Does biochar help warm the soil?

That was my thought the very first time I was introduced to biochar 15 or so years ago.  That the dark color of the biochar would absorb more heat from the sunlight and kickstart growth in the spring.  If so, probably a good thing for plants that can handle a bit of frost, maybe not such a good thing for tender plants prone to frost kill, unless it can absorb enough to reradiate at night and prevent the temp from dropping below freezing.  Thoughts?

One thing that I have read about is that putting ashes on snow will melt the snow.

Putting biochar around plants, I have no idea.

Yes, it warms the soil. If there's nothing shading it, biochar on the surface or mixed into the top layer darkens the soil, absorbs more solar energy, and gives a few degrees of extra warmth. I did this in my kūmara (sweet potato) beds last year and it meant I could plant the shoots a few weeks earlier, and they got going a lot quicker compared to previous seasons, presumably because there was faster root development.

This is an old trick in these parts, apparently. Māori in certain regions used the charcoal and ashes from their earthen ovens (umu) as a garden soil additive. This allowed them to grow kūmara, which is a crop of tropical origin, in places with cool summers, and since this was their main staple crop that was a big deal.

The black color of the biochar should heat up the soil. However, I have read that biochar shouldn't be spread on the surface. I think the issue is that there is then less interaction with the soil food web and a greater chance that it will dry out. If it dries out, the microbe population would decrease, I think.  Bigger chunks of biochar could retain more moisture, but feature less surface area and less interdynamics of microbe circulation.  I dig my biochar, once it's crushed and inoculated, into the soil, anywhere from 0 to 10 inches deep. It soon becomes covered with a layer of dirt/mulch/soil etc.

John S
PDX OR

I would think that bio char and ash, is most natural as a surface application. My first experiment with ash, was leaving it in a pile, it was an extremely dry period, ash never getting wet. When I went to remove the dry ash pile, though the pile was dry, the surface of the soil, was wet, meaning it draws up water like a chimney. So the black would act like a chimney, drawing water up. I also think that charcoal is lowest pressure when dry, meaning the sooner it dries out, the more moisture will be left in soil. Also used like this I believe it builds a slight charge, killing parasites. Nature knows what’s best and how to use fire most efficiently.

I agree that nature has its own timeline. Around here, nature provides biochar in a giant forest fire.  I understand that there are many species that depend on a post fire, black landscape to thrive.  However, I don't want to do that to my own property.  Burning down my house and my orchard probably would be good for nature in the long run, and yet it would be a disaster for me.  

Biochar dug deeper into the soil holds the moisture at the roots, where the plants in my food forest need it.  Plants adapt to the summer by retaining water in the soil.  They also will be able to adapt to our rainy waterlogged winters by draining better than our pure clay soil.  The roots aren't on the surface.  It also fosters the kind of microbe interaction that turns mineral nutrients into bioavailable nutrition for the plants.  Dried out, there is much less microbial interaction in the biochar.

John S
PDX OR