Hillier's Chris Francis said: "Like for like sales for the month were 20% ahead of last year.
"Highlights included Nursery stock +26%, Restaurants +13%, growing media +8%.
"Financial year (from 1 September 2016 to date) sales are +15%"
Notcutts chief executive Nick Burrows said: "We've had an encouraging March - a good start to the season. Terrific to have the weather with us and we've seen strong customer numbers across our centres."
Paresh Raithatha, of West London's Ansell Garden Centre, said sales last week were 88% up on the same week in 2016.
Ansell Garden Centre burned down in November 2016 and is now only able to trade from outside with one-third of the stock it had previously, but despite this, sales were only 8% down on March compared to March 2016.
"That's not bad going considering we have no buildings," he said. He plans to open on Easter Sunday because he can with no indoor trading so that could help Ansell to beat April sales if the weather stays good. Ansell is drawing up plans for a new centre, which could open in a year's time.
Alton Garden Centre director Andy Bunker said: "I'm sure it's the same all round."
He said he had completed his "best ever" March and best ever first quarter", joking "yep, I guess Brexit is really biting at Altons".
Bunker said despite "awful" weather forecasts on Sunday, the weather was good and good sales were continuing into April.
Mother's Day kept the growth coming, as centres beat figures from the slow March of 2016.