Delamore MD Eady recruited Hayloft Plants' Jarman to run at the recent IPM Essen show and has also persuaded Thompson & Morgan's Hansord to run the race.
Jarman said the race would be quite a challenge and the growers were already losing weight in training.
Hayloft is having a sale of surplus stock on www.bidspotter.co.uk from 6-11 February.
Meanwhile, New Leaf Plants sales director David Higginson has completed his Kilimanjaro challenge for the Everyman cancer charity.
The clematis specialist said: "It was certainly the hardest challenge I have ever attempted but at least I did managed to reach the summit."