Perennials can be a gardener's best friend. There are plenty of beautiful annual plants to choose from, but they require a lot of work to establish and will only last a single season. With perennials, you simply need to keep the garden plot watered and mulched, then watch as the plants return year after year.

Over time, however, perennials may start to grow too large for their own good. Marie Iannotti, writing for the home design site The Spruce, says that as perennials expand outward, the central area can become faded and wilted.

Dividing a perennial plant keeps it at a more manageable size, allowing it to maintain its health. Taking this step can have other benefits as well. The Clemson University Cooperative Extension says dividing a perennial allows you to easily gain new plants to establish elsewhere in the garden. You can also separate a piece of the plant to establish in a container and give away as a gift.

As a general rule, it is best to divide spring blooming perennials in the autumn and autumn blooming plants in the spring. The seed company Burpee says the plant is less likely to be stressed by hot or dry conditions during these seasons, and it can also concentrate its energy on strengthening its roots instead of supporting leaves or flowers.

Dividing a plant on a sunny or hot day can cause the exposed roots to dry out. The Clemson University Cooperative Extension recommends dividing perennials on cloudy days, especially if light rain is expected in the near future.

Prepare the plant and garden site as much as possible before starting the division. Iannotti says you should water the plant deeply a day before you begin. Trim back the leaves to make the job easier and to reduce the amount of energy needed to support the foliage. Dig a hole or prepare a container where you would like to plant a portion of the divided plant.

Most perennials should be divided by first excavating the entire plant. Use a spade or shovel to dig at least six inches down and work your way around the plant. You'll want to loosen the root ball and eventually be able to pull the entire plant out of the ground.

The methods of division will vary depending on the type of root system. The Clemson University Cooperative Extension says some plants can be separated by hand. If a tougher root ball is present, you can spear it with two garden forks placed back to back and use these tools to pry the roots apart.

Plants whose roots start from a central clump can be separated using shears or a knife. This method will also work well for rhizomes and tuberous roots. If a root system is particularly tough and fleshy, you may need to break out an axe or saw to break it apart.

One simple option is to use a spade or shovel to break through the plant and separate it while it is still in the soil. This method can work well for plants with weaker, quick spreading root systems. You'll still want to moisten the soil and prepare a new plot to avoid root damage.

You may need to make multiple divisions before the perennial is ready for replanting. The National Gardening Association says each new division should have a portion of both the root system and the foliage. Cut away any dead or damaged portions of the plant.

Be careful when using sharp tools to separate perennials. Iannotti says the garden fork method can also be hazardous if the roots are too hardy, since the tool handles might break while you are putting pressure on them.

Plant the divided perennials into their new locations. Make sure they are getting enough water, which can help the disturbed root system to recover. If the leaves are showing signs of damage, you may want to shade the plant in the afternoon.

Some perennials are not good candidates for dividing, since the process will damage them. Burpee says plants with long, deep taproots cannot be easily divided and will not transplant well.

Plants may need to be divided every year, but many can grow for several seasons before they are divided. Some perennials only need to be divided if you want to get new plants. Check the recommendations for individual species to see how often you should divide them.