Bearded Iris really offer so much to the mixed perennial garden. The beauty they offer in the spring is uncontested, but we often get questions about what to do with the foliage after the spring bloom has faded. Culturally speaking, the foliage must remain intact through the summer growth phase. The foliage converts the energy to feed the growing rhizomes. Shorter foliage can limit the energy conversion. That said, we ourselves trim the foliage when we prepare our plants for order fulfillment. This practice of trimming foliage is also generally followed when gardeners divide and transplant Iris in their home gardens. The shorter foliage facilitates planting — the long blades of the Iris foliage can often prove too heavy for the newly planted rhizome to bear, causing the plant to become dislodged. Established Iris, of course, with their larger root systems, can bear the weight of the foliage.
Thus, we recommend leaving the foliage untrimmed throughout the summer months. Planted among other summer blooming perennials and shrubs, the vertical lines of the Iris foliage provide a wonderful counterpoint to other forms in your garden. The images here illustrate this point. These photos were taken in our Display Gardens in late July.
Iris bed in mid-summer. Vertical lines contrast with shorter annuals and greenery.
Summer days, summer gardens. Most enjoyable. For the Tall Bearded Iris in your garden, summer is also the perfect time to grow, to expand, to be transplanted.
Bearded Iris experience two root growth cycles in their annual growing cycle. The springtime growth we all eagerly anticipate in our Iris beds begins with the lengthening of the foliage upward and the root system outward. The rhizome uses its stored-up nutrients.”….As the bud swellings appear in the new fans there is a quickening of the new roots that will supply the plant with nutrients for new growth during and after bloom. The old roots from the previous year’s growth then wither and decay.” ( The World of Irises, p 314) After the springtime color display of full bloom has passed for the year, the underground development begins in earnest.
The Iris revel in the long summer days. During the six to eight weeks post bloom, the plants absorb the necessary nutrients for next spring’s growth and bloom. The rhizomes send out new increases which will become new self-contained, self-supporting rhizomes by early to mid-July. Once the summer growth is complete, the Iris takes a well-earned rest. Enter the gardener, spade in hand, plan in mind. Now is the time to dig, divide, share and transplant.
Here, in the Willamette Valley our Iris bloom season ends early- to mid-June. Therefore, at Schreiner’s Iris Gardens, we begin digging our fields early to mid-July. On a smaller scale in your garden, consider digging your Iris to transplant this summer if the clump is three to five years old. Share the divided Iris not only in your own garden, but also with the neighbors, friends and family….garden clubs, retirement homes, 4H clubs, and so on. Allowing Iris clumps to become over grown can lead to poor or no blossoms, smaller and smaller rhizomes, and outbreaks of rhizome-based diseases (such as bacterial soft rot).
Remember that the latest date for transplanting depends on local conditions. Newly planted Iris require a minimum of 6 weeks to set their new roots. Thus, they should be in the ground a minimum of six weeks before the first hard frost. Consult local resources to determine the frost dates in your area.
What’s happening in the July garden? To trim or not to trim the foliage…Depending on your location, you may have a handful of lingering Iris blossoms, or all of your bloom stalks might be sporting the papery remains of the seasons’ blooms. When all blossoms on the stalks have finished, carefully trim the bloom stalk at its base. Leave all green foliage, though, in place. They offer an elegant vertical visual throughout the garden. You may remove any browned and dry leaves. Keep the Iris beds clean and free of weeds. Well-established Iris plants are drought tolerant. Newly planted Iris, though, do require a good long drink approximately every 7 to 10 days if the weather is very dry. Reblooming Iris also prefer irrigation between the spring bloom and summer/autumn re-bloom times. We recommend an application of a low-nitrogen fertilizer (such as 6-10-10) approximately one month after blooms have finished. Superphosphate and bonemeal also work well as a fertilizer for Iris.
Summer brings the promise of long days enjoying our gardens and all aspects of our lives. The season also brings with it our annual Summer Sale. You’ll find over 300 varieties of Tall Bearded Iris at deeply discounted prices.
First, let’s be clear: we are referring to Bearded Iris in this discussion. The myriad of other lovely Iris varieties come with their own set of operating instructions.
Our last two blog posts generated a number of very worthwhile questions. After doing a bit of reading on the subject, I came across a couple of useful bits of information. The first is a series of photos on planting Bearded Iris, see below. These come from William Shear’s, “The Gardener’s Iris Book” (Taunton Press, 1998), page 43. How deep should the rhizome be? We are in agreement with Mr. Shear on this question. “It depends,” he writes. “In light-textured soils, it can be covered by as much as 1 (one) inch of soil, but for average to heavier soils, the top of the rhizome is best left exposed to the healthful influences of sun and air. Remember that the rhizome is a stem, not a root, and needs to breathe!” You can see in the third photo below that the top of the rhizome is still peeking through the soil.
Steps for Planting Bearded Iris, “The Gardener’s Iris Book”, pg 43.
On the subject of trimming the foliage, I found a bit of tidy wisdom, the kind you keep clipped into your pocketbook, or saved on our phone, for easy reference. This comes from, “A Guide to Bearded Irises: Cultivating the Rainbow”, by Kelly Norris (Timber Press, 2012). In his myth-busting section he addresses the question of trimming. “Myth: Bearded irises are so much work. You have to trim the foliage back every summer!” Mr. Norris reassures us that in fact this may be an “unnecessary chore”. There is no real need to trim the foliage in the summer, except that during dividing and transplanting shorter foliage eases the handling of the plants. He reminds readers that “needlessly trimming the foliage back in the middle of the season actually breaks an iris’s dormancy, kick-starting foliar production. This can take away from root mass accumulation and even from reserves meant to support flowering the next spring.”
The long and short of it is to plant shallow and leave the leaves alone. Thanks for reading and happy gardening!