Fall is a great time to be dividing some of your clumps of perennials in the garden, especially during the month of October.

Rooting best takes place when the soil temperature is greater than the outdoor air temperatures.

Because of the summer sun warming up the soil all summer, it is still warm enough for root growth to happen.

How do you know, though, which ones can be divided to this time? Which ones should be divided? And what is the best way to divide them?

Here are some tips to help you out.

One of the reasons for dividing perennials is to rejuvenate older plants. As some perennials age, you may see the clumps will have started to die out in the middle with only new growth appearing on the outer edges of the clump.

Or, you may have noticed the plant may not be blooming as heavily as it used to and the leaves may appear stunted.

These are all signs the plant is losing its vigor and needs to be dug up and divided in order to thrive again.

Unfortunately, there is no set formula as different types of plants require dividing at different times.

For some, they may need it every three to four years and for others, it may be longer.

The key is to examine them early spring to see if they are thinning in the middle.

If you have ever grown black-eyed Susans before, you know some perennials will just spread wildly year after year and you need to control the size of the plant before it takes over the entire garden.

Some perennials grow much more aggressively than others. By dividing the clump into smaller sizes, you can keep the plant size under control.

The third reason to divide your perennials is to propagate more plants.

Dividing perennials is an easy and inexpensive way to increase the number of plants in your garden especially new areas. It is also a great way to share plants with friends, family or neighbours.

Now that we know why we need to divide perennials, the next question is: when is the proper time to divide?

The general rule of thumb of when to divide is:

Divide spring and summer flowering perennials in late summer or fall, e.g. irises, salvia;

Divide late summer and fall blooming perennials in early spring, e.g. sedums, coneflowers and mums.

Here are the steps to follow when dividing your perennials:

If you can plan to divide your perennials on an overcast day with showers in the forecast, it will greatly help the plant recover from the roots being damaged. It would also be helpful to thoroughly water the plants a day prior to dividing.

When dividing in the spring, wait until new shoots are about one inch tall.

Using a spade or garden fork, dig into the soil about six to 12 inches beyond where the shoots emerge.

Dig all around the clump then pry up on root ball. Dig up the entire clump entirely before dividing and sit it on top of the ground or on a tarp.

When you just stick the shovel in the ground and pull up on a portion of the root ball without seeing the entire thing, you have no way of knowing how much root you will get and could be wasting parts of the plant.

Using a sharp spade or knife, gently cut through the roots, dividing clump into as many pieces as desired. Each division should have at least three to five vigorous shoots and a healthy supply of roots.

If the centre of the plant has died out, divide the living, outer portions into smaller clumps and throw out the dead, centre portion.

To help get the new clump of to a good start, enrich the soil in the new planting areas with compost, composted manure or triple mix before planting the new divisions.

Fertilize new plantings by scattering a handful of bone meal in the bottom of the planting hole. Bone meal is high in phosphorus, which will help stimulate root growth.

Fill in around the plant roots with triple mix or compost. Make sure that the plant is in the soil at the same depth it was previously, then water well.

Keep your garden flourishing by dividing your perennials when needed. Remember, it is only in gardening that you can multiply by dividing.

Joanne Young is a Niagara-on-the-Lake garden expert and coach. See her website at joanneyoung.ca.