My multimeter says 11
degrees, still a bit chilly for seeds
Testing soil temperature for seed sowing wasn’t always
scientific. It wasn’t too long ago that farmers would test the soil temperature
by pulling down their pants and putting their bare bums on the soil (not all
farmers I might add) If it felt cold on their cheeks then it was too cold for
seed planting.
There were easier, less fun ways of testing the soil without
baring all, you could simply place the back of your hand on the ground and
again if it felt warm, the seeds could go in. People still check temperatures
with their limbs but it’s usually to test the baby’s bathwater which so far as
I know has always been the method of temperature gauging and no buttocks have
ever been used.
Soil Temperature
Soil temperature is the factor that drives germination, transplanting,
blooming and composting. It’s said that the ideal soil temperatures for
planting most seeds and plants are 65 to 75 F. (18 to 24 C.). Most seeds will
germinate over quite a wide range of soil temperatures but the speed of
germination will vary. Too cold and they’ll be very slow to sprout and too hot
will also reduce the speed of germination. Far too hot or cold also increases
the risk on none of the seeds germinating which is what used to happen to me
when I was in a rush to get seeds sown.
If you have heated propagators and sow seeds under
protection most of the guesswork is done. If you are sowing directly into the
ground outside you might need to take more notice of the conditions.
I would think the best time to check the soil in the ground
would be when the sun isn’t shining on it, the same for a compost bin – these
like temperatures of over 60 F (16C) to work well. Soil readings for seeds are
done in 1 to 2 inches of soil. Sample at least 4 to 6 inches deep for
transplants. You can use your hands or invest in a soil thermometer (the same
as on you use in the kitchen for probing meat) with a long metal rod. Insert
the thermometer to the hilt, or maximum depth, and hold it for a minute. Do
this for three consecutive days.
The perfect temperature for planting varies dependent upon
the variety of vegetable or fruit. Planting before it is time can reduce fruit
set, stunt plant growth and prevent or reduce seed germination.
Simple methods
Apart from buttocks and back of the hands, there are other easy
ways to check the soil.
If weeds are germinating and growing, it's time for us to
get growing.
If spuds in the compost are growing, then you can put spuds
in.
One suggestion (non-scientific I might add) is to wait until
you can go out and garden without a cardigan on.
A few points to keep
in mind:
The temperatures quoted are soil or compost temperature, not
air temperature. A sunny day in April may be 20 C but the soil temperature is
most likely stuck around 8 C.
A soil thermometer
can be bought very cheaply, typically less than £10.00, which will give you an
accurate figure to work from. I use my multimeter which has a very accurate
temperature guage.
Beware the sunny day when propagating in the greenhouse.
Temperatures can soar, basically cooking your seeds or seedlings.
Higher Temperatures
The ideal temperature for germination is often far higher
than we might expect and in some cases it is higher than is ideal for growing. Take
carrots for example, their ideal germination temperature is 27 C, which is
nearly an oven temperature. The optimum growing range for carrots is between 7
C and 29 C with far faster germination rates once the soil hits 10 C.
Tomato seeds are the same enjoying really high temperatures
to kick start themselves into germinating. Like a lot of gardening pursuits it
can become an obsession to get just the right conditions but seeds are tougher
than we think and only need a few things to thrive. I for one err on the side
of caution and leave my seed sowing until late spring which usually meets the
seeds needs without us needing to fret or raid the kitchen drawer looking for
the meat thermometer.
You can get an early- weed free start by warming up the soil
outside by a few degrees if you cover it with horticultural fleece or better still
use a cloche which can make a surprising difference to germination rates and
times.
