Someone must have sung ('performed') Seeds of Love in a way that caught the attention of Cecil Sharp's source.

Hmmm... The idealist in me believes that Mr England overheard some other gardener singing it only the day before and was free-styling his variant just as Mr Sharp was passing.

I can, of course, think of dozens of Traditional Singers who were keen & consummate performers - my hero Davie Stewart, for example, was a master craftsman in all respects & once(according to legend) busked the audience as they queued to attend his performance at the Cecil Sharp House. A man of great skill, craft & cunning, listen to him at length, c. 1957, over at the Alan Lomax Archive.