Christmas Grapes

Christmas A seedling or sport of Isabella developed by Luther Burbank. The old American grape Isabella has produced sports and seedlings which are tetraploid, having twice the normal number of chromosomes. Tetraploids often have larger fruit than the parent variety, and also have larger, thicker leaves and shoots, though there are fewer shoots on a tetraploid. This seems to fit Christmas well. There is debate in the literature as to whether Christmas is a seedling or a sport of Isabella, or some other descendent of Isabella. Christmas has all the traits of a tetraploid, including thick, heavy leaves, large, thick shoots, and poor roots. Tetraploids usually have fewer roots than ordinary grapes and are slower to establish, so that they are often grafted on vigorous rootstocks. Hardiness of Christmas is unknown as it was selected in California, though it's probable parentage suggests it would be hardy to at least -15 F. Prune it to cordons with spurs. Ripens two weeks or more after Concord.