Geoff Hamilton's Barnsdale Gardens in Rutland (now run by his son Nick) demonstrates two built-up asparagus containers, each about 1m cubed, made of railway sleepers. They garden on heavy clay, so had to use large containers for the light soil preferred by asparagus. Interesting - one is in full sun and the other in partial shade, and the shaded box looks very sad next to the one that's had the benefit of full sun.

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not every situation requires a big onion