Bitter beetroot

Hi, this year I grew beetroot for the first time from seedlings I bought at our garden centre. Much to my disappointment, after cooking I found they were all bitter, not at all like the bought ones from the supermarket. I grew them in a raised bed with fresh garden compost also from the garden centre. Does anyone have an idea what might have caused the bitterness or was I just unlucky with the type of seedlings?

I know that a lack of magnesium is thought to make tomatoes taste bitter so maybe it's the same for beetroot.  Also, if your soil is acid, some plants can find it difficult to take up magnesium so try giving them a weak dose of Epsom Salts every couple of weeks next year - 1 tsp to a gallon - poured over the foliage and around the plant but not on  sunny days.

Hallo obelixx, thanks so much for your tip, I'll try that next time, but first I'll have to Google what Epsom salts are called in German!