The borough has been handed the prestigious Britain in Bloom gold award by the Royal Horticultural Society.
Hillingdon also won the large city category for its 'impeccable' parks and green spaces in the nationwide contest.
Parts of Uxbridge, Ruislip and Eastcote were assessed.
Britain in Bloom judges visited the borough in August to inspect green spaces, including the Rural Activities Garden Centre in Hillingdon, Eastcote House Gardens, Stockley Park, Uxbridge town centre, Eastcote House Gardens, Eastcote Station and Manor Farm in Ruislip.
above: Stockley Park
Below: Sunflowers in Hillingdon
Hillingdon won a Britain in Bloom gold in 2015.
Darren Share, one of the judges, said: “It was great to hear how committed the council is to open spaces and it’s so nice to see the amount of community activity and volunteering that you all do in Hillingdon. Everything we saw was really impressive.”
Hillingdon has more than 200 parks and green spaces which are regularly maintained by Hillingdon Council employees, residents, and volunteers. In addition to its success in Britain in Bloom, Hillingdon was also awarded the highest number of Green Flags in the UK earlier in the year and won the gold award for large city borough in the London in Bloom competition.
Councillor Jonathan Bianco, Hillingdon Council’s Cabinet Member for Finance, Property and Business Services, said: “We are absolutely delighted to win gold in the large city category as well as category winner in Britain in Bloom against such strong competition.
“This is a fantastic achievement for Hillingdon and will add to our long list of accolades for outstanding parks and green spaces.
“We’d like to thank all the council employees, residents and volunteers who have put so much time and effort into making Hillingdon such a wonderful place to enjoy and visit, and would encourage more people to go out and explore our green spaces.”
Roger Burnett, Chair of the RHS Britain in Bloom judging panel, said: "Britain in Bloom really brings out the best in people and is a force for good across the UK. What started out as a civic pride campaign, has evolved into something that helps tackle some of our most pressing issues.