Out of keenness to cover myself properly, I wear very long clothes which touch the earth. Given that, are my clothes considered impure and I cannot pray wearing them?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

It is narrated that the slave-mother of Ibraaheem ibn ‘Abdur-Rahmaan ibn ‘Awf asked Umm Salamah, the wife of the Prophet, sallallaahu ‘alayhi wa sallam: “I am a woman who wears clothes with a long tail and I walk in filthy places; (then what should I do?).” Umm Salamah replied: “The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said, ‘What comes after it (the dirts) cleanses it.’” [Abu Daawood]

Given that, when you walk in a dirty place and then walk in a clean one, the lower part of the garment becomes pure thereby, regardless whether the impurity is solid or liquid. It is narrated that a woman of Banu ‘Abdul Ash-hal said to the Messenger of Allaah, sallallaahu ‘alayhi wa sallam: “Our road to the Masjid has an unpleasant stench; what should we do when it is raining?” He asked: “Is there not a cleaner part after the filthy part of the road?” She replied: “Yes.” He said: “It makes up for the other.” [Abu Daawood. Al-Albaani: Saheeh]

Mentioning matters that are not necessary to be cleansed under Sharee‘ah, Ibn Al-Qayyim said: “Likewise, the tail of the woman's garment, according to the sound opinion. It is narrated that a woman asked Umm Salamah: “I am a woman who wears clothes with a long tail and I walk in filthy places.” Umm Salamah replied: “The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said, ‘What comes after it cleanses it.’” [Ahmad and Abu Daawood] The Prophet, sallallaahu ‘alayhi wa sallam, permitted the woman to lower the tail of her garment the length of a cubit. Though this part would be affected with filth, the Prophet, sallallaahu ‘alayhi wa sallam, did not command her to wash this; rather, he ruled that the earth purifies it.”

This is applicable when one is certain that he passed over impurity. But if you are uncertain, then the road is pure and clean in principle.

Allaah Knows best.