Getting the Best Tasting Raspberries

A while ago, I thought I read you can add something to your raspberry patch (in the soil) to increase the sweetness of your berry harvest. Could you please tell me if this is true and if it is what is it?

Get the best flavor and biggest harvest by selecting a flavorful variety and keeping it healthy. Select a cultivar known for it flavor and the desired use. Boyne has long been a favorite of the summer bearing raspberries. Look to some of the newer introductions for even better tasting fruit. Gardeners in zone 5 or warmer can try the large fruited Reveille or Haida. Both berries are sweeter than Boyne. Festival is has good flavor and is hardy in zones 3 and warmer. Proper pruning, watering and fertilization will keep the plants healthy, reduce pest problems, and ensure the best possible flavor.