Some plants don't like to be divided or moved at all. Which perennials can be divided? Dividing perennials can help manage the size of the plant. Plus, most of them can be divided into new plants – making them cost-effective as well. Many perennials will grow quite large after several years. Perennial flowers work in multiple situations: in whole garden beds, in combination with annuals and bulbs, as accent to shrubs and trees, and in containers and windowboxes. Sometimes you can divide garden plants with your hands, as with many bulb species, while the use of a sharp knife or garden spade is oftentimes necessary to get the job done when dividing plants. Plants with fibrous roots can often be pulled apart into smaller portions by hand or back-to-back forks; others (such as hostas) can need a … Even though I am in zone 7b, my annual dianthus will still grow well for me after a cold winter, and is a very pretty addition that gives color in early spring. Here’s a list of dozens of perennials and the best way to divide them. The overcrowded irises take on a circular cluster shape – so you will know when it’s time. The best time I found to divide them is actually right after they bloom. Perennials can be divided at any time of the year if you give the plant appro­priate care afterward, and I do just that. The Best Time of Year to Divide Perennials. Their root structures starts to become overcrowded. Why & How To Divide Perennials In The Summer After They Bloom. Perennials That Should Not Be Divided: Baby’s breath, Baptisia, Candytuft, Clematis, Delphinium, Euphorbia, Flax, Foxgloves, Lupines, Monkshood, Rosemary, Russian sage, Trillium, Yucca. You can find out the details for each specific plant with this handy guide to dividing 45 different perennials. You'll be rewarded with healthy, vigorous growth and a crop of new plants. The following flowering perennials are easy-to-grow and have exemplary characteristics that make them garden essentials. But many perennials can be divided using the following method: Step-by-Step Instructions. Perennials that have been container-grown and have gone dormant through one winter season in the pot are considered “hardened off” plants; they will be winter hardy. There are two types – tender perennials, which are hardy in zones 8-10 and are treated as annuals in colder zones, and also hardy dianthus which can take the cold in zones 3-10. Photo: Neil Hepworth. Shallowly replant the smaller rhizomes. Ornamental grasses, daylilies, irises and stonecrop are some examples. Preparing for Division Although dividing perennials is good for the plants in the long run, it's still a shock to their system. Iris can stop blooming if not divided routinely. These homebodies include peonies and tree peonies, foxtail lilies, bleeding hearts, goatsbeard and butterfly milkweed. These plants actually perform best when they are younger and have room to grow where they are planted. In early spring, dig up the perennials just as new growth begins to appear. Even the oldest of perennials can be rejuvenated back to a full, happy life full of blooms! How late can perennials be divided and transplanted? Divide your perennials to keep plants vigorous, improve the health of their foliage and to increase the number of blooms. Primroses, for instance, can be dug up and divided into numerous piece in late spring, giving them an entire season to recover before flowering again the following year. Dividing or splitting a single perennial into multiple plants helps the plant perform better. When perennials are divided, there is more space for roots to grow and absorb nutrients and water. Divide Perennials: Step 3 Divide perennials: some perennials can be separated into smaller portions by hand. If they are not divided, the center sections will no longer have enough soil for their roots and may stop producing flowers. But for the best return on my time and the quickest reestablishment of the perennials, I divide when the soil is warmer than the air for at least part of every 24-hour period. And peonies, goatsbeard, foxtail lillies, bleeding hearts and butterfly milkweed hate to be moved or divided … Dividing herbaceous perennials is a quicker way to propagate the plants than growing them by seed; in fact, some will not come ‘true’ from seed. Other perennials that can be divided in spring include coreopsis, daylily, garden phlox, speedwell, and hardy zinnia. And they will grown almost anywhere in the USA or UK. For most perennials, the best time is spring, while they are still dormant. I don’t like to see spring-flowering perennials divided while they are blooming, but doing it immediately afterwards often works just fine. 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