Perennials, grown outdoors or in cold frames can be planted whenever you can work with the soil. Plants grown from greenhouses are best planted after the risk of frost has passed for the spring, or no less than one month before the first autumn frost. Plants that are fairly hardy, or are situated in less than perfect sites are usually best planted in May or June, because it allows them to become established before the winter season.

To prepare the planting site, remove any large rocks, old roots and dead plant material. Then loosen soil with a spading fork, add two to three inches of peat moss or other composted organic matter, and thoroughly mix with the soil.

Most perennials are available in gallon, four inch or smaller pots. To plant, remove the perennial from its pot and place it in a hole. Make sure the top of the rootball is flush with the soil level. Gently firm the soil around the rootball to eliminate large air pockets. Then, thoroughly water your newly planted perennials. Keep them watered, and don't allow them to dehydrate for at least a month in summer weather.