In the lab:micropropagation was originally developed for crop research but has since benefited gardeners
 Photo: Getty Images/Science Photo Libra

As a 20-year-old, working in a lowly post in vegetable research, I was in a
small team that used micropropagation to eradicate virus from rhubarb stock
plants owned by commercial growers in Yorkshire. The technique was to cut
pieces from the growing tips and place them in glass flasks full of gel-like
growing media under light and heat.

The virus was eradicated by raising the temperature of the flasks, rather as
our bodies do when we develop a temperature to fight off influenza. The
simple technique saved the “Yorkshire triangle” rhubarb industry.

Micropropagation is a method of producing certain plants in much larger
numbers than you could by natural methods. There are two major difficulties,
though.

First, time is needed to perfect the growing medium for each type of plant.
Our base ingredient was coconut milk so our lab was always full of coconuts.
The flesh was a waste product and I put my excellent dental health down to
chomping my way through large chunks of the white stuff day after day.

The second problem was weaning, the term for transferring the soft bits of
blobby plant tissue, which looked like plump green buttons, from the
gel-like media to compost.

Everything had to be sterile too, and a lab bench and spirit lamp were key
equipment. On one occasion I blew too hard and ignited the spirit underneath
the lamp’s wick, removing most of my eyelashes and my fringe. But even in
the early Seventies we realised that micropropagation could produce certain
hard-to-propagate plants in commercially viable numbers.

However, I didn’t foresee a use for “microprop” in general horticulture. How
wrong I was. Today it is widely used. If you’ve bought a double primrose, an
agapanthus, a lavender, a lupin, a heuchera or a hosta recently, the chances
are that it started life in a glass flask under light and heat.

For example, orchids are a cinch once the necessary mycorrhizal fungi is added
to the growing medium. And we all know, orchids, for home and garden, are
now available at a fraction of their former price.

Bob Brown, of Cotswold Garden Flowers, was one of the first to realise the
potential of micropropagation. He rediscovered an ivory-white ornamental
blackberry called Rubus rosifolius ‘Coronarius’ in a front garden in America
in the late Eighties and reintroduced it into Britain.

“There was so much demand for it and I couldn’t produce enough of by normal
means,” Bob says. “Everybody wanted it. I was approached at the Malvern Show
and asked if I wanted anything micropropagating and I selected three plants.
Within a year I had too many and decided to sell the surplus plugs to cover
the costs.”

Bob founded Just Must Perennials in 1994 and the company now supplies hundreds
of nurseries with plugs. His biggest success is the maroon-red thistle
Cirsium rivulare ‘Atropurpureum’, a sterile plant that sets no viable seed.
As it has a tap root, it isn’t amenable to traditional division either, so
it’s almost impossible to propagate by normal means.

At Chelsea Flower Show 2000, this thistle became an “it plant” after being
used in Gardens Illustrated’s Best Show Garden designed by Piet Oudolf and
Arne Maynard.


Science in action: micropropagation is a method of producing certain
plants in much larger numbers than you could by natural methods

The designers used it with deep blue Salvia nemorosa ‘Caradonna’ and the red
Astrantia major ‘Ruby Wedding’. Micropropagation made all three widely
available and all are still much admired today although, according to Bob,
‘Ruby Wedding’ has been superseded by ‘Ruby Star’.

Dahlia ‘Murdoch’, a red water lily form, is another plant the nursery has
always struggled to supply enough of. It was passed to Bob by a Mr Murdoch
and raised locally by traditional methods. Their raiser has now retired, so
Just Must has commissioned 5,000 plugs. Dahlia ‘Murdoch’ will now become
widely available through other nurseries.

“The microprop process isn’t mega-fast,” Bob explains. “Ideally, the stock
plants need to have ten growing points each before you can start.” The
growing tips are harvested to be used in the lab, and the average cost per
plug is roughly £1.

As microprop is a labour-intensive process it is only feasible for plants that
are difficult to propagate naturally. Most of Just Must’s plugs are grown in
countries such as Poland, Indonesia and El Salvador in order to keep costs
down, before being shipped back to Britain.

Global effort

Patrick Fairweather, of Fairweather’s Nursery in Hampshire, produces
lavenders, agapanthus, hostas, heucheras and a range of herbaceous
perennials almost exclusively through micropropagation. Twenty years ago he
used British laboratories, but now he uses a broker who farms the work out
to China, India and Indonesia.

“The link with the supplier is more tenuous than it was, but our nursery stock
is carefully monitored for consistency. New plants, consistent to type,
refresh the process every three years,” he says.

Bob Brown readily admits that micropropagation has its critics. “Some say the
plants change character and mutate and some say they lose scent. This is
wrong, although if a plant is naturally mutable when traditionally
propagated, as hostas tend to be for instance, changes will also occur
under micropropagation.

“There is also resentment,” Bob goes on, citing the classic lacy fern
Polystichum setiferum ‘Pulcherrimum Bevis’. “This is very slow to grow and
was held by only a few select nurserymen who guarded it jealously. They are
not at all pleased that it’s now more readily available.”

The handsome ‘Pulcherrimum Bevis’ is for sale more often than it used to be,
but many plants are not true to form, says Angela Tandy, the fern expert at
Fibrex Nurseries. She believes that many of the micropropagated plants are
atypical. She has also noticed that fern modules (or plugs) are reticent to
grow because micropropagated ferns produce lots of crown, but little root.
Growing ferns on from the plug stage can be difficult, as I can confirm
myself, having lost five ‘Bevis’ sporelings so far.

Fibrex Nurseries sticks to traditional propagation methods. Once it sent some
aspleniums (hart’s tongue fern) for micropropagation, but: “They came back
looking very different so we renamed them,” says Angela. “However, they only
survived for three years. Often when a thing is rare, it’s rare for a
reason. It’s just slow.”

Professional opinions

David Howard (of the eponymous dahlia fame) and his daughter Christine run a
traditional Norfolk wholesale nursery with 60 acres of field-grown
herbaceous plants. They lift two million plants a year propagated
traditionally by top cuttings, root cuttings and division. “There are pros
and cons,” says David. “We’ve found that micropropagation works well with
kniphofias, but we’ve gone back to raising our verbascums from root cuttings
because the microprop plugs produced such weak plants.”

His worry is that good plants could be lost to cultivation because they don’t
react well to the microprop process. He cites Potentilla ‘Gibson’s Scarlet’,
a plant micropropagated in the early Eighties.

“It came back a poorer plant and I haven’t seen the true ‘Gibson’s Scarlet’
for many years,” he adds.


Some plants, such as Potentilla ‘Gibson’s Scarlet’ don’t react well to
micropropagation

Brian Ellis of Avondale Nursery near Coventry sees microprop as a necessary
evil. “I use some plugs, although most of my propagation is done
traditionally. Like most nurserymen I love propagating,” he says. “I like to
sell plants that can’t be acquired elsewhere.” He’s currently swapping stock
with several European nurseries. “We do grow pinks and echinaceas from
plugs, but some customers have complained that the echinaceas are
short-lived.” However, Brian puts this down to their parentage rather than
the process.

On a personal level, I find that when I go to a plant fair attended by many
nurseries the same plants, grown from widely available plugs, crop up across
the board, diminishing my choice. So I am grateful that nurseries such as
Avondale are still raising most of their plants traditionally. It would be
very tedious if every nursery began to stock the same few things, especially
if they came and went quickly.

However, micropropagation is a useful tool, especially with plants that can’t
be propagated traditionally. As with everything in life, it’s swings
and roundabouts.

A BEGINNER’S GUIDE TO MICROPROPAGATION

Micropropagation, also known as in vitro propagation or tissue culture, is
more than 100 years old. However, it became more widely used in the Sixties
and Seventies. Usually it involves growing plants in glass containers partly
filled with growing medium, rather than soil. The amount of daylight and
heat is controlled and hormones added to produce maximum growth. The flasks
are usually rotated to develop even growth. Using this method, one head of
cauliflower cut into small pieces can produce thousands of clones within
weeks rather than years. The purpose of micropropagation from a commercial
point of view is to produce large numbers of plants that would otherwise be
scarce because they are difficult to propagate.

Pros

You can raise difficult-to-propagate plants in commercially viable numbers,
including sterile and double-flowered plants that are much in demand from
gardeners.

Micropropagation can clean up plants prone to disease. Trollius x cultorum
’Alabaster’, for instance, was weak and prone to virus until it was
heat-treated under micropropagation. Now lots of ornamental stock plants are
routinely cleaned up before being used for cuttings and traditional
division.

The constant shimmying of the glass flasks under lights produces symmetrical
rosettes on grasslike plants such as Ophiopogon planiscapus ’Nigrescens’ and
Carex oshimensis ’Evergold’. Agapanthus also make neater rosettes with even
growth on every side.

Cons

It’s highly skilled and therefore expensive. In order to justify the costs of
micropropagation, thousands of one plant are produced which can swamp the
market. If a glut remains unsold, that particular plant may not be
propagated again for some time, if at all.

Some plants make a lot of top growth and little root, so some microprop plugs
take a long time to make a strong plant.

Nurserymen and gardeners report that some plants do change under microprop
conditions.

Certain plants that do not reproduce easily and do not respond well to
microprop may disappear altogether.


The dark-eyed pink ‘Patricia’ is only available to gardeners because of
micropropagation

PLANTS WE WOULDN’T HAVE WITHOUT MICROPROPAGATION

Double primroses

Double flowers rarely produce seeds and many heritage double primroses were
almost impossible to buy because they couldn’t be divided easily without
losing vigour. Now they pop up everywhere and are widely grown.

Sterile hardy geraniums

Sterile flowers can’t set seed, but they flower their hearts out as they try
and fail. The lovely ‘Rozanne’, the true-blue ‘Orion’ and the dark-eyed pink
‘Patricia’ are only available to gardeners because of micropropagation.

Agapanthus

Once it would have taken 10 years or more for a new agapanthus to be available
in great numbers. However, newer beauties, such as ‘Northern Star’ bred by
Dick Fulcher of Pine Cottage Plants in Devon, were available within four
years of being named.

Bananas

All banana plants for commercial plantations are raised by tissue culture
these days, to produce higher yielding, healthier plants. Blueberries are
also raised this way.

Heucheras

All heucheras are raised from tissue culture and new colours often appear
during the process. The range constantly evolves because plants can be lost
either through a loss of vigour or contamination of the growing media.

Melanie Hancill

Journalist at Mirror
Sugar-free, home & garden writer for the Mirror and Sunday People news outlets.