Division, in horticulture and gardening, is a method of asexual plant propagation, where the plant (usually a herbaceous perennial) is broken up into two or more parts. Each part that is divided must contain an intact root and crown. The technique is of ancient origin and has long been used to propagate bulbs such as garlic and saffron. Over time, perennials will begin to show signs that they need to be divided. There are multiple ways to divide different types of perennials because of their parts.
Division is used by gardeners to increase the stock of plants and support plant performance in the long run. Over time, many perennials that are herbaceous tend to expand from a central crown and start to clump up in the middle. If there is no periodic division that is occurring, these clumps can become overcrowded and stressed out. The main purposes of dividing perennials include:
Overcrowding prevention - as perennials expand outwards, root systems start to compete for resources such as oxygen, nutrients, and soil moisture. A lot of root density in one area limits access to these resources, which eventually leads to reduced plant vigour. Dividing the congested clump restores a more balanced root-to-soil ratio.
Vegetative propagation - division is a reliable form of clonal propagation because each division genetically has the same tissue. For this reason, the final divided plants keep the characteristics of the parent plant.
Making older plants more lively - a lot of perennials start to experience reduced productivity as their central crown ages. When division is completed with the woody or senescent parts being removed, it allows younger and healthier growth to form. This enables more and healthier flowering performance and improves the overall plant structure.
Improving the airflow and reducing the likelihood of pests and diseases - when plants are overcrowded in one area, the air circulation within the canopy is reduced. This leads to other issues, such as an increase in humidity around the foliage. Having higher humidity can encourage fungal pathogens such as leaf spot diseases or powdery mildew. Overall, division improves microclimate conditions and reduces the susceptibility to diseases.
It is recommended that most perennials should be divided and replanted every few years to keep them healthy. Plants that do not have enough space between them will start to compete for resources. Additionally, plants that are too close together will stay damp longer due to poor air circulation. This can cause the leaves to develop a fungal disease. The best time to divide a perennial is when it is not blooming, so perennials that bloom in the fall should be divided in the spring, and perennials that bloom in the spring/summer should be divided in the fall. The ideal day to divide a plant is when it is cool, and there is rain in the forecast.
There are multiple root and crown systems in perennials, which affects how you divide them. The five types of root and crown systems are:
Clumpers - these plants often contain fibrous roots, and sometimes are called offsets. Many smaller plants can be found growing from the base of the original plant. Each offset creates its own root system that can be divided into separate parts, which allows easy hand division with little damage. Examples of clumpers include daylilies and hostas.
Runners - these perennials often have thin rhizomes and stolons, and tend to spread/trail in the ground. They root along their nodes and send up new shoots above the soil. This creates multiple parts that can be divided. Examples of runners include bee balm and goldenrod.
Woody crowns - these plants usually contain fairly thick roots, where buds are compacted on a hardened base. To divide these, it is a little more difficult, as one has to wait until the plant is older with a mass of healthy roots. It is recommended to wait until the plant is large enough to divide into 3 to 4 pieces. Examples of woody crown plants include baptisia and peonies.
Thick rhizomes/tubers - these are considered stems that grow along or under the soil. They are modified roots that are thick and fleshy for food storage. Cutting through these roots is not hard, so using a knife or pruners is recommended to slice them into sections that include one or more buds. Two examples of thick rhizomes/tubers are cannas and dahlias.
Taproots and woody perennials - these are perennials that are classified as undividable. It is recommended not to divide this type and leave it alone. Examples of taproots and woody perennials include lavender and butterfly weed.
Division is typically performed by digging a circle around the plant about 4-6 inches from the base. Next, dig underneath the plant and lift it out of the hole. Use a shovel, gardening shears, or knife to physically divide the plant into multiple "divisions". This is also a good time to remove any bare patches or old growth. Each division should have a good number of healthy leaves and roots. If the division is not being replanted immediately, it should be watered and kept in a shady location. The new hole should be the same depth as the original hole. After the hole has been filled in, firmly press down on the soil around the base of the plant. This helps remove air pockets and makes the plant more stable. Plants that are divided in late fall when the ground is freezing should also be mulched. Continue to water the division(s) once a day until they have properly established themselves.
Over time, perennials will begin to show signs that they need to be divided. These are:
It produces less and lower-quality flowers than in recent years.
Its leaves are becoming smaller and weaker.
It is in an overcrowded environment and is trying to compete with nearby companion plants.
The middle develops a dead spot/hole, looks sparse, and has weaker inner flower stalks.
The bottom has sparse foliage.
It cannot support its own weight.
The tools typically used to divide perennials are:
Roundmouth or squared shovel.
Spade.
Non-serrated knife.
Garden forks.
Hand pruners.
Loppers.
Shears.
Gloves.
Asexual propagation types include cuttings, layering, and division. The main types of cuttings are stem, leaf, and root. For stem cuttings, this is split into multiple types. These include tip/medial, cane, single eye, double eye, and heel. Layering includes tip, simple, compound, mound, and air.