David Maxwell

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since Jul 26, 2016
Atlantic Canada (NS), zone 5b
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Recent posts by David Maxwell

I realised that I never posted a follow-up with my experiences.  When I was posting previously I had only my two tanks of water, heated by air-to-water heat exchangers (car radiators), controlled by a differential thermostat.  Since then I added black plastic pipe buried about 8" deep in the grow beds with the water from the storage tanks circulated through them continuously.  I did not anticipate how effective this would be.  The temp in the water storage does not increase nearly as much through a sunny day as it it used to, but nor does it drop down at night the way it did.  I reckon I have effectively more than doubled my heat storage capacity.  The soil used to get down to freezing on really cold nights, (didn't seem to bother the greens...); now the soil remains consistently ~ 10 degrees C +/-. (Lowest soil temp so far this winter 8 degrees).  Air temps still drop to just under 0 C on really cold nights.  I reckon the only way to modify this is to add movable thermal curtains of some sort over the glazing.
4 months ago
A number of comments:
1) If you rip out your existing trees and try to plant new ones, with the apples at least, you may have problems with replant disease.  (This will stunt your new trees.  Commercial growers fumigate the soil to sterilise it to prevent this)
2) You can certainly prune your existing trees to a fruiting wall form, by lopping off all branches which intrude into the alleyways, (and if necessary, fostering the growth of new branches in the plane of the tree row)
3) Commercial apple orchards are now almost all planted with relatively dwarfing rootstocks, supported on trellises, and trained to a flat fruiting wall.  Interestingly, these are treated as "crops", with an expectation that they will last 20 years or so, at which time they will be ripped out, (the soil fumigated), and replanted.  If you have larger rootstocks, they will last far longer - 100 years for full size roots.
4) In passing, peaches: yes peach trees are relatively short-lived, much shorter than apples.
5) If you do not prune/train to a fruiting wall, a very effective understory management plan is to spread cardboard under the trees, covered by a thick mulch of wood chips, (ideally with "ramial" wood chips, branches up to 2 3/4" in diameter, (see research done at Laval University,  in the 80's or 90's)
6) Espalier, properly, involves a lot more than training to a relatively flat plane.  It involves both training to a specific geometric pattern and regular summer pruning to encourage development of fruit spurs rather than vegetative growth.  (This is not intuitively obvious, but a fruit bud has 5 leaves for each bud, while a vegetative bud has only one.  So while the tree is markedly controlled in shape and size, the photosynthesis area is maintained.)
7) If, after all this, you still want to "start afresh", you could consider sawing off the existing trees a couple of feet off the ground, and grafting in new scion wood, (with bark grafts) in the spring. (Place as many scions as will fit comfortably on each stub - that way even if some fail, you are likely to have at least one succeed on each tree.  Cut out extras the following year, when you are sure your graft is healthy and solid.)  Then carefully prune and train your new growth into whatever shape you fancy.  You could also take the opportunity to introduce new cultivars into your orchard.
5 months ago
From what I have read, the main heat loss in small-scale greenhouses occurs at the edges of the curtain, which needs to be sealed.  So, multiple smaller curtains suffer from the problem of multiple edges. Hence a single wide blanket is preferable..  
How best to seal the edges?  Neatest way I have seen is to fasten magnetic tape to the sides of the curtain, and build ledges along the outer walls to support the edges, also equipped wth magnetic tape.  The two magnetic tapes will automatically align themselves, avoiding the issue of the roll getting off-centre.  The long section of curtain is supported by wire cable stretched parallel with the joists, (metal clothesline has been suggested).  The designs I have seen urge the incorporation of  weights to maintain an equal tension on the wires so they don't sag as the temperature rises, but I am not convinced an 8 ft. length of wire is going to change in length that much.  Have any of you any experience here?
1 year ago
Just noticed the line about getting only one chance to get the graft perfect when you move from practice to actual surgery.  This is not so;  if your first cut isn't right, you just make another cut a little farther back.  As long as you still have wood, you can keep hacking it back.  What the poster may be referring to is the idea that it is best to make a single clean slice, (with a very sharp knife), so as to get a continuous smooth cut, rather than whittling the cut, (which never gives a smooth flat surface).  But all you really need is cambium-to-cambium contact over as large an area as possible, and the trees will forgive less-than-perfect technique.  If your grafts fail, it is simply that you did not get cambium in contact with cambium.
And, unless it was not apparent in my first posting, those delta grafting tools look good, but work only under ideal conditions, (when both stock and scion are almost perfectly matched in diameter).  They are damned expensive, and useful only in very restricted circumstances.  A good sharp knife is a lot cheaper, and works in all circumstances.  And if anybody wants to pursue grafting to its full depth, the "bible" is a book by R.J. Garner, called "The Grafter's Handbook"
1 year ago
This is pretty straightforward:  the scion wood for apple and pear has to be dormant, and the best success with field grafting will be when the rootstock has just broken dormancy.  You can cut your scion wood any time between now and spring before the scion wood breaks dormancy.  (I cut mine about March.  I am in zone 5b).

But you are going to have difficulty with your grafting tool if you are grafting onto established trees.  These gadgets work only when both scion and rootstock are virtually identical in diameter.  If you are trying to graft onto established trees you need completely different techniques - cleft grafts or what Stephen Hayes calls rind grafts, (on this side of the Pond, more usually called Bark grafts), (or, if you want to get fancier, things like oblique side grafts, inlay grafts, kerf grafts etc.).  I second the recommendation to check out Stephen's videos.  He is a bit wild, but one of the best on the web - YouTube, look for HayesUK, or just enter "grafting" and Hayes

Stone fruit indeed does best budded in June up to August, and here indeed you go from growing mother tree to rootstock tree.  But this, again, is a different technique from grafting, and is done with a single bud, cut with a sharp blade. (Stephen has excellent videos demonstrating the technique)
1 year ago
There are degrees of complexity in "Active".  How complex is perceived as appropriate for a "Permie" is probably variable, but I do agree that there is a bit of a bad rap in many people's minds for any form of active controls.  In practice, my system does have some technology.  The pumps to pump the water through the radiators (my "heat exchangers") are controlled by a differential thermostat, so that they run only when the temperature of the air, (in the peak), is higher than the temperature of the water.  It was apparent that the heat was coming out of the water in the tanks reasonably efficiently, as the temp in the tanks drops as much as 20 degrees C overnight.  But I have gilded this lily a little - I am pumping the water through black plastic piles buried  8" down in the growing beds, 24 hours a day, (at least when the cheap pumps are still working).    I did this on the principle that heating the plants' toes made more sense that trying to heat the entire volume of air in the greenhouse.  But it had an unexpected effect - it added the soil in the growing beds to the thermal mass.  The temperature in the tank with a functioning soil pump runs about 2 degrees lower than the other one, and the soil temperature in the the "circulated" beds, runs 2 degrees higher than the ones without circulating water.  In addition to the pumps, I have 4 large computer fans which draw the air from the peak through the radiators.  All these  pumps, fans and controllers run off a 90 Watt P-V panel with a small battery storage (actually the battery from my ride-on mower) which carries the  soil pumps through the night.
Obviously, since I am able to quote these temperatures, I also have a monitoring system capable of storing a log of data drawn from, (in my case), 4 separate channels..  (Mine currently polls the temp sensors every 10 minutes).  
And that is the extent of my "active" technology.
Does movable thermal curtain insulation count as "active"? (That is my next "refinement", after I get, and install, some new pumps, which hopefully will last a little longer.)
1 year ago
May I add some refinements?  The thermal mass does indeed act as a "flywheel".  But there are significant issue associated with the efficiency of moving the heat in and out of the mass.  At one point in the past I used multiple 1 Gal jugs, laid on their sides, (so that the heat could flow from one to another by conduction).  This worked to a degree, but the heat in the greenhouse was rising faster than the heat sink could absorb it by radiation and conduction from the surrounding air, so the water would warm up only a few degrees in the course of the day.  I was able to roughly double the amount of heat captured by hanging a sheet of plastic in front of the jugs, and blowing air sucked from the peak of the greenhouse through the wall of water.  (Essentially I was adding extra heat in the form of heated air, a very crude air-to-water heat exchanger.)  I eventually abandoned this because the plastic jugs deteriorated and leaked after a year or so.

I then moved to bulk storage.  And here there is another element introduced:  the water in your 55 Gal drums, (and my large (450 L) fiberglass tanks) will stratify.  That is the heated water rises to the top, and when it reaches the temperature of the surroundings will not absorb any more heat.  (Feel your drums some day when the sun is shining on them - you will find that the bottom portion remains cold - obviously not storing heat).  This effect becomes relevant whenever the water volume exceeds somewhere around 25 Gal., and gets worse as the volume increases.  (Parenthetically, this is why the smaller jugs work better - the stratification is confined to small distances, and the heat in the top of one jug gets conducted into the bottom of the jug above it.)  What to do?  I don't have a solution for the 55 Gal drums. but my large tanks are kept more uniform by the use of small pumps sitting in the bottom.  Actually there is an additional element here - I pump the water from the bottom of the tank through used car radiators in the peak of the greenhouse, to capture the heat from the air, before returning it to the tank.  One of the pumps failed recently, affording an unplanned experiment.  The water in the tank with circulation through the radiator, on Oct 28, 2017, reached a peak temp of 31 C, while the uncirculated tank reached 23 C .  (Oblique comment: the $15 pumps from China on eBay aren't worth it.  They die after a few months. Spring for higher quality up front).  Conclusion: heat delivery takes place over a rather short time frame;  heat capture needs to try to follow as closely as possible the rise in available calories.  And there are ways to optimise this.
1 year ago
For what it is worth, I have concrete figures, if it helps answer your question.  Simple passive radiative heat accumulation in large tanks is very inefficient - the surface area-to-volume ratio declines progressively as the tank volume is increased.  The temperature gain in my 450 Litre tanks with just radiation on the front surface, and conductive heat gain between the air through the tank walls, in the course of a day in March where the air temperature in the greenhouse reached 28 degrees, was about 2 degrees.  Adding active heat capture by pumping the water from the tank through a salvaged car radfiator, with the air in the peak blown through the rdaiator by computer fans, resulted in a 10 degree rise in temperature of the water (8 to 18 degrees) on a day when the air temperature hit 32 degrees.  (Outside temperature was -5 degrees).  Incidentally, the peak air temp was reached at about 3 pm, but the peak temperature in the water wasn't reached until 7:30 pm.  That is, there was a lag in the ability of the system to capture the heat available, but there was still useful heat to capture, stored in the air long after the sun set and heat gain had ceased. (The peaks of temperatures of air and water were offset by 4 1/2 hours.).  At the same time, the next day was heavily overcast, and very little heat was gained - the water temperature fell to 4 degrees (from 18) over the next 24 hours. (Soil temperature fell from 12 to 7, and remained around 7 over the succeeding several days of cloudy, snowy weather.  (In general, soil temperatures varied over 2 or 3 degrees, water temperatures varied over 5 to 10 degrees, and air temperatures varied over anywhere between 15 and 25 degrees over the course of a day.)
1 year ago
You are absolutely correct that wood flat across, where water will accumulate leads to invasion by fungi, and rot of the wood.  But 1) painting it with any form of goo does not prevent this, and 2) if cutting, (as opposed to branches and trunks breaking off), the cut should be vertical, so the water does in fact run off.  (If one is removing the entire limb, it should be cut just at the edge of the branch collar, which is where the tree is going to heal over the wound, at least on the living part..  But basically, the wood of the tree is dead.  The wood gets recycled by fungi, which are omnipresent, and nothing you can do as a human intervenor makes any difference to to this process.  The rot was not caused by inappropriate actions on anybody's part in the past.  And nothing you do now is going to prevent any similar activity in future.
1 year ago
>whoever previously cut away major deadwood didn't seal that either, so the core is punky.

Actually, this is false.   Painting cut ends has no beneficial effect - the tree seals the cut itself.  And the rot is not the result of any failure of anybody in the past.
1 year ago