Yedder

[…] you shall set your stakes at the brim of the water, each a yard apart, and so yedder them with your yedders, and so stake them with your strut stowers, that they may stand three tides without removing by the force thereof.

they whack wi' their yedders

Hence the request that they should repair to the wood on Ascension Eve to prepare their stakes, their stowers, and their yedders, and bring them on their backs to the place fixed upon for their planting by "nine in the morning." Of course, Ascension Day is determined by Easter, which is regulated by the moon, and the moon regulates the tides[…]

"But 'e's biddable as a yedder, an' never [has] a fixed idea of 'is own. I dun't rightly think 'e's ever called owt else.” She realised my confusion. “A yedder's weaved through a stake to make a fence or bind an 'edge, you see. It bends this way an' that[…]"

[…] you shall set your stakes at the brim of the water, each a yard apart, and so yedder them with your yedders, and so stake them with your strut stowers, that they may stand three tides without removing by the force thereof.