From: Peter Boyce <phymatarum at googlemail.com>
on 2012.01.20 at 05:40:44(22509)
Hi Don,
I grew a lot of Arum in pots in the past. You need to use deep
straight-sided pots at least 12 inches, preferably 15 inches deep; the
problem is that pots this deep tend to be very wide too, so you may have to
shop around.
Growing media for the Mediterranean species (such as those that you list)
needs to have a good proportion of mineral soil and also should to be on the
alkaline side of neutral (8.5 or thereabouts). I used to mix a proprietary
peat-based soilless-potting medium with the same volume of good quality
sieved topsoil. To every 10 gallons of this mix I would add a heaped 6 inch
pot of 1/2 inch limestone chippings.
Tubers need to be planted ca half way down the pot. I used to re-pot
annually in late N Hemisphere summer (late August); by this time the tubers
will be becoming active but there won't be much root growth. Plant and then
water well and then don't water again until the shoots appear above soil.
Arum are greedy plants and well-repay heavy fertilizing by producing larger
tubers. I used to use a fertilizer branded for use on tomatoes. When
actively growing I would fertilize on every watering and the manufacturers
rate.
Under glass Arum need a buoyant atmosphere and high light. Ventilate well on
all but the very coldest days. The pots should also be given a fair bit of
room between - too close together and the plants can become very etiolated
and become prone to leaf fungus such as botrytis.
Arum flower towards the late middle of their growing cycle. Some gardening
books advocate easing back on water and ceasing fertilizer when the
inflorescences appear. This is wrong. The plants still have a few weeks
growing ability during flowering and it is at this time that nutrients from
the leaves are absorbed by the tuber; curtailing the growing period can mean
smaller tubers. I recommend that you keep the plants actively growing as
long as possible to ensure a decent sized (or better still, more) tubers for
the next year.
Once it is clear that the plants really are dying back (most leaves yellow)
stop fertilizing and reduce watering to just enough to stop the pot becoming
completely dry. While the plants are dormant it is better to leave the
tubers in the pot and not take them out. I experimented quite a lot of
tubers of which I had an excess and can say that tubers removed from the
soil and stored were always weaker than undisturbed tubers. It is also
important that the resting pots do NOT ecome excessively dry. Despite the
desiccated appearance of the Mediterranean countryside during summer digging
down a few inches always reveals damp soil. Arum (indeed all Med. aroids)
are always deep-buried in nature and certainly never become totally dry. It
is also worth keeping the resting pots someplace not too hot and certainly
not exposed to sun - again the soil in the wild is always cool at the level
the tubers occur, no matter how parched the countryside.
Hope this helps some
Pete
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