Gravel colour affecting germination rate?

[Paul Tyerman]

Howdy All,

This is an odd question.......

When potting up seeds for all my bulbs and tubers (i.e including Aroids) I
place the seed on top of the mix and then cover with around 1cm of 3-5mm
gravel.  I have used this now for 3 years and has worked fine and
hunkey-dorey.

Recently I received from a friend a bunch of Arisaema sikokianum seed that
she received from the AGS (or was it Nargs?...... I can't remember
offhand).  2 packets, each containing about 15 seeds.  There were two other
species as well.  I sowed all of these, but mixed the two packs of A.
sikokianum seed as they had the same identifier and therefore I assumed
same source.  As there were so many seeds I spread these over two pots.
The seed was definitely mixed so the chances of me having neatly split the
two packets between the two pots is pretty darn small.

They have started germinating now, all popping their seeds above the gravel
and sending up a shoot from there.  So far two have unfurled leaves, with
two more shoots emerging, plus another 5 or so have their seed pushed up
through the gravel, this being the precursor to the leaf emerging.

It happened that I ran out of gravel when I finished one of the pots and
had to open a second bag.  The first bag was brown gravel, whereas the
second bag was a black ironstone gravel (I have used this previously for
Arisaemas and it has not inhibited germination as far as I can see so I
don't believe that the actual composition of the gravel is a problem).
Both pots were identical sizes and shapes, identical mix, similar size of
gravel (obviously gravel itself varies even within a packet) but one was
brown and the other black.  All the germination so far has been in the
brown gravel covered pot, with no signs above gravel yet in the black.

Now here comes my question.... is it possible for the colour of a gravel
mulch to affect the rate of seed germination?  The two pots are side by
side in the same terrrarium, with the same light conditions, watering etc.
The only difference is the colour of the gravel.  A couple germinating in
one pot would not be something to notice, but having 2/3 of one pot
germinate before the other even starts is VERY noticeable.

OK, you probably think I am a nutter by now, but I thought it was at least
worth asking if anyone has seen anything like this before.  I have
definitely had seed germinate in the ironstone covered pots before,
including Arisaema as I recall that I only had the ironstone last year when
the AEG seedex arrived (still checking the mail everyday for this years...
Sigh!), but obviously I could not compare rates of germination, nor would
have thought too.  This is just so noticeable when everything is identical
including type and source of seed, yet one pot is so far ahead of the other.

Does anyone have any ideas on this?  I thought it was at least worth asking
as it has struck me as so odd.

Thanks in anticipation.

Cheers.

Paul Tyerman
Canberra, Australia.  USDA equivalent - Zone 8/9
mailto:ptyerman at ozemail.com.au

Growing.... Galanthus, Erythroniums, Fritillarias, Cyclamen, Crocus,
Cyrtanthus, Liliums, Hellebores, Aroids, Irises plus just about anything
else that doesn't move!!!!!