Hugelkulture and higher soil temps

Hi All,

One thing I haven't really seen discussed on this board is the substantially higher soil temps much earlier in the season with very large hugelbeds. We consistently measure soil temperatures over 20 degrees higher (about the same for air temps too - not as cool) in our hugelbeds than the surrounding soil, especially since we have about 14-16 hours of southwest exposure a day.

This aspect of Hugelkulture has turned out to be a HUGE deal for us as we are in a cold climate with "cold soil" - we have had flower sets on our tomatillos and tomatoes for over a week - those we planted in flat beds are still struggling to establish. The big difference seems to be ~55 degree soil temps vs ~75 degree soil temps. Those big raised beds constructed from jet black earth gather and hold heat extremely well.

Our growing season is too cool (though not too short) to grow many crops that require heat to do well - some melons come to mind - Hugel (if the pattern holds) should allow us to grow these crops well due to higher soil temps for a much longer period throughout our growing season.

Just to be clear the elevated temps we are talking about are due purely to the raised bed having better sun exposure and a smaller mass of soil to heat - not the heat that comes from the decomposition of the organic material in the center of our beds.

Has anyone else noticed the benefits Hugel provides to soil temps? After all soil temps are at least as if not more important than air temperature to good plant growth - has anyone else seen an extension in their "productive season" (time actually in harvest) vs. "absolute season" (days without frost).

Thanks!

I can't tell you too much since this is my first year planting hugelkultur beds, and I haven't been so scientific or systematic as to take temperature readings. But I can tell you that we had a strange, late Spring this year in my area. Our average last frost date is mid-April, so I waited 'til after that to plant my more delicate veggies, but then we had 2 inches of snow in the first week of May. Other people in my area lost their gardens & had to replant, but the plants in my hugel beds didn't suffer a bit. So just from that anecdotal evidence, I would say you could probably extend your estimated growing season quite a bit if you're using hugelkultur.

Thomas West wrote:Has anyone else noticed the benefits Hugel provides to soil temps? After all soil temps are at least as if not more important than air temperature to good plant growth - has anyone else seen an extension in their "productive season" (time actually in harvest) vs. "absolute season" (days without frost).

I have both hugelkultur and non-hugelkultur beds in my garden. They are new beds since Sept, mixture of hardwood leaves, compost, mixed clay soil, straw, grass clippings, and horse manure. These mounded raised beds are mostly on contour with trench mulch paths on either side. All beds are about 2 feet below and above ground, heavily mulched with straw.

With my compost thermometer I've been monitoring temperatures of beds because I was concerned the high percentage of organic material would compost active. Right now my compost pile is steady 100 degrees F, while hugelkultur remains 80 degrees F, and regular beds also are 80 degrees most of the time. Beds with less sun will go down to 70 degrees F, and regular beds during rain will go down too.

Interesting enough the hugelkultur bed maintains 80 degrees F at every check. Compost might be 100 degrees, hugelkultur will be 80, other bed might be 75 degrees F. Beds really weren't ready till early February and testing started in April -- so I don't know what winter numbers might be. I don't measure the temperature every day, just out there weekly at different times to see whats going on.

Testing started to see when I could plant seed. With warm beds I thought seeds would germinate but they don't. Some cover crop seeds continue to grow, but broadcasted and planted seed doesn't seem to grow. I'm putting starts big enough to tolerate slugs. It is possible birds or slugs got any seed starts. Worms are very active which is good to see.

There was a cold snap here March-April and cold rains May. On a few really hot days recently beds stayed 80 degrees, but air temperature was only higher in direct sun. My plants kept growing, everything looks great now. Slugs are under control now that I've put some shelter out for frogs and birds have picked up.

Beds were cover cropped before planting out -- root growth is awesome, starts have root growth spread out where I'm putting holes a foot away. I like the warm beds and hope they maintain.

Best,

Justin

Has anyone done testing with beds that are between 5'-8' tall? The base of ours are much closer to "ambient soil temps" but when you get more than about two feet up the bed the soil temps start jumping and hit the maximum temperature on the top. We have been systematic about testing mostly because this is our first year doing large scale production with Hugelkulture and we basically had no idea how to plant our beds. So far we have not noticed much if any temperature difference due to the composting organic matter - however given that our garden did not physically exist 3 months ago its not surprising - not much time for the soil food web to get moving. Our observation is that temperature seems directly related to the height of the bed, position of the plant on the bed, and sun exposure.

We used our temperature gradients to inform our plant selection for a given space on the bed - crops that tend to bolt in higher temperatures are planted towards the base, while those that love the heat, such as tomatoes and peppers, are planted near the crown. As the season continues we will continue to take measurements (including differences in productivity, if any) between the same vegetable that has been planted in different locations. The idea is to take a "shotgun" approach to polyculture and companion planting based on our early, and limited, data on soil temps, sun exposure etc. Hopefully over time this will allow us to systematically fine tune where we grow what on our Hugelbeds - we intend to share this information freely as we develop and refine it.

Hooray for doing new things!

Thomas West wrote:We used our temperature gradients to inform our plant selection for a given space on the bed

Good expansion on the topic of hugelkultur bed temperatures. I'm measuring temperature center of bed (deepest part, core) and can now see a bunch of wholes in my methodology. It's possible bed was warmer in early months due to composting, later due to holding suns heat, and in between a combination of both.

Because I'm only measuring center using a compost thermometer, I'm getting a combined temperature. It is possible the soil on a hot day is 100 degrees F on the surface and 70 degrees at bottom. On a cold day, I may have surface temperatures of 70 degrees but retained heat of 80 degrees for majority of the rest of pile.

I did notice today that straw mulch on beds is much warmer on the sun side than it is on the back. As for planting, I'm in a race with a vole to get as many plants in the ground in a polyculture grid according mature plant size -- placement also impacted by available sun. I'm using the "plant the crap out of it" method.

Best,

Justin

Justin Hitt wrote: I'm using the "plant the crap out of it" method.

Best,

Justin

I couldn't have described our method better - when in doubt (basically along the lines of I THINK their might be space for just one more pepper) we put in more seedlings. In fact I would say at we over planted by at least 50% with the idea that areas that become overcrowded will be thinned and harvested earlier in the season. One thing we try to remember when doing polyculture is that the mature plant size isn't the only factor you can rely on in increasing the productivity of this method. A good for instance is that the space around many of our tomatoes and other taller starts is packed at the moment with sprouting greens and seasonal herbs like Basil- which will be harvested and removed before they put any real competitive pressure on the plants around them. In other words you can play with the pace of growth, and not absolute plant size, to incorporate more plants into your polyculture system.

Back to the topic of combined soil temperature readings - I think these are very useful in determining the bacterial activity of your hugelbed over time and determining absolute season. As you hinted the reason we took more specific measurements in more places was to identify microclimates, if any, created by our gigantic hugelbeds, This summer should tell us if this was a huge waste of time - as we broke our system deliberately on a few beds to make sure mapping plantings to micro climates makes any real difference.

There used to be a rectal thermometer (mercury type) at least 18'' long that Veterinarians used to take rectal temps with, before it was generally known how dangerous
mercury was.

For a probe long enough to reach the center of a hugel bed I am visualizing something as long as a walking Staff . Could I see a picture or two and get an idea of price,
and temperature range !? Because this seems like it would have to be uber durable, and certainly capable of being the last one I would ever need, this is more than Idle
curiosity ! Thanks in advance ! Think like Fire, Flo like Gas ! PYRO - Logically Big AL !

Late note; Thomas, shouldn't that be plant the crap into it ?

allen lumley wrote:Late note; Thomas, shouldn't that be plant the crap into it ?

I stand corrected - and yes thats a hilarious mental picture - thinking of the worlds largest rectal therm stuffed right up mother natures... nvm. I am going to get myself into trouble here. We use a cheap sensor we bought on ebay for I think $20 or so that has a 15' lead connected to a 6" long temperature probe made out of what looks like steel to me. We piece of pipe with the sensor stuffed inside into the bed where we want to measure and then remove the pipe far enough to expose the probe and take a temperature reading.

That being said we care a lot more about the gradient in the first 6"-12" of the soil as that is where it impacts the root zone the most - those measurements can be taken with the sensor and standard lead without any futzing at all.

Here is a thermometer that is very close to the one we are using:

http://www.ebay.com/itm/Trerice-V80025-Thermometer-20-to-100-Degree-With-15-Lead-New-in-Box-/150755597997?pt=LH_DefaultDomain_0&hash=item2319bbdead

We use 2 pieces of pipe nested inside each other with the probe inserted into the center pipe - we pound this combo in and then remove the first pipe to take a reading - keeps the probe from being damaged - the only downside is that you need to leave the probe in the hole for a bit to ensure the pipe temperature at insertion doesn't contaminate your measurement.

Easier to replace, repair if you break it - I cant see a walking stick style solid therm being a good fit for this - it can take quite a bit of force to get to the center of our beds. We have been considering pounding capped off pipe into the beds and just dropping the probe in to get a meausurement. We are going to test this later in the summer to determine if we get the same or similar readings from a permanently installed temperature monitoring point (e.g. pipe permanently pounded into the ground) vs a one time reading. We are really hoping a permanent pipe will work better as its a PITA to pound one in every time you want to get a temp.

Thomas West :Thanks thats helpful ! I was able to keep a straight face in this discussion right up until you resorted to the use of the 'probe' word ! , Under the category
of who knew ?, think of the time and the Thomas saved by placing in some pipes as it was being built ! Thanks again Big Al !

allen lumley wrote:Thomas West :Thanks thats helpful ! I was able to keep a straight face in this discussion right up until you resorted to the use of the 'probe' word ! , Under the category
of who knew ?, think of the time and the Thomas saved by placing in some pipes as it was being built ! Thanks again Big Al !

Re-reading that I can see how there would be the appearance of the gratuitous use of the word "probe". I would have saved a lot of time if I had buried the pipes as we built the beds - however it was well after the excavator left that this occurred to me. :-/ A piece of 3/4" galvanized steel pipe and a post pounder work well enough - we are experimenting with the built-in pipes because we are a bit concerned that the pipe itself might contaminate the measurement as it is exposed to multiple temperature gradients within the bed and could therefore provide some "averaging" effect.

Ultimately we want to build the sensors in permanently - you can get 2-wire temperature sensors for around $5 online and the box needed to aggregate and remotely monitor around 20 feeds is only $100. The nice thing about systems like this is that you can incorporate data other than temperature. Things such as relative humidity, barometric pressure, soil PH, soil moisture level, etc can be monitored with off the shelf components for well less than $1k if you have the skills to assemble such a system. You can also use the same box to take action based on a change in parameters - e.g. engage the irrigation system on an irrigation zone automatically when the soil moisture reading falls below a set value.

As a former DOD engineer this sort of automation is my bread and butter. Fun too.

As we integrate and build this tech we are more than happy to share any/all details, schematics, knowledge, and/or back of the envelope calculations with anyone who cares to look. At some point we are going to start publishing them under OHANDA which is the engineering equivalent of the Open-Source GNU Public License - essentially anyone can take what we have done, improve and/or modify it freely, as long as they share the knowledge they gain back with the community.

As all known and potential knowledge has its genesis in thought and discoveries that came before it we believe we are ethically obligated to share anything/everything we learn freely with the larger community. If, however, you wanted us to consult on-site or solve a particular problem for you, we would charge for that. The application of knowledge as a skill deserves compensation, the knowledge itself is the collective property of humanity, independent to the degree you add to it or not.

Thomas West wrote:The application of knowledge as a skill deserves compensation, the knowledge itself is the collective property of humanity, independent to the degree you add to it or not.

You sir have earned a place on my wall ... this quote should have a thread of it's own! While I won't likely be as scientific about temperature testing on my hugelkultur beds, this thread has opened up my eyes that different sections of beds are likely to have different temperatures.

It's likely beds will have bands of microclimates with surface and soil temperature, as much as they have microclimates between elevations. With distribution of plants in polyculture these variation in temperatures may produce lower chance of full crop failure from heat/cold spells.

Since I eat a lot of the greens across their maturity, plus tend to plant in cycles I'm hoping warmer beds will extend my season. If not, I'm sure something will survive as I've had brassica's across a mild winter when I lived further north. Now if I can just keep my neighbor from stepping on the sides of the beds.

Best,

Justin

Those Jesuit professors will warp a mind in the process of improving it. Thanks for your kind words.

This has me really curious. Can one create enough heat between composting and solar gain to grow through the winter? How many zones will this gain?

What if you put a hoophouse/hightunnel over a big hugel like the one Toby describes here at about 4:00



You will still have the light problem if you are in northern latitudes, but high elevations with enough daylight should be able to grow lots of crops through the winter.