Responding to Pope Francis' call for Catholics around the world to observe Sept. 1 as a Day of Prayer for the Care of Creation, St. Charles Borromeo Seminary in Philadelphia planted a tree on its grounds on Tuesday.

The planting of a white oak was done in partnership with the Pennsylvania Horticultural Society, and was followed by a blessing of the new tree by the seminary's rector, Bishop Timothy Senior.

The seminary's tree was the 500,000th in the society's "Plant One Million" campaign. The effort aims to plant 1 million trees throughout 13 counties in southeastern Pennsylvania, southern New Jersey, and Delaware.

"The annual World Day of prayer for the Care of Creation offers to individual believers and to the community a precious opportunity to renew our personal participation in this vocation as custodians of creation," Pope Francis said in his letter announcing the day of prayer for the care of creation.

He modeled the day on a practice already observed among the Eastern Orthodox, and encouraged Catholics to organize both prayer and practical initiatives for the event.

The Pope added that it was to be an act of "raising to God our thanks for the marvellous works that he has entrusted to our care," while also "invoking his help for the protection of creation and his mercy for the sins committed against the world in which we live."

Francis led a Liturgy of the Word at St. Peter's Basilica for the day of prayer.

The Archdiocese of Philadelphia participated in the initiative not only through the tree planting at the seminary, but also by inviting all its 219 parishes to pray at Mass for the care of creation, and with personal prayers as a way to be aware that we are "custodians of creation."

All parishes of the archdiocese were invited to include this intention among their prayers of the faithful: "For the protection of God's gift of creation, that this effort on the part of government leaders and everyone will help to overcome the routine abuse and neglect of our common home. Let us pray to the Lord."