Question

why was it still winter in one corner of the garden?​

Answer 1

because summer didn't come to that part of the garden

Answer 2

If I am not wrong, it's from "The Selfish Giant"!!

And the answer is here:-

The isolated corner was to remind the Giant that he also needed to take some steps to keep the gloominess away. The presence of symbols of winter in that corner is to symbolize the past deeds of the Giant which led to overall unhappiness in the garden.