What soil temperature each crop needs to germinate

The table below gives the lowest soil temperature at which seed starts to germinate, for each of the 88 plants in the Row & Bed reference library that record one. Where a plant is put in on a soil reading, that number is the one the app uses to open its planting window. Alabama extension publishes germination conditions by crop, and the readings sit far enough apart that no single planting date covers a garden with more than one thing in it.¹

The number is a soil reading, not an air reading, and the two part company in spring: bare soil warms behind a run of mild afternoons and lags further under mulch. Alabama extension notes that a soil thermometer settles it directly, which is worth more than any calendar.¹ Take the reading at seed depth, in the morning, in the bed you actually intend to sow.

A floor is not an optimum

Seed sown at the floor germinates slowly and unevenly. Utah State extension gives the practical band for leafy greens as 55 to 70°F, with emergence taking anywhere from 3 to 15 days across it, which is the spread you are choosing between when you sow early.² Penn State puts spinach at 45 to 68°F, a range rather than a single number for the same reason.³

A published range like that one is not measuring the same thing as the table. The table records the coldest reading at which germination begins; a range is the band in which it happens quickly and evenly, so a spinach floor in the table can sit well below the bottom of Penn State's band without either being wrong. Services differ from each other too. Alabama extension gives lettuce a germination range of 40 to 80°F, wider at both ends than the practical leafy-green band above.¹

There is a ceiling at the other end, and for cool-season greens it is closer than gardeners expect. Above 80°F the seed of lettuce and spinach goes dormant instead of merely slowing, and it waits for cooler soil rather than coming up late.² For a late-summer sowing that is the reading that decides the outcome.

Where these numbers come from

Each figure is the germination floor recorded on that plant's species planting profile in the reference library, drawn from cooperative-extension publications rather than from our own beds. Alabama extension's germination table by crop is one of those sources.¹ Follow a plant name into its plant page to see the sources recorded for it.

Every threshold here is species-level: it is the floor for the plant as a whole, and individual varieties refine it in the reference library, so a variety page can carry a different number from its species row without either being wrong. For taking the reading in your own bed, and for the late-summer case where the soil is too warm rather than too cold, read what soil temperature fall greens need alongside this table.

How to read a row

Some plants here are not put in on a soil reading at all. Garlic and shallots go in relative to first frost, asparagus and rhubarb start as dormant crowns, sweet potato goes in as slips, and the perennial herbs are set out as plants, so for those the row is a germination floor and not the date planting opens. Garlic timing is its own question, answered in when to plant garlic in the south.

The season and start columns describe how each plant is normally grown in the library rather than how it has to be grown. One marked as transplanted is usually set out as a started plant rather than sown in place, and one marked either way is grown both ways, which is why the same threshold can read as a sowing date for one gardener and a setting-out date for another.