Well, fertiziler granules crossed my mind too, but I filled the pots myself last year with plain B&Q compost, no granules included. Also, they seem to be mostly at the bottom of the pots, as though something had snuck in through the drainage hole. Besides, fertilizer granules just turn to powder if you crush them, whereas these things contain a gooey gritty substance. Help! These eggs are taking over my mind!

I know what you mean about 'slow release' though - went to give the roses a winter feed and found last years' granules still hanging about!

Bob