Lawn fertilizer schedule — month-by-month NPK guide

Lawn fertilizer schedule — month-by-month NPK guide

Fertiliser is the highest-leverage input on a lawn after correct mowing — but only when applied to the right grass type in the right season. The most common and most damaging mistake is feeding cool-season grass heavily in spring (a flush of soft top growth that then collapses in summer) and skipping the autumn feed (the one that actually builds the lawn). This guide gives the month-by-month schedule for both grass families, explains what the three NPK numbers on the bag actually do, and lists current US and UK products. The governing split is the same cool-season vs warm-season divide covered in lawn care basics.

Feed at the right time: Add your zip code (US) or postcode (UK) to Growli and the app sets your fertiliser dates by grass type and climate — including the all-important autumn window and a warning not to feed during heat.

Reading the NPK numbers

Every fertiliser bag carries three numbers, e.g. 25-0-10. They are the percentage by weight of:

• N — Nitrogen: drives green colour and leaf growth. The dominant nutrient for lawns. The first number is the one to watch.
• P — Phosphorus: root development and establishment. Important for new seedlings and starter feeds; in many US states phosphorus lawn fertiliser is restricted by law (to protect waterways) unless a soil test shows a deficiency or you are establishing new turf — hence the "0" middle number on many maintenance products.
• K — Potassium: stress, drought, cold, and disease tolerance. The key nutrient for the autumn feed because it hardens the lawn for winter.

Two more terms that matter:

• Slow-release (slow-release urea, sulphur-coated urea, methylene urea, or organic): releases nitrogen gradually over weeks. Strongly preferred for lawns — it avoids the surge-and-crash growth and the burn risk of fast soluble nitrogen. Most quality lawn products are at least partly slow-release.
• Burn risk: too much soluble nitrogen, or granules left on wet blades, scorches the grass. Apply to dry grass, at the labelled rate, and water in.

A typical green-up product is high-N, low-or-zero-P, moderate-K — something in the region of 25-0-10. An autumn/winteriser product shifts toward higher potassium.

Cool-season schedule (US zones 3 to 7, all UK lawns)

Cool-season grass grows in spring and autumn and is heat-stressed in summer. The schedule follows that rhythm. Autumn is the most important feeding season of the year — that is when the grass is photosynthesising hard but putting energy into roots and reserves rather than top growth, which is exactly what you want to feed.

That is two autumn feeds plus one modest spring feed — three applications total for most lawns; a fourth (a second light spring feed) only on poor soils. Resist the urge to pile on spring nitrogen for early green colour: it produces soft, disease-prone growth at the expense of roots, then leaves the lawn weak for summer.

Warm-season schedule (US zones 8 and warmer)

Warm-season grass is dormant and brown in winter and grows hard through summer heat. The schedule is the mirror image of cool-season — feed into the heat, not away from it.

The critical warm-season rule: stop nitrogen feeding by early September (timing shifts with latitude). Late nitrogen pushes tender new growth that has no time to harden before the first frost, causing winter injury. Never apply a "winteriser" high-N feed to warm-season grass the way you would to cool-season turf — it does the opposite of what is intended.

Use the frost date calculator to set your local green-up start and your last-feed cut-off.

Month-by-month — cool-season lawn

• Jan – Feb: dormant. No feeding.
• Mar: generally too early in most of the cool-season belt; wait for steady growth.
• Apr – May: one light spring feed once the lawn is actively growing (modest N, e.g. ~20-0-10).
• Jun – Aug: no fertiliser during summer heat stress. Feeding now invites disease and burn.
• Sep: the year's most important feed — higher-N slow-release. Pair with aeration and overseeding.
• Oct – early Nov: winteriser (higher-K) while the grass is still actively growing and soil is above ~10°C / 50°F.
• Dec: dormant. No feeding.

Month-by-month — warm-season lawn

• Jan – Mar: dormant/brown. No feeding.
• Apr: green-up beginning; do not feed until fully green and actively growing.
• Late Apr – May: first feed once fully greened up (high-N slow-release).
• Jun – Aug: monthly feeding through peak growth.
• Early Sep: final feed of the year — moderate, then stop nitrogen.
• Oct – Dec: no feeding; lawn entering dormancy.

Products — US

Fertiliser safety: Lawn fertilisers are concentrated chemicals. Follow the bag's labelled rate and spreader settings exactly — over-application burns the lawn and pollutes waterways. Apply to dry grass and water in. Keep children and pets off treated areas until watered in and dried (check the label). Store in the original sealed container away from food and out of reach of children and pets. Many US states restrict phosphorus lawn fertiliser by law — use a zero-P maintenance product unless a soil test or new seeding justifies phosphorus.

• Scotts Turf Builder / WinterGuard — the dominant big-box synthetic line; WinterGuard is the autumn/winteriser formula (notably high N with potassium for cold hardiness). Widely available.
• Scotts Turf Builder Starter (around 24-25-4) — high-phosphorus starter for new seed and overseeding.
• Milorganite (~6-4-0) — a slow-release organic nitrogen product; low burn risk, builds soil, well suited to monthly warm-season feeding and as a gentle cool-season option.
• Espoma Organic Lawn Food — organic, slow-release; two moderate organic feeds in autumn can match one heavy synthetic feed while improving soil.

Avoid combined weed-and-feed products on any lawn you are overseeding — the crabgrass preemergent in them also blocks grass seed (see crabgrass control).

Products — UK

The same fertiliser-safety rules apply. UK pesticide and weed-and-feed product approvals change; confirm current status with the RHS or the product label before buying.

• Westland SafeLawn — an organic, child- and pet-friendly granular feed with added grass seed and soil bacteria; widely sold at B&Q, Homebase, and garden centres and stocked via RHS Plants. Marketed for fast greening without burn risk.
• Aftercut (e.g. Aftercut Ultra Green) — a popular fast-greening granular feed-and-condition range.
• Miracle-Gro Lawn Food / EverGreen — established UK liquid and granular lawn feeds; the EverGreen Complete range is a 4-in-1 feed-weed-and-moss product (avoid 4-in-1 types if overseeding).
• Westland PureGreen lawn seed is a newer UK introduction for overseeding alongside feeding.

UK feeding follows the cool-season schedule: a spring feed in April–May and an autumn feed in September, with the RHS recommending a lower-nitrogen, higher-phosphate/potassium autumn feed on thin or poor soils to strengthen roots for winter rather than force soft top growth.

US vs UK summary

US

Three feeds for cool-season (light spring, key September, October/November winteriser); four-to-five for warm-season (late-spring through monthly summer, stop by early September). Watch the state phosphorus restrictions and never apply late nitrogen to warm-season grass.

UK

All cool-season: a modest spring feed and the more important autumn feed, with the autumn product leaning lower-N and higher-K on poor soils per RHS advice. No summer feeding during dry spells; if a hosepipe ban is on, hold granular feed (you cannot water it in safely) until rain or the ban lifting.

Related

• Lawn care basics — the full month-by-month lawn calendar
• Types of grass — identify cool vs warm-season before feeding
• Types of fertilizer — NPK formulas and slow-release explained
• How to overseed your lawn — starter feed at sowing
• Crabgrass control — why weed-and-feed conflicts with overseeding
• Lawn watering guide — watering feed in correctly
• How to make compost — organic top-dressing as a feed
• Frost date calculator — set green-up and last-feed dates

Sources: Milorganite application rates and schedule; Scotts lawn fertiliser schedule guidance; Penn State and NC State Extension seasonal turf fertilisation; RHS lawn feeding advice; university Extension nitrogen-timing research.