> I'm not sure I'd know how to grow the plant in Summer even if I
> wanted too (other than providing artificial conditions to emulate
> Winter, which defeats the object). I quite like these Winter growers,
> which provide pleasure when not much else is growing. I onlt give
> them whatever natural light comes through the windows into the
> house, or into the greenhouse.
>
> What are people's thoughts on what controls the cycle of D. peltata
> and other similar plants?
>
> My plants start into growth in the Autumn (Fall) - about October in
> the N. hemisphere. It can't be the day-length that does it (since the
> tubers are deep underground), and it can't be water, since they
> come up even if I don't give them any (though I don't suppose they'd
> like it if I *still* didn't water them after they came up). That
> only leaves two choices: (1) the declining temperatures, or (2) the
> tuber knows it's been dormant for a few months, so it must be time
> to come up again.
>
> As for the onset of dormancy, again we have choices. This time the
> plant has leaves, so it can see the light and the long days of
> Summer. The temperatures are high. The plant has grown it's single
> stem terminated by flowers, has perhaps produced seed, has developed
> one or more new tubers, so what else is it to do other than go
> dormant?
>
> --
> Clarke Brunt (clarke@brunt.demon.co.uk)
>
I have always assumed that the dormancy of tubers is regulated by a simple 6
months up, 6 months down cycle. There are some other factors such as
temperature and water but I suspect that they are contributory rather than
major factors in the breaking of dormancy.
I have sucessfully adapted a number of tubers from the southern
hemisphere (SH) conditions which might throw some more light on the
issue. Tubers from the SH will stubbornly refuse to restart growth
until February at the earliest which presumably corresponds to their
usual SH cycle. Attempts to force the plants into growth earlier by
watering are always unsucessful and often lead to rotting of the tuber.
Once growing the SH plants usually have a reduced growing period,
becoming dormant again by June or earlier. Once down they keep to the
six months of dormancy coming back into growth around the end of
November. The second year of growth is virtually normal, the plants
having settled into the NH cycle. I have always assumed that the reason
why the plants go dormant early rather than growing through the summer
is because they require a shorter winter photoperiod. However without
conducting any experiments to eliminate other factors I cannot reach any
firm conclusion.
I must admit that I too prefer to grow these plants during the winter
when most of my other plants are dormant. I have not tried to keep any
of my plants growing through the summer and if anything has not gone
dormant by early summer I will force it into dormancy by reducing the
watering and placing it in a shady position. I had some tubers of D.
stolonifera ssp Compact a few years ago which showed every intention of
growing all summer before I enforced dormancy on them. I also suspect
D. pulchella is a bit of an opportunist and will grow through the summer
if it has the right conditions. I'm sure I remember reading somewhere
that this plants does just that at certain locations in Southern parts
of Australia.
-- Phil Wilson