Among the stranger Welsh practices on Nos Galan Gaeaf (the eve before the start of winter) was at Tenby, Pembrokeshire, was any cross-roads where spirits were supposed to linger. Trefor M Owen, the curator of St Fagans Museum, says in his book, Welsh Folk Customs: "It was at a cross-roads that the custom of "sewing hemp" was carried out by women. Having raised a little of the ground, the women would chant:

Hemp seed I sow, hemp seed I'll mow;
Whoever my true love is to be
Come sow this hemp seed after me.

The shape of the person would appear and rake the hemp seed."

What Owen doesn't divulge is why this hemp seed was expectly to grow after being sown on the eve at the start of winter - a waste of good whacky baccy, indeed. He does say: "This custom was widely thoughout Wales and in other parts of the British Isles; often it took place in a churchyard."

In answer to PoppaGator, the Gower rhyme was said as part of the custom held to observe the eve of winter, not Christmas. The verses:
"If thou hasn't got a penny, a ha'penny will do..." are known across the whole of Wales at Nos Galan Gaeaf (i.e. Gresford and Llanyblodwel in North Wales.) My guess about the popular rhyme "Christmas is coming, the goose is getting fat" is that Christmas (or the winter solstice) was/is such an important festival that this rhyme was lumped together in the Christmas rhymes file. Christmas is coming? You bet it is - and it's not two months away!