Fertilising Your Lawn by Season: A Simple Annual Plan

Fertiliser is often sold as the answer to every lawn problem, but a lawn that is mowed too short, watered shallowly, or compacted will not be fixed by more feed. Feed helps a lawn that already has the basics right: sensible mowing height, deep watering, and soil that roots can penetrate. This guide gives a simple annual plan, season by season, and explains how to read a bag, how much to apply, and what to avoid, so you feed the grass you have rather than the weeds you do not want.

Reading the bag: N-P-K and what it means

Every fertiliser bag shows three numbers, such as 20-5-10 or 12-6-6. Those are the percentages, by weight, of nitrogen (N), phosphorus (P) and potassium (K), in that order. Nitrogen drives leaf growth and green colour. Phosphorus supports root development and seed establishment, and is often restricted in some areas because excess phosphorus can run off into waterways — check local rules before buying a high-phosphorus product. Potassium supports overall plant health, stress tolerance and winter hardiness.

A bag labelled 20-5-10 therefore contains 20% nitrogen, 5% phosphorus and 10% potassium by weight. If you apply 1 kilogram of that product per 100 square metres, you are applying 200 grams of nitrogen per 100 square metres, or 2 grams per square metre. That calculation matters, because fertiliser recommendations are usually given as nitrogen per area, not product per area, and different products have different nitrogen percentages.

A common guideline for an established lawn is 10 to 20 grams of nitrogen per square metre per year, split across the season. For a 100-square-metre lawn, that is 1 to 2 kilograms of actual nitrogen per year. With a 20% nitrogen product, that translates to 5 to 10 kilograms of product per year, split into two to four applications. With a 10% product, you need twice as much product to deliver the same nitrogen. Always work from the nitrogen figure, not from how much product “looks right” in the spreader.

Slow-release and fast-release products behave differently. Fast-release fertilisers green up a lawn quickly, often within a week, but they are more likely to burn grass if overapplied or applied to dry grass, and their effect fades faster. Slow-release products, often coated granules, release nitrogen over 8 to 12 weeks, green up more gradually, and are more forgiving. For most home lawns, a slow-release product is the safer choice, especially if you are new to fertilising.

Spring: wake the lawn up gently

In spring, as soil warms and grass starts growing actively, a light feed helps the lawn green up and thicken after winter. Wait until grass is growing and you have mowed at least twice, and soil temperature is consistently above about 10 degrees Celsius. Feeding a dormant lawn in early spring wastes product, because roots are not yet taking up nutrients efficiently.

A typical spring application is about 5 grams of nitrogen per square metre, using a balanced, slow-release product. For a 100-square-metre lawn with a 20% nitrogen product, that is 2.5 kilograms of product. Apply on a calm day, when grass is dry, and water lightly afterwards if the product label directs it, or if no rain is forecast in the next day or two. Watering in helps granules reach the soil and reduces the risk of burn, but do not wash the product off the lawn with a heavy watering.

Summer: feed lightly, or not at all

Summer is the season to be most cautious with fertiliser. Heat-stressed grass does not need a push to grow faster; it needs water, shade from taller mowing, and time. A heavy summer feed can burn grass, especially if applied to dry grass in hot sun, and it can encourage soft, lush growth that is more vulnerable to disease and drought.

If your lawn is growing well and looks healthy in summer, skip a summer feed. If it looks pale and thin despite good mowing and watering, a light summer application — about 2 to 3 grams of nitrogen per square metre, slow-release — may help, applied in the evening or on a cool, overcast day, and watered in lightly. Avoid feeding in a heatwave, during a drought, or when the lawn is dormant and brown. A dormant lawn is not hungry; it is waiting for rain, and feeding it will not wake it up safely.

Autumn: the most important feed of the year

For many lawns, the autumn feed is the most valuable application of the year. Grass is still growing, soil is warm, and the plant is storing energy for winter and for spring growth. An autumn feed, typically in early to mid-autumn, helps roots develop, improves winter colour, and gives the lawn a head start in spring without the flush of soft growth that a heavy spring feed can cause.

A typical autumn application is 5 to 7 grams of nitrogen per square metre, with a higher proportion of potassium than a spring feed, because potassium supports hardiness. Look for a product labelled for autumn use, and follow its label for rate. Apply when grass is dry, water lightly afterwards if the label directs it, and avoid feeding very late in autumn when growth has stopped, because nutrients will not be taken up and may wash away.

Winter: mostly leave it alone

In winter, most lawn grasses grow very slowly or not at all, and fertiliser applied now will largely sit on the surface or wash away. There is no need for a winter feed on an established lawn. The one exception is a specific winter fertiliser product applied in late autumn, before growth stops, which is really an autumn feed with a different label. Do not apply fertiliser to frozen ground, to a frosty lawn, or to a lawn covered in snow.

How to apply evenly and safely

Use a spreader for any lawn larger than a few square metres. A drop spreader drops product in a precise strip and is good for edges and small lawns, but it leaves stripes if you overlap or miss a strip. A rotary, or broadcast, spreader throws product in a wide arc and is faster for large lawns, but it can throw product onto paths and beds if you are not careful. Calibrate the spreader using the product label setting as a starting point, and test on a small area first. A typical hand-held or push spreader costs £25–£80 or $30–$100, and a basic model is enough for most home lawns.

Apply in two directions, at half rate each time, walking at a steady pace. This cross-hatch method, like the method for overseeding, avoids stripes of overfed and underfed grass. Keep product off paths, driveways and hard surfaces, and sweep any spillages back onto the lawn or clean them up, because fertiliser on hard surfaces washes into drains with rain. Wear gloves, wash hands after handling product, and keep children and pets off the lawn until the product label says it is safe to return, or until after watering and drying if the label does not specify.

Common mistakes

• Feeding a lawn that is actually compacted, shaded or drought-stressed, and expecting fertiliser to fix it.
• Applying product by eye, without working out the nitrogen rate for your lawn area.
• Feeding in hot sun, on dry grass, or in a heatwave, and burning the lawn.
• Using a fast-release product at a high rate for a quick green-up, then watching it fade and burn.
• Applying weed-and-feed to young grass, or to areas that do not need weed control.
• Feeding in winter, on frozen ground, when grass cannot take up nutrients.
• Leaving fertiliser on paths and driveways, where rain washes it into drains.

A simple annual plan — a light spring feed, a cautious summer approach, a solid autumn feed, and nothing in winter — will serve most lawns well. Add a soil test every two or three years, follow how to mow a lawn properly, and water deeply, as described in a lawn watering schedule that actually works, and you will need less fertiliser, not more, to keep a lawn green and dense. Feed is a tool, not a cure, and used sparingly and at the right time, it supports the lawn rather than forcing it.