Gemma's Post on the Use of Greenery for Altar Flower Arrangements

 

It is well established that the general rule is there should be no altar flowers during Lent.  This is governed by General Instruction of the Roman Missal (GIRM) section 305. Since GIRM does not reference greenery one way or another,  some interpret this to mean that arrangements consisting only of greenery that does not have flowers is permissible, whereas others do not.  Given this ambiguity, the important thing to bear in mind is that if greenery is used it should be very restrained in keeping with the penitential season

Gemma has published the definitive post on the use of greenery in altar flower arrangements.  Please see her full post at the link.

Ash Wednesday

Elena Maria Vidal has an informative post at Fountain of Elias about Ash Wednesday and Lent in general  She discusses prayer, fasting, and almsgiving as well as the fact that Friday is still a day of abstinence. Read more here

About Church Flowers during Lent

The word Lent is used in English in lieu of the Latin quadragesima, which refers to the 40 days leading up to the celebration of Our Lord's Resurrection.

The general rule is that there are to be no altar flowers during Lent.  Exceptions are made for the Fourth Sunday of Lent, Laetare Sunday, as well as solemnities and certain feasts. (General Instruction of the Roman Missal section 305.) The solemnities are the Solemnity of St. Joseph, Spouse of the Blessed Virgin Mary on March 19 and the Solemnity of the Annunciation of the Lord (March 25).

The reason for the rule, of course, is that Lent is a penitential season of fasting and penance. The return of flowers on Easter helps express the joy of the resurrection.
 
Liturgically, Lent ends just before the Mass of the Lord's Supper on Holy Thursday, which is when the Easter Triduum begins. It is both customary and entirely appropriate to decorate the Altar of Repose with flowers. It is also appropriate to decorate the altar for Holy Thursday Mass because that Mass celebrates the institution of the Eucharist and of the Priesthood.  But of course the main altar is stripped after Holy Thursday Mass, and there are no altar flowers on Good Friday.