Just wondering if you know what kind of Columbine you might have. I assume it's the European Columbine Aquilegia vulgaris. I'm more familiar with the North American native Columbine, Aquilegia canadensis.

The American Columbine likes a sandy soil that isn't too rich, so if you're using a specialty garden soil for potted plants, it may be too intense for it. You might try adding some coarse sand or even very small pebbles to the soil to give it better drainage. Remove plant from pot, mix sand with soil, then re-plant. I would also add larger pebbles to the bottom of the pot, about 8 to 11 centimeters (three to four inches) deep if you haven't already.

Also, how hot is it in Greece? The American Columbine doesn't like temeratures over 43 degrees celsius (110 degrees fahrenheit). If the temperature gets too hot, the leaves will go dormant and turn brown, but plant will get its leaves back when the temperature gets cooler. Here it grows wild in a partly-shaded woodland type of habitat.

Is your Columbine getting direct sun during any part of the day? The American Columbine is considered suitable for shade. Our Columbine are growing in fairly deep, dappled shade of blackberry bushes right now and they seem happy.

You could try posting this same question on the GardenWeb's Mediterranean forum, or even the "Gardening in the UK" forum, because they may be more familiar with the European Columbine than I am! The Euro version may require different conditions than the U.S.A. one.

Hope this helps...

P.S. I've read that the European Columbine will go dormant once the summer comes if it's grown here in the U.S., which might mean that your Columbine has simply had its bloom time and is now "dying back" or going dormant due to the summer heat.

It's very possible it will simply grow back next year. I have a Bleeding Heart (Dicentra spectabilis) that goes dormant around July here in the U.S., but next spring it will pop right back up in its spot in the garden, re-leaf and bloom beautifully for months. In the meantime, we're left with the unsightly wilted, brown dry leaves for the rest of the summer. Some people cope with this by planting annuals or ferns to sort of cover up the dormant foliage.

Did you save the Columbine seeds? You also can try planting them for next year too.

Here is a link that might be useful: Mediterranean Garden Society