Dividing is one of those beneficial gardening tasks that deliver heaps of results. Whether you’re looking to boost the growth of older plants or double your stock, dividing is an easy way to achieve your goals.
But when considering dividing perennial plants, it’s vital to do so at the right time. This could be the difference between a thriving garden and a few sad (or worse, dead) plants.
Understanding the mechanics of dividing will help you pick the perfect time for your plants, turning this task into a garden goldmine.
The Benefits Of Dividing Perennials
Division of perennials offers numerous benefits, including improved growth, control, and propagation benefits.
Division is not just a garden chore to tick off your list. The practice has many benefits for yourself and your plants, particularly when dividing perennials.
The primary reason to divide perennial plants is to improve growth. Plants can become overcrowded and dense after a few years in the same spot. The central growth may start to die off, creating empty gaps surrounded by lush new growth. Most importantly, plants will produce fewer blooms as the years progress.
Division provides almost instant rejuvenation to these tired plants. The roots get a little extra room to breathe, and the plant doesn’t have to expend energy on maintaining dying leaves and stems. Once replanted, you’ll see growth perk up again as if you were planting for the first time.
While you can use division to boost growth, you can also use it to control growth. Some perennials can spread vigorously and may crowd out other plants without control. Lifting and dividing them is a way to manage their growth and keep unruly plants in line.
Finally, there is the benefit I look forward to the most – more plants. Division is an instant propagation method that will instantly double or triple your stock. Whether you want to move plants to a new part of the garden, plant in containers, or share them with family and friends, there is always a reason to propagate.
When To Divide Perennial Plants
Unfortunately, there is no ‘right time’ in the year to divide all your perennials. Like most things in gardening, the answer to when to divide is “it depends.” Several factors will determine when you should divide, from the plant you are growing to the conditions in your garden.
Let’s look at a few influences on dividing time and how you can use them to determine the perfect time to divide your specific plants.
Flowering Season
Perennials are usually divided in spring or fall for optimal root establishment, avoiding seasonal stresses.
Generally, spring-flowering perennials are divided in fall, and fall-flowering perennials are divided in spring.
This isn’t a strict limitation – many perennials can be divided in either season. However, these alternating times take advantage of a period where the plants are not actively flowering, allowing them to focus on establishing new roots after transplanting.
Little division is done over the summer and winter months. Temperatures in summer are often too high to transplant, resulting in root stress and uprooting the plants when they may be in the middle of flowering. Winter temperatures often drop too low for most perennials to establish roots, stunting growth and potentially killing the plant.
You can wait until late summer or sneak a few weeks in late winter or early spring, depending on the climate in your region. But your safest bet is to stick to spring or fall.
Climate
Timing for a fall division depends on your climate and USDA growing zone.
Your climate and USDA zone also play a role in when you can divide, specifically for fall division.
When dividing perennials in fall, you need to give the roots time to establish before any chance of frost. If you divide and transplant too late, cold temperatures may kill off new and vulnerable roots, preventing any establishment over winter.
The exact time will depend on the speed of growth of your plants. Typically, you need to plant in the window around four to eight weeks before the first frost, with slow growers needing the most time to establish.
If you live in a lower USDA zone where frost arrives quickly, it may be better to divide in spring. This avoids any risk of root damage, even if you sacrifice a few spring flowers that season.
Plant Age
Perennials benefit from division every two to four years to prevent overcrowding and encourage growth.
Perennials usually grow best when divided every two to four years to limit overcrowding and boost growth.
The number of years differs slightly depending on what you’re growing. Slow growers that don’t spread much can wait around five years or even longer before they need to be divided. That doesn’t mean you can’t divide sooner if conditions are right, just that you don’t have to divide sooner if you don’t want to.
Other plants with deep root systems should be divided early because their roots dislike disturbance once established. Splitting one or two years after growth limits the chances of transplant shock in these fussier plants. If you wait until the plant is more mature, it may develop issues.
It’s essential to understand your plants’ specific requirements and growth habits. But here is a general guide for some common perennials:
| 1-3 Years | 3-5 Years | 5+ Years |
| Astilbe | Black-eyed Susan | Bleeding heart |
| Heuchera | Gaillardia | Lady’s mantle |
| Garden phlox | Daylily | Peonies |
| Coreopsis | Coneflower | Oriental poppy |
Size
When dividing perennials, be sure each section has enough roots to survive.
It is possible to divide sooner than the plant’s age requires. You can divide to move plants around your garden or to propagate. But you do need to ensure your perennials are large enough to withstand division before you pull them out.
For mature and established plants, you can usually split them in half without trouble. But for smaller ones, you need to ensure each section will have enough roots to survive on its own. You also need to consider the reduction in the size of the new plants in your beds before you decide whether it’s worth dividing.
Health
Dividing perennials can rejuvenate tired and overcrowded plants but may not solve other plant stress issues.
Dividing is a way to improve health and boost growth in tired and overcrowded perennials. But for plants that are stressed in other ways, dividing may not be the answer to your problems.
If your perennials look lackluster due to incorrect care (such as underwatering) or problems with pests and diseases, pulling and splitting the plants will typically add to the stress, increasing the time it takes to recover. It’s best to resolve the issues first and bring your plants back to good health before you put them through the trials of transplanting.
In cases of root issues or incorrect positioning in your garden, lifting and dividing can be a resolution. In other cases, wait until growth has stabilized before inducing stress and risking transplant shock.
Temperature
Opt for cooler mornings to maintain plant hydration and avoid root drying.
The previous factors influence general timespans. In terms of the day-to-day, the last thing to consider is temperature.
Divide on days that are cooler, preferably early in the morning. Dividing on hot days dries out the roots, leaves, and soil quicker, increasing your chances of transplant shock. Well-hydrated stems and leaves are essential to help the plant handle the division process.
This is why division is done in spring and fall rather than summer or winter. If there is an unusually hot or cold day forecast (as happens more often these days), wait until the weather is milder before dividing.
How To Divide Perennial Plants
Dig several inches around the root zone, lift the plant from the bottom, remove loose soil, and divide the root ball with a clean knife.
After weighing these factors, you should know when to divide based on your plants and garden environment. Now, all there is left to do is grab your spade and get started:
- Dig into the soil several inches around the root zone of the plant. You want to keep as much of the root system intact as possible.
- Using your spade, lift up the entire plant from the bottom. Plants with deeper root systems will be harder to lift. Shake off any loose soil to get a closer look at the roots.
- Pull apart or cut into the root ball using a sharp and disinfected knife. Smaller plants can be cut in half, while large plants can be divided further.
- Replant immediately into newly prepared soil to limit root exposure to the air. Water after planting to encourage the roots to settle in their new homes.
Final Thoughts
Staples of perennial gardens will likely need a refresh after a few years through division. These factors determine when to divide your perennial plants for a lush and abundant garden.
