Perennials decorate our gardens year after yearVariety of bright colorsand unique leaf shapes. However, after a few years in the garden, these perennials may begin to produce smaller flowers, develop a "bare spot" in the center of their crown, or need support to keep their stems from falling over. All of these are signs that it is time to divide the plants. In today's article we will explain which perennials you should divide in spring and which in autumn and when the right time is in autumn.
Why should perennials be divided?
- To rejuvenate the plant and stimulate new growth
Overcrowded plants compete for nutrients and water. Restricted air circulation can lead to illness. Dividing plants reduces this competition and encourages new growth and more vigorous flowering.
- To reduce the size of the plant
Because plants grow at different rates, division can be used to keep perennials that spread quickly under control.
- To increase the number of plants
Division is an easy and inexpensive way to increase the number of plants in your garden.
Most perennials are best divided every three to four years.
Which perennials to divide and when?
Here is the basic principle:
- Spring bloomers can be divided and transplanted in the fall, a few weeks after flowering.
- Late summer and autumn bloomers can be divided and transplanted in early spring, before budding. These include, for example, asters,Hosta Stauden, Coneflower and Fat Hen. Perennial ornamental grasses should also be divided in spring because they bloom or go to seed in late summer and fall.
The main goal is to leave the plants alone while they bloom and fruit and plan for repotting or root division in the off-season.
But there is another indicator of the right time to divide plants – their roots. Generally, perennial plants that have a tuber should be divided in the spring. Perennials with fleshy roots such as peonies (Paeonia spp.), oriental poppies (Papaver orientale), and Siberian irises (Iris siberica) are best divided in fall.
Which perennials shouldn't be divided?
While most perennials benefit from being divided every few years, there are some perennials that do better when left intact. Avoid sharing these varieties:
- Indigolupine (Baptisia)
- Heart Flower, Bleeding Heart (Dicentra)
- Milkweeds (Asclepias)
- Nieswurz (Helleborus)
- Diptam (Dictamnus)
- Lavendel (Lavandula)
When is the right time in autumn?
Divide perennials on a cloudy day, as sun and high temperatures can cause plants to dry out. Ideally, you should divide the perennials in the fall when a few days of rain is forecast so that the new plants receive adequate moisture.
If you divide the perennials in autumn, the months of September and October are ideal for this. As a rule, you should do this four to six weeks before the ground freezes so that the roots of the plants can establish themselves. If you move the plants too late, for example in winter, they will not have time to develop functional roots.
Basically, ground frost occurs when a light layer of ice forms near the ground. This can also happen at air temperatures of 5 degrees. Humidity plays a crucial role. If there is high humidity in combination with strong wind and fog, the chance of ground frost is low. If the humidity is low, you can expect ground frost.
5 Perennials That Should Be Divided in Fall
Peonies
Peonies are beloved for their gorgeous flowers and sweet scent. They are easy-care, long-lived plants that survive even cold winters. They need to be divided every three to four years in the fall. Each peony cutting should have three to six “eyes”.
Tall perennial phlox
This long-blooming perennial has large, showy flower clusters that delight the eye all summer long. To keep the phlox blooming year after year, you should separate the clumps every two to four years.
If you divide garden phlox in the fall, it is recommended to mulch it after transplanting. A 10 to 15 centimeter thick layer of straw, pine needles or similar material should protect the newly planted cuttings from ground frost.
Dividing Iris Perennials
Ideally, bearded irises should be divided six weeks after flowering (usually in August). However, it is not too late in autumn. After cutting back the foliage, dig up the iris rhizomes and cut them into sections with a sharp, clean knife. Each rhizome can be divided into three or four parts. Take the pieces and plant them flat in compost-treated soil.
Divide lilies perennials
Daylilies enchant with their very long summer blooms and their fascinating display of colors. Summer-blooming perennials like daylilies can usually be divided before or after flowering.
When dividing daylilies in autumn, it is recommended to cut the foliage back to 15 to 20 cm. Each division should have two or three pairs of leaves. Daylilies should be cut back in the fall, even if they are not divided.
Divide poppy perennials
Poppies are best known for their large, scarlet flowers, but there are many types of poppies in many colors. Divide these perennials when the above-ground parts die back in the fall.
