Apple varieties generally produce more fruit when the blossom is fertilised with pollen from a different variety. In order for this to take place it’s necessary to have varieties that reach the appropriate stage of flowering at “about” the same time. The flowers of cider apple varieties go through the same stages of development as do eating apple varieties and the critical period of the blossoming is between king-bloom and full-bloom.
Apples generally have flowers in clusters and king-bloom is when the first (generally central) blossom opens. Full-bloom is when all the blossoms of a cluster have opened and before petals start to fall.
Because there is a lot of variation of blossoming stage within a tree and between trees, it is not possible to precisely define when a particular variety reaches these stages. Essentially the ascribing of a date for king-bloom or full-bloom is by “averaging” the blossom stages of a given tree. For this reason it is obvious that some flowers will be open ahead of and behind the nominal dates, but the period of receptivity is at a maximum in the nominated period.
Other factors such as weather and bee activity will also naturally play a part in determining how efficient the pollination period will be in setting a crop. When the king-bloom to full-bloom period occurs can vary year-to-year as can the duration. 2015 blossoming was over a very short period. The dates will also vary within districts depending on local microclimates and between districts depending on altitude etc. Generally the sequence of varieties flowering is relatively stable – but not absolute!
The chart below is for the cider varieties just finished blossoming in 2015. For other years please contact davidp at cideroz.com Double-click the chart to get a clearer image. The variety Granny Smith is not generally considered a “cider” apple although is can be useful for adding acidity to a blend. The main reason for including it in the blossoming chart is to give a reference point so that it is possible to get an idea when the cider varieties will bloom.