Time to emergence from soil temperature
The number of days from direct sowing to emergence at the measured soil temperature. The value is taken from a published table; nothing is computed between its columns.
Quantities
| Symbol | Quantity | Unit |
|---|---|---|
T | soil temperature at sowing depth | °C |
T̄ | mean daily soil temperature over three days | °C |
t | time to emergence | days |
d | sowing depth used in the source trial | cm |
T_l, T_u | nearest table columns below and above | °C |
Formulas
Averaging of the model series
T̄ = (T_−1 + T_−2 + T_−3) / 3
Three complete consecutive days ending today are required. With fewer days the value is not computed: a two-day mean is not a three-day mean.
Adjacent table columns
T_l = 5 · ⌊T̄ / 5⌋, T_u = 5 · ⌈T̄ / 5⌉
No interpolation is performed between columns: the source publishes values at discrete points, not a function. At T̄ = 12 °C both values are given — for 10 °C and for 15 °C.
The table
The source is the table “Number of days for vegetable seeds to emerge at different temperatures” in UCANR Garden Notes 154, which goes back to the leaflet by Harrington and Minges (1954). Its columns are given in degrees Fahrenheit (32, 41, 50, 59, 68, 77, 86, 95, 104), which corresponds exactly to 0…40 °C in steps of 5 °C. The trial used a sowing depth of ½ inch (1.3 cm).
Three states of a cell
A cell holds either a number of days, or a marker for no emergence (0.0 in the source), or a marker for an untested combination (---). The first two are results of the trial, the third is its absence; the states are not merged. When adjacent columns hold different states, both values are reported and no date range is computed.
Source of the temperature
The first available of three is used: a bed sensor reading (valid for 24 h), a manually entered soil thermometer reading (valid for 7 days), or the three-day mean of the 0–7 cm layer from the ECMWF IFS model. These differ in method and in depth, so the source actually used is stated next to the value.
Coverage
The table covers fifteen of the catalogue's forty-nine crops. For the rest the reason for the missing row is given: not grown from seed, no row in the source, the species is not named by the source, a cover crop, or not raised from seed in a garden.
Verifiability
For every crop the corresponding row name in the source and the sowing depth are shown. The figures were transcribed from the UCANR edition and checked row by row against a second edition of the same table (WSU Extension).
Applicability and limitations
- Fifteen of the catalogue's forty-nine crops are covered.
- The trial used a sowing depth of 1.3 cm; none of the temperature sources measures that depth.
- Daily averaging hides the diurnal range: at the soil surface it reaches 16 °C while the daily means differ by less than 1.5 °C.
- Soil moisture is not part of the calculation; the table describes moist soil.
- Cultivar, seed age and germination rate are not taken into account.
- The model that publishes the 0–7 cm layer is selected by the plot's coordinates; for some coordinates the value is absent.
- The difference between forecast models at the locations checked is 0.1…1.3 °C.
- The figures come from a reprint; in another edition of the same table the eggplant row is shifted by one column (5 °C).
- A manually entered reading carries no depth and no time of day.
Sources
- University of California Cooperative Extension, Sacramento County, 2017. Soil Temperature Conditions for Vegetable Seed Germination. Garden Notes 154; таблица сроков — по Harrington, J. F. & Minges, P. A. (1954), Vegetable Seed Germination, University of California Agricultural Extension Leaflet — full text open Open
- Washington State University Extension. Soil Temperature Conditions for Vegetable Seed Germination. Раздаточный лист; данные собраны J. F. Harrington, Department of Vegetable Crops, UC Davis. Вторая перепечатка, по которой шла построчная сверка — full text open Open
- Open-Meteo. Weather forecast and historical weather API. open-meteo.com, CC BY 4.0 — full text open Open