On 2013-08-29 20:43:53 +0100, Roger Tonkin said:

I have a number of dahlia tubers, all from the same
source (as do many people round here!. We divide them
regularly and share them around, or sell them at
church coffee mornings).

This year, I planted some in the back garden, south
facing and near the house, so quite warm, and some in
the front, much cooler and no sun from 10am to 5pm.

After the usual battle with slugs, all have grown
strongly and one flower opened in the back first.
Front have now started flowering well, but in the
back, although there are lots of buds, the flowers are
not opening, just swelling very slowly.

I admit that they have been planted in the same bed
for the last few years, but I've never had this
trouble before.

Any ideas as the possible causes, plants all look
healthy and same as the ones in the front.

Cold spring, late start? Our full sun ones are doing well, our
slightly shadier ones will be lucky to flower before first frost, imo
and are going to be moved altogether. One variety D. Blackberry Ripple
never emerged at all this year, so I reckon the wet last winter done it
in.
--

Sacha
South Devon