A number that is calculated to summarise a group of numbers. The most commonly used average is the mean, the sum of the numbers divided by however many numbers there are in the group. The median is the middle value in a group of numbers ranked in order of size.
Perennials: cutting back. Perennials are not demanding plants, but trimming them after flowering finishes in autumn helps improve their appearance and flowering. However, you can leave some stems over winter to provide homes and food for wildlife, and then trim back in spring.utting back herbaceous perennials during autumn restores order and tidiness to the garden. However, this removes potential winter interest, in the form of height and structure, plus food and habitat sources for wildlife.
Examples of perennial flowers include the hyacinth, daffodils, tall bearded iris, and day lilies. In addition to these flowering plants, gardeners may choose from numerous other perennials. Perennial flowers or plants can be divided into different types: tender, hardy, herbaceous, and woody.hese terms are used as a means of identifying and separating certain types of flowers. What makes them different from one another is the life cycle of the plants and how long they produce blooms. When planting flowers or creating a garden, it is necessary to understand which plants are perennials and which are annuals.