Conductivity varies depending on the material. In general, wood has a pretty low thermal conductivity. I’m sure the commonly reported values are for lumber so I would expect live wood to be slightly higher, but probably still not very high. Since you mentioned pencils and I had a few nearby, I put one in a cup of ice water and left another out as a control. After about 20 minutes, I still couldn’t tell a difference in temperature between the top of the pencil in ice water and the one that was left out. If I think about it, maybe I’ll do it again tomorrow for a longer time.
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I love this discussion. @alan You reflect radiative heat; but you insulate from conductive heat (air temp, or as @Klondike_Mike points out, conducted up the trunk ) Maybe that clears things up.
@bradkairdolf Since wood does have a low thermal conductivity one must more closely dupilcate the time scale occuring with the wood in nature which is measured sometimes in days, not minutes. That will effect the result.
I’m looking forward to doing this experiment. I’ll report, you decide, LOL.
No Anne, doesn’t quite clear things up. Heat conducted up the trunk from the soil sounds interesting as a theory, but is there any research to support this idea?
It’s the first time I’ve read of this idea but if it worked significantly all one would have to do is wrap trees around their trunks and over their canopies to protect them from freeze- but it doesn’t seem to accomplish much where I’ve seen people try this with figs, for instance. Of course this is purely anecdotal.
What works much better is covering a tree with a tarp that is secured to the ground below the canopy radius with no gaps, to trap ground heat around the tree- I’ve saved figs by doing this, but there wasn’t enough conducted heat to protect the tips touching the tarp.
Mike, your link about mulch was not very convincing- just a suggestion from an extension bul. for home growers. Those things are not necessarily carefully edited or science based. Look harder and I think you can find some actual research that will refute your suggestion.
If mulch could delay bloom, I believe you are flat out wrong that some commercial growers wouldn’t be extremely interested- often a week delay would save an entire crop and any light mulch, like spoiled hay would work. The process would be about 100 times less labor expensive than,say, hand thinning peaches.
It is an obvious idea that I’ve seen discussed several times over the years in literature that I’ve lost track of. If I’d found any source that convinced me of its usefulness I’d have adopted the method.
If anyone wants to test it for themselves, probably two trees of the same variety and rootsock standing next to each other would be all you’d need to probably nail it. Just heavily mulch one of them. Not quite full proof if the mulched one has significantly prolonged dormancy, but it would be enough to convince me. Just take a photo.
OK, I just found what may be the greatest discovery of grafting and perhaps mankind in general for the last 1000 years! (ok, slight exaggeration). It’s called “self sealing silicone repair tape”. Why isn’t this the first line of every article ever written about grafting? I am a grafting novice to be sure, but this stuff really does seem to be spectacular for grafting.
Simply put, it is self-sticking, meaning it isn’t at all sticky on either side and won’t stick to anything but itself. As an added bonus, it is extremely elastic/stretchy so its very, very easy to wrap it around a graph really tight to hold the scion and rootstock together very firmly. Better still, because it has no stickiness to it, there is no need to place some type of non-stick first layer the way most people who use regular electrical tape usually do before applying the regular tape. That is because it won’t stick to the bark at all. If you unwrap it, it just falls away. Here is a tiny bit more info about it at the Ace Hardware web site.
http://www.truevalue.com/product/Self-Sealing-Silicone-Repair-Tape-Black-1-In-x-10-Ft-/63780.uts
I actually bought mine at Wal-Mart and it is “Duck” brand. Anyway, I’m in love with the stuff. Of course I know it’s not the be-all-end-all that I’m making it out to be. I know many if not most of you like to use parafilm so you don’t have to remove it at all once the graft takes. But for those using electrical tape with parafilm or other plastics under it, this stuff really is great. Its inability to stick to the bark along with its elasticity that makes it easy to get tight and its thick, strong make-up that firmly hold scions in place all make this stuff wonderful for me.
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You wouldn’t need days, only needs to be done until it reaches steady state. If I get a chance, I’ll allow it to reach steady state and actually measure the temp. The values are pretty far from what happens in the field though. Given the actual temperature differential in the field, the thermal conductivity of wood, and the distances from the roots to the blooms, I doubt there is any significant contribution from conduction of heat through the wood.
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Sounds great I’d love to hear a little more from anybody who has used it for a while.
I got some of that from Appleseed last year (thanks) and yes it does work well but it is expensive. It stretches well and is easy to remove with a sharp blade since it doesn’t stick to the wood. It’s like a rubber band that doesn’t require tying.
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Oh I totally agree. The conduction issue I was addressing initially was from the surrounding air. I hadn’t considered the wood conduction, mainly because the temp affecting the branches (aka canopy) is the same as that affecting the trunk when temps warm up in the winter. But in designing any experiment (which I used to do at NASA) it is the assumptions that get you in trouble, LOL.
There are many labor-intensive ways to delay blooming. I was trying to conceive an easier yet effective way…and it is easy enough to test out.
You mean I’m not the first person in history to discover its usefulness for grafting!?!?! ha. I think @marknmt and I would both like to hear from @Appleseed70 if he has used this stuff for a while, just to be sure I’m not missing something.
I didn’t think it was that bad in terms of cost- I paid less than 5 dollars for the “Duck” brand I bought at walmart and it lasted me for a lot of grafts. Glad to hear you agree that its great stuff. Not sure why more people don’t sing its praises!
If its an obvious idea I’m surprised you haven’t tried it yourself as an experiment. Maybe you should. If anyone else here did you would likely debate the parameters and variables of their experiment. I have, I’ve seen the results, and I’m convinced.
Alan, besides the source I cited there are many more, by reputable organizations/institutions, anyone here can google it.
Wow, don’t think I would say that to anyone who makes a suggestion on this board. You disagree, shouldn’t you then do the research, cite your source, and then kindly readjust my thinking. Next time I post a suggestion I’ll first contact MIT to verify, kidding.
Alan, look, I love this board, I love hearing suggestions from neat people from all over the country, and then weighing those suggestions in my own mind and deciding which ones to try. And a little debate is good, and healthy, and educational, yet I think we have to be careful not to be too quick to jump on each others suggestions half cocked (i.e. before doing research) as it can actually stifle participation and discussion.
Agreed, dead wood not very conductive. It would be interesting to know how conductive live wood is. Water is very conductive, thats why we’d die much quicker of hypothermia in 50 degree water vs 50 degree air.Live wood, esp. young fruit trees have quite a bit of moisture. . . .
I found some serious work that at first I thought meant that I’d totally have to eat crow, but then I looked a bit closer and maybe just a few nibbles.
A substantial reduction in soil temps does seem to lead to a meaningful delay to bud break in apples. However, when I looked at the graft it seems like the couple degrees reduction of mulching (remember it also holds heat in when outside temps are colder than the soil) likely would not make a substantial enough difference to matter.
I’m pretty tired so I may not be calculating this so well in my head- I’m also not sure about the amount mulch cools soil. I am posting it now so maybe someone else can go over it while I sleep and I won’t have to do the work.
It was enough just to come up with the study.
Thanks for hanging in there Mike- maybe I will learn something from this.
Incidentally, I always mulch some of my peach and nectarine trees (ones that haven’t reached full size) and haven’t experienced a difference in bud emergence between those that I mulch and those I don’t- I compared them today, in fact. Some of the mulched peaches and nects have a nice airy, thick hay mulch- some wood chips.
Thanks Alan, sleep well
Thats Academia for ya!
Mulch wise last fall I put about a foot of oak leaves on the whole orchard and 2 to 3 feet on my peaches and cherries (my most borderline trees) after the ground froze. I’ll pull back most of the mulch on the peaches and cherries after frost danger has passed. The rest of the orchard will be leaf free by July- thank you worms!
Just an observation about mulching- leetle bark-eatin’ critturs loves it, so I hope folks are pulling it well back from the trunk …
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Based on that article there is benefit in keeping the soil cold but how do you do that? A high level of insulation is required to keep the soil temperature in the 40s or lower and timing of mulch application is critical. As long as air temperatures are in the 40s or lower no mulch is best. When air temperatures will be in the upper 50s or higher add mulch. The more the better in an attempt to keep the soil at the original cold temperature. When air temperature drops to the forties again, remove the mulch to keep the soil at colder air temperature. If someone was actually going to attempt this then a soil temperature gauge along with air temperature predictions should be used to decide when mulch should be added or removed. Seems very complicated if it is going to be effective.
Let me know how it works out.
I keep my records on a [blog](http://naomisorganicgarden.blogspot.com/), some of the pages are private but most are public. If I forget what I did, I just go back to the blog.
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Not too complicated. 1. Let the ground freeze. 2. cover with mulch
The presence of a good layer of mulch in spring insulates the cold ground and slows the warming of the ground from the suns rays and surrounding air
Here’s some highlights from that Oxford study Alan cited in which 3 groups of Braeburn apples were exposed to the same air temp while the root zones were kept at 7, 15, and 25 deg. C
From the summary, “Both the proportion and timing of bud break were sig- nificantly enhanced as root-zone temperature increased. Rate of floral cluster opening was also markedly increased with in- creasing root-zone temperature.” , “Irrespective of underly- ing mechanisms, root-zone temperatures influence bud break and flowering in apple trees.”
This is from page 109, “For each 1 °C decrease in soil temperature across this temperature range, time to 50% bud break would be reduced by about 1.3 days, 2.2% fewer buds would break and 2.4% fewer clusters would open. Thus, from the warmest to the coolest region, bud break could be delayed by as much as 12 days and the proportion of buds and floral clusters opening could each be reduced by as much as 20–22%.”
and the conclusion,"our results demonstrate that, in addition to the well documented air temperature control of bud break and bloom (Tromp 1980, Whitworth and Young 1992, Zhu et al. 1997), root-zone temperature also has a physiological role in the con- trol of apple tree bud break and floral cluster development. This finding may have implications for commercial apple pro- duction.
Hey whether its lights, tarps, mulch I guess we’re here to share ideas and encouragement to not always let nature take its course but to fight her kicking and screaming to keep our fruit
But that would probably mean a delay of not more than about 2-3 days at most- and to my mind, probably less. Remember that mulch only keeps the ground cooler for the first couple inches- those two or three inches do the same thing as mulch for deeper soil.
Unfortunately, the experiment was done heating the entire root structure- I will look further because I’m fairly certain there have been experiments done with mulch that support my original position on this. At any rate, the exchange has become interesting to me. Thanks for that, Mike.
My brain is ready for another day!
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