What kind of MTB's did you try to grow, diploids or tetraploids ? Our
tet MTB's thrive under the very same growing conditions as the TB's.
They have the characteristic of loosing their foliage in very hot or
very cold conditions in mid summer or mid winter. the term 'aphylla'
literally translates as "leafless"! The rhizomes remain firm and as
soon as the weather warms up/ cools down the foliage returns and so do
the bloom stalks. Now most of our iris are several generations away from
the species so some tend to die down early, others do not.