money on fertiliser, this has been a hard year to do it. When the Strait of Hormuz closed in early March, it choked off supply from the Persian Gulf, which typically provides about 40% of Australia’s urea. Within weeks, urea had climbed from a little over $800 a tonne to about $1,450 at its April peak.

Prices have eased since, but not all the way. In mid-October, global urea prices were still about 19% higher than a year earlier, and researchers at IFPRI have warned that fertiliser markets are unlikely to return to normal before the end of the year.

You can’t do much about the price of a bag. You can do a lot about how much of it reaches your plants. A widely cited study estimated that only about a third of the nitrogen applied to the world’s cereal crops was recovered in the harvested grain. The rest was lost along the way.

Home gardens can beat that comfortably. You’re feeding a few square metres, not thousands of hectares, so you can feed with far more precision than any farmer.

We sell fertiliser, so this might sound odd coming from us: most gardens could get the same results from less of it. Here’s where fertiliser goes missing, and how to keep more of every gram working.

Why fertiliser costs more this year

Nitrogen fertilisers like urea are made using natural gas, and the Middle East supplies about a third of the world’s urea exports. When fighting closed the Strait of Hormuz, much of that supply was suddenly stuck.

Farmers felt it first. In a March snap survey of 150 vegetable growers by AUSVEG, more than half reported fertiliser shortages, and 27% had cut back or stopped planting.

Garden fertilisers are made from the same raw materials, so home gardeners aren’t immune, even if the price of your usual bag hasn’t moved yet. Prices change quickly, so treat every figure here as a snapshot.

Where your fertiliser actually goes

Fertiliser only earns its money once it’s inside a plant. On the way there, it can leak out in four main ways.

Where does your fertiliser go?

Tap each route to see where fertiliser escapes, and how to stop it.

Into the plant

The only route that earns its keep. Roots take up dissolved nutrients from moist soil, and the plant puts them to work.

Tap the other routes to find your leaks.

Feed little and often

A plant can only take up so much at once. Give it a season’s worth in one hit, and most of it sits in the soil waiting, exposed to heavy rain, overwatering and gas loss, until the plant is big enough to use it.

Smaller, more frequent feeds solve that. Fertiliser maker Incitec Pivot notes that a little-and-often approach allows nutrient supply to be more closely matched to what the plant takes up.

One big feed vs little and often

Switch between the two approaches to see how closely the fertiliser in the soil matches what a growing plant can use. Hover or tap the chart for details.

One big feed floods the soil early, when the plant is small and can use little of it. That surplus sits exposed to rain, watering and gas loss. By the time the plant is growing fastest, supply has run short.

A simplified illustration of the principle, not measured data. Real results depend on the plant, the soil and the weather.

This is where water-soluble fertilisers earn their keep. Our NPK 20-20-20 dissolves completely, so you can mix a small, measured dose into a watering can every week or two while plants are actively growing. Our free Smart Fertigation Planner works out the dose for your plants and soil, and our NPK 20-20-20 guide covers the rates.

Little and often doesn’t mean more in total. The aim is the same amount or less, with more of it ending up in the plant.

Make every gram of urea count

Urea packs more nitrogen into every gram than any other common solid fertiliser: 46%. That also makes it the most expensive one to waste.

Left on the surface, urea can turn into ammonia gas and drift away. In Australian field measurements, broadcast urea that wasn’t worked into the soil lost an average of about 8 to 12% of its nitrogen this way, and up to 29% in poor conditions. The worst case is urea spread on damp soil that then dries out in warm, windy weather.

The fix costs nothing. Water it in straight after spreading, and make it a proper soak. Montana State University researchers found it took about 12 mm of water in one go to move urea safely into the soil, and that light, patchy rain could make losses worse. Or rake it lightly into the soil: Incitec Pivot notes that about 3 cm of cover suppresses the loss.

Take extra care on alkaline soil, where losses tend to run higher, and keep urea away from seeds and seedlings, where too much in one spot can burn. If you use our Urea, our urea guide has rates for lawns, veggies and fruit trees.

Measure, don’t guess

A handful is not a unit. Hands vary, scoops vary, and a bit extra for luck is pure waste. Weigh doses on kitchen scales, or weigh one spoonful once and write it on the lid, then stick to the label rate.

More fertiliser doesn’t buy better plants, either. Soil scientists at the University of Connecticut list it among the myths that cost home gardeners money, warning that extra nutrients don’t automatically mean extra health, and that surplus fertiliser can damage roots and leaves.

Feed only what’s missing

Plants grow only as well as their scarcest nutrient allows. Soil scientists call it the law of the minimum: growth tracks whichever nutrient is in shortest supply. If a plant is short of iron, extra nitrogen won’t green it up, and every gram you add is wasted.

So diagnose before you feed. Leaf symptoms are a good start, and our Leaf Scan AI can help you read them from a photo. A soil test every few years tells you what your soil actually holds, and the UConn team suggests treating the results “as a ceiling, not a suggestion to exceed”.

Check your pH while you’re at it. At the wrong pH, nutrients get locked up in forms roots can’t use. Phosphorus, for example, is most available in slightly acidic to neutral soil; in more acidic soil it’s tied up by aluminium and iron, and in alkaline soil by calcium. Our soil pH guide explains how to adjust it.

Keep nutrients where the roots are

Organic matter works like a nutrient sponge. It holds on to nutrients such as potassium, calcium and magnesium, and sandy soils rely heavily on it to stop them washing away. It builds slowly, over years, so start now with compost, mulch and plenty of living roots. Our piece on organic vs synthetic fertiliser explains why the two work best together.

Spread fertiliser evenly over the area where the roots are, not in a heap against the stem. And feed when plants can use it: in mild weather, on moist soil, while they’re actively growing. Feeding just before a heatwave or a downpour is money down the drain, as we explained in our El Niño garden guide.

Seven habits that waste fertiliser
Habit	Why it costs you	Do this instead
Spreading urea and walking away	Some of it escapes as ammonia gas	Water it in with a good soak, or rake it lightly into the soil
One big feed a season	The plant can’t use it all at once, so the surplus is exposed to loss	Feed smaller amounts every week or two while plants are growing
Feeding just before heavy rain	Nitrate washes below the roots, especially in sandy soil	Check the forecast, and feed once the rain has passed
Guessing the dose	Over-feeding wastes money and can burn roots	Weigh it, and stick to the label rate
Adding nutrients the plant isn’t short of	Growth is held back by whatever is scarcest	Diagnose first, from the leaves or a soil test
Ignoring soil pH	Nutrients get locked up in forms roots can’t use	Test your pH and correct it gradually
Feeding stressed or dormant plants	Roots in cold, dry or baking soil take up little	Feed in mild weather, on moist soil, during active growth

The cheapest fertiliser is the one your plant uses

Fertiliser prices may keep bouncing around for a while yet, and none of us can control that. What you can control is how much of each bag ends up in your plants instead of the air, the drain or the subsoil.

Water it in, feed little and often, measure every dose, and feed only what’s missing. Your plants won’t notice the difference. Your wallet will.

Not sure what your plants are short of? Try our Leaf Scan AI, use Find My Fertiliser to match a product to your plant, or work out exact doses with the Smart Fertigation Planner.