Just one in 50 people (2%) were able to identify all five pictures of the common trees they were shown, while only 5% were able to name all the most common shrubs, the poll of more than 2000 people for BBC Gardeners' World Magazine found.
People scored better on wildflowers, with a third of those quizzed able to identify all five common blooms they were shown.
The survey revealed that the over-55s were generally much better at identifying plants than youngsters, while women scored higher than men on all of the plants they were quizzed on.
In the wake of the results, top gardener and TV presenter Alan Titchmarsh warned that many people were now more familiar with technology.
Titchmarsh said: "It is worrying that the next generation is not being awakened to the delights of the great outdoors - once common knowledge but now a mystery to millions more familiar with Facebook.
"We can't turn back the clock, but we can ensure that our knowledge of the living world is not lost. It's high time the population was reconnected with nature."