Ansell Garden Centre, Sipton Village Garden Centre and John Train Plants will be bulldozed if the multi-billion-pound development takes place. Transport secretary Geoff Hoon has been considering some 70,000 responses to the Government's consultation on its proposals for a third runway, sixth terminal and 220,000 more flights a year.
John Train Plants manager Tim Cousins said: "The business will go. But the Government has delayed the decision by two months and is running scared. There will be an uproar if it goes ahead."
Cousins said the business would continue from its Windsor site but it would lose local custom, which is already falling as homeowners let their houses because they fear the noise of a new runway.
The bedding plant grower, who has been based near Heathrow for 14 years, added: "This will make the area uninhabitable. I wouldn't want to live here. There will be less business for us if they pass it, even if it doesn't go ahead for years. The last thing landlords letting their houses want to do is spend money on the garden. The indecision will kill the market."