I have seeds that state that they're to be planted when the soil
temperature is over 60 degrees. Now, lacking my handy soil thermometer,
can I assume that when the ambient temp. is over 60, that the soil will
be too? Or does the darker color of the soil absorb heat and become
warmer than the air temp.? Does the soil stay warmer at night, so that
it only has to be around 60 during the day?

I'm a little embarrassed at not knowing this after four or five years of
gardening, so thanks for any help.

M.
--

B - - - - - - - - - - - - -

Melinda Tennielle

M10TVC15 (at) yahoo.com

Melinda Tennielle wrote:
I have seeds that state that they're to be planted when the soil
temperature is over 60 degrees. Now, lacking my handy soil
thermometer,
can I assume that when the ambient temp. is over 60, that the soil
will
be too? Or does the darker color of the soil absorb heat and become
warmer than the air temp.? Does the soil stay warmer at night, so that
it only has to be around 60 during the day?

I'm a little embarrassed at not knowing this after four or five years
of
gardening, so thanks for any help.


The ambient temperature (the air temperature) is irrelevant.

The soil will warm as it absorbs sunlight, but except for the very
surface of the soil, it will hold a fairly steady temperature, and not
change anywhere near as quickly as the air.

Think about this: Put a brick in the oven, and turn the oven to 300. The
air in the oven will probably be up to 300 in about 10 minutes, give or
take. It will take a couple hours for the brick to reach that
temperature all the way through. Now (carefully) take that brick out of
the oven, and let it sit at room temperature. It'll be quite a while
before the surface temperature drops anywhere near the ambient
temperature, and it'll be many hours before the brick cools all the way
through. The brick, being far more dense, and having far more mass than
the air surrounding it is much slower to change temperature than that
air.

Same thing with your soil. When spring comes, the air can make wide
temperature swings each day. The soil warms up much slower. If you're
measuring the soil temperature three or four inches below the surface,
you're probably not going to see it change more than a degree or two
between day and night even if the air temperature makes a 30 degree
swing. And once the soil slowly warms up, it will take just as much to
cool it down again.

The closer to the surface you're measuring, the more you'll notice the
soil temperature trying to change with the ambient temperature. Measure
far enough down, like 30 or 40 feet, and you may not even notice a
change between the winter and summer temperatures even in the harshest
climates. Even by the time you reach 6 feet, or so, the temperature is
going to be fairly stable in most areas. That's why the fresh water and
sewers don't freeze even in Wisconsin. (Water main breaks are normally
caused by shifting of the subsoil that breaks the pipe, not by frozen
pipes like you might find in an unheated house.)

So once the soil temperature at the proper depth reaches the target
temperature, unless the "proper depth" is less than an inch, you're
probably not going to see any significant decreases in that temperature
unless there is an extreme, consistent and lengthy downturn in the
ambient temperature.

Any doubts? Measure the soil temperature in the late afternoon just
before the sun stops shining on the surface. Then get up early the next
morning, and measure it again before the sun comes up, and the air
temperature is still near it's lowest. If you're measuring more than an
inch or two down, you won't notice a significant change even though the
air temperature may differ by twenty degrees or more.


--
Warren H.

==========
Disclaimer: My views reflect those of myself, and not my
employer, my friends, nor (as she often tells me) my wife.
Any resemblance to the views of anybody living or dead is
coincidental. No animals were hurt in the writing of this
response -- unless you count my dog who desperately wants
to go outside now.

If you want to go to the effort of raising soil temps
you can lay black plastic sheeting down to absorb the suns
rays.

Some leave it on and x-slot for plantings. But mulch or hay a heavy
layer when the temps get hot to keep things cool below. Or else bake
the roots. Or would that be steam them...

I've started seedlings 8 weeks ago indoors here in the SF Bay Area.
We've had some unusual late heavy rains and cool evenings (45 f).
It's almost time to plant...

J



Melinda Tennielle wrote:

I have seeds that state that they're to be planted when the soil
temperature is over 60 degrees. Now, lacking my handy soil thermometer,
can I assume that when the ambient temp. is over 60, that the soil will
be too? Or does the darker color of the soil absorb heat and become
warmer than the air temp.? Does the soil stay warmer at night, so that
it only has to be around 60 during the day?

I'm a little embarrassed at not knowing this after four or five years of
gardening, so thanks for any help.

M.
--

B - - - - - - - - - - - - -

Melinda Tennielle

M10TVC15 (at) yahoo.com

On Fri, 18 Apr 2003 12:05:32 -0700, jhultman
wrote:

If you want to go to the effort of raising soil temps
you can lay black plastic sheeting down to absorb the suns
rays.

Some leave it on and x-slot for plantings. But mulch or hay a heavy
layer when the temps get hot to keep things cool below. Or else bake
the roots. Or would that be steam them...


A really heavy layer of mulch !!! I used plastic one year to keep
the weeds down... (weedblock didn't do the job). did the x- cuts
and planted miniature roses.

In less than two weeks, I was digging up the plastic... The poor
roses were fricasseed, This was in Maryland during the
summertime.

On the other hand, when overwintering shrubs after a late season
clearance sale digging a trench, inserting the containered
plants, covering with leaf mulch and then plastic sheet (with holes
for rainwater) kept the plants healthy all winter long even though
temps were hitting -10.




Melinda Tennielle wrote:

I have seeds that state that they're to be planted when the soil
temperature is over 60 degrees. Now, lacking my handy soil thermometer,
can I assume that when the ambient temp. is over 60, that the soil will
be too? Or does the darker color of the soil absorb heat and become
warmer than the air temp.? Does the soil stay warmer at night, so that
it only has to be around 60 during the day?

I'm a little embarrassed at not knowing this after four or five years of
gardening, so thanks for any help.

M.
--

B - - - - - - - - - - - - -

Melinda Tennielle

M10TVC15 (at) yahoo.com