How to Choose the Right Autumn Lawn Fertiliser
To choose the right autumn lawn fertiliser, look for a feed that is low in nitrogen and high in potassium, with some phosphorus for roots and ideally a little iron for colour and moss resistance. A granular, slow-release autumn feed suits most lawns, applied from early September to late October while the soil is still warm.
As autumn approaches, the feed your lawn needs flips on its head. The fast-acting, nitrogen-heavy fertiliser that gave you lush green growth all summer is exactly the wrong thing now. Pick the right autumn lawn fertiliser and you toughen the grass for winter; pick the wrong one and you force soft growth that frost and disease will punish. Here is how to read the bag and match the feed to your lawn.
What NPK should you look for in an autumn lawn fertiliser?
The three numbers on every bag are the NPK ratio: nitrogen (N), phosphorus (P) and potassium (K). For autumn you want the first number low and the last relatively high. Nitrogen drives leafy top growth, the last thing you want heading into winter, so a low-nitrogen feed avoids soft, frost-prone growth. Potassium is the star: it strengthens cell walls and hardens the grass against cold and disease. A little phosphorus supports roots while the soil is still warm, and magnesium (shown as MgO) helps hold a healthy green. In short, you want a feed that toughens the lawn rather than pushes it to grow — our own autumn lawn feed is built to that 10-5-10 +2MgO pattern. For the full reasoning, our guide on why apply autumn lawn fertiliser covers the benefits.
Granular slow-release or liquid feed for autumn?
For autumn, a granular slow-release feed is usually the better pick. Slow-release granules drip-feed the roots over several weeks, matching the way the grass winds down so the potassium is there throughout the autumn window rather than in one quick hit. Liquid feeds act fast but flush through quickly, so they suit a growing-season pick-me-up more than a steady autumn hardening. Granular feeds are also more economical for a whole lawn; they just need a spreader for even coverage and a little moisture to wash them in. Our guide on liquid vs granular lawn fertiliser compares both.
What about added iron for moss and colour?
Iron (sometimes shown as Fe on the bag) is a useful extra in the cooler months. It deepens the colour of the grass without forcing growth, and it knocks back surface moss, which thrives in the damp British autumn and winter. A feed with a touch of iron helps a tired late-season lawn look richer and stay denser, giving moss fewer gaps to colonise. It is not a dedicated moss killer, but it is a handy bonus in an autumn or early-winter feed. If moss has already taken hold you need a proper iron-based moss treatment alongside the feed rather than instead of it — our autumn lawn feed and moss killer range pairs the two, and our guide on how to get rid of moss in your lawn covers treating it directly. One thing to avoid at this time of year: a three-in-one weed, feed and moss killer, because its selective weed killers only work while weeds are actively growing, roughly May to August.
How do you match the feed to your lawn and the timing?
Match the feed to where you are in the season. In early autumn, while the soil is still warm and the grass is growing, a balanced autumn lawn fertiliser like a 10-5-10 gives potassium to harden up plus a little nitrogen and phosphorus to keep roots ticking over. As the grass all but stops in late autumn, switch to a very low or zero-nitrogen, high-potassium winter lawn feed, ideally with iron, to protect colour and resist moss without forcing growth. Avoid feeding once the ground is frozen or waterlogged, as the grass will not take it up. This is the key difference from spring and summer feeds: those are nitrogen-led to drive green growth, where autumn and winter feeds are potassium-led to drive toughness. For the month-by-month picture, see our UK lawn feeding calendar and the essential lawn care calendar for UK gardeners.
MyLawn is Mowd's free DIY lawn-care app. It looks at your postcode's weather, the season, your grass type and what you have already done, then tells you the single best next thing to do, in plain English, with a reminder so the autumn feed never slips past its window. Take a look at MyLawn.
Related Mowd guides: Why Apply Autumn Lawn Fertiliser · UK Lawn Feeding Calendar · Liquid vs Granular Lawn Fertiliser · Shop autumn lawn feed
Frequently asked questions
What is the best NPK for an autumn lawn feed?
- Look for a low-nitrogen, high-potassium ratio, such as a 10-5-10, with some phosphorus for roots and ideally a little magnesium or iron for colour. The aim is to toughen the grass for winter rather than push soft top growth, which is why the nitrogen figure should be much lower than in a summer feed.
Is granular or liquid autumn lawn feed better?
- Granular slow-release feed is usually the better choice for autumn because it releases potassium steadily over several weeks, matching the lawn's slow wind-down. Liquid feeds act fast but flush through quickly, so they suit a quick growing-season boost more than a steady autumn hardening.
What is the difference between autumn and winter lawn feed?
- An autumn feed has a little nitrogen and phosphorus alongside its high potassium to keep early-autumn growth and roots ticking over, while a winter feed is very low or zero nitrogen and even higher in potassium, often with iron, purely to protect and harden the dormant lawn against frost and moss.
When should I apply autumn lawn fertiliser in the UK?
- Apply it from roughly early September to late October, after the summer heat eases but while the soil is still warm enough for the roots to take up the feed. If the grass is still growing enough to need the odd mow, it can still use an autumn feed.
Can I use an autumn lawn feed and moss killer at the same time?
- Yes. Pair a potassium-led autumn feed with a separate iron-based moss treatment, either together or a fortnight apart. Avoid a three-in-one weed, feed and moss killer in autumn: the selective weed killers in those products only work while weeds are actively growing, roughly May to August, and the extra nitrogen forces soft growth just as the lawn should be hardening off.