Download Climbing Lonicera trial

Trial
of climbing
Lonicera
(subgenus
Lonicera)
A recent trial at
RHS Garden Wisley
assessed climbing
honeysuckles.
Christopher
Whitehouse
summarizes
the results
10
H
oneysuckles are among
our best known garden
climbers. Valued for their
beautiful scent and prolific flowers,
they are an essential feature of many
gardens. While flower colour can
range from palest yellow to bright
orange or deep red, the prized scent
can be disappointing or even nonexistent if the wrong cultivar is
chosen. Furthermore, cultivars with
coloured leaves have recently
become available, as well as hybrids
of more unusual species.
RHS / Barry Phillips
Lonicera periclymenum Serotina Group ‘EM84’
The trial
In 2006 the RHS began a trial of
climbing honeysuckles with the aim
of helping gardeners choose the best
cultivars to grow. The trial focussed
on species and hybrids of subgenus
Lonicera – these are the ones with
flowers in whorls at the end of the
branches. Hence, the rather weedy,
though strongly fragrant, Japanese
honeysuckle, Lonicera japonica, and
its relatives, were not included. They
belong to subgenus Chamaecerasus,
which also includes all the shrubby
honeysuckles, and have their flowers
in pairs in the leaf axils.
Lonicera periclymenum
The archetypal honeysuckle must be
the UK native, L. periclymenum. It is
common throughout the woods and
hedgerows of northern Europe.
Therefore, it is not surprising that
numerous selections of this fine
plant have been made.
Two of the oldest, ‘Belgica’ and
‘Serotina’, date from the 17th century
and are known as early Dutch
March 2012
Plantsman
The
March 2012
Lonicera periclymenum Belgica Group ‘Belgica Select’
you a reliable garden plant. However,
if you want to make sure of a high
quality clone, then search for one
labelled ‘EM84’. This clone was
selected by the East Malling
Research Station as the best from
a selection programme they held
for Serotina Group.
A similar selection was conducted
in 1977 by the Royal Boskoop Horti­
cultural Society in the Netherlands
for Belgica Group, which resulted in
‘Belgica Select’, although the plant of
this performed poorly in the trial.
While the Dutch honeysuckles
may be the oldest cultivars, more
recent selections of L. periclymenum
have been made. Several of these are
named after where they originated,
such as ‘Munster’, ‘Red Gables’ and
‘Chojnów’. However, they were not
significantly distinct or better than
the Serotina Group. But two
selections did stand out.
The first is ‘Graham Thomas’,
probably the longest lasting and most
floriferous of all the honeysuckles in
the trial. It also seemed to have the
strongest scent, although this might
have been due to the sheer number
of flowers. In contrast to the more
popular selections of L. periclymenum,
this cultivar does not have a red
flush on the flowers but is a more
consistent yellow and white.
On the other hand, ‘Serpentine’
has superb dark foliage, which
➤
accompanied the dark red-
RHS / Christopher Whitehouse
RHS / Christopher Whitehouse
Lonicera periclymenum ‘Graham Thomas’
RHS / Christopher Whitehouse
honeysuckle and late Dutch honey­
suckle respectively. The distinction
between these early cultivars in the
literature was never clearly laid out.
The primary difference appears to
be based on flowering times, which
nevertheless overlap. What is
available today under these names is
not consistent and almost certainly
has changed considerably since the
names were first used. It is
recommended, therefore, that they
be employed as Group names rather
than cultivars. However, the Groups
can still only be tentatively
circumscribed as their definition is
based partly on their relationship to
each other in flowering time.
Regardless of the naming
difficulties, there is no doubt that
there are fine garden plants available
under these names, with striking
bicoloured flowers of yellowish
white flushed deep red, and a strong
scent. Unfortunately, in the trial, the
plants submitted as part of the
Belgica Group performed poorly,
which frustrated a good comparison
with the Serotina Group. In
contrast, the plants submitted as
part of the Serotina Group were
floriferous and strong.
Although there was some variation
among those submitted, buying one
from the Serotina Group should give
Lonicera periclymenum ‘Serpentine’
11
Rhs trials
flushed flowers and made a feature
of the red berries. Unlike the
variegated honeysuckles in the trial,
the leaf colour did not appear to
impede growth and it proved almost
as vigorous as the Serotina Group.
Lonicera x americana
RHS / Barry Phillips
Lonicera caprifolium ‘Inga’
RHS / Barry Phillips
12
Lonicera x italica
RHS / Katy Prentice
Lonicera x italica
The next commonest honeysuckle
found in gardens is Italian honey­
suckle, L. x italica, a hybrid between
L. caprifolium and L. etrusca. It can
look superficially similar to Serotina
or Belgica Group, and has sometimes
been mis-sold under those names,
but unlike those L. periclymenum
cultivars, L. x italica gives a one-off
spectacle. Flowering in spring before
L. periclymenum, it produces no
further flowers, whereas most
L. periclymenum will continue to
produce some flowers after their
initial flush. Botanically, the two can
easily be told apart, as the leaves at
the base of the flowerheads of L. x
italica are fused together, whereas in
L. pericly­menum they are separate.
There is debate over whether the
common form of L. x italica found in
gardens should be attributed to
‘Rubella’ or ‘Atropurpurea’. Rehder
(1903) regarded both these names as
forms, describing f. rubella as flushed
purple and f. atropurpurea as flushed
deep purple. The distinction is mild.
As f. rubella is the earlier epithet, if
someone wants to recognize the
garden form with a purple flush to
the flowers, it would be better to use
the name L. x italica f. rubella.
Despite the limited flowering
season, L. x italica is reliable and has
good scent. However, the variegated
cultivar of this hybrid, L. x italica
Harlequin (‘Sherlite’) is a weak plant
and should be avoided.
The name L. x americana has also
been confused with L. x italica, but
this misapplication was dealt with by
Gorer & Harvey (1990). The former
is later flowering than L. x italica, and
Plantsman
The
continues to flower through the
season. While L. x americana is
botanically distinct, the plant in the
trial did not perform well and
showed no advantage over the hybrid
that once usurped its name.
RHS / Barry Phillips
Lonicera caprifolium ‘Anna Fletcher’
Lonicera caprifolium and
L. etrusca
Lonicera caprifolium was the earliest
to start flowering in the trial, beginn­
ing in April. It is fragrant and
produces some of the showiest
berries of the genus. Unfortunately,
its early flowering means it starts to
go over the soonest, the leaves
beginning to brown by June. This
can leave an unsightly mess for the
rest of the summer, so its positioning
should be considered carefully.
Nevertheless, for the time it is
looking showy, it is worth the effort
of growing, especially if you choose
one of the cultivars. The ones that
stood out in trial were ‘Anna
Fletcher’ (the plant grown in trial
was entered as ‘Spring Bouquet’ but
this is a synonym), and ‘Inga’, which
was found in the wild in the Caucasus.
Lonicera etrusca was best represented
in the trial by the cultivar ‘Superba’.
And this was a superb cultivar in
every respect, being vigorous,
floriferous, resistant to aphids, and
well-scented. It is much later
flowering than either L. caprifolium
or L. x italica, peaking in June. The
other cultivars of L. etrusca in trial,
‘Donald Waterer’, which has darker
stems and redder flowers, and
‘Michael Rosse’, with lovely greyblue leaves, never established well
and flowered poorly.
Lonicera etrusca ‘Superba’
RHS / Christopher Whitehouse
March 2012
Lonicera sempervirens and
hybrids
While the previous species are
grown for the their scent and
flowers, L. sempervirens lacks scent
and is grown solely for its flowers. Its
advantage is the much bolder flower
colour, typically deep red with
orange inside the tube. The flower
shape is also distinctive, being
narrowly tubular with only short
lobes. However, the species does not
do particularly well in the UK. The
two cultivars in the trial, red ‘Cedar
Lane’ and yellow ‘John Clayton’ both
struggled. They are best-suited to
connoisseurs who can give them the
care they need.
However, the species has been
used as a parent in crosses designed
to combine vigour with the colourful
and distinctive flowers. The one that
retains the most characteristics of
L. sempervirens is L. x brownii
‘Dropmore Scarlet’. This hybrid with
L. hirsuta has long, tubular, 2-lipped,
red flowers with a few glandular hairs
on the outside. In the trial it did not
offer much improvement on its
parent in terms of vigour.
In contrast, L. x tellmanniana, a
cross between L. sempervirens and
L. tragophylla, was vigorous. Cultivars
of this hybrid had the largest, most
striking flowers in the whole trial. The
best was ‘Mandarin’ with an abund­
ance of bright orange flowers. Strictly
speaking, this is not L. x tellmanniana
as its parents are L. tragophylla and
L. x brownii, but it shows little
evidence of the third species,
L. hirsuta, in its parentage.
Lonicera x heckrottii is a cross
between L. x italica and L. sempervirens,
but is much closer in appearance to
L. x italica, only really gaining its
➤
bolder orange from the more
13
Rhs trials
RHS / Christopher Whitehouse
Lonicera sempervirens ‘John Clayton’
Lonicera x brownii ‘Dropmore Scarlet’
RHS / Christopher Whitehouse
RHS / Christopher Whitehouse
Lonicera sempervirens ‘Cedar Lane’
differences between species in the trial and their hybrids
Leaves below Inflorescence
inflorescence arrangement Leaf
Flower
persistence shape
Flower hairiness
(exterior)
stalked, often in clusters
of 3 inflorescences at
end of shoot
deciduous
two-lipped
short glandular hairs
L.etrusca
united
stalked, often in clusters
of 3 at end of shoot
deciduous
two-lipped
glabrous*
L. caprifolium
united
sessile, sometimes with
deciduous
two-lipped
another whorl below
long hairs interspersed
with short glandular hairs*
united
L. x italica
stalked or sessile, subtended deciduous
two-lipped
by much reduced united leaves; up to 3 inflorescences
clustered at end of shoot
long hairs interspersed
with short glandular hairs
as above
glabrous**
L. periclymenum free
L. x americana
united
evergreen
two-lipped
united
as above
deciduous
two-lipped
L. x heckrotii
L. sempervirens united
stalked, sometimes with more than one whorl
deciduous
lobes +_ equal glabrous
united
stalked
deciduous
lobes equal
L. x brownii
L. x tellmanniana united
very sparse short glandular hairs on young buds
very sparse short glandular hairs on young buds
stalked, sometimes in deciduous
two-lipped glabrous
clusters of 3 infloresences
at end of shoot
* in cultivated specimens in trial; some wild collections differ in hairiness. ** based on the single sample in trial.
14
March 2012
Plantsman
RHS / Katy Prentice
RHS
The
Lonicera x tellmanniana ‘Mandarin’
Lonicera ‘Spring Purple’
RHS
RHS / Christopher Whitehouse
Lonicera x heckrottii ‘Goldflame’
colour­ful parent. Unfortunate­ly, it
seems to have inherited reduced
vigour from L. sempervirens and the
plants in the trial were badly affected
by pests and die-back in some years.
However, it performed well in other
years and the best was ‘Goldflame’
which has larger flowers and more
deep yellow than the typical cross.
Cultivars derived from
Lonicera prolifera
Two cultivars in the trial had
L. prolifera in their parentage. These
would best be classed as foliage
plants, having limited floral beauty,
but with intriguing cup-like bracts
surrounding the flowers. They were
at their best when fruiting, as the
AGMs awarded to climbing lonicera subgenus lonicera
Lonicera caprifolium *
Lonicera etrusca ‘Donald Waterer’ *
Lonicera etrusca ‘Superba’ •
Lonicera x heckrottii ‘Goldflame’ #
Lonicera x italica f. rubella # (AGM
previously assigned to L. x italica)
Lonicera ‘Mandarin’ #
Lonicera periclymenum ‘Graham
Thomas’ •
March 2012
Lonicera periclymenum Serotina Group •
Lonicera x tellmanniana #
AGM recommended for removal for
poor performance: L. tragophylla
* AGM 1993
• AGM 1993, reconfirmed 2011
# AGM 2011
Lonicera ‘Fire Cracker’
glaucous bracts set off the orange
fruit well, and they could make
unusual components for flower
arranging. Both were raised by
plant breeder Peter Moore. Lonicera
‘Spring Purple’ has purple-tinged
spring foliage and creamy flowers
while L. ‘Fire Cracker’ has red
flowers and more striking berries.
Conclusion
Overall, the trial emphasised that
some reliable old plants, such as
L. periclymenum Serotina Group and
L. x italica, are still among the best
when it comes to choosing a
honeysuckle. However, there are
some new innovations such as
L. ‘Mandarin’ and L. periclymenum
‘Serpentine’ that are worth keeping
a look out for if you want something
that bit different to climb over an
unsightly part of your garden.
Christopher Whitehouse is
Principal Scientist of the botany
team at RHS Garden Wisley and
runs the RHS Herbarium
references
Gorer, R & Harvey, JH (1990)
The disappearance of Lonicera x amer­
icana. The Plantsman 12(2): 100–105
Rehder, A (1903) Synopsis of the
Genus Lonicera. Missouri Botanical
Garden, St Louis
15