TOW Tuberous Pelargonium - Part 2
David Victor (Tue, 24 Aug 2004 10:55:36 PDT)

Dear all,

I trust that you enjoyed part 1, so here is part 2!

So to Section Hoarea, a Section that is totally dedicated to tuberous
species and which contains some 30% of all the species in the genus, some
70 out of 250. The species in this Section can be easily separated from
other tuberous Pelargonium as they do not have plant stems. Having said
that, I should add that they do have flowering stems, a scape, which
support groups of flowers. Also, the tubers of this Section are covered
with papery sheaths, to stop them drying out when dormant.

The plants in this Section mainly come from the winter rainfall area of
South Africa, that is the South West of the country, from Cape Town
northwards and eastwards. Typically, they grow in arid areas and are
adapted to suffer long, hot, dry summers by dying down and becoming
dormant. Typically, they grow under the shade of other plants and have
long flower stems to help find pollinators. Unlike the plants of Section
Polyactium, which flower whilst carrying foliage, plants in this Section
mostly flower after their leaves have fallen.

However, both the flowers and the foliage have something very special to
offer. Let's start with foliage, which starts to emerge after the winter
rains and then goes through a development cycle, which is repeated each
year. This cycle is unusual in that each leaf that unfolds is more
complicated than the one before. Early leaves are simple ovals, with no
lobes or indentations. Final leaves can be extremely complex, with many
lobes and indentations. Having said that, the foliage is not only
interesting, it is also very attractive. I have included separate
photographs on the WIKI to show the foliage of plants, before
flowering. In one or two cases I have been able to show the whole plant,
with both foliage and flowers, but these are unusual.

The flowers are also very interesting, as well as beautiful. The number of
petals can be 2, 4 or 5, depending on the species. Their colour can vary
from white, through cream, yellow, pink or purple and can vary, often,
within a species. The upper (more correctly rear) two petals are very
frequently marked with feathering in a wine red colour, as sometimes are
the other three. The stamens, a key indicator for identifying the species,
vary in both their relative positions in the flower and the number of
fertile stamens present (which varies from 2, through 3, 4 or 5).

A reminder that many pictures of the species of Section Hoarea can be found
on the WIKI at:

http://pacificbulbsociety.org/pbswiki/index.php/…

There I have included one or more photos of each of the following species
from Section Hoarea: P. aciculatum, aestivale, asarifolium, auritum,
bubonifolium, caledonicum, campestre, carneum, caroli-henrici, dipetalum,
fasciculaceum, grenvilliae, incrassatum, leptum, longifolium, luteolum,
moniliforme, oblongatum, parvipetalum, petrosellinifolium, pilosellifolium,
pinnatum, proliferum, radiatum, rapaceum, reflexum, triandrum,
trifoliolatum, undulatum, vinaceum and violiiflorum. I have also included
on that came to me as P. incrassatum but is not and I have not yet
identified it and another one which is yet to be named.

Incidentally, I have also included photographs of P. appendiculatum and
torulosum, tuberous species that come from Section Ligularia.

Cultivation I grow most of my mature plants in deep pots to give their
tubers plenty of space. It also allows me to give them good drainage by
putting a couple of inches of sharp gravel at the bottom of the pot. I
plant them in a mix of soil-based compost, with an equal amount of a sharp
sand and gravel mixed in. The tuber is place with its neck and half the
tuber sitting above soil level and then sharp gravel is placed around it,
but leaving the neck of the tuber above it. I tend to re-pot every two or
three years and, when doing so, I remove most of the old sheaths: I find
this helps stops rotting problems around the neck.

I grow the plants in a greenhouse where I maintain a minimum temperature
just above freezing. I grow my plants from seed and their time cycle tends
to be six months behind South Africa the times that I have shown on the
WIKI are their times in habitat. So, my season is just finishing, with
most having gone dormant and only one or two species still flowering. As
they go dormant, they go under the bench, where they stay dry until I think
they should be waking up. Then I give them all a little water and watch
carefully for growth to start.

Watering is a key issue. I water my plants when they need it, which tends
to mean when I get around to it! In their growing season it's about once a
week, but they don't seem to care if I leave it for a couple of
weeks. It's not surprising as they get a much tougher time in the
wild. My guess is that the only key issue is not to water them too
often. I only feed once or twice a season, with a dilute, liquid tomato feed.

It's easy to get seed to germinate, but difficult to keep them through
their first dormancy. As a result, I try to keep them in growth for as
long as I can to build up their strength.

More Information

If you would like to read more about tuberous Pelargoniums, the following
books should be of interest:

*** "Taxonomic Studies in Pelargonium Section Hoarea", PhD.
Dissertation Dr Elizabeth Marais, Reprinted by The Geraniaceae Group,
2000. The definitive work on the subject, with a full revision of the
whole Section and all its species.

*** "Geophytic Pelargonium Field & Cultivation Studies of Pelargonium
Section Hoarea" Charles Craib, privately published, 2001. A very useful
guide to a number of the species by a field expert.

*** "Pelargonium" Edition 5, Part 4 of the Geraniaceae Checklist
Series Richard Clifton. Published by the Geraniaceae Group, 2004. A
checklist, with limited descriptions, of all of the names used for
Pelargonium species, as well as a full overview of the genus and its history.

*** "Pelargonium, a gardener's guide to the species" Diana Miller,
Batsford Books, 1996, ISBN 0 7134 72839. Covers the whole genus, but has
useful sections on Section Hoarea and Polyactium.

"Pelargoniums of Southern Africa" Prof. JJA van der Walt. In 3 volumes,
but now out of print. The standard work on the genus, but covering
various species of all Sections.

The Geraniaceae Group holds stocks of those marked *** and also publishes a
quarterly newsletter covering developments in the Geraniaceae. If you
would like more details about them, please contact me privately.

I hope that you have all enjoyed this foray into Pelargonium, with its
fascinating and beautiful plants and I look forward to answering any
questions you may have or discussing any issues you wish to raise.

Best regards,
David Victor