Brunnings Sulphate of Ammonia, and how not to burn a crop

What sulphate of ammonia does, and why it needs a light hand

Sulphate of ammonia is about as blunt as garden fertiliser gets. It's a straight nitrogen product with nothing else much in it, and it dissolves so fast that the plant has hold of it almost immediately. That's exactly why people like it and exactly why it causes trouble. Nothing in the garden shed will green a leafy crop up faster and nothing will burn one faster either.

Check that the yellow really is nitrogen

A pale leaf is not automatically a hungry one, so it's worth 20 seconds of looking before you buy a bag. Nitrogen shortage shows up on the oldest leaves first, down low, and the whole leaf goes evenly pale because the plant is pulling the nitrogen out of the old growth to build the new. That is the one this product fixes.

If instead the yellowing is between green veins, or it's showing on the newest leaves at the top while the old ones stay green, then you're looking at a trace element or a pH problem and more nitrogen will not touch it. Same goes for a bed that's waterlogged, where the roots have simply stopped working. A pH test kit sorts out the second of those in about 5 minutes.

What it's good for

• Leafy crops where the leaf is the thing you're eating. Lettuce, silverbeet, spinach, cabbage and the rest of the brassicas all respond quickly.
• A lawn that's gone pale and needs pulling back into colour.
• Soil that has drifted too alkaline, because the sulphate side of it acidifies as the nitrogen is taken up. That's a slow effect rather than a quick correction, and it's a useful side benefit rather than a reason to buy it.
• A compost heap that's gone all brown material and has stalled, where a small scatter gives the bacteria the nitrogen they're short of.

Where it does more harm than good

Push nitrogen into a fruiting crop and you get a magnificent bush with very little on it. Tomatoes, capsicums, chillies and pumpkins all do this, and so do citrus if you keep feeding straight nitrogen instead of a balanced citrus food. Once a plant has moved into flowering it wants potassium rather than more leaf, so a bag of potash is the better call at that point.

It's also the wrong product for soil that's already acidic, since you'd be pushing the pH further down a direction that's already causing problems. And it has no place around the phosphorus sensitive natives or in a bed you've just limed, because lime and an ammonium fertiliser together drive the nitrogen off into the air as ammonia and you lose most of what you paid for. Leave a few weeks between the two.

How to put it on without burning anything

• Go by the rate on the bag and resist the urge to be generous. The margin between a good feed and a burn is narrower with this than with almost anything else you'll buy.
• Keep it off the foliage. Granules sitting on a wet leaf will scorch a hole straight through it, so apply to dry leaves and brush off anything that lands.
• Water it in straight away, properly, so it's washed off the surface and down to the roots.
• Never put it on a dry, stressed bed. Water first, feed second, water again.
• Keep it well clear of the stems and the trunks, the same as any concentrated fertiliser.

Dissolving it in a watering can rather than spreading it dry is the safer way to do a small bed or a few pots, because you get an even spread instead of a hot spot wherever a clump landed. Store the bag somewhere properly dry, since it takes up moisture out of the air and sets into a brick if you leave it open in the shed.

The honest limitation

This is a fast fix and it doesn't build anything. It feeds the plant in front of you and it leaves the soil no better than it found it, and the nitrogen that isn't taken up washes down past the roots with the next decent rain. If the bed goes pale on you every single season, the answer isn't more sulphate of ammonia, it's organic matter going in year after year until the soil starts holding its own nitrogen.

Shop related products

• Brunnings Sulphate of Ammonia 2.5kg. Fast nitrogen for a leafy crop or a pale lawn.
• Brunnings Urea 2.5kg. The other straight nitrogen, and it behaves differently once it's in the soil.
• Manutec Soil pH Test Kit. Worth doing before you acidify a soil you haven't measured.
• Brunnings Garden Compost with Seaweed 25L. The slow answer to a bed that goes pale every year.

Did you know we also carry garden lime and gypsum in the shop in the bigger bags, which is what you want if the pH test sends you the other way. They're not all on the website, so give us a ring on (08) 8536 4333 to check what's on the shelf, or come and have a look through the garden centre.

Read next

• Brunnings Urea, what it does and when to use it
• What to do when your soil is too acidic or alkaline
• Soil amendments, and which one your garden actually needs

I keep this one on a high shelf on purpose, because it's the bag I'm most likely to be too generous with when the lettuce looks sad.

Cheers,
Candeece

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