Gadenin日本語Get the appEarly spring: uncover, inspect, feed lightly
The first job of the year is to go along the bed and see what winter has done to the rhizomes. Frost heave lifts newly planted pieces out of the ground and rain moves soil over established ones. Push any lifted rhizome back down and firm it, and scrape soil, leaf litter and stray mulch off the top of any that has been covered. This one pass does more for the coming display than anything else you will do.
As the new leaves start to push, give the light low nitrogen feed described in the care guide, scattered on the soil around the clump and watered in. Do not feed heavily and do not use anything designed for lawns. If your soil is acid and it has been a few years, this is the season for a light dressing of lime, but not in the same week as the feed.
Weed thoroughly now, while you can still see the ground. Once the fans are full height, weeding among them means treading on rhizomes and snapping leaves. Clear a hand's width of open soil right around the outside of each clump and keep it that way.
Mid spring to early summer: the flowering weeks
Flower stems rise from the center of the fans and each carries several buds that open in turn over a week or two. Watch the leaves closely during this period for the dark wet streaks that mean iris borer, because this is the only stage at which the caterpillar can be dealt with by simply squeezing the leaf.
Tall kinds in an exposed spot may need a discreet cane and tie, particularly if the ground is wet and windy while the stems are at full height. Snap off each bloom as it collapses, and when the last bud on a stem is done, cut that stem right down to the base rather than leaving a hollow stub that collects water.
Unless you specifically want seed, remove every developing pod. Seed formation drains a great deal of energy from the rhizome that should be going into next year's flower buds, and seedlings from a garden iris will not resemble the parent anyway.
Late summer: the one window for division
About six to eight weeks after the last flower fades, the plant enters a quiet spell and the soil is still warm. This is the only good time to lift and divide, and it is also the best time to plant new rhizomes, because divisions made now have time to root before the cold. Divide any clump that is three or four years old, or any clump whose flower count dropped noticeably this season.
Give the low nitrogen feed a second time in this window, whether or not you divided, since it goes into building the rhizomes that carry next year's buds. Keep watering to almost nothing unless the summer has been genuinely dry, in which case a deep soak every two or three weeks around the base is enough.
Take the chance to look at the whole bed rather than individual plants. Has a shrub grown up and started shading the row? Has a neighbor flopped over the rhizomes? Has soil washed down and buried the front of the planting? These are the slow problems that reduce flowering over years, and late summer is when you can see and fix them without damaging anything in flower.
Autumn and winter: the cleanup that decides next season
Once the foliage is battered and yellowing, cut the leaves back to 4 to 6 in (10 to 15 cm) and rake the bed absolutely bare. Take every scrap of dead leaf away rather than leaving it or composting it in place. This removes the overwintering eggs of the iris borer and the spores of leaf spot in a single pass, and it is the highest value job in the whole year.
Do not mulch over the rhizomes for winter as a general practice. In a region with hard frost, newly planted rhizomes in their first winter benefit from a loose covering of evergreen boughs or coarse straw, which must be pulled off completely as soon as the worst cold has gone. Established clumps in the ground for a year or more need nothing.
Through winter the job is simply to look occasionally. After a hard freeze and thaw, check that no rhizome has been heaved out of the soil, and push back any that has. There is nothing to water, nothing to feed, and nothing to cut.
| Season | Main jobs | What to watch for |
|---|---|---|
| Early spring | Uncover rhizomes, light low nitrogen feed, weed the bed clear | Rhizomes heaved by frost or buried by winter rain |
| Mid spring | Inspect leaves closely, stake tall kinds if exposed | Dark wet streaks and notched leaf tips meaning borer |
| Flowering weeks | Snap off spent blooms, cut finished stems to the base | Seed pods forming, which drain the rhizome |
| Late summer | Divide clumps three to four years old, plant new rhizomes, second light feed | Crowded rhizomes climbing over each other, fewer stems than last year |
| Autumn | Cut foliage to 4 to 6 in (10 to 15 cm), rake the bed bare, remove all debris | Any soft, foul smelling rhizome, which must be cut out now |
| Winter | Nothing except an occasional look | Rhizomes lifted by freeze and thaw |
The three dates worth writing down every year
First flower and last flower. Those two dates define your local season and, six to eight weeks after the last one, they tell you exactly when your division window opens. General advice cannot give you that, because it varies by garden and even by which side of a wall the clump sits on.
The date you first spot borer damage in spring. It repeats closely from year to year, and knowing it means you can inspect at the right moment rather than discovering the damage when a fan wilts in summer.
The number of flower stems per clump. Written down each year beside the clump's position on your bed sketch, this single figure is your early warning that a clump has become congested, usually a full season before flowering falls away badly enough to be obvious.