Sunday, March 09, 2014

Rejuvenating the iris beds

Photo courtesy 

Regular readers of this column will know I have a fascination for the members of the iris family, in particular the species and cultivars that make up the Pacific Coast Native Irises of North America.  A large area of the garden is devoted to a bed of these plants, from which I selected likely-looking parents for breeding, and into which I plant a couple of hundred seedlings each year.
But even though these are my favourites, I also grow quite a range of other irises, usually just spotted in between other plants in general beds. 
It might come as a bit of a surprise to learn that I have dug out a whole lot of iris plants over the past weeks, and thrown them away.  They were all bearded iris I had been growing for over ten years, and I decided that it time for me to replenish the bearded iris beds, both in terms of soil, but also in terms of replacing the varieties.
Bearded irises area little bit fussy about the conditions they will do best in, although those conditions are easily enough met.  As with most plants, it pays to consider where the plants you want to cultivate occur naturally in the wild.  In the case of the bearded irises, they almost all grow in full sun, in very well-drained soil that is derived from limestone. 
In the garden it pays to replicate those conditions, with an open sunny site, with fertile, free-draining soil with at least a neutral pH.  For my part, I added some extra compost to the beds, but also added general fertiliser and a good dressing of lime.  Most compost is low in pH and if used for lime-loving plants it pays to add some lime.  I used lime flour, which is quick acting, but coarser material, which releases more slowly, is probably better.
When deciding what to replace my old irises with I had a particular purpose – I wanted to grow some of the irises breed by the late Ron Busch, a Christchurch-based iris breeder who had bred some outstanding varieties over the past twenty years, some of which are still being released to the public.  They tend to be very colourful varieties, often with bold colours in contrast, and stitched with extra colour in a pattern that iris lovers call ‘plicata’.
I had to look around a bit but did find an on-line store that stocked a lot of his varieties, and although I could not obtain all the varieties I was interested in, I did manage to find quite a few, and they will arrive any day soon.
When I plant them out I will copy the way they grow in the wild again, placing the rhizomes on the surface of the soil, with the roots tucked in well into the soil, allowing the sun a chance to mature the rhizomes over summer.  Although some will undoubtedly flower next spring, it will be a year before they are at their best – but they will be well worth waiting for.

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