Grass Seed Germination Calculator — Estimate Germination Time
Estimate germination time based on soil temperature and seed type.
How We Calculate This
This calculator estimates germination time from seed type and soil temperature, using typical UK ranges from horticultural seed suppliers (Grass Seed Online, Lawn UK).
At ideal soil temperature: perennial ryegrass germinates in roughly 5-14 days (it needs only ~7-8°C, so it is the fastest and most cold-tolerant), red fescue 10-21 days (needs ~10-11°C), and bent grass 11-21 days (needs ~15°C and is the slowest). Micro clover 7-14 days; wildflower mixes 14-30 days.
Times are adjusted for the soil temperature you enter. Below the species minimum, germination roughly doubles to triples and may fail; in the cool band (below your cold threshold, default 10°C) it slows by ~1.5-2×; through the ideal band (up to your optimal max, default 18°C) the standard range applies; above that, germination speeds up until soil gets too hot and dries out, when results turn variable. Germination is a biological range, not a fixed number — treat these as estimates and keep the seedbed consistently moist.
Frequently Asked Questions
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Last updated: February 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.