Julius Caesar famously said, “Veni, vidi, vici,” and now is the time for you to proclaim the same!
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.
Why bother? In most cases, crowding reduces flowering. After a time, the center of the clump may die as well. Dividing rejuvenates growth.
Incidentally, 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 and are not shrubs, trees, or some succulents.
How to Divide
Many plants form large clumps, and can be hard to divide. Examples are aloe, agave, garlic chives, and 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 break out the ax.
Many perennials and groundcovers spread out across the ground and root at the nodes. Examples are verbena, iris, and coreopsis. These you can dig up just the spreading portion rather than the whole clump.
Timing is Important
Many perennials should be divided now, but plants with tropical ancestors are best divided in spring. Think “tropics are warm,” and divide them as the soils warm – not before the winter, which they barely tolerate. Thus, if you don’t see it here, it probably should be done in spring. Look for a post on “Spring Division” in early March 2020.
Landscape Plants to Divide in Fall
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 Fall.
Fortnight lily, also called peacock flower (Dietes bicolor) and butterfly iris (Dietes vegeta) [both formerly in the genus Moraea]. Divide the rhizomes every three to four years. 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. Divide in Fall after flowering is done.
Germander, Creeping (Teucrium chamaedrys var. prostratum). Creeping germander spreads to fill the bed it is in, divide as needed to control spread, in Fall is best. Upright germanders are shrubby and do not require division.
Ginger. If you are growing this delightful spice, harvest “roots,” technically rhizomes, now for drying and grinding into 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 fall. Roots at outer edges and dies from center over the course of several years. Dig up edges and replant center as needed.
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, then move the rhizomes to an average of one foot apart. Best in Fall.
Iris, Siberian. Best done every three to four years, then move the rhizomes to an average of two feet apart. Best in Fall.
More to Divide in Fall
Lavender (Lavendula species). Does not tolerate division. Best grown from cuttings.
Lily of the Nile (Agapanthus orientalis). Bulbs form a dense cluster. Divide every two to three years. You may need a sharpened shovel to cut them apart. 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, the rampant ones, such as mint, horehound, monarda, pennyroyal and catnip.
These rampant growers spread everywhere, yet in a pot can get root bound and die. Divide as needed to control spread, but also to keep from getting root bound. Spring of early Fall.
Rain lily (Zephyranthes species). These bulbs do best with some crowding, therefore division is usually not needed. If you wish to move some to other parts of the yard, then early autumn or late spring is ideal.
Society garlic (Tulbaghia violacea). Division is generally not needed because these bulbs tolerate some crowding. Divided as needed to move (propagate) around the yard in early autumn or late spring.
Verbena. Roots 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.
Violet. These relatives of the pansy have small underground rhizomes like an iris. The center of the patch will die out. It is best to dig up and replanted every 3 to 5 years. Divide in Fall or Spring after bloom is done.
Yarrow. This lovely flowering herb can become root bound with itself. Does best when divided every two to three years. In Fall.
About the Author
If you live in Southeastern Arizona, please come to one of my free lectures that I mention on my Facebook page. After each event I will be signing copies of my books, including “Month-by-Month Guide to Gardening in Arizona, New Mexico, and Nevada” (Cool Springs Press). This link is to Amazon and if you buy the book there I will get a few pennies.
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