|We have several large, older beds of Iris at a Community College. The beds at 1st became overgrown and were not flowering well because of the need to be divided. The maintenence crew began at that point to mow the entire beds during the summer which has now created fewer rhizomes and naturally, a grassy, weedy mess with a few flowers returning. We are wondering how we can rejuvenate the beds and keep them at a low-maintenence level. How long would it take to restore the beds, what kind of mulch could we possibly use, should the leaves ever be mowed or cut after flowering and can a pre-emergence herbicide be used in the spring to reduce the grass problem?|
| are certainly good sturdy varieties.
Good luck with your project -- you will be well rewarded by the display! over top of the rhizomes since mulch will hold moisture against them and invite rot. You could use any organic mulch such as shredded hardwood bark, half finished compost, or leaf mold. Some gardeners will use a pre-emergent herbicide closer to the rhizomes; in my experience corn gluten works well for crabgrass. Unfortunately, you will still need to do hand weeding from time to time.
Iris require a routine "eyeballing" to check for insect activity such as borers as well as for fungal problems and to catch any weeds that may be starting up. The foliage should be trimmed back in mid summer when it begins to deteriorate. This will encourage fresh healthy growth. Although I have seen this cutting done by lawnmower set on high, in my experience it is better done by hand so that you can check the individual rhizomes for any problems at the same time. In addition, the lawnmower wheels tend to damage the rhizomes and this in turn invites rot.
The bed should also be gone over carefully to remove any discolored or damaged foliage in the fall, to remove any faded foliage in late fall and again in the early spring to remove any deteriorated foliage, as well as at any time you notice a problem beginning. The spent flower stems should also be cut off at the base and removed promptly. Always remove and destroy and trimmings. Sanitation is in many ways the key to maintaining a healthy iris bed.
All of this sounds like a lot of work, and in this respect iris are no different from most "low maintenance" perennials. In my experience that is a bit of an oxymoron, especially when a planting is an extensive one. Depending on the condition of the rhizomes, your bed could bloom beautifully next spring or it may take a year to recover its strength before it puts on a good show. Often a neglected bed responds eagerly to the attention and renewed soil, especially since the "survivors" are certainly good sturdy varieties.
Good luck with your project -- you will be well rewarded by the display!