Grass Fertiliser Guide: Which One Should You Use?
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Choosing the right grass fertiliser isn't complicated - but it does require knowing what your lawn actually needs and when. Use the wrong feed at the wrong time and you'll either waste money or actively set your lawn back. Get it right and the difference is visible within days.
Here's everything you need to know.
Why Your Lawn Needs Feeding
Grass is a plant, and like any plant it needs nutrients to grow. Every time you mow, you're removing leaf blades and forcing the grass to draw further nutrients from the soil to replace them. Nitrogen - the nutrient most responsible for green growth - is also highly soluble and washes out of soil readily during heavy rain.
The result, over time, is nutrient-poor soil and a lawn that looks pale, patchy and increasingly attractive to weeds and moss. A good grass fertiliser restores what's lost and gives the lawn what it needs to stay thick, green and resilient.
Understanding NPK: What the Numbers Mean
Every lawn fertiliser carries an NPK rating. These three numbers tell you the ratio of the three primary nutrients:
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Nitrogen (N) - the primary driver of green leaf growth. Pale or yellowing grass is almost always a sign of nitrogen deficiency
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Phosphorus (P) - develops and strengthens the root system, making the lawn more resilient in dry weather
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Potassium (K) - improves grass durability, hydration and disease resistance; critical for helping turf handle drought and cold
Knowing this makes it much easier to choose the best fertiliser for grass at each point in the season - high nitrogen in spring for growth; high potassium in autumn for hardening.
Seasonal Feeding: When to Apply What
Spring (February-May)
This is when grass comes back into active growth. A spring lawn fertiliser should be high in nitrogen to drive strong leaf development and get the lawn back into good shape after winter. Apply once the grass is visibly growing - feeding too early, before roots are active, wastes product.
Summer (May-August)
If the lawn looks pale or tired mid-season, a top-up feed helps. But don't overfeed -applying lawn grass food more frequently than recommended triggers excess leaf growth at the expense of roots, weakening the turf over time. In drought conditions, wait for rain before applying any feed; grass goes semi-dormant and can't use what you give it.
Autumn (September-November)
Autumn is the second most important feed of the year. Switch to a high-potassium, high-phosphorus formulation with lower nitrogen - this hardens leaf blades for frost, promotes deep root growth and prepares the lawn for winter. Applying a high-nitrogen lawn fertiliser in autumn is a common mistake that leaves soft, disease-prone growth vulnerable to the first cold snap.
Liquid vs Granular Grass Fertiliser
Both have their place, and the best programmes use both.
Granular: more cost-effective for larger lawns; apply with a spreader on a day when soil is damp and grass is dry; water in after application; slow-release options feed for 6-16 weeks. The best fertiliser for grass in spring and autumn in terms of long-term soil nutrition.
Liquid: faster-acting - absorbed through the leaf blade rather than the root, with results visible in days rather than weeks. Ideal for mid-season top-ups, smaller lawns, and situations where a rapid response is needed. Follow dilution rates carefully; too concentrated a solution can scorch the leaf.
The Organic Option: Why Seaweed Is Worth Considering
Most conventional grass fertiliser products - particularly liquid ones - carry a meaningful scorch risk in dry summer conditions, which limits their application window.
Oceanic Organic liquid seaweed fertiliser works differently. It's a biostimulant - rather than flooding the grass with salts, it improves how the plant absorbs and uses nutrients from every other feed in the programme. It builds stronger root systems through natural growth hormones, increases chlorophyll production for deeper colour, and helps grass retain water during dry spells through naturally occurring betaines.
Crucially, it can be used from March through to November with almost no scorch risk - removing the timing anxiety that comes with conventional liquid feeds. For a dedicated look at how it performs on turf, read our guide to liquid seaweed for lawns. For commercial supply at scale, our bulk fertiliser is available in 200L drums and 1000L IBC.
Quick Reference: Which Feed When
|
Season |
Feed Type |
Key Nutrient |
Apply When |
|
Early spring |
High nitrogen granular or liquid |
N |
Grass actively growing |
|
Late spring-summer |
Slow release granular + liquid top-up |
N + K |
Soil moist, grass dry |
|
Summer top-up |
Liquid (organic preferred) |
Balanced |
Avoid drought conditions |
|
Autumn |
High potash, low nitrogen granular |
K + P |
September-November |
|
Year-round |
Organic liquid seaweed |
Biostimulant |
March-November |
The right lawn fertiliser programme doesn't have to be complicated. Feed in spring to drive growth, top up through summer as needed, harden in autumn, and run a quality good grass fertiliser like liquid seaweed through the whole season to keep soil biology healthy and make every other feed work harder.