[header] How to keep perennial plants from taking over your garden [title] Understand the concept of plant division. [step] Dividing perennials means splitting 1 large plant into several smaller plants. Plant division helps keep perennials healthy, promotes blooming and may extend the life of some plants. 
In the case of plants that are overtaking a garden, dividing a perennial will reduce the plant's size and keep it from crowding out other plants. [title] Determine when to divide your perennials.