What kind of soil are they in? How often do you fertilize? How much sun do they get? Does your pot have drainage?

I'm not anywhere close to be professional, so no idea about soil ,only know that there is a coconut fiber added in a soil. bought them with flowers and no, no fertilizers were added after that. I live in the Netherlands, so you might have an idea that we don't have much sun here and yes there is a drainage in the pot :)

oh yes, I've read that might be nitrogen deficiency and I added some coffee ground to the soil.