This is a common mistake, and a question that comes up frequently on exams. When you have the gerund at the beginning of the sentence (V+ing), the subject of the phrase with the gerund is the SAME subject in the main part of the sentence. Eating ice cream, she was happy (=when she ate ice cream, she was happy) Forever complaining, he was not a fun person to be with. (he was always complaining -- he was not fun to be with (He always complained about things and for that reason, it was not fun to be with him) In your sentence, Crashing into a garden, a tree was knocked down by a car. -- it would mean that the TREE crashed into a garden. So it's incorrect. The correct form would be: Crashing into a garden, John knocked down the tree with his car. OR John drove into a tree and knocked it down. This shows you that JOHN is the one who crashed into the garden AND the person who drove into the tree.

This is a classic case of a dangling participle. https://blog.oxforddictionaries.com/2011/09/26/participles-how-not-to-dangle/ You can only begin the sentence with a participle clause - in this case 'Crashing into a garden' - when this refers to the subject of the sentence. The mistake is that the subject of the sentence is the tree, while the subject of the participle is the car. It was the car (not the tree) which crashed into the garden. This can be fixed by making 'a car' the subject of the sentence: "Crashing into a garden, a car knocked down a tree". Alternatively, you could put the participle clause at the end: "A tree was knocked down by a car crashing into a garden". Putting at the end makes it clear that the participle refers to 'the car'.

ok thanks alot:- But Where are you from?

I think 'The car crashed into the garden, knocking over a tree' sounds more natural. But otherwise maybe 'Crashing into the garden, the car knocked over a tree' should be ok