BBC: The future of English mistletoe is still at risk because of disappearing orchards, experts have warned.
A national campaign began in 2009 to try to preserve the traditional Christmas shrub.
But there are fears it could disappear from woodland within 20 years as traditional orchards decline.
Most of the mistletoe bought in Britain comes from traditional cider-producing orchards in Somerset, Gloucestershire, Herefordshire and Worcestershire.
But wildlife experts say mistletoe management and harvesting techniques are being lost.
The Sussex Wildlife Trust warned that if the loss continued, there could be a threat to species linked to orchards such as bees, butterflies, moths and dead wood invertebrates.
The decline in orchards may also lead to people having to rely on more expensive European imports of mistletoe for their Christmas kisses.
Jess Price, from the Sussex Wildlife Trust, said: "Although we don't want to stop Christmas kisses, we want people to appreciate mistletoe and the threat it faces."
Mistletoe has long been associated with Christmas and mid-winter customs.
It is believed to date back to pre-historic times when it was used as a symbol of ongoing life during the winter months.
According to the National Trust, traditional orchards have declined by more than 60% since the 1950s, and by up to 90% in Devon and Kent.
Its disappearance is proving a concern because it helps support wildlife, providing winter food for birds such as the blackcap and mistle thrush.
It also supports six specialist insects, including the scarce mistletoe marble moth, some sap-sucking bugs and the affectionately-named "kiss me slow weevil".
A project was started two years ago by the National Trust and Natural England to help reverse the loss of the habitat by restoring traditional orchards, supporting small cottage industries producing cider and juices and promoting the growth of community-run orchards.
A National Trust spokesman said: "Orchards remain a key area of work for the trust and mistletoe is a major part of their story and history.
"Across England, orchards have disappeared, so mistletoe has dwindled. It's important that we support this plant for wildlife reasons.
"It needs to be harvested or will kill off trees, and to support local farmers who sell mistletoe and to maintain this Christmas tradition.
"People can also grow their own mistletoe. The best time is February to graft it on to fruit trees."
Conservation warning over supply of Christmas mistletoe
The future supply of traditional English mistletoe is under threat, conservationists have warned.
Mistletoe thrives in established apple orchards but such habitats have seen a big decline over the past 60 years.
The National Trust is urging people to buy home-grown mistletoe in the run-up to Christmas in a bid to ensure revellers can go on kissing under it.
Trust ecologist Peter Brash said it would be a "sad loss" if mistletoe disappeared from its traditional areas.
At least 60% of old orchards in the "cider country" of Somerset, Gloucestershire, Herefordshire and Worcestershire have disappeared since the 1950s.
The decline has been even more dramatic in Devon and Kent, where the figure is as much as 90%.
Mr Brash said: "Mistletoe is part of our Christmas heritage and has a special place in a wonderful winter landscape.
"It would be a sad loss if mistletoe disappeared altogether from its heartland. We could end up relying on imports of mistletoe from mainland Europe for those festive kisses."
The trust also wants people to ask where the mistletoe they are buying is sourced from.
Mistletoe is a parasitic plant that favours the domestic apple tree, but can also be found on lime, poplar and hawthorn trees across the UK.
The market town of Tenbury Wells in Worcestershire holds an annual mistletoe festival with a procession led by druids.
One of the druids, Suzanne Thomas, said of the plant: "It's magic. It's just amazing stuff. It's got this lovely energy about it."
Mistletoe expert Jonathan Briggs said the plant benefited from a managed environment.
"Unchecked, it will swamp its host tree and ultimately cause it to die," he said.
"Regular, managed cropping will ensure that the host tree remains productive while ensuring that a healthy population of mistletoe will persist."
Agriculture minister Jim Paice said there was more to mistletoe than its "traditional amorous role".
"Buying mistletoe helps traditional British cider apple orchards thrive by removing mistletoe from apple trees," he said.
"By buying mistletoe at Christmas, you're continuing a tradition that helps apple trees to flourish."