Iris’ unique flower forms, color combinations and bold, spiky foliage have been a mainstay of flower gardens for generations. Over time iris plants can outgrow their space or simply need to be reinvigorated. Most perennial plants in general reach full maturity three to four years from the time they’re first planted. From that point on iris will continue to slowly expand in size; growing outward, losing vigor and eventually encroaching on other nearby plants.
Dividing your iris is a great way to obtain more plants, but it’s also good for the overall health of the plant. Here are some of the additional benefits of dividing iris and other perennial plants:
- Reduces crowding in the garden and allows plants to display their full form.
- Creates space for air to move between plants which helps prevent disease and discourage some insect pests.
- Plant divisions can be used in other areas of the landscape or shared with friends and family.
- Lifting plants from the ground improves condition of the soil by loosening compacted areas.
- Dividing perennials can help keep more aggressive plants contained. Fast growers can be divided every one or two years if needed.
When to Divide Iris Plants
German Iris plants can be divided any time spring through fall, however the best time is in the early spring before the plant leafs out or in late fall, before the ground freezes. Either of these times give the plant’s roots a chance to settle back in with the least amount of stress. If you must divide plants in the summer don’t divide until after flowering is complete and be sure to check the transplants daily for water until they are well-established.
Iris grow from a thick root called a rhizome. Rhizomes grow horizontally along the ground sending out smaller roots and occasional plant sprouts along the way. The rhizome typically grows in the top inch or so of soil while the smaller roots grow deeply into the ground. It’s not unusual to see rhizomes exposed at the soil surface and this quite normal. In fact, it’s important to avoid burying a rhizome too deeply and mulching should be done surrounding the plant, not right on top of the rhizome.
Pro tip: Cloudy days are especially good for dividing plants since the hot sun can cause wilting and stress both during the process and after the plant divisions are replanted.
How to Divide Plants
Groundcover (tarp, newspaper, cardboard, etc.)
Garden gloves (optional)
1. Assume that the root ball extends as far as the tips of the foliage. Using your shovel, cut a circle an inch or two further past the foliage tips, around the outside of plant.
2. Work your way back around the plant again, pushing the shovel even deeper and towards the center of the plant, gently lifting the root ball up as you go.
3. To keep things tidy have a wheelbarrow, tarp or newspaper ready to set the uprooted plant on.
4. It’s easiest to cut the roots apart using a sharp knife. Cut the plant at the base between the rhizomes, making sure each rhizome has at least one fan of foliage.
5. The weight of the foliage can cause new plant starts to lean and loosen from the ground. Cut the foliage down to about six to eight inches to provide some stability while the new roots get established.
6. The plant divisions are now ready to plant in new location or pot up to share with your plant-loving friends. Plant the rhizome horizontally with the smaller roots buried in the ground and the large rhizome on the soil surface. Planting too deep will result in a healthy plant but with few or no flowers. Space at least 12-24 inches (30-60cm) apart so as not to overcrowd the new plants.
7. This is a good time to nourish the soil by mixing some compost into the planting holes, before placing the plants. After planting, water thoroughly and apply a light layer of mulch, avoiding the main rhizome, to help retain moisture and get the new plants off to a good start.
Your new plants should settle in quickly and start producing flowers the following year. Meanwhile the bold, sword-like foliage is great for creating interest and contrast when grown next to plants with either broad or very fine texture.
Flowering annuals are a great way to add continuous color as perennial plants go in and out of their bloom seasons. Take a look at these heat and drought tolerant annuals that would make perfect companions to your sun-loving iris plants.