A seed comes up from the warmth of the soil, not from a date on the calendar. Each kind of seed has a soil-temperature range it germinates in; sown into ground colder than that range it comes up slowly and patchily or rots before it can emerge, and ground hotter than the range stalls it too.
Promising · suboptimal if ignored → advise
How it works
Germination is driven by temperature-dependent enzymes that mobilise the seed's stored reserves, so in soil below the species' range those enzymes work too slowly for the seedling to emerge before soil fungi rot the water-swollen seed, and in soil above the range that same enzyme machinery is suppressed - which is why the reliable signal is the soil's own temperature, not the day of the year.
What to do about it
Read the soil, not the calendar: a soil thermometer pushed to sowing depth for a minute gives the number. Sow each crop once the soil sits in its germination range - warm-season crops wait for warm ground even after the frost has passed, and cool-season crops go into cool soil on purpose - or start seed in a warm flat indoors and set the young plants out. Each plant's own range is on its page.
How much it matters: No date or degree figure is invented here - soil warms on its own schedule at each site and every crop's range differs, which is the point. The rule advises checking the soil rather than the calendar; it never blocks, because the app has no soil-temperature feed and a gardener with warm ground or a warm flat is right to sow.
The evidence
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
OSU Extension Service / J. F. Harrington (Dept. of Vegetable Crops, Univ. of California, Davis), 'Soil temperature conditions for vegetable seed germination', extension.oregonstate.edu/gardening/soil-compost/soil-temperature-conditions-vegetable-seed-germination (published April 2013, reviewed 2024; fetched in-container 2026-09-20, read 2026-09-20): the table 'Days to appearance of seedlings at various soil temperatures' gives an optimum soil temperature per crop (e.g. bean optimum 80 F, lettuce 75 F, asparagus 75 F) and marks 'Little or no germination' at the cold end of each crop's row (e.g. bean at temperatures below 50 F). It states the germination range but does not state the cold-soil rot mechanism, which the Wisconsin source below supplies.
UW-Madison Extension, Wisconsin Horticulture / Lisa Johnson, 'When Is the Right Time to Plant Vegetable Seeds? Check Soil Temperature', hort.extension.wisc.edu/articles/when-is-the-right-time-to-plant-vegetable-seeds-check-soil-temperature (revised January 2025; fetched in-container 2026-09-20, read 2026-09-20): 'In our rapidly changing climate, a calendar date is not the best predictor for an extra early onset of spring weather in March or an extremely late, cold and wet April'; 'A better method to gauge when to put seeds in the ground is to test soil temperatures'; 'If you plant too early in cold soil, the seed may rot, but if it does germinate, it will be slow to do so and likely to produce stunted plants that are more prone to disease.'
Where this rule stops
A STANDING SEED-SOWING ADVISORY (trigger.kind always, universal like the seed-starting another rule here/115), so it surfaces on the Why page and can be cited by the germination guides; it gates nothing and docks no score, because the app cannot read a bed's soil temperature. It is the GENERAL statement of which another rule here is the acute special case: another rule here names the imbibitional-chilling injury a warm-season bean takes in cold ground, while another rule here is the same signal for every sown crop, the cool-season ones included, whose range simply sits low. Each species' own germination_soil_temp_c (O163) carries the number; this rule carries the reason.
Change history
Every change to this rule is one commit. This is what the project's version history records — the date and the reason — not a summary of it.
- corpus(another rule here): promote to verified — maintainer read the sources (2026-09-20)
- corpus+content: renumber the new germination rules to another rule here/162/163
Cite this page
Milpa Gardens. "A seed comes up from the warmth of the soil, not from a date on the calendar. Each kind of seed has a soil-temperature range it germinates in; sown into ground colder than that range it comes up slowly and patchily or rots before it can emerge, and ground hotter than the range stalls it too." Evidence grade: Promising. https://milpa.garden/rules/seed-comes-up-from-warmth-soil-not/
A garden-planning corpus: every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.