Head gardener John Anderson said: "We always welcome rain in June and July because this is the period when the rhododendrons put energy into next season's flower buds. They have lapped up the rainfall."
However, he added: "It isn't just the rhododendrons that enjoy the rain - grass, bracken and brambles are growing too and need to be kept on top of."
To promote the New Forest garden's lushness, Exbury has launched a poster to promote its "Fifty shades of green".
Commercial and marketing manager Nigel Philpott said: 'Visitor numbers are down this year by 25 per cent. We have had to close the gardens due to high winds on three occasions since April and have had coach parties cancelling due to the wet weather."
He added: "There hasn't been a spring and summer like this in living memory. But I would recommend donning waterproofs and admiring Exbury Gardens' greenness while these conditions persist'."
A steam railway and buggy tours mean that visitors to the site can also see parts of the gardens under a degree of cover, said Philpott.