I am sure I have bored you before with my tale of wanting to develop
alder as a grain crop. Simply by walking around I have found some
promising variations, the problem now is to combine them. That means
cross-breeding them. It takes 6-7 years for an alder seed to grown
into a tree which produces seeds, a few cycles of that and I'll be
dead. So I want to collect my seeds in year 0, germinate them and grow
them up onto seedling over the winter of year 0-1,and graft them onto
"adult" trees in year 1 to produce fertile cones and catkins in year
2.

But I am having great difficulty in getting the grafts to work, my
woodwork looks OK and I am told that alder is recognised as a
difficult tree to graft. One method that seems to work it "hot pipe".
You take a potted tree, graft it, lay it across a hot pipe and the
graft takes! You can't do that with a rooted tree, so I have looked at
electrical heating.

I have found that if I tape a 2KOhm resistor to an alder twig and wrap
it with 10 cms (about 3 turns) of bubble-wrap (bubble-wrap as a form
of insulation that won't get water-logged) the temperature is raised
about 10°C above ambient and if I use a 1KOHm resistor, I get 20° C
above ambient. I found that grafts with these resistors were these
temperatures above ambient after 6 weeks on a tree. To "electrify a
tree" sounded fantastical, futuristic, an awful lot of bother, but
after setting aside my prejudices, and working out how to do it, I
found it very convenient, in fact so convenient that it might even be
more convenient than "hot pipe" methods, which I have no experience
of.

But the bad news is that it didn't work! All of them died!

(The bubble-wraps were often infested with earwigs. Is that
significant?) What's the difference, why do "hot pipe" methods work
and electrical heating don't?

Possibilities:-

Wrong time of year.
Hot pipe methods heat the whole tree.
The heat was too hot. If you cut an alder twig it will look green, I
found that the stock of these grafts looked dead and brown and none
had knitted with their scion. So was it too hot? 40°C with 1 KOhm
resistors might indeed be too hot but 23 °C with 2 KOhm resistors
looks liveable. Looking at grafting trails which have tried other
approaches (all failures!), the stocks have stayed green to the end,
so this looks a possibility.
The heat should be turned off when it has done its work.

The challenge is to take seedlings which have been grown under light
and 23 °C (that's the heat output of the lamps), "harden them off"
(maybe I have given too little time for this) and then graft them onto
adult trees in March - April, not very warm months!

Any suggestions?

Michael Bell

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