To anyone zone pushing...

[KarenRei]

... you may find this paper about soil heating to be of interest 

https://www.keilir.net/static/files/KIT/PDF/1power2013-98172.pdf

In Iceland... where *July high temperatures* are usually only about 15°C / 59°F on average - with soil heating they were growing and fruiting tomatoes and zucchini outdoors.  They grew a banana plant to and past the first frost (though obviously did not attempt to overwinter it). They basically got the same sort of results you get with polytunnels, simply by heating the soil.

Definitely worth some followup research......

[SeaWalnut]

Thats free heat from geothermal sources wich is not soo common.
I add another source of free hot water,nuclear power plants.
In winter we go fishing near the nuclear reactor where the power plant dumps the hot water .
Because the water its warm,fish are active and eating there in the winter.
I allready see mr Burns growing tomatoes near the nuclear power plant  .

[850FL]

Ever catch a three eyed fish? LOL

As for the OP, I go around to all the coffee shops and grab their used grounds, then mix that in with bags of fresh grass trimmings and a some partly decomposed leaves. This mix often gets around 140-150 degrees F. There’s always steam eminating when I go to mix it up.. So maybe have some mulch piles like these around your plants as well?

[brian]

After building my greenhouse I found myself wishing I had used hydronic (water tubes w/boiler) heating of the soil instead of heating the air.   I could still do this, but it would require another heating source which would take up space. 

I mean, mine is still working great with its insulated foundation, but I can't help but think it would do even better with heated soil

[Daintree]

We have a lot of geothermal in our area, and many historic homes are heated that way. We have a large commercial greenhouse that heats with geothermal. Property in the lower areas where they have access to it is pretty much worth its weight in gold.
Alas, I live on the "cheap" side of town...

Carolyn

[Kevin Jones]

Solar heated water is a possibility.

Kevin Jones

[SeaWalnut]

Solar heated water is a possibility.

Kevin Jones

In Reykjavik in the middle of the winter Sun shines just 4 hours and night its 20 hours.
Too short daylight but they are lucky with the geothermal energy
During the summer peak,the night there lasts just 4 hours.20 hours of daylight.

[SeaWalnut]

Ever catch a three eyed fish? LOL

Not iet.
The fish is good to eat ,joke asside.
There you meet in winter the most addict fishermans.Somme  of them are soo crazy that wouldnt leave their fishing spot even if the nuclear reactor was in flames ,if the fish bites .

[KarenRei]

Thats free heat from geothermal sources wich is not soo common.

Quite true. How useful it is depends on how affordably you can heat it.  For example, the way they had it set up it was averaging 0,155kW/m² across the year. If you tried to do this with US electricity at a rate of $0,13kWh, that's $0,48/d/m², or $176/yr/m².  Pretty pricey.

A couple things of note that could improve it:

1) They were raising the temperature about 20°C / 36°F, which is a huge heat increase.  Conduction heat loss is linear with respect to temperature differences, but radiation from the surface is the difference of (temperature^4).  Iceland is also very windy and very wet, both of which sap energy.  During snows they were also melting the snow, which is a huge energy sink.  I bet if one was only targeting ~10°C / 18°F, in a less wet / windy climate, energy consumption would be ~1/4 to 1/3rd as much.

2) They did no insulation of the surface.  Insulating the surface should dramatically lower the energy consumption.  Depending on how much insulation and what type, potentially 1/2 to 1 order  of magnitude.

3) You only have to pay for more energy if you don't already have to heat something. for example, if you're already heating a greenhouse, heating it through the soil would be much more beneficial than heating the air, since soil temperature determines root activity.

4) Other forms of heating in the US would be cheaper than electric in most places, including NG and solar water heating.  But of course requires a more complicated setup.

5) There's passive forms of solar heating one can do too, such as suppressing weeds with black matting, to soak up solar heat.  Limited heating potential, but some.

But yes, we're very fortunate to have geothermal - it certainly makes this a lot more affordable!    More importantly, it can be waste heat. It would amazing to see some of that nuclear power waste heat be used to cultivate a huge tropical garden!    I was just amazed to see heat-loving plants like tomatoes and zucchini fruiting outdoors here, in such cold air.  Really goes to show how much of a plant's health relates to those roots.

[SeaWalnut]

Nobody will buy the fruit grown in a greenhouse heated from that nuclear power plant and even if they make a tropical botanical garden there,people would be skared to visit it.
That hot water its for the fish to enjoy and for fishermens.
We have geothermal springs ,warm lakes with native tropical fish  but those are rare .

I like heat pumps ( air conditioned used for heating)  more than resistance electric heating.
A heat pump can be up to 400 % more efficient than resitance heating.It consumes 1 Kw and gives 2,3,4 Kw depending on the temperature difference and its up to 4 times cheaper .
I would make a heated flower bed by using the heat pump of a lab fridge .That way the heat discarded by the fridge could be used to grow a few plants like 1 or 2 square meters.
A fridge consumes 100 watts and makes up to 400 watts of heat .

[850FL]

Are nuclear particles like uranium and radon found in substantial quantities outside the reactor, in the water and air? I’d think so, unless they control that entirely within the reactor somehow..

[SeaWalnut]

Are nuclear particles like uranium and radon found in substantial quantities outside the reactor, in the water and air? I’d think so, unless they control that entirely within the reactor somehow..

Do you realise what type of scientists work there are measure everything ?
Im not pro nuclear power but the water and the fish are safe to eat and swim in it.
We make soup from that water and fish right on the spot.
There cant be a bigger joy for a fisherman in winter here than to go fishing near the nuclear reactor.

It also happens that im a professional enviromentalist ( ie scientist not politician that tells you to eat the kids) and my job its to measure air,water and soil,study the ecosistems health and take actions over it.
But i didnt tested anything there because they have much more specialised enviromentalists that work there than me.

[brian]

I live right near a nuclear plant.  Good clean power, IMO

[SeaWalnut]

If i go to the nuclear power plant with my commie friends and knock on the gate.
Knock knock knock
Who is it?
Enviromental police ,Greenpeace.Greta Thurnberg !

The guys there will have a hard laugh at us and will tell us to colect the garbage somme fishermans leave near the canal,rake somme leaves,etc.
But if they fail...
I have not formed an opinion about nuclear reactors iet.
Somehow i hate the dams much more than nuclear reactors iet people still consider the dams to be green energy.

[KarenRei]

I would make a heated flower bed by using the heat pump of a lab fridge .That way the heat discarded by the fridge could be used to grow a few plants like 1 or 2 square meters.
A fridge consumes 100 watts and makes up to 400 watts of heat .

That's... really friggin clever    Waste heat from refrigerators never occurred to me.  Industrial-scale refrigeration churns out a ton of waste heat.  Come to think of it, industrial scale almost-anything has a lot of waste heat that they need to get rid of...

Somehow i hate the dams much more than nuclear reactors iet people still consider the dams to be green energy.

Same here.  They make up more of our power than geothermal.  I really want to see that reversed 

Basically, the ideal place for a dam is a deep, narrow canyon with a high-flow raging river.  E.g. somewhere unique and spectacular.  And then you drown it...

[SeaWalnut]

The problem with the dams its that they fill with mud and debris,rocks until the lake behind the dam becomes something like a shallow water swamp with the old river passing through it in the middle.
Basically dams ( not all but most of them) come with an expiration time .