Grower Champagnes are sparkling wines made within the designated Champagne region of France. And produced by the estate that owns the vineyards from which the grapes are grown. While large Champagne houses like; Pol Roger and Piper Heidsieck use grapes sourced from many different family owned vineyards. Grower Champagnes look to express a specific niche terroir, and are typically sourced from a single or closely located family owned vineyards in and around a village.
There are around 19,000 independent grape-growers in the Champagne wine region, accounting for approximately 85% of the areas vineyard ownership. There are some *5000 growers producing wine from their own grown grapes.

 

*Though less than 50% actually bottle their own, with Co-ops producing the rest - (and most of these are blended). An estate bottled - Grower Champagne can be identified by the initials RM (meaning Récoltant-Manipulant) which appears before a number on the wine label.
Approximately 85% of Champagne produced is ‘Négociant Champagne’ - meaning wines made with grapes purchased from dozens to hundreds of different grape-growers throughout the Champagne region. But they own lees than 15% of the vineyard area - making it a necessity for them to buy grapes from independent growers. On average a Grower Champagne producer makes fewer than 5000 cases of wine annually.
The popularity of Grower Champagne is a relatively recent trend. Since the 18th century, large Champagne Houses have dominated the regions wine production. These family houses or Négociant buy grapes from several owner-growers to blend in their Champagnes.
As of 2015, there were around 5000 Grower Champagnes labels available for purchase within France - but only around 2000 actually made (bottled) their own. Distributors and retailers started to promote the comparative value and lower cost of Grower Champagnes versus those from larger Champagne houses - *but this was not actually accurate.
For Grower Champagnes - terroir is at the forefront, rather than an emphasis on a consistent ‘house style’ that can be made year after year. Some growers will craft their wine to reflect the terroir of a unique village, especially if they own vineyards in one of Champagne's Grand Crus - rather than selling them to the larger houses where they become part of a generic blend. Often Grower Champagnes are released earlier than larger house expressions, due typically to the lower financial resources available for long term aging and storage. Compared with Négociant Manipulant bottling, many Grower Champagnes also have a lower dosage added, and occasionally no dosage.
A common critique of Grower Champagnes is the potential for variable quality, especially from vintage to vintage. While larger Champagne Houses and Négociants have the ability and flexibility to buy grapes from all over the region to smooth out these vintage variations. While Grower Champagne producers are limited to only their own grapes. 
These artisan Champagnes are hand-crafted by small growers in one of the world's best known wine regions. They capture their senses-of-place, plus in recent years there has been subtle shift away from the domination of the larger Champagne Houses. They are also making essentially rare Champagnes, in small volumes. There have been rapid increases recently in the quality of the wines and interest in the significance of each origin.
The appeal of Grower Champagnes - is there bespoke nature - as they do not aspire to a consistent house style like that of the larger Champagne Houses. Instead, their Champagnes are made simply to reflect their location in a literal sense. Hand-crafted in one specific place and from one specific source. The resulting wines are seldom consistent, but instead, the combination of a truly individual geography, geology, climate and the creation of a taste that expresses a true sense of place.