The Secret Garden

The following extract describes Mary Lennox's first impressions of the secret garden:

"It was the sweetest, most mysterious-looking place any one could imagine. The high walls which shut it in were covered with the leafless stems of climbing roses which were so thick that they were matted together. Mary Lennox knew they were roses because she had seen a great many roses in India. All the ground was covered with grass of a wintry brown and out of it grew clumps of bushes which were surely rose-bushes if they were alive. There were numbers of standard roses which had so spread their branches that they were like little trees. There were other trees in the garden, and one of the things which made the place look strangest and loveliest was that climbing roses had run all over them and swung down long tendrils which made light swaying curtains, and here and there they had caught at each other or at a far-reaching branch and had crept from one tree to another and made lovely bridges of themselves. There were neither leaves nor roses on them now and Mary did not know whether they were dead or alive, but their thin gray or brown branches and sprays looked like a sort of hazy mantle spreading over everything, walls, and trees, and even brown grass, where they had fallen from their fastenings and run along the ground. It was this hazy tangle from tree to tree which made it all look so mysterious. Mary had thought it must be different from other gardens which had not been left all by themselves so long; and indeed it was different from any other place she had ever seen in her life."

Question: In the description, the branches and sprays are said to look "like a sort of hazy mantle spreading over everything." What does the phrase "hazy mantle" suggest about their appearance and the overall atmosphere they create?