How to Plant and Care for Tall Bearded Irises
Tall Bearded Irises are remarkably easy to grow. They are tough, and tolerant of extremes of heat and cold (as high as 35C and as low as -20C). If you follow these guidelines, they should last for years.
- Chose a sunny site.
- Soil should be PH neutral, if too alkaline, add some peat, and if too acidic, add some lime
- It is vital that the soil drains freely. If your soil is heavy, it is essential to improve the drainage by adding brick rubble
- Plant the rhizomes, leaving the top half exposed to the sun
- Keep the rhizomes clear of other plants to prevent shading
- Feed the irises twice a year in Spring and Autumn
- Keep an eye out for rot in the rhizome
- Slugs are the most serious pest, small black slugs the worst
Tall Bearded Irises thrive in hot dry conditions, but are susceptible to rot if the rhizome becomes waterlogged. This is most likely to be caused by poor soil drainage.
They can be planted in a dedicated iris bed, or mixed with other plants, depending on the size of the garden. If planted with other herbaceous plants, make sure that the rhizomes are open to the sun, and not shaded or covered by the leaves of other plants.
- Chose a sunny position where your irises will not be crowded by other plants. (This is important because the exposed iris rhizome needs to be ‘baked’ by the sun to generate the flower cells for the following year)
- Before planting trim the leaves of your iris into a ‘fan’ shape from 4”/6” in height
- Make a circular mound, by scooping out the soil around it to leave a small ‘channel’ at the foot of the mound
- Place the rhizome on top, with the roots spaced evenly either side, and hold the roots down so that they are spread evenly around the mound
- Fill the ‘channel’ with soil so that the rots are covered, and the top of the rhizome is exposed to the sun and level with the soil around the plant
- Plant rhizomes in groups of three, preferably of the same variety, 9” apart, leaving 18” between each group of plants. Leave 18” between rows
- Place a small bamboo cane (approx 6”) in the ground behind each rhizome and secure this to the plant with a split ring which is passed through one of the leaves in the iris ‘fan’. This will prevent ‘rocking’ in windy conditions when the ground is dry
- Apply fertilizer as directed (see later)
- Rake this in and then water the irises
- Continue to water the plants until you see the leaves starting to shoot. Once this happens, test the plant to see that the roots have taken hold
You can then relax!
Tall Bearded Irises need feeding twice a year in Spring and Autumn. EIC offers a bespoke iris food in 2kg bags.
Apply in March/April to give your irises the nutrition required to ensure good and sustained flowering. Our mix includes bonemeal , potash for root growth and superphosphate to stimulate flowering (8:1:1). One good handful is required per clump of plants, fork lightly into the soil and water. In dry periods water well after applying feed.
Apply bonemeal only after flowering in late June/July/August to give the plants a boost and ensure they are in good condition before the winter/dormant period. One good handful is required per clump of plants, fork lightly into the soil and water. In dry periods water well after applying feed.
Regular feed applied this way will keep your plants in top condition.
PLEASE NOTE THAT NITROGEN BASED FERTILISERS SHOULD NOT BE USED. THESE STIMULATE LEAF GROWTH AND INCREASE CONSIDERABLY THE LIKELIHOOD OF RHIZOME ROT.
Tall Bearded Irises need dividing to ensure continued flowering and good plant health. Failure to ‘split’ your irises will result at best in a steady spread of rhizomes through the bed, with a proportionate reduction in flowering.
At worst the mass of irises will increase to clog your beds, and the irises will simply stop flowering altogether. Division is an essential part of the growing cycle. This is which is why we think it is important covering the subject in some depth.
There are two schools of thought:
The Traditional Method
Divide the iris rhizomes after four/five years. Dig up the iris plant, discarding the old rhizome but retaining the healthy fat younger rhizomes. Replant these in groups of three/five for each variety, following the Planting Instructions.
This can cause some disruption to the flowering cycle. In year 1 after division, a good proportion of your irises may not flower, but by years 2/3 they should be reaching their peak, in year 4 you should expect some reduction in flowering, and by year 5, the reduction is most marked.
The point to make is that over five year cycle, you are likely to have two poor years (Years 1 and 5), but this is something many established iris growers have learned to expect. However, the full impact on your garden can be mitigated, by dividing irises in different beds in alternating years.
This is where the Doddington method has some appeal.
Described by Antony Jarvis from Doddington as a trouble free way to divide irises, this system has been used successfully in their gardens for the last twenty eight years. He describes the advantages as a regular flowering, combined with speed and physical convenience.
Antony has worked on the premise that irises set their flower initials in August,; this determines how many flowers each stem carries the following year . The traditional method involves disturbing the flowers at the critical point that flowers are being set, and this is borne out by the poor flowering record noted the year after ‘splitting’ takes place. This makes it an attractive alternative and well worth a try.
- Split the irises every year just after they have finished flowering in June
- Split the individual plants with a light spade, leaving the part to be retained in the soil. Remove 30-50% of the plant mass. See illustration on where to cut
- After splitting, cut back the early summer leaves on the remaining stems, and cut or break the stems at the base
- After splitting top dress the plants with bonemeal that is raked in between the plants
- When deciding which plants to keep, chose fat, first year shoots, with two shoots carrying the early summer leaves. Chose rhizomes that point in the direction you wish the plant to develop
- One further advantage of the system is that the whole process can be done from a standing position, using a light fork and spade, with a pair of shears.. With no replanting of irises involved, the task is far quicker than the traditional method
- If you find awkward gaps, irises can be replanted to fill the spaces, and because this is done in June, there is every prospect they will flower the following year
- When switching to the Doddington system, it may take a year or two before you reach a steady state
Watch David Logan, Doddington’s experienced and enthusiastic Head Gardener explain the Doddington method in the following video:
Depending on weather conditions, your irises may benefit from staking with a thin bamboo cane of approx. 4’ height. Use a single plastic coated ring, and leave room for the flowering spike to develop, and remember to move the ring up the flowering spike as it grows.
Staking is recommended in windy/exposed sites. It take little time and can deliver substantial benefits.
Tall Bearded Irises are hardy and largely pest and disease resistant. A few tips will help keep your plants healthy and in good condition.
- Check regularly for slug damage. Slugs are the biggest problem, particularly the small black variety that can cause real and lasting damage if not detected early enough. Slugs will eat the rhizome and in extreme cases destroy it. Regular application of slug pellets is advised , particularly during damp conditions. Try to find some that cause the least damage to Song Thrushes, Blackbirds and Hedgehogs
- Keep an eye out for snails, and check regularly for leaf damage. The best tactic is to remove snails at night, or set beer traps
- Wireworms can be a real problem in land that has previously been used for grazing. Treatment is difficult and expensive. Watch for signs of small holes bored through the iris rhizome and plants that are wilting or leaves that die back unexpectedly. It is possible to measure the severity of a wireworm infestation by placing a potato in the ground and checking after two days whether it has been eaten. Two wireworms indicates a modest infestation, more than four is more serious
- Rust is the most common disease. This can be treated with a general fungicide, suitable for treatment of roses which also suffer from this disease. Agronomy advice points to the use of ‘Systhane’ as an effective treatment, although there is concern in the gardening press that this chemical may be withdrawn from the market shortly. Do not compost iris leaves
- Scorch is a more serous problem. The symptoms are leaves dying back suddenly, turning brown. Scorch affects both individual and clumps of plants. At the first sign of attack, the affected plant /plants should be removed from the ground and burned. It can spread quickly if not treated quickly. Do not compost leaves