When should you feed your lawn in the UK?
Feed bags say "apply in early spring." Early spring isn't a date — some years it arrives in February, some years it's still not here by April. Turf Alert's spring-feed trigger replaces that guess with a specific, measured condition.
The actual rule
Soil temperature (0-7cm) needs to hold at or above 5.5°C for 5 straight days. That's the point UK grassland agronomy science and professional turf-fertiliser guidance (ICL) independently converge on for perennial ryegrass specifically — where nitrogen actually gets taken up by the grass instead of washing straight through unused. It's not a "feels like spring" threshold; it's a biological one.
Worth saying plainly: the first version of this trigger used 12°C, a guess that felt like a reasonable margin above freezing. Checking that guess against real UK agronomic sources found it was roughly double the actual figure for this species — a mistake that would have delayed every feed alert by weeks. Corrected once checked, not left as "close enough."
Why it's not the same as the moss-and-weed window
Turf Alert also tracks a separate pre-emergent trigger — the window before moss and weed germination typically gets going — at 8.0°C for 3 straight days. That's a higher temperature bar than the feed trigger, but a shorter one to sustain, and germination biology is a genuinely different threshold from nitrogen uptake, not a lower version of the same thing.
The interesting part: even though 5.5°C is numerically easier to reach than 8.0°C, the pre-emergent window opens first almost every year — checked against 86 years of backtest data, it happens in every single one. The shorter 3-day sustain requirement reliably completes before the feed trigger's longer 5-day one does, even starting from a higher bar. Two real, independent thresholds, not a single number with two labels.
Two safeguards against a false start
On its own, 5.5°C is low enough that a mild spell in early-mid January can satisfy it in London's climate — which is obviously not "spring." Two gates stop that:
- Daylight: a day only counts toward the streak if it also has at least 9 hours of daylight — the lowest floor that reaches zero January false starts across the full 86-year backtest.
- Frost: even once the streak completes, firing is delayed (not cancelled) while a hard frost is forecast in the next 3 days. Feeding right before frost is wasted at best, damaging to new growth at worst.
So when should you actually feed?
Whenever your own soil crosses that line — which is exactly what checking your region's live forecast shows, updated daily. Or skip checking manually and sign up to get told the moment it opens, alongside the separate pre-emergent alert if moss and weeds are more your concern this year.
If it's mowing rather than feeding on your mind, the same "measured, not guessed" approach applies there too.
See the full model on how it works.