Re: Cannas in cool climates
- Subject: Re: Cannas in cool climates
- From: D* P*
- Date: Sun, 14 Oct 2001 06:57:12 +0100
Although Cannas do reasonably well in shade in warm climate regions,
they are best afforded full sun in colder areas. They are very heavy
feeders, growing and flowering well if given lavish fertilising and
masses of water. In fact, when in active growth, it is almost
impossible to overwater Cannas - some folks even use them as pool
plants with their roots submerged. The best for this treatment are
the slender leaved, blue-grey forms of Canna glauca such as 'Ra'
(canary yellow) 'Tamey' (brick-red), but the large flowered
'generalis' hybrids also perform given similar treatment.
In cooler regions where there is a gentle spring warming (as opposed
to the type of sudden heat surge so often seen in many of the southern
US states), they take too long to get going if left in the ground. As
a result, flowering can be delayed or even prevented. Lifting the
roots and storing them frost free in old potting soil or similar is
the best means of over wintering. Personally, I do not ascribe to
cleaning the rhizomes since this can cause them to dry out too much,
resulting in failure in some of the less vigorous varieties. The
golden veined Canna 'Pretoria' ( 'Striatum', malawiensis 'Variegata')
is a devil for failing to grow if allowed to dry out.
In most parts of the UK, northern Europe (and presumably British
Colombia), Cannas are best cut down to about 12" high before the
return of heavy frosts. The rhizomes should be lifted, and gently
shaken clean of loose soil. Over-long roots can be trimmed back and
the plants then boxed up pouring old, reasonably dry potting compost
over them. Any remaining leaves can be cut away as they die off and a
light dusting of sulphur will help avert fungal diseases. Store in a
frost free place until early spring, when they can be cleaned
properly, divided (if necessary) and potted-up ready for starting into
growth. Planting out can take place when all danger of frost has
passed. This usually ensures a good start and enables the plants to
commence flowering from the middle of June onwards - depending upon
local climate. Container grown plants can be simply brought under
cover and kept nearly dry after cutting back. However, they will need
cleaning and re potting with fresh compost in spring.
Somehow I manage to pack about 20 varieties and species into my tiny
patch, growing them both in the border and various containers. Here
it is warm enough in winter for them to remain out of doors
unprotected. Although we don't get the continental-styled heat-surge
in spring, the plants do not become fully dormant in winter and since
spring arrives here by early February, they usually push through new
shoots around that time. Growth is slow initially, but by early May
they are growing well and the first flowers appear at the end of that
month. Since most carry on flowering through to Christmas and beyond,
they are invaluable for summer and autumn colour.
One species (C. limbata), which is very similar to a diminutive Canna
indica, flowers throughout the year here, ignoring the few light
frosts that we have. Similarly, forms of Canna glauca are rarely
without flowers and I don't cut down the old flowering stems ('Ra'
gets up to 10 feet or more) until the new growths are well advanced in
March. Others such as 'Wyoming', 'Florence Vaughan', Black Knight
etc. are partially cut back in winter to prevent 'wind-rock', which
can dislodge the roots. Once new growths are well advanced, they are
top dressed with well rotted manure, and the remaining old stems cut
down to ground level.
David's mention of Canna 'Panache' prompts me to add that a 'new'
variety for me this year has been one which was 'bumping around in
southern Africa for a good few decades before arriving in the UK. It
is currently known (here at least) as 'Lesotho Lil' and has been a
triumph in my garden so far. In this, the leaves are large and broad,
bright blue-grey and prominently edged with red. The tall spikes rise
well above the foliage and carry large, vivid mandarin orange flowers
which are almost tulip=like when young. It is almost certainly a
hybrid between 'Wyoming' and C. glauca, but unlike those plants, the
flowers fall away cleanly as they fade, without the need to tap the
spikes with a cane.
David Poole
TORQUAY UK
