Fall is time to divide your plants – at least some of them. Yes, it is still fairly hot out there at mid-day, and not so much fun to work outside – but this is a task that will reward you next spring!

Why Divide?

Just like you separate quarreling sibling humans, you need to separate a clump of sibling perennial plants that are growing too close together. They may look friendly above ground – but down in the soil the roots are fighting for space, and nutrients, and even water. This means they will be less healthy overall, more likely to die from insect attack, and certainly will produce fewer flowers.

Yes, crowding reduces flowering (“Fighting for nutrients” – remember? Less nutrients to go around means less nutrients to flower with). Also, with many plants, crowding and lack of division means that after a time, the center of the clump may die.

Many plants do better with a little rejuvenation every so often – and today we look at the perennials that are rejuvenated by division. (Rejuvenation pruning of woody plants will be another article.)

Word Nerd: “Perennial”

The term “perennial” is used for plants that live for many years and are mostly non-woody. Basically, they are plants that live all year but are not shrubs or trees.  Many succulents are perennials. Perennials are not “annuals.” Annuals live for a only year or less, like our beautiful  annual wildflowers.

Timing of Division is Important

Many perennials should be divided now – in Autumn. BUT! Plants with tropical ancestors are better divided in Spring. Tropicals in spring because the warm weather they enjoy is just around the corner. If you divide tropicals in Autumn, the cold season that they barely survive is just ahead. Examples include plants like agaves, aloes, cannas, and the slipper flower (Pedilanthus macrocarpus, now called Euphorbia lomelii). Dividing them just before this challenging cold time may cause them to die. Thus, if you don’t see it listed here, it should be done in Spring.

How to Divide Plants

Dividing Clumping Plants

Many plants form large clumps, and can be hard to divide. Examples are aloe, candellia, slipper plant, garlic chives, and rain lilies, and more. Think “day lily.”

Dig up the clump, then divide it into smaller clumps for replanting. Depending on the plant and the soil it was growing in, you can use your hands, the blade of the shovel, a pruning saw, or even a hatchet to break the clump apart. You want to do as little damage as possible, but sometimes it cannot be avoided, and it’s time to bring out the hatchet.

Dividing Spreading Plants

Many perennials spread out across the ground and root at the nodes. Examples are verbena, creeping germander, rosemary, and coreopsis. These you can dig up just the spreading portion outer edges – rather than the whole clump.

Plants to Divide in Fall

(Remember – if it isn’t here – divide in Spring.)

Daisy family flowers, including coreopsis, Shasta daisy, echinacea, and Blackfoot daisy. Plants have a spreading habit and often root where they touch the ground. Divide as needed to control spread. Fall or Spring.

Day lilies. Yes, you can grow them in the Southwest – some cultivars that is. Divide every two to three years in Autumn.

Fortnight lily, also called peacock flower (Dietes bicolor) and butterfly iris (Dietes vegeta) [both formerly in the genus Moraea]. Grow from rhizomes that should be divided every three to four years. Separate the clump and move the rhizomes to an average of two feet apart. Best in Fall. Basically, treat like Siberian iris (see iris below).

Garlic chives (Allium tuberosum). These bulbs do well with some crowding. Divide every three to four years or as needed for propagation. Fall after flowering is done.

Germander, creeping not shrubby (Teucrium chamaedrys var. prostratum). Prostrate or creeping germander spreads to fill the bed it is in, divide as needed to control spread, in Autumn is best. Upright germanders are shrubby and do not require division.

Ginger & turmeric. If you are growing these delightful spices, harvest “roots,” technically rhizomes, now (in Autumn) for drying. Freshly dried ginger makes the tastiest holiday gingerbread cookies. Division is best every two to three years, like a bearded iris (see iris below).

Hearts and flowers (Aptenia cordifolia). Spring or Autumn. Roots into the soil at outer edges and dies from center over the course of several years. Dig up edges and replant center as needed.

Divide Iris

Iris, general. Spreading rhizomatous forms need dividing more often than the clump forming rhizomes. For the spreading forms, save only the outer rhizomes. Do not crowd transplants or set too deeply. Early autumn.

Iris, bearded hybrids. Best done every two to three years. Move the rhizomes to an average of one foot apart. Best in Fall.

Iris, Siberian. Best done every three to four years. Separate the clump and move the rhizomes to an average of two feet apart. They like more space than the bearded iris.  Best in Fall.
Lily of the Nile (Agapanthus species). Bulbs form a dense cluster that should be divided every two to three years. You may need a sharpened shovel to cut them apart, or even a hatchet! (Sharpen garden tools – here) Best in Fall.

Lirope. Divide clumps every three to four years, in fall or early spring. Set clusters of three to five bulbs six inches apart.

Mint family – often rampant growers.
Includes mint, horehound, monarda, pennyroyal, catnip, and a number of other cultivated culinary and medicinal herbs.
These rampant growers easily spread everywhere, yet in a pot mints can get root bound and die. (Been there and done that!) Divide as needed to control spread, but also to keep from getting root bound. Spring or early Fall. More about growing mint in the desert on my YouTube – here.

Penstemon. Division usually not needed except for propagation or to reduce overall size within beds. You can divide them now – in Autumn – to introduce them to other areas of your yard.

Last Group

Rain lily (Zephyranthes species). These bulbs do best with some crowding, division is usually not needed. However, if you wish to dig some up and move to other parts of the yard, early Autumn or late Spring is ideal.

Rosemary (Salvia rosmarinus), creeping not shrubby. Prostrate or creeping rosemary spreads to fill the bed it is in, divide as needed to control spread, in Autumn is best. Upright rosemary are shrubby and do not require division.  Pruning yes, division, no.

Society garlic (Tulbaghia violacea). These bulbs appear to do best with some crowding, division is usually not needed. Divided as needed to propagate around the yard in early autumn or late spring.

Verbena (some are now considered Glandularia). These plants root at outer edges and dies from center over the course of several years. Dig up edges and replant center as needed. Best in late fall as they start their winter growth.

Violets.  Some violets grow from rhizomes, like sweet violet (Viola odorata). If you have the kind with little rhizomes, divide in Autumn. If they simply grow in clumps – divide as needed for propagation (to grow more plants). Best in Autumn in our region. Summer is really stressful for them so Spring division not recommended.

Yarrow. This lovely flowering herb can become root bound with itself. Does best when divided every two to three years. In Autumn.

Zinnia, desert (Zinnia acerosa). Short lived with single taproot, division not required.

Zinnia, prairie (Zinnia grandiflora). Divide as needed for propagation or to control spread. Generally in Fall or early Spring.

Go Forth!

So, in the words of Julius Caesar, “Veni, vidi, vici.” (I came, I saw, I conquered.)  Fall is the time to go out into your garden, look around, and conquer any overcrowded clumps of perennials. You conquer these clumps by dividing them.

More on What to do Each Month:

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