Irises are a signature plant of Doddington Hall, Lincoln, and have been cultivated in the Walled West Garden since the 1980s. Grown within box- and grass-edged parterres, they create a striking tapestry effect.

'The flowers are held high in the air and their translucence makes them particularly beautiful in evening light,' says Antony Jarvis, whose family inherited the estate in 1830. 'They provide a surprisingly long show when well grown to produce the full number of flowers per stem, and out of season, the foliage makes an attractive groundcover.'

We asked Antony for his tips on cultivar choice, and about getting the best from these elegant blooms.

Antony Jarvis's favourite iris cultivars:

Iris Langport WrenIntermedia cultivars

  • 'Langport Wren' (pictured): A wonderful deep mahogany iris, tough and always full of flower.
  • 'Stop Press White': A picotee with dark blue. An elegant plicata; makes a good foil to 'Langport Wren'.

Tall irises

  • 'Wabash': A striking bicolour, sky blue over purple (not in the Doddington collection at present).
  • 'Ma Mie': A newcomer to Doddington, this is a wonderful unruffled plicata bred by Cayeux in 1906. Currently being bulked up in the Kitchen Garden.
  • 'Blue Florentine': A very old cultivar, bright French blue and scented.

The 'Doddington system' of iris division

The garden team finds its 'Doddington system' a trouble-free way to divide irises. 'Irises need an absolute minimum of attention under the Doddington system. Some of the older cultivars continue to flourish after 28 years in the same beds,' says Antony. He says the key advantages are a completely regular flower display, speed and physical convenience.

The system is underpinned by two characteristics of iris plants:

1. They set their flower initials in August, determining how many flowers each stem will carry the following May.

2. To set the maximum number of flower initials, the plants need to be undisturbed and warmed by autumn sun between August and October.

'The traditional system of autumn thinning every three to four years allows the irises to become overcrowded, leading to shading,' says Antony. 'In a thinning year, it also disturbs the plants at the very moment they are trying to set flower initials, resulting in an unreliable show of flowers and contributing to irises becoming unpopular.'

Step-by-step guide:

1. Split the irises every year, immediately after flowering has ended, during June. At this point the early summer leaves and flower stems have started to die back, and the late summer leaves have started to grow.

Iris division2. Split individual plants with a light spade, leaving the part to be retained undisturbed in the soil.  Remove about 30-50% of the total plant mass – see diagram (right) for an illustration of where to cut. The aim is to leave plants about the size that would fit under an A5 sheet of paper, with a clear space of 23-30cm (9-12in) in all directions between other plants. Irises have a considerable power to colonise bare ground, so don't be shy with the spade!

3. After splitting, cut back the early-summer leaves on the remaining plants, and cut or break off the flower stems. Finally, topdress the plants – at Doddington Hall, a dressing of 70-100g per square metre (2-3oz per square yard) of bone meal is raked into the soil between the plants.

4. When deciding which parts of a plant to keep, look for fat, first-year rhizomes with a pair of shoots carrying the early-summer leaves.  These are the initials for next summer’s rhizomes and flower stems. Choose rhizomes that point in the direction you wish the plant to move – it advances perhaps 13cm (5in) a year and so can be guided to fill gaps in the overall plant pattern.

5. A major advantage of this system is that the whole job can be done from a standing position, using a light spade and fork and a pair of shears. With no replanting of irises (which is a tricky job to do well), the task of thinning is far quicker than the traditional method.

6. If there is an awkward gap in the iris plants, it might occasionally be necessary to plant a rhizome or two. These, if planted in June, will flower with the rest in the following May.

7. If switching to the Doddington system, you may have a transitional year or two before you reach a steady state. The actual size of the clumps of rhizomes you choose to leave is not critical, and larger clumps can have larger gaps between them.

More seasonal maintenance tips

For maximum flower set, iris rhizomes need to be warmed by the sun in August and September. Avoid overcrowding of plants as this shades the rhizomes, meaning few or no flower initials will be set.

  • If a bed has looked poor the previous May, try a light mulch of compost in November. Antony finds mushroom compost excellent.
  • Remove late-summer withered leaves when they will pull away from the rhizomes (or they can be left until spring, for shelter).
  • Remove deadheads using shears. This job becomes more important as the flowering advances, and finally whole spent flower stems can be removed.

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