Soil TemperatureSoil Temperature

Temperature key to successful Temperature key to successful germinationgermination

Should guide vegetable planting Should guide vegetable planting scheduleschedule

Soil – not air – temperature triggers Soil – not air – temperature triggers germinationgermination

Soil temperature changes gradually, Soil temperature changes gradually, even though air temperature even though air temperature fluctuates wildlyfluctuates wildly

Dates and rates for soil warm-up vary Dates and rates for soil warm-up vary each yeareach year

Often vary within single yard or Often vary within single yard or gardengarden

Factors that affectFactors that affect

Exposure to sunlightExposure to sunlight

TextureTexture

Moisture contentMoisture content

Surface level (low-lying, flat, mounded)Surface level (low-lying, flat, mounded)

MethodMethodMetal probe thermometerMetal probe thermometer

with flat dialwith flat dial

(not oven thermometer)(not oven thermometer)

Available at garden supply, Available at garden supply,

auto supply stores auto supply stores compost thermometercompost thermometer

MethodMethod

Insert 2 inches into soil for early Insert 2 inches into soil for early season, small seeded vegetablesseason, small seeded vegetables

Greens, beets, broccoli, Brussels Greens, beets, broccoli, Brussels sprouts, cabbage, carrots, sprouts, cabbage, carrots, cauliflower, leeks & onions, peas, cauliflower, leeks & onions, peas, radishes, turnipsradishes, turnips

MethodMethod

Insert 4 inches for warm season Insert 4 inches for warm season vegetablesvegetables

Tomatoes, eggplants, peppers, Tomatoes, eggplants, peppers, cucumbers, squash, corn, melonscucumbers, squash, corn, melons

Repeat performanceRepeat performance

Take temperature at same time each Take temperature at same time each day for several days and averageday for several days and average

Best time - mid-day – between 10 Best time - mid-day – between 10 and 11and 11

Take in several locations and averageTake in several locations and average

Strong, long-lasting cold front can Strong, long-lasting cold front can take soil temperatures down but it take soil temperatures down but it happens slowly. happens slowly.

Reaching 45 or 55 degrees usually Reaching 45 or 55 degrees usually means it’s safe to plantmeans it’s safe to plant

When to plantWhen to plant

Cool season crops - 40-45 degreesCool season crops - 40-45 degrees

Warm season crops - 50-55 degrees Warm season crops - 50-55 degrees

Must consider risk of killing frost after Must consider risk of killing frost after seeds emergeseeds emerge

Being planted too early isn’t always Being planted too early isn’t always fatal for seedsfatal for seeds

Simply sit and wait for soil to warmSimply sit and wait for soil to warm

Warm-loving crops – Warm-loving crops –

May be damaged if the temperature May be damaged if the temperature falls muchfalls much

Do NOT leave thermometer in groundDo NOT leave thermometer in ground

Clean and store indoors between Clean and store indoors between readingsreadings

http://www.greencastonline.com/SoilThttp://www.greencastonline.com/SoilTempMaps.aspxempMaps.aspx

http://aggie-horticulture.tamu.edu/seeds/http://aggie-horticulture.tamu.edu/seeds/