Hardy perennials

The seedling date palms (germinated from date stones that sprouted) that got accidentally forgotten in their pots at the bottom of the garden over the winter turn out to have survived the frost and snow perfectly well.
According to the Web, date palms are actually hardy down to -8C -- possibly because they live in deserts which get extremely cold at night?

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The alyssum on my windowsill overwintered happily and is now coming into bloom again( further survivals )