Germination Time & Days to Emerge from Heat
Germinates maize
Seeds germinate by accumulated heat above a base temperature — enter your mean and base temperature plus the crop's thermal time to get the days to germinate.
Set soil temperature
Next: expect seedlings in about 4 days; keep the seedbed warm and evenly moist so accrual doesn't stall.
Thermal time (degree-days) assumes adequate moisture and a roughly constant mean. Base temperature and target °D are species-specific.
Germination by temperature — key facts
- Degree-days/day
- mean − base temperature
- Days to germinate
- thermal time ÷ degree-days/day
- Below base
- no degree-days, no germination
- Thermal time
- ≈ constant heat sum per crop
- Cool-season base
- ≈ 2–5°C (lettuce, peas)
- Warm-season base
- ≈ 10–15°C (maize, okra)
- Warmer soil
- faster emergence (within range)
- Privacy
- Runs in your browser; nothing uploaded
Seeds count heat, not days
A seed in cold soil sits and waits; the same seed in warm soil races away. That's because germination is driven by accumulated heat above a base temperature, not the calendar. Every day the seed banks degree-days equal to the mean temperature minus its base temperature, and once the bank reaches the crop's thermal time, it emerges. Below the base temperature nothing accumulates — and nothing germinates.
This tool gives the degree-days per day, days to germinate, the thermal time and the mean temperature you entered, so you can time sowing, choose warmer windows, and decide whether row covers or a propagator are worth it. Pair it with the Growing Degree Days, Seed Priming and Seed Germination Test tools for a full establishment plan.
Time the sowing
Pick warmer windows so seed emerges sooner.
Skip cold-soil failures
Avoid sowing below the crop's base temperature.
Justify the cover
See how much faster warm soil germinates.
Plan the rotation
Slot the next crop once emergence is predictable.
Frequently Asked Questions
How does temperature control germination time?+
Seeds germinate by accumulating heat above a base temperature, not by counting calendar days. Each day adds degree-days equal to the mean temperature minus the base temperature; once the accumulated heat reaches the crop's thermal time the seed emerges. So warmer soil germinates seed faster, and below the base temperature it does not germinate at all.
How are days to germinate calculated?+
Degree-days per day = mean temperature − base temperature. Days to germinate = thermal time ÷ degree-days per day. For example a crop needing 60 degree-day units at a mean of 22°C with a base of 10°C accumulates 12 degree-days a day, so it germinates in about 5 days.
What is base temperature?+
Base temperature is the lowest temperature at which a crop's seed will develop — below it, no degree-days accumulate and germination stalls. It is crop-specific: cool-season crops like lettuce and peas have low bases (around 2–5°C), while warm-season crops like maize, cucumber and okra have higher bases (around 10–15°C).
What is thermal time?+
Thermal time (or heat sum) is the total accumulated degree-days a seed needs above its base temperature to germinate. It is roughly constant for a crop across temperatures, which is why it predicts emergence: a fixed amount of heat must be banked, whether quickly in warm soil or slowly in cool soil.
What is mean temperature here?+
Mean temperature is the average soil or air temperature the seed experiences over a day — typically the average of the daily high and low. Use soil temperature at sowing depth where you can, because it is what the seed actually senses and it lags air temperature, especially early in the season.
Why don't seeds germinate below the base temperature?+
Below the base temperature the enzyme and metabolic processes that drive germination effectively stop, so no degree-days accumulate. Sowing into soil colder than the base wastes seed and invites rot — wait for soil to warm past the base, then count degree-days from there.
Does warmer soil always germinate faster?+
Up to a point — faster within the crop's favourable range because more degree-days bank each day. But above an upper optimum, high temperatures slow or prevent germination (thermo-dormancy in lettuce, for instance). This tool assumes temperatures within the crop's working range above the base.
How can I speed up germination?+
Raise the soil temperature toward the crop's optimum with row covers, plastic mulch, a propagator or warmer sowing dates; this adds degree-days faster and cuts days to emerge. Seed priming also reduces the thermal time needed. See the Seed Priming calculator for that.
Are the figures precise?+
They're solid planning estimates. Real emergence varies with seed lot vigour, sowing depth, moisture, soil crusting and day-to-day temperature swings. Use measured soil temperature, re-check as conditions change, and treat the result as a guide to timing rather than an exact date.