Potting Up Iris Rhizomes – These Plants Grow Really Well In Containers With The Right Care
Elizabeth is a Permaculture Garden Designer, Sustainability Consultant and Professional Writer, working as an advocate for positive change. She graduated from the University of St. Andrews with an MA in English and Philosophy and obtained a Diploma in Applied Permaculture Design from the Permaculture Association.
Reviewed By COLIN SKELLY
Colin is a Horticulturist and Horticultural Consultant with experience in a range of practical and managerial roles across heritage, commercial and public horticulture. He holds the Royal Horticultural Society’s Master of Horticulture award and has a particular interest in horticultural ecology and naturalistic planting for habitat and climate resilience.
Contributions From SIMON DODSWORTH
Simon is the Founder of The English Iris Company, an award-winning plant nursery based in the UK. In 2015, his nursery’s iris collection was awarded National Collection status by Plant Heritage. More recently, the nursery provided irises that featured in the Gold Winning British Iris Society Centenary Stand at the RHS Chelsea Flower Show in 2022.
IN THIS GUIDE
Irises are a varied group of flowering plants which are suited to growing in a wide range of different situations, from borders to garden ponds.
However, if you are considering growing irises, you might be wondering about container growing.
Should You Grow Irises In Pots?
“Many of us have small gardens and container growing is a prerequisite,” explains Simon Dodsworth, owner of The English Iris Company.
“Tall, bearded irises grow really well in pots as long as you provide the correct care.”
As Simon says, almost all irises can be grown in containers as long as they are given the right environment and cared for correctly.
However, the irises best suited to container growing are those which like full sun and free draining conditions: bulb irises and border irises.
Bulb irises are the most common choice for container growing, but shorter types of border irises can also often work very well in pots.
Taller species can also be grown in containers, but will usually require some support.
Choosing Suitable Containers
When choosing a container for irises, one key consideration will be which specific iris you plan to grow, as they can vary significantly in size.
Smaller bulb irises, like Iris reticulata, will grow to around 15cm tall and need to be spaced just 5cm or so apart.
However, some border irises can grow up to 1m in height and require a lot more space.
When choosing a container for irises, you will not only need to consider the size of the plant and its specific requirements, but also its age.
“Choose a pot that is wide and shallow, rather than one which is narrow and deep,” says Simon.
“Depending on how many irises you want to grow, I would recommend starting with one that is 38-44cm across and 20-26cm deep. This will allow you to plant at least five irises.
“You could also try something smaller and start with planting three and see how you get on. For this, use a pot with a width of 28-33cm and a depth of 20-26cm.”
Remember that most bulb types and border irises require free-draining conditions, so make sure that the container you choose has drainage holes so that water can drain freely from the base.
“Fill the base of the pot with crushed-up plant pots or brick rubble, with a mix of coarse gravel to ensure good drainage,” Simon suggests.
Irises which like free-draining conditions should be planted in a general-purpose potting mix with some horticultural grit mixed in, or a homemade equivalent.
“I use a peat-free compost with plenty of pea shingle mixed in for my potted irises,” says Simon.
However, remember that the medium must also retain water reasonably well and you should mulch the top to help aid in this.
Potting Up Iris Rhizomes
Bulb irises can be planted on their own in a container or as part of a mixed bulb lasagne planting scheme alongside a range of other spring ephemerals.
Plant the bulbs as soon as possible after you purchase them.
Bulbs are typically planted at a depth of twice their height, though for more long-lasting container displays, planting iris bulbs at least 15cm deep can be beneficial.
Planting at this depth can mean that the flowers bloom more reliably the following year.
Border (rhizomatous) irises which come in containers are potted up in much the same way as any other perennial.
“Leave the top of newly planted iris rhizomes exposed so that they can be sun-soaked during summer, but be careful to work the soil back in amongst the roots to anchor the plant well,” shares Master Horticulturist Colin Skelly.
New border iris rhizomes are planted between July and October, while potted irises should be potted up between March and mid-November.
How Many Rhizomes Can You Plant Per Pot?
At a minimum, bulb irises should be planted around 5cm apart for longer-lasting displays or around bulb width apart for a seasonal container display.
It is a good idea to layer different irises which bloom successionally for a blooming display through spring and into the summer.
Individual border irises purchased in pots should usually be placed into a container just a little larger than the one in which they came, though you could also consider growing these in a larger container alongside other plants which like similar growing conditions.
If planting more than one border iris, note that larger plants require 30cm between them and dwarf plants should be placed around 15cm apart.
Simon recommends planting tall bearded irises at a spacing of 22cm.
Potted Iris Care
Water iris bulbs but take care not to overwater when grown in containers.
Aim to keep the soil for all irises that like free-draining conditions moist, but remember that they don’t like sitting in waterlogged soil.
Otherwise, Iris bulbs are very low-maintenance.
Just leave the foliage to die back naturally after spring flowering.
With bearded irises, remove any yellowing leaves through the season if desired and deadhead when the flowers have turned brown or wilted.
“Apply bone meal or seaweed feed to your potted irises,” says Simon.
“Also, be very vigilant for slugs and snails.”
If you no longer wish to pot up border irises, you can divide the plant and place the sections each in its own pot.
