I've just heard someone claim that Mother's Day was an invention of florists, with the aim of selling more flowers on that day.
Is there any evidence that the flower-selling industry is responsible for creating Mother's day, or at least for pushing it to the popularity it has now?
Well, Google has their handy little graphic set up for today, and I found a page entitled Mothers Day History ~ The Complete History of Mother's Day
Some relevant quotes from this:
Only recently dubbed “Mother's Day,” the highly traditional practice of honoring of Motherhood is rooted in antiquity, and past rites typically had strong symbolic and spiritual overtones; societies tended to celebrate Goddesses and symbols rather than actual Mothers. The personal, human touch to Mother’s Day is a relatively new phenomenon. The maternal objects of adoration ranged from mythological female deities to the Christian Church itself. Only in the past few centuries did celebrations of Motherhood develop a decidedly human focus.
Basically, there is a long tradition of celebrating mothers. Which seems natural given what we know of anthropology and human nature. The article goes on further to talk about the American origins and history of the holiday (which seems to be the main idea you are driving at):
The first North American Mother’s Day was conceptualized with Julia Ward Howe’s Mother’s Day Proclamation in 1870. Despite having penned The Battle Hymn of the Republic 12 years earlier, Howe had become so distraught by the death and carnage of the Civil War that she called on Mother’s to come together and protest what she saw as the futility of their Sons killing the Sons of other Mothers.
However, this didn't catch on:
Despite the decided failure of her holiday, Howe had nevertheless planted the seed that would blossom into what we know as Mother’s Day today. A West Virginia women’s group led by Anna Reeves Jarvis began to celebrate an adaptation of Howe’s holiday.
But, someone took up the call:
After Anna Reeves Jarvis died, her daughter Anna M. Jarvis campaigned for the creation of an official Mother’s Day in remembrance of her mother and in honor of peace. In 1908, Anna petitioned the superintendent of the church where her Mother had spent over 20 years teaching Sunday School. Her request was honored, and on May 10, 1908, the first official Mother's Day celebration took place at Andrew's Methodist Church in Grafton, West Virginia and a church in Philadelphia, Pennsylvania. The West Virginia event drew a congregation of 407 and Anna Jarvis arranged for white carnations—her Mother’s favorite flower—to adorn the patrons. Two carnations were given to every Mother in attendance.
She finally had some success with her holiday:
Anna Jarvis quit working and devoted herself full time to the creation of Mother's Day, endlessly petitioning state governments, business leaders, women groups, churches and other institutions and organizations. She finally convinced the World's Sunday School Association to back her, a key influence over state legislators and congress. In 1912 West Virginia became the first state to officially recognize Mother's Day, and in 1914 Woodrow Wilson signed it into national observance, declaring the second Sunday in May as Mother's Day.
The fight about commercialization seems to have come after the creation of the day.
And as the article states:
By the time of Anna M. Jarvis's death, over 40 countries observed the Mother’s Day. Here is the history of the spread of Mother's Day throughout the rest of the world:
And then goes to list dates and traditions for other countries.
Is there any evidence that the flower-selling industry is responsible for creating Mother's day, or at least for pushing it to the popularity it has now?
Yes.
In the USA, the current Mother's Day holiday was enacted by a joint resolution of Congress on May 8th, 1914.
Prior to being made a federally recognized day, florists did play a role in promoting the idea.
In the August 1910 Proceedings of the 26th Convention of the Society of American Florists it is recorded Anna Jarvis's attempt to create Mother's Day "has proven so beneficial to the business" and a unanimous resolution was passed to publicly recognize her efforts.
In the 15 May 1913 The Florist Review, volume 32, page 17, there is an article LESSONS OF MOTHERS' DAY:
Chief of the lessons of Mothers' day is that of the power of publicity; second, the effectiveness of concerted effort.
The florists made Mothers' day. But for the florists the lady to whom we are indebted for the beautiful idea would never have got anywhere with it.
Mothers' day has made progress just in proportion to the push the florists put behind it—where the florists sat supine, there Mothers' day is practically unknown
Also in the 1913 American Florist, Volume 40, page 823 there is an article "Mothers' Day":
...So this is the warning florists should heed: Mothers' day is yet a young institution. Indeed it is of such recent birth it can hardly be called an institution yet. The next two or three years will probably decide whether it is to live or to die out as suddenly as it sprang into being. And its future rests with the florists themselves... And in a few years the day will be remembered as a fad that did not last. But if they make the flowers as cheap as possible they will be repaid time and time again for years to come. To make Mothers' day popular it is necessary to induce as many people as possible to wear flowers. To do this it is necessary to make the flowers cheap. Whether Miss Jarvis' beautiful idea is to die abornin' or is to live in proclamations and people's hearts depends solely upon the florists themselves.
Only the following year was Mother's Day federally recognized.
Florists did not invent Mother's Day, Anna Jarvis did. However, Anna Jarvis initially linked Mother's Day to carnations. A previous attempt by Julia Ward Howe to create a national Mother's Day, had no relationship to flowers, and was celebrated for a few years around 1873, but quickly died out. Florists made efforts to prevent the current Mother's Day from dying as a fad, prior to being federally recognized, because it was great for business.
