The business has acquired more than 180 acres (73ha) of new orchards in Shiplate, near Bleadon in the heart of the Mendip Hills, just eight miles from its Myrtle Farm base in Sandford.
Thatchers chairman John Thatcher said: "We shall be planting upwards of 70,000 new trees at Shiplate during the next two years and a further 30,000 at our orchards in and around Sandford."
He added that this long-term project, which in April saw 26,000 apple trees planted, means that trees being planted now will be ready to crop commercially in about 10 years' time.
Varieties to be used across Thatchers' range of blended ciders include traditional cider apples such as Tremlett's Bitter and Dabinett and the later cropping varieties of Angela, Prince William and Harry Masters Jersey.
This year has been a busy one for Thatchers because 2010 has seen the launch of its new fruit cider Ciderberry, the addition of Green Goblin cider into its product portfolio and the airing on 10 May 10 of its first television commercial.
Managing director Martin Thatcher said: "We like to think that here at Thatchers we do things quite a bit differently from other cider makers. We are immensely proud to be a family-run company. Dating back to my great grandfather, my family has been crafting ciders for more than 100 years.
"Using fine apples from our own orchards, the expertise we put into our ciders has taken over a century to acquire. So through this campaign we are looking to focus on the values that make Thatchers unique."