Opal is probably the best-flavored early plum variety - indeed it is sometimes called a gage-like plum thanks to the excellence of its flavor. However the flavor depends crucially on developing sugars during the short growing period, and in northern gardens Opal really benefits from being grown in a sunny aspect. In less favourable situations it will still give good crops but with a less intense flavor.
The fruit is medium-sized, colored dusky red with a heavy bloom, becoming blue when overripe. The plums ripen over a period of about 1-2 weeks, so you don't have to deal with a glut. The flesh is straw-yellow and fairly juicy. Opal is a free-stone plum - the stone falls away easily from the flesh. If picked on a warm July day and placed in a fruit bowl Opal also has a wonderful aroma.