Plant in the Fall / Perenials and Shrubs

Platycodon grandiflorus common name Balloon Flower
http://en.wikipedia.org/wiki/Platycodon_grandiflorus

Home gardeners are used to doing most of their planting in spring because of tradition. Back when the average flower bed was filled with annuals, this was the norm, as annuals are tender plants that only live for one season. When perennials came into the fore, the spring planting habit simply carried on. Yet most perennials (as well as many shrubs and trees) do best planted in fall; when plants go into the ground in spring, they're faced with cool soil that slows down their rooting, but soon have to cope with warm air temperatures that stimulate leaf growth and flowering. Then come the summer droughts, which further hinder root formation. As a result, many spring-planted hardy plants fail to root properly and spend their first summer looking stressed and scrawny. In contrast, fall-planted specimens go into warm soil at a time of year when, in most of Canada, rainfall is abundant and evaporation is low. This combination of warm soil and even moisture is ideal for root growth, which continues long into the season, well after the aerial (above the soil surface) parts of the plant are dormant.

Typically, a fall-planted perennial will reach its full size the first summer, while a spring-planted one can take two or three summers to become well established. Though the difference is less dramatic, the same holds true for many trees, shrubs and conifers.