By Bob Hollingworth
Clear pink is a color we do not much associate with
Siberians. There is white, blue, violet, lavender, red-violet, purple and now
red/yellow blends, but not really a true pink. Pink is the poor relative as a
color. Pink in irises can come from one of two sources, either from carotenoid (yellow,
orange and pink) pigments or anthocyanins (blue, red, lavender and violet colors).
Bearded irises have both types, and so clear pinks are not uncommon – think 'Beverly Sills' for instance. But, so
far, there is no evidence for a carotenoid pink in Siberians (or other beardless
irises to the best of my limited knowledge). So pink has to come through the
anthocyanins, and of course this can give pinkish Siberians, but always with a
bluish cast (lavender-pink, orchid-pink) – e.g. 'Pink Haze' (McGarvey, 1980) or 'Mary
Louis Michie' (AM Miller, 1995). The fact that there has been little advance
in achieving clearer pinks in Siberians in many years suggests that this is not
necessarily an easy field to cultivate, but for that reason it is tempting as
well as challenging.
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| 'Pink Haze' |
As with so many other things, working in this
area came to my mind as an afterthought a few years ago when a batch of seedlings seemed to give
some marginal improvement in “pinkness”. These still tend to the blue side of
pink, but truly I think could be termed peppermint pink. One (09F3A3) is under
evaluation for introduction. Perhaps line breeding can slowly improve these
further, but I have a few other thoughts about where cleaner and
richer pinks might come from.
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| 09F3A3 |
The pinkest Siberian I ever remember seeing was Pink Haze
growing in a far part of our garden in
Indiana years ago. It was almost flamingo pink and seemed quite different from the usual
color, so I checked the soil pH. For some reason it was 7.5, about the upper
limit for Siberians to grow. Maybe that could explain the unusual color shift.
So this brings us to the first thought. The color of anthocyanin pigments is quite
complex and can be greatly altered by soil pH. Just think how the color of hydrangeas
can be changed from pink to blue by adding aluminum salts to the soil. The
pigment is the same but when it is complexed with aluminum, it changes from pink
to blue. And, to make a hydrangea pinker, increasing soil pH helps, since this
limits the uptake of aluminum. Could this be an explanation why Pink Haze looked
so pink growing at an unusually high pH?
I guess we’ll never know for certain, but
certainly the soil pH can greatly affect flower color. Which raises another
question - are pink Siberians pinker here in the Midwest (with generally
neutral soils) than on the east or west coasts (often quite acid soils)? A
study of the effect of soil pH on Siberian flower color would be an interesting
thing to try.
Just as external pH changes these colors, so does the pH
inside the cell (which is not directly affected by soil pH). Also, different metals and the interaction with other co-pigment
molecules can change color in a complex way that goes well beyond the bounds of
this blog. Subtle change in cell pH (as small as 0.1 unit) can cause a surprisingly
large change in the blue-pink color balance of flowers. Several tactics could work in theory to
take advantage of this to give purer pinks - increased cell acidity, greater
uptake of metals (aluminum) etc., but there is no obvious way to control these
as a hybridizer, so you can only make promising crosses and hope for a lucky
break in seedlings. Perhaps this is not just a pipe dream. There are quite
clear pink Japanese irises with similar pigments to those in the Siberians.
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| 10J4A5 |
I’m hoping that we saw such a break this year with one seedling
(10J4A5). This stood out quite strongly in a group of new seedlings as a
stronger, clearer deep pink than the others. One year does not a breakthrough make,
so we will need to see this bloom again to be sure it wasn’t just a weird
aberration in what has been a very weird and nasty growing year, but that’s
what makes hybridizing so addictive.
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'Fiona'
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| 'Fancy This' |
The other means to brighter, pinker pinks is to play a subtle
game of combining the current lavender pinks with a light yellow underlay. Too
much yellow makes brownish shades that can be interesting but are not the objective.
I think this effect may be what lies behind two recent introductions from Jan
Sacks and Marty Schafer, '
Fiona' (2010)
and, particularly, '
Fancy This' (2012).
To my eye these have a distinctly richer
pink color than previous Siberians.
Even more exciting is the thought that if you can get purer pinks with less
blue influence through mechanism 1 and then combine this with yellow in mechanism
2, you could head towards true orange. Dreams, dreams.
