Praise be to Allaah.
Firstly: The Muslims have acquired from the kuffaar the practice of giving flowers to the sick and putting garlands of flowers on the graves of their deceased. Both actions are reprehensible, on the one hand because these bad customs have been taken from the kuffaar, and on the other hand because they are a waste of money. What benefit is there in roses and flowers for which money should be spent on them and which will fade after a short while when no one, living or dead, benefits from them?
Secondly: Some researchers have stated that wearing a garland of flowers is a custom that was originally taken from the Christians, and is something that they do in their church. A study has been undertaken on this topic.
‘The crown of flowers: Wearing a crown or a garland of flowers: the origin of this custom is what was done in the church. It says in their books: after the blessing and after the newly married couple prepared to leave the church, it was customary to adorn them with a crown or garland of flowers, as a symbol of victory and of their chastity.’
(End quote from Ta’ammulaat wa Waqafaat ma‘a ba‘di Mazaahir al-‘Ars by Dr. Faatimah bint Muhammad Aal Jaar-Allah.)
What we have mentioned is no different from the ruling on wearing a garland of flowers on the occasion of marriage or for the ‘aqeeqah or on other occasions.
It should be noted that the issue of customs varies from one country to another and one place to another. If the matter in your country is as mentioned here, namely that this custom was originally taken from the kuffaar, whether Christians or others, or it is a custom that is only for the kuffaar in your country, or for a group of them, such as the Hindus, as they are known for having this custom, or from some other group, if that is the case it is haraam to do this action, which is one of the actions of the kuffaar that is unique to them or was taken from some of their religious traditions or is done in imitation of the kuffaar, in one way or another, and is something that is unique to them.
And Allah knows best.