Temperature benefits of a small poly tunnel.

[Jimmy]

I have erected a small polythene tunnel/cloche.
The type that uses wire hoops and is about 12 Inch high.
It's been up for about three weeks now.
I placed temperature monitors in the soil about 3 inch down, both inside the tunnel and just outside.
The temperature difference only seems to be about 1 deg C difference.
I was hoping for a bit more.
Any comments ?
Thanks
Jimmy

[Penellype]

I wouldn't expect a great deal of difference in the soil temperature at that depth in a small, narrow tunnel. Heat in general flows from hot to cold in an attempt to even itself out. If there is no barrier to this process it will occur quite rapidly. At this time of year the important thing is the temperature of the air near the ground at night, and the extra degree or 2 provided by the plastic tunnel can make the difference between frost and no frost. You do need to be careful that things don't cook during the day when it is sunny, as the small volume of air will warm up very quickly in the sun.

[Jimmy]

The monitors have a soil and air temperature sensor.
Currently is a bit overcast with odd bursts of sun.

The air temperature seem to be 14.0 outside 18.0 inside

I will monitor things over night as they keep logs.
Thanks
Jimmy

[bario1]

I've got two rows of spinach sown next to each other, one with a tunnel cloche and one without, as an experiment. Sown on 28th March, neither row showing yet....

[Jimmy]

Interesting, I was hoping to put some dwarf french beans in for an early crop !

[bario1]

Go for it. The cloche will probably come off as soon as my spinach germinates, I just wanted to see if it would affect germination speed. French beans will appreciate the extra heat (and shelter) as they grow on.

[Jimmy]

Last nights log from midnight attached.
Soil Spike 1 is outside the tunnel and Soil Spike 2 is inside.
The rest are at points in my greenhouse.

Jimmy

[Penellype]

That's a great illustration of how useful cloches are. The unprotected pink line gets perilously close to 0 degrees while under the cloche it bottoms out at about 2.5. It won't work if you get a really sharp frost (say -2) but it can make a big difference at the current temperatures.

[Jimmy]

That's a great illustration of how useful cloches are. The unprotected pink line gets perilously close to 0 degrees while under the cloche it bottoms out at about 2.5. It won't work if you get a really sharp frost (say -2) but it can make a big difference at the current temperatures.

Hmm 0 and 2.5 , I get -0.5 and 1.5 from legend
Jimmy

[Penellype]

Hmm 0 and 2.5 , I get -0.5 and 1.5 from legend
Jimmy

Ok, its hard to see on the picture exactly where the line is, and my eyes are not as good as they were

[Jimmy]

OK that's why I did the legend.
On the real web page you can hover over the points and a popup will show you the date/time/temperature
Jimmy