Answer: Asian pears do require a second variety for pollination. You can choose any Asian pear that blooms at the same time your 20th Century blooms. As long as the bloomtime overlaps, you'll have no trouble producing fruit from both your Asian pear trees. Here's the breakdown on compatible pollinatores: The early-blooming varieties Ya Li, Tsu Li and Seuri are compatible and should be planted together. Later-blooming varieties comprise most of the Japanese and hybrid varieties and selections. Notably Niitaka is pollen-sterile; Kikusui does not pollinate 20th Century; Seigyoku and Ishiiwase are poor pollenizers. Most other varieties pollinate each other.
The earliest flowering Japanese variety is Chojuro which flowers at the same time as Anjou or Winter Nelis. Late flowering Japanese varieties are 20th Century and Okusankichi which reach full bloom with Bartlett. Most years the last third or half of Chojuro bloom overlaps the first third or half of 20th Century bloom.
Hope this helps you choose a pollinator for your 20th Century Asian Pear.
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