Impatiens tinctoria
John Grimshaw (Mon, 18 Aug 2008 14:58:23 PDT)

I am very familiar with Impatiens tinctoria both in cultivation and the wild
and think it's a fabulous plant. If you don't know it, it's a big herbaceous
perennial, with large fleshy tuberous roots, easily getting to 2 m in a
season if amply wet, and where frost-free its fleshy stems survive for some
time and can become almost woody. I have seen it up to 3 m + in the wild.
The leaves are largish, ovate-lanceolate, dark green, and the flowers hang
over them like big white butterflies. The flowers are principally formed of
two large white lower petals, marked with red in their centre, and have a
long spur at the back. They are strongly scented, particularly in the
evening, and are evidently moth-pollinated. I think that I've mentioned
before that I believe it forms part of a pollination syndrome with Gladiolus
callianthus. The weather has been so foul this year that we haven't had much
opportunity to sit out by the pond in an evening and enjoy its scent, but
this is a feature that makes it well worth growing.

In the wild it grows in wet places in the mountains of East Africa, from
Ethiopia south to southern Tanzania, with various subspecies varying
principally on the size of the flower, spur length etc, and with some
geographical distinctions (see Grey-Wilson, 'Impatiens of Africa', 1980).
Despite searching for it elsewhere, I have seen it only in Kenya, in the
Cherangani Hills and on Mt Kenya, both times growing in and at the edge of
running water in open forest conditions. This is not a plant that likes heat
or drought! In Kenya it is represented by subsp. elegantissima, and I
believe that this is the only subspecies in cultivation. So far as I know,
most material in (at least British) gardens derives from a collection made
by an expedition to Mt Elgon and Rwenzori on which Patrick Synge was a
member - in 1930, I think. Thereabouts, anyway. He wrote a book about it
('Mountains of the Moon', 1938, but reprinted) that is well worth reading.

I. tinctoria can be treated as a hardy perennial in British gardens at
present, with no special attention needed, though I usually insulate the
crown with some cut-down fern and soil on top - but that is perhaps just a
legacy of when we had colder winters and it may not be so necessary now. I
do think, however, that one has to strike a balance between its requirement
for moisture in summer and not getting the roots too wet in winter, so I
grow it in juicy soil adjacent to the pond, rather than in the boggiest
areas. In a dry, hot year it can look a bit scraggy, but soon recovers with
autumnal coolness and moisture. All growth above ground is killed by frost,
but it reappears vigorously in spring. There is usually a crop of flowers in
about June, followed by a lull in the heat of summer, then a magnificent
show through September and October. This year, however, it has flowered
constantly, as there has been no heat to put it off. In my experience there
are very few Impatiens that like heat - commercial I. walleriana's tolerance
of it is probably in part a result of selection, though as a wild plant it
grows at lowish altitudes - and the montane African species hate it. I.
tinctoria very seldom sets good seed here and I've never seen a self-sown
seedling (one of very few non-prolific Impatiens in my garden), but in Cape
Town a cutting from my original plant is prolific with seedlings.

It is easily propagated from cuttings, but these should have a heel for best
chance of success, and be taken in plenty of time for the plant to make a
tuber before winter. Spring cuttings from the emerging shoots, taken as one
would a Dahlia cutting, are very successful.

Ernie DeMarie mentioned its relative, I. flanaganae from the coast of the
Eastern Cape, which has lovely pink flowers on a lower plant. This survives
outdoors here as tubers, but doesn't make a good plant: I think this does
need a bit more warmth to get it growing. A third member of the clan is I.
rothii, from Ethiopia, with smaller, salmony-pink flowers on a thick bush,
also growing from thick tubers. It has surprised me by being fully hardy
here since 2004, unprotected in the open border and just getting bigger and
better every year. Originally only two seedlings germinated: one went to the
National Collection holder and I kept the other. Now it self-sows like mad
and I have to weed out seedlings - as I do for most species! To conclude
this brief account of the group I should mention that there is also I.
polhillii from southern Tanzania, with white flowers - I've never seen
this - and I. fischeri from Kenyan forests with comparatively small, bright
blood-red flowers, which I have lost, unfortunately.

There are a number of hardy perennial Impatiens from Asian forests, but I.
namchabarwensis is an annual with lovely flowers but terrible self-sowing
capacity. I weed it out in barrowloads.

John Grimshaw

Dr John M. Grimshaw
Sycamore Cottage
Colesbourne
Nr Cheltenham
Gloucestershire GL53 9NP

Tel. 01242 870567

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Sent: Monday, August 18, 2008 9:17 PM
Subject: [pbs] Impatiens tinctoria