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:…

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 

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