The things we learn about triffids...

The triffid fruit is growing visibly...

And I learn that triffid plants (and pumpkins too) have both male and female flowers. This is clearly a female. That explains this...

... A generous lot of flowers with no fruit. These are the male flowers. Plenty of bees around, so I can let them sort themselves out. 

And the best bit ...

... I can see it all from my desk!