Pheasant Acre Plants owner Rob Evans, who won gold last year for its gladioli, said:
"Things growing well came to a dead stop in the last couple of weeks. In some of our later shows we will have fewer varieties of gladioli available to us."
Devine Nurseries owner Tony Devine said he was "starting to panic a bit" about the alliums and eremurus he has been growing outdoors in East Yorkshire because of the "iffy weather" bringing halting growth.
Chris Beardshaw, who has designed the Furzey show garden at Chelsea, said azeleas, rhododendrons and digitalis were proving problematic to get ready in time.
Potash Nurseries Mike Clare added of the fuchsias he will show at Chelsea: "It's difficult growing weather. One minute you're opening the vents and the next it's a hailstorm. The plants don't know what to do."