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How To Grow Delphiniums:
The delphinium is
a genus of fully to half-hardy perennials, biennials and annuals so
much admired particularly in the cottage garden setting. Delphiniums
are tall, majestic plants with showy open flowers on branching
spikes. Each flower has 5 petal-like sepals with 2 or 4 true petals
in the centre called a bee.
Delphinium species include all three primary
colours, blue, red, and yellow. Hybridisation of delphiniums has
resulted in many new colours and attractive flower forms and growing
heights. Flower colours range in shades of blue from palest sky,
through to gentian and indigo; rich purple, lavender, pink to purest
white.
The modern delphinium is the result of hybridisation of delphinium
species from wide and varied parts of the world. Crosses made by
growers keen to improve specimens they were able to acquire have
resulted in the modern plants, which are truly spectacular. In
England Blackmore and Langdon, nurseryman and leading breeders of
Delphiniums continued this work from early in the 20th century
producing named varieties of large well-formed delphiniums. Others
have also added their skills and developed the most dramatic and
eye-catching plants to grace our gardens.
Many are varieties that are disease resistant,
offering protection against both powdery mildew and black spot. They
are good cut flowers and will last about 6 to 8 days in a vase.
Delphiniums give their best performance in well-drained soils in
full sun but they can be grown in dappled or part shade. They are
heavy feeders and therefore quire extra nutrients particularly in
early spring and later in the season. Mulching with manure at the
start of the season and a liquid feed every two to three weeks
throughout the summer will giving them a rich diet for the
development of their flowers. Stunted growth and yellow foliage are
signs the plants need additional fertilizer.
Some varieties of delphiniums may grow up to 6 ft. (180cm) tall,
making them excellent background plants. The Chinese delphinium
(Delphinium grandiflorum) grows 2 to 3 ft. (60cm-90cm) tall and
therefore suited to the middle or front of the perennial border.
Just like most other varieties, it will bloom throughout the summer
if the plants are cut back regularly.
The Belladonna delphinium (Delphinium x belladonna) is a cross
between D. elatum and D. graniflorum. These plants produce multiple
flower stems that grow to 3 to 4 ft. (90cm-120cm) 'Dwarf Pacific'
hybrids grow only 2 ft. (60cm) tall. 'Blue Butterfly' is one of the
shortest delphiniums maturing at 15 in. (34cm).
PESTS & PROBLEMS: Slugs unfortunately relish delphiniums. At
the first sign of spring your plants will be bursting into life -
and they will need protection from these slimy creatures otherwise
they may not survive to grace your garden. Many people will
automatically reach for the slug pellets, these do work of course
but they are life threatening to other creatures in the garden,
other creatures that we would like to encourage because they work
with us, helping to eliminate other pests around our gardens. Beer
traps work well, just put some beer into a shallow container that
has steep sides, the slugs love the stuff and when they have drunk
their fill they simply drown. Seeing their stranded brethren does
not seem to deter their fellow snails from slithering into the same
fate.
Another good trap is to place a half of either grapefruit or melon
skin with the flesh removed. Place them upside down on the ground;
here the slugs gather over night; these can be collected the next
morning and disposed of.
Mildew can be a problem if the plants are situated in a spot where
they get poor air circulation or in areas that have high humidity;
but it is easily remedied and in general only affects plants that
have been neglected. Growing a disease resistant variety may be an
option too. If you encounter Black spot, this is easily treated with
a fungicide, especially if it is done early.
Waterlogged soils in winter will cause the crown to rot and that is
why excellent drainage is absolutely essential. Also, any damage
done to the crown by a slug or snail, or by a hoe when weeding,
could cause water to enter the crown and cause it to rot during the
winter. It is also thought that repeatedly heavy applications of
nitrogen may add to crown rot. Plant breeders and exhibitors
consider it good practice to spray their delphiniums with a good
systemic fungicide in early June.
CULTIVATION: Select your site carefully, because mature
delphiniums do not like to be moved. The location must be sunny and
the soil as deep and rich as possible. The soil must be well
drained, as they will not tolerate 'wet feet' especially during the
winter. If the soil is heavy or does not drain well, add plenty of
compost and grit to loosen it up. If your soil is prone to water
logging then the raised bed method is a good way to over-come these
conditions. The edges of the beds will require some form of
retention either wood or edging bricks will do the job well. Stones,
rubble, pebbles can be placed at the base of the bed, then build up
the soil level to a suitable depth with either loam or a good
quality compost.
Prepare a large planting hole, mixing in some peat moss, compost or
well-rotted manure with a handful of bone or fishmeal your existing
soil. Be sure the crown of the plant is placed right at ground
level. Do not plant them under large trees or too close to a wall or
tall hedges; too much shade will cause the flower spikes to become
too tall and spindly. To get the very best results, at least six
hours of full sun is required daily. Plant the delphiniums in groups
of three or five each at least two feet apart; this will create a
pleasing group picture. Surprisingly, odd numbers of plants work
better and balance up the group and appear more natural.
Most delphinium hybrids bloom from early to mid-summer. The flower
spikes are hollow and therefore brittle. In all most all locations
other than the very sheltered spots, tall growing hybrids should be
staked as wind and rain on the heavy, flower-laden spikes could
cause the stems to snap and break. Using four dark green, thin
canes, inserted into the ground, forming a square around the plant,
is one of the best methods of staking. The dark green colour of the
canes gives some camouflaging qualities so that once the plant takes
on some bushiness the canes will not be visible. The canes should be
4 ft. (120cm) tall. The first tie should be tied tightly to the
canes, 10 to 12 in. (25cm-30cm) up from the ground. The second tie
should be placed 24 in. (60cm) up from the ground, and situated just
below the first bottom floret and tied loosely but securely. This
method of staking permits the heavy flower spikes to move a little
within the confines of the twine without breaking. If the flower
spike is tied to the stake, it will break at the base of the tie.
Immediately after flowering, cut off the old flower stalk to
encourage additional flowering in late summer or even early autumn.
The spikes should be cut off under the first bottom floret on the
spike and allow the green stems and the foliage to die down
naturally. When they are entirely brown, cut them off at ground
level. If you cut down the entire spike to the ground after it has
bloomed and when it is still green, you will force the delphinium
into an immediate second growth when the crown does not have
sufficient energy, which will shorten the life of the plant.
The second crop of flowers will not be as large or as bountiful as
those of the first, the new growth of a second bloom will be about
12 in. (30cm) high but never the less, they will still have much of
the beauty and are of course most welcome.
The usual failures in germinating delphinium's seed are these:
1) Keeping the soil too wet.
2) Sowing the seed too deeply. Seeds should only be covered with
approximately 1/8" of soil.
3) Trying to germinate old seed. Delphinium seed loses its vitality
after one year.
Try the Pacific Giants variety; they are reputedly the easiest to
germinate.
Many seedsmen recommend a period of pre-chilling for some varieties
this greatly aids germination. Sow the seeds in pots or in a tray in
September to April. After sowing, seal the container in a polythene
bag and place on the bottom shelf of a fridge for 3 weeks. Check
regularly to monitor germination. Then, move to an optimum
temperature of about 15C (59F), keeping the surface of the compost
moist but not waterlogged.
SOWING: You can start new delphinium plants from seed at
almost any time. From April to September the seeds can be sown
directly into the garden about 1/8 in. (3mm) deep. The seeds can be
started early during the winter months of January, February and
early March, indoors. Plants started from seed during the winter
will generally flower a little the first year. Those started
outdoors, do not flower until the following year. As the seedlings
grow they must be thinned out to 9 in. (23cm) apart to give them the
space to grow healthy and well.
AFTER CARE: When the tall growing varieties are about 2 ft.
(60cm) high, stake with canes. During dry spells make sure that the
plants are well watered. Keep the surface of the ground around the
plants loose and free of weeds. Each spring apply a handful of bone
or fishmeal around the plants and a good mulch of organic fertilizer
such as well rotted manure. This it an important time when the
plants are beginning to burst into growth. The added food will
replenish the goodness in the soil for growth building requirements.
About every 3 years it may be necessary to divide the roots. This is
an early spring job, just when the shoots are breaking through the
ground. Dig up plants carefully; cut clumps into sections, each with
plenty of fibrous roots and one strong stem. Plant immediately in
well prepared fibrous soil, setting plants so the crowns will be 2
in. (5cm) below the surface.
THINNING: This is essential to promote proper growth and to
ensure that the plant will be long lasting. Newly planted, first
year seedlings should have only one flower spike. Second year
delphiniums should only be permitted to have three flower spikes.
Older and established delphiniums should be permitted to have only
five flower spikes. When the new spring growth is two-to-three
inches high, select the correct number of the strongest shoots to
remain and cut off all other shoots at ground level.
A properly grown 8-year-old delphinium can have
as many as twenty to fifty shoots in early spring. If all were
permitted to grow on, the plant would literally bloom itself to
death. When the delphiniums die down and become dormant in late
autumn/ early winter, cut down all stems and foliage to ground
level, and remove all leaves, debris, stakes, and weeds around the
crowns. This will greatly diminish the hiding places where pests may
over-winter. If you have heavy infestations of slugs and snails,
late winter and early spring can be times when they cause excessive
amounts of damage. Covering the tops of the crowns with coarse
gritty sand helps to deter them.
Article ©MrsGreenFingers.co.uk
2005 No Unauthorised Distribution in full or in part without express
written permission.
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