By Maggie Asplet
Aril and Arilbred Iris are not something that you would expect to see a lot of in New Zealand. We are very fortunate to have Bill Dijk and his wife Willy, living in Tauranga, North Island of New Zealand.
Bill is one of those very lucky people with green fingers. Whatever he does, it just works and is very able to get the impossible to be possible in our climate, with a lot of hard work I must say.
This article was been written by Bill and he has given me permission to publish his take on Aril and Arilbred Irises.
I. acutiloba susp. lineolate growing in coarse material.
When we talk about the aril irises, two very different types
of irises are grouped together under the term "aril".
These are the oncocyclus and regelia irises
of the Near East.
Although they have
beards, they are not classified with the other bearded irises because they are so
different in their makeup. Aril irises have derived their name from a little cream
aril or a collar-like fleshy appendage of their seed.
Aril seed cut - showing the embryo
The arils show dark signal spots below the beards with much
veining and speckling, in an unbelievable range of colours. Unfortunately, the
arils are difficult to grow in all but the warmest and driest regions of New
Zealand. I will start off by showing a few true aril oncocyclus/regalia species.
Close-up of spcekling on I.samariae x I. hermona) X I. kirkwoodiae
In this
century, hybrids were produced from crossing the arils with the more common
bearded irises. These are called "arilbreds" (ABs), and are usually
very easy to grow and still display the spectacular features of the arils. The
arilbreds are as diverse in colour and form as they are in their genetic makeup
and the combinations of these features make this an exciting and challenging
group of irises. Unlike their aril ancestors, arilbreds can be grown
successfully in a wide range of climates. They give gardeners the opportunity
to enjoy the beauty of aril-type flowers without having to provide the special
environment the pure arils require. They usually bloom earlier than the TBs,
with the SDBs and the IBs.
I. Sheba's Jewel
Culture of Aril and
Arilbred Irises
Arils and arilbreds have a reputation for being difficult to
grow. This is partly deserved, but also partly the result of misunderstanding. Unfortunately,
the word aril is often used rather carelessly to refer to both arils and
arilbreds. These two types, however, are very different in their cultural
requirements and their capacity to grow and thrive without special attention.
Growing the pure arils like the oncocyclus and regelia
species successfully is a real challenge, and it’s often a question of
understanding their cultural requirements and adjusts them accordingly. Not
always easy with our sometimes excessive wet, and humid climate in the Bay of Plenty in New Zealand. A warm and dry climate like central Otago would be more
suitable, somewhat similar to their native habitat.
I. paradoxa atrata. Note its small, dark purple falls.
Today's AB’s (arilbreds) are not hard to grow in most
climates. A selection of arilbreds interspersed among a bearded iris planting
will find that most of them will grow and flower without any special attention; however, some understanding of their cultural preferences increases the odds,
ensuring a greater rate of success.
Although pure arils are not widely grown, a quick review of
their cultural requirements is valuable, because it casts some light on the
needs of their arilbred descendants.
The aril irises are the oncocyclus and regelia species from
the Middle East and hybrids having only aril irises in their ancestry. The
oncocyclus in particular have always posed a challenge to gardeners living
outside their native region. They go completely dormant in the summer, which
leaves them susceptible to rot in rainy climates. Furthermore, they don’t apologise
for being temperamental, sometimes thriving for four or five seasons and then
simply dying for no obvious reason. Regelia’s are much more adaptable, but
still prefer dry hot summers.
Many different methods have been used for growing/protecting
oncocyclus irises, especially during their summer dormancy when they must be
kept dry. In cool, wet climates, most growers make use of a shelter/cover/frame,
greenhouse or any other form of protection. I build this structure (picture) which
is open on both sides for extra ventilation, and elevated bed for extra
drainage, that is covered with polycarbonate plastic cover to keep the rain out.
I prefer to leave it on all season in
our New Zealand climate to control the often excessive rainfall, warm temps and
high humidity at the wrong time during the summer, which could results in
rotting of the rhizomes.
Raised protected bed for Arils
This way I do control the cultural requirements like watering
when needed, air circulation, feeding, and spraying for any fungal or insect
problems.
Knowing the cultural requirements of the pure arils, one can
take a few basic steps to improve the rate of success with arilbreds. If you have a choice of planting locations, arilbreds
should be placed where light and air circulation are best and where drainage is
particularly good. Take steps to avoid or reduce excessive soil acidity. Don't
make the mistake of coddling them in a sheltered corner for protection from
winter cold; such locations may be shadier and damper during the summer months,
and lead to more harm than good. It will not be necessary to dig them or
protect them totally from rain during the summer, as most arilbreds do not go
completely dormant and are not as vulnerable as the pure arils. However, it is
still wise to practice very clean culture and keep an eye out for densely
overgrown clumps that could benefit from division. Plan on dividing arilbreds
every other year; you may even find a few benefits from annual division!
In general, arilbreds of less than half aril content (this
includes most arilbred medians) are to be grown exactly like the bearded
irises. Giving them special treatment is unnecessary and may even be harmful,
if it causes you to depart from tried and true practices that your bearded
irises thrive on.
Those of more than half aril content should receive some
preferential treatment. They should not require the full-blown summer
protection preparations demanded by the pure arils but will appreciate the best
drained, most open, preferably slightly raised location your garden can
provide.
Preparing the site
For all arils: first
and foremost, sharp drainage is important and the prime requisite for
successful culture. They are desert plants, so they need full sun for at least
two-thirds of the day. If possible, some protection, or shelter, from rain and cold
is helpful.
Washed brick sand,
granite, course pumice, or other coarse material, can be worked into the soil
to improve drainage. There should be a good supply of calcium. (Gypsum can be
used to provide calcium and loosen heavy soil.) If the soil is acid, lime
should be added. Planting the irises on hills or ridges can help the drainage
in marginal soils. Many people plant arils in raised beds where sharp drainage
can be "built in."
To summarise:
- full sun
- sharp drainage
- no water in summer for the pure aril
irises while dormant.
Normally, the colours of aril blooms are extremely pure as
well as clear. Alternatively, their blooms may even have wonderful blotches
that contrast the colour of the flowers. When arils are hybridized with the
standard bearded irises, the progenies retain a number of these attributes,
while some other progenies may have new, but mesmerizing hues, patterns and
streaks.
The falls of aril flowers have another typical
characteristic. They may have veins and dotting or stippling in subdued or
strong shades. These features may also appear in the standards of aril flowers.
The dark, circular spots, also known as "signal", which appear at the
end of the falls, are another typical trait of the flowers of oncocyclus
irises, which distinguishes them from other iris flowers.
Iris mariae
Ideally, arilbred irises should be planted when they are
just getting out of their hibernation or dormant period. You should avoid
planting irises during the summer heat, as it is very stressful at this time of
the year. Similarly, irises should not be planted during the late autumn just
before the harsh winter months. In fact, the best time for planting irises is
actually subject to the climatic conditions in your region.
Classification: Nine Types of Arilbreds? Yes, Really
Although for awards purposes, the American Iris Society
sorts all arilbreds into only two classes (less than 1/2 aril content and 1/2
or more aril content), the Aril Society International uses a more detailed
system of categories that tracks not only the amount of aril content, but also
the type of aril content (oncocyclus, regelia, or both).
Close up of Iris paradoxa
An arilbred with only oncocyclus and bearded ancestry is an
oncobred (OB). One with only regelia and bearded ancestry is a regeliabred
(RB). If both oncocyclus and regelia ancestry are present, it is an
oncogeliabred (OGB). This is by far the largest category.
If the arilbred has less than 1/2 aril content, it is marked
with a "-" sign. If more than 1/2, with a "+" sign. If it
has 1/2 aril content exactly, neither a "-" or "+" is used.
Aril seed as a rule are not easy to germinate, and there are
several methods of germination:
Stratifying, cutting and
forced germination. Aril iris seeds can
be germinated with the following technique.
Forced germination" this is a technique that is often
used for pure aril seeds to hasten germination. This method bypasses the need
for any cold treatment. The forced
germination procedure involves cutting
with a scalpel or razor blade across the micropyle, across the end of
the endosperm and embryo, in order to create an artificial rupturing of the
micropylar barrier, which in natural situations germination could take a long time
sometimes years to archive. I use a
special sharp grafting knife which I find personally more reliable and safer.
After soaking the seed for a few days in water (with some
fungicide) to soften the seed, the aril and half the seed coat is removed, followed
by cutting or slicing enough of the endosperm to expose the end of the embryo. I
also borrow my wife’s art-craft 5X magnifying desk lamp with build-in lights for
more close-up, hands free detail when slicing or cutting the seed.
Most people do not do this with arilbreds, which germinate
more easily.
Some people would try to stratify them and see what
germinates first. Sometimes temperature
cycling is used as well. After all of that you could then try cutting or slicing
them for faster germination. Be sure to sterilize the seeds before cutting
them, especially for fungal protection when germinating seed in plastic bags or
damp sterilized paper towels or whatever method you decide to use.
Points to recommend and remember:
1. Hydration: Soak
the seeds for up to a week in water with systemic fungicide.
2.
Remove the aril
carefully (if it's an arilated species), cut the skin and slice a little layer
to expose the embryo, which will be visible in the little hole of the endosperm.
Slicing aril seed
You need to be careful not to slice off too much of the
embryo or you will negatively affect root formation and also risk damage to the
embryo.
3. After cutting, put the seeds in damp perlite or
vermiculate in little plastic bags.
I prefer damp sterilised kitchen paper towels for
germination.
4.
When germination
takes place in 2 or 3 weeks -
I prefer to very carefully transplant the little delicate seedlings directly into
a 7cm X 9 cm peat pots, with a spray of systemic fungicide, outdoors in a cool,
frost free place. Peat pots have the added advantage of no root disturbance when
planted on into its permanent place or suitable container.
Having initial success with the germination, either forced
or the traditional method is just the start of further necessary and ongoing
special cultural treatment of the beautiful oncocyclus/regalia group.
After cutting/slicing I prefer germinating the seed in damp
folded sterile kitchen towels, the moisture content when damp imho is just
right for steady germination. I then
place the folded kitchen towels in an ice-cream container with the lid securely
in place to prevent moisture loss, in a cool part of the nursery ( 10-15 C ). I
inspect the seed at regular intervals for any sign of germination, with many
seeds showing a radicle after 2-3 weeks in the damp kitchen towels.
I then proceed to very carefully prick out the sprouted
seed, one at a time, in a 7cm X 9cm cm peat pot with 50/50 mixture of compost/fine
pumice, water carefully to settle in the little seedling properly. Usually the
seedlings ( 5-10 cm) will be ready for transplanting in its permanent place
after 4-6 weeks. The very important advantages of the peat pots is no
transplanting shock to the delicate seedlings, roots will easily penetrate the
peat wall with no loss of growth. Don’t forget to spray the young seedlings
with an appropriate fungicide at regular intervals for any possible fungal problems.
As is often the case with any specialist area of
horticulture, complacency is the biggest killer and there is no substitute for
constant observation, care and proper treatment. The Oncocyclus and Regelia irises constitute
an incredible group of plants that deserve nothing but the best. The sight of just a single flower takes your
breath away and a sight to behold.
To quickly summarise again :
full sun.
sharp drainage.
dry for the
pure aril irises, no water in summer while dormant.
These are some cultivation notes on how to grow the beautiful
aril and arilbreds irises.
Editor's Note: For more information about aril and arilbred iris, contact The
Aril Society International. For more information about irises in general, contact The American Iris Society.
