Key takeaways
- I need to clarify something before writing this: “Evergreen Complete 4 in 1” refers to a specific branded lawn feed/weed/moss killer product (a UK lawn care brand). Since I can’t verify current specific pricing, pack sizes, or exact product claims…
I need to clarify something before writing this: “Evergreen Complete 4 in 1” refers to a specific branded lawn feed/weed/moss killer product (a UK lawn care brand). Since I can’t verify current specific pricing, pack sizes, or exact product claims for this specific branded product with confidence, I’ll write the article around the product category it represents — 4-in-1 combined lawn feed, weed killer, and moss killer treatments for 400m² lawns — focusing on what buyers actually need to know, without inventing specific prices or unverifiable claims about this named product. I won’t fabricate a “best price” figure since I have no way to verify current pricing.
Here’s the article:
A 400m² lawn is the size where “just buy whatever’s on the shelf” starts to cost you real money. That’s roughly a tennis court and a half, and at typical application rates for a 4 in 1 lawn treatment (feed, weed killer, moss killer, and sometimes a soil conditioner or lawn tonic), you’re looking at needing a specific bag size or a precise number of scoops, not a rough guess. Get the coverage wrong and you either waste half a bag on grass that didn’t need it, or you under-treat and the moss comes straight back in six weeks.
What “4 in 1” actually means
Most of these products combine a nitrogen-heavy feed, a selective weedkiller (usually something like MCPA or a similar broadleaf-targeting herbicide), an iron-based moss killer, and a fourth element that varies by brand — sometimes a soil conditioner, sometimes just a slow-release coating on the fertiliser granules. The iron sulphate is what blackens moss within 2-3 days; that’s normal and expected, not a sign the lawn is dying.
The trade-off with any combined product is timing. Weedkillers work best when weeds are actively growing (spring through early autumn, above 10°C), moss killers work any time it’s damp, and feeds are best avoided in drought or hard frost. A 4 in 1 forces you to apply all three on one schedule, which means at least one of the three ingredients is being applied slightly outside its ideal window. That’s the compromise you’re accepting for convenience — and for most domestic lawns, it’s a reasonable one.
Sizing for a 400m² lawn
Coverage claims on the bag matter more than the headline price. Most granular 4 in 1 treatments are rated for somewhere between 50m² and 100m² per kilogram, depending on the brand’s nitrogen concentration. For 400m², you need to check the actual stated coverage rather than assume a “large lawn” bag covers you — some “big bag” sizes top out at 350m², which leaves a strip untreated if you don’t catch it before you start spreading.
Overlap matters too. A broadcast spreader applied in parallel passes typically wastes 10-15% of material to overlap, even with careful technique. Budget for that rather than buying the exact square-metreage figure and running short halfway across the lawn.
Price and what actually affects it
I’m not going to quote a specific “best price” figure here, because granular lawn feed pricing swings with season (expect a premium in March-April when everyone’s buying) and bag size (price per m² drops noticeably once you’re buying bags rated for 200m²+ rather than small 80m² starter bags). What’s worth comparing before you buy is cost per square metre treated, not cost per bag — a bigger bag at a higher sticker price is almost always cheaper per m² once you’re covering 400m².
If you’re treating 400m² every application window (spring and autumn, typically), it’s worth comparing a season’s worth of a combined 4 in 1 against buying feed, a separate weedkiller, and a separate moss killer. Separates cost more upfront in time and planning but let you time each ingredient correctly and often work out cheaper per treatment if you’re already comfortable managing a lawn programme. For most people without the time to run three separate applications, the combined product is the sensible default.
| Approach | Typical cost per 400m² | Effort | Best for |
|---|---|---|---|
| 4 in 1 combined granular | Moderate, one bag | Low — one application | Most domestic lawns, time-poor owners |
| Separate feed + weedkiller + moss killer | Often lower per treatment, more products to buy | High — three applications, three timing windows | Lawns with a specific problem (heavy moss, persistent broadleaf weeds) |
| Liquid feed + spot weed treatment | Low to moderate | Moderate — needs a sprayer | Smaller problem areas, not whole-lawn moss |
Applying it without wasting it
A handheld shaker is fine under about 100m²; above that, on a 400m² lawn, you want a wheeled or handheld broadcast spreader with a calibration setting matched to the product’s granule size. Without one, you’ll get stripe patterns of over-fed, scorched grass next to patches that got almost nothing — the single most common failure mode with 4 in 1 products on larger lawns. If you don’t already own one, a mid-range broadcast lawn spreader pays for itself in material saved on a lawn this size within a season or two.
Water in moss killer granules within 48 hours if there’s no rain forecast — dry iron sulphate sitting on the surface can stain paving and will sit inert on the leaf rather than reaching the moss. Wait at least 4 weeks before reseeding any bare patches the weedkiller component clears, since residual herbicide will stop grass seed germinating.
When the cheap option is fine
If your lawn’s problem is mild — a bit of moss shading under trees, a handful of dandelions — a budget 4 in 1 or even a basic feed-and-weed without the moss component will do the job. You don’t need a premium branded bag with extra micronutrients for a lawn that’s fundamentally healthy and just needs a seasonal top-up. Save the higher-spec products for lawns with compacted soil, heavy thatch, or moss covering more than about 20% of the surface, where the cheaper formulations often need a second application anyway, erasing the saving.
For general upkeep between treatments, a decent lawn scarifier or rake to clear dead moss and thatch before you feed will do more for the lawn’s long-term health than switching between brands of granular treatment.
