For centuries, our relationship with weeds was one of peaceful co-existence.
We tolerated them in our gardens and fields as part of the natural order.
Weeds can be useful to us as well as beautiful.
But they're more than that.
They're a vital resource for insects and wildlife.
They can help us unlock mysteries about the entire plant kingdom.
And they're key to maintaining the most basic processes of life on Earth.
'Having worked as a professional gardener for the last 20 years at Kew Gardens, Edinburgh Botanics
'and Westminster Abbey, I've fought a low-level war
'against those plants which I condemn as weeds.'
I've probably condemned thousands of plants to the compost bin over the last two decades.
'But now I'm starting to wonder what turned me against them in the first place.
'After all, we've always made good use of them in natural remedies.'
- It's used for joint problems, arthritis and rheumatism. - Ho!
'Today's problems really started when we began to bring in non-native wild plants from abroad.
'Many of these plants looked pretty appealing at first, but there was one small problem.'
This is one of the most invasive species in Britain today.
Each one of these racemes is capable of producing hundreds of seeds.
'We ended up throwing everything we could into the fight against weeds,
'a battle I've been part of myself.'
Applying a poisonous emulsion, it works 40 acres a day...
But ultimately it's a war I will lose
as these highly opportunistic plants have inventive ways to make sure they survive in the natural world.
'In turning them into enemies, we forgot what they can be like as friends.'
We see them as vegetable trash.
They're like maggots or vultures. There's more and more all the time.
'Time to repair our relationship with these humble, but essential plants before it's too late.'
'In the last 50 years, there's been an all-out war on weeds.
'The weeds have got tougher and so have the weapons.
'It wasn't always like this.
'Out in the countryside, weeds, if they weren't exactly our mates, were part of the natural order.
'People thought weeds were something we'd lived with since we got kicked out of the Garden of Eden.
'But then something came along which made weeds feel very unwelcome.
'Gardens.
'Once gardening was a pastime only for the aristocracy,
'but in the 19th century, red-brick terraces sprang up across Victorian England.
'And they all came with their own little garden.
'For the first time, every British man and woman could control nature for artistic effect.
'The chance to impose order on the natural world really caught on
'and now no one loves their gardens more than we do.
'This is our own precious patch of ground, where weeds are strictly not invited.
'We've been firmly told there's no room anywhere for weeds.'
These are the seeds of annual weeds. They will compete with my seedlings for light and moisture
unless I do something about it.
'But what we haven't been told is that the more we struggle to keep them out, the more they come back.
'They move in like an invading army. They are plants that thrive where we least want them.
'We think of them as intruders from an alien world.'
Monster plants on the march!
'The irony is there'd be no such thing as weeds without our very efforts to get rid of them.
'And it's taken me a long time to realise why.
'My personal relationship with weeds started with my formal training.'
When I was a student here at Edinburgh Botanics, I was sent out to defend these plants.
One of my foes was this little chap here - Cardamine hirsuta or the bittercress.
I begrudgingly admired this plant because I'd get my tweezers and pick it out of the ground,
but as I did it, I found out it had an exploding seed head.
It was almost as if I pulled it out and the seed shot everywhere, it was saying, "I'll see you next week."
'When I left Edinburgh, weeds were still my enemies.
'It wasn't until I took over at Westminster Abbey that I saw differently. Although weeds seem
'like the lower orders, they're not going to be pushed around by anyone.'
When I first came here as Head Gardener, following nine centuries of gardeners,
I knew it was a special place.
The first real event I was to experience was a celebration of the Battle of Britain.
We had a sovereign, lords and ladies, Knights of the Order of Bath, politicians and our veterans.
In such esteemed company, I developed an obsession with weeding.
'The truth is that the more we try to get rid of them, the more they come back. That's what they do.'
What I learnt was that weeds are rebels. They adhere to no boundaries
and conform to no rules. The fact that they did that within the walls of the establishment led me to have
a great sense of admiration for them.
'To me, weeds' willingness to grow everywhere and anywhere
'represents regeneration and new life, surely something to celebrate.
'I think we've forgotten what a weed is and what it does,
'what makes it so special, so I'm going to start at the very beginning. What is a weed?
'Surely there must be an official definition.
'Gardeners' Question Time organic gardener Bob Flowerdew has always championed the plants
'most people think of as useless weeds.'
All the textbooks will say a weed is a plant in the wrong place, which is fairly true.
They're not as pretty as the flowers you want to cultivate, or as productive. Would you want carrots
or weeds choking them all? Carrots.
- Weeds are this potential resource. - Yeah.
Most, all of our garden plants were once weeds. They were wild plants.
And we've improved them by giving them better culture and by selection.
- Botanically, there's no such thing as a weed. - There's no difference.
It is just a plant that we haven't discovered the virtues of yet.
When I started gardening, it was very meticulous - pruning, edge the green, stripe the lawn.
Have attitudes to weeds changed? We're more relaxed?
There's a time and place for everything. Some people love neat.
However, they won't have as many butterflies or other interesting things as they haven't the resources.
They also will have bare soil and have to buy in fertiliser.
It's bizarre, but they're throwing away what makes fertility for free.
- So they have a place in your garden? - Oh, very much so.
'There are over 40 different definitions of a weed, but none of them is definitive.
'They're all really just descriptions of our attitudes to weeds, not botanical categories.
'Calling a weed unattractive or unwanted makes sense if you're a suburban gardener,
'but not if you want to look at the plant kingdom as a whole.
'Richard Mabey has been writing about wild plants and weeds for the last 30 years.'
Well, there have been masses of definitions. In America,
a weed is any wild plant which grows six inches above the ground in a garden and it's illegal!
Somebody, an American writer, Ralph Waldo Emerson,
said a weed is simply a plant for which a use has not yet been discovered.
The most popular one is that a weed is a plant in the wrong place,
but that means somebody's got to decide what the right place is.
'To show me the difference between a right place and a wrong place,
'Richard took me to the 12th-century abbey at Bury St Edmunds.'
There's a very graphic illustration of the extent to which there are minute differences
in what can be the right and wrong place. Here we've got Aubretia in the wrong place in two ways.
It's a native wild flower of southern Europe, brought into this country
as a rockery plant. It's escaped onto the walls of the abbey where it's tolerated
only if it's about five feet above the ground. If you come down here,
the Aubretia has been the subject of weed killer spray.
It injects so much subjective opinion into it. Some people if they get bluebells in their garden,
you know wild bluebells, regard them as a weed
because they should stay in the woods where they belong. Conservationists regard the Spanish bluebell,
a slightly bigger, more aggressive sort that people grow,
when that gets out and into woods, that's a weed!
So there's enormous kinds of social and convention and even fashion which come into this definition.
'If the definition of a weed just depends on fashion, then you can bet that what counts as a weed
'has changed again and again over the last 300 years.
'In fact, the story of our changing attitude to weeds is really the story of our changing attitudes
'to civilisation and nature.
'In the 18th century, buccaneering plant hunters set sail
'in search of new non-native wild plants.
'One of their prize discoveries was Senecio squalidus, commonly known as Oxford ragwort
'and today a confirmed pest.
'It started life as a native wild flower on the slopes of Mount Etna in Sicily
'where it had thrived on the volcanic clinker.
'It was brought to England and arrived in Oxford in the 1700s, where it was studied carefully.'
Its first recorded point of arrival was here at the Botanic Gardens in Oxford,
hence its name. It was either brought by collectors
or snuck in on the root ball of one of the many plants being collected.
'It was recorded by Joseph Banks, the great 18th-century plantsman,
'as growing within the garden quite happily in the 1770s.
'By the turn of the century, seeds found their way into the walls,
'the lime of the mortar suiting their taste for a high pH.
'But it wasn't long before the plant escaped and spread throughout Britain.
'The seeds wafted over the walls,
'down the lanes and past the colleges,
'past the Sheldonian Theatre.
'By 1830, the plant had arrived at Oxford railway station.
'The dry rocky shingle used as ballast along the railway line soon became a home from home
'for the newly-escaped ragwort,
'mimicking perfectly the conditions it would have enjoyed in its native land.
'As well as getting onboard via the soles of passengers' shoes,
'the seeds were also carried along by the trains' slipstream.
'And as a result of all this help from the wind, trains and humans,
'Oxford ragwort spread quickly around the entire railway network.
'But if the 18th century was the great age of plant hunting in the name of science,
'by the 19th century, our attitude had changed again.
'Victorian plant hunters looked, above all, for colour and drama
'and they didn't worry about what mischief the plant might do
'in our temperate, accommodating climate.'
- Any idea of what it is? - Not really.
A foreign import of some sort. I know not what of.
'Little did they know that many of the plants prized for their beauty
'would, years later, be vilified as pests.
'And when exotic plants were brought back from abroad by our 18th-century forebears,
'no one gave a thought to the effect they might have on native species.
'Three plants in particular, highly-prized as ornamental blooms in the 19th century,
'have now been officially blacklisted as plant pariahs to be hunted down and exterminated.
'And each of them tells us something different about our changing relationship with weeds.
'Buddleja Davidii or the butterfly bush came from China,
'the first of these aggressive plants that have since escaped from our gardens
'and into places that remind them of their native land.'
This is one of the most invasive species in Britain today.
Each raceme is capable of producing hundreds of seeds.
A plant would produce thousands, each one capable of germinating in ballast, mortar or even concrete.
'Like Oxford ragworts, Buddleja feels completely at home along the rocky railway tracks
'where it has spread the length and breadth of the country.
'Preventing these plants damaging the thousands of miles of Britain's railway lines
'is a costly process for Network Rail.'
Neil, a big weed problem. How much is it costing?
To deal with the weeds on the track, every year it's £3-£4 million.
To deal with all the vegetation on the network, dangerous trees and the weeds, £30-£40 million.
- And I suppose one of your biggest problems is going to be Buddleja. - Yes.
I know these come from China where they're on lime cliff faces.
- Is there a connection with here? - I think there must be.
The retaining walls have a lot of lime mortar holding the bricks in.
The pH must be just right for the seeds to germinate and thrive.
- You can't pull that out. It's solid in the ground. How do you attack it? - It would be a chemical treatment.
For the small plants, we use a leaf application, so it's just dealing with that one plant.
For the larger ones, our new technique is to cut the stumps
and rather than putting a herbicide onto the stump itself, because you can get issues with run off,
what we're looking at as a new system is using these plugs
whereby you drill a hole into the stump itself, hammer it in,
this then splits the casing and that herbicide dissolves directly into the sap of the tree or Buddleja
- and gets straight into the system. - So that's very targeted.
- That's systemic. - Yes. - So when the chemical is released, it goes into the vascular bundle,
which poisons the entire plant. Right down, nothing left.
All being well, what it means is it's very good at killing the whole plant, so we don't have to come back,
so guys don't have to go up to height on the mobile platforms and it's done.
- So that is the magic bullet. - It's the targeted application of herbicide to kill that plant.
'Magic bullets are all well and good, but we're fighting a losing battle here.
'The Buddleja is always likely to get the upper hand and it doesn't even know it's in a war.'
The Buddleja is a plant only doing what comes totally naturally to it.
It's a survivor. If we've got problems with it, maybe that's down to us.
'Despite our best efforts, Buddleja has found a comfortable niche in the overlooked spaces of our cities.
'It's a garden escapee that has got above itself
'and for some reason we've decided we can't tolerate it living beyond our back yards.
'It's not just in towns that fashions have changed.
'In one of the most remote and rural parts of Britain, the Isle of Bute in Argyll,
'another much-loved Victorian bloom has been reclassified as a menace to society.
'Scotland has thousands of square miles of forest.
'From the millions of acres of Forestry Commission spruce to the ancient pines of Glen Affric,
'remnants of the Caledonian forest.
'And thanks to our Victorian forefathers, a very un-Celtic plant
'is spreading unchecked, fit to choke the glens, say its critics.
'It's Rhododendron Ponticum and it's roused the ire of the Scots.
'One of the most invasive weeds in Britain today, it came from the north-west of Spain in the 1840s.'
At the time, it was a gardener's delight with its thick, waxy leaves and its sprays of purple flower.
'And it wasn't just Victorian gardeners who embraced it.
'Rich landowners snapped it up as part of their impressive botanical collections.
'On shooting estates, Rhododendron Ponticum was introduced to provide ground cover for game birds.
'This was a fatal mistake.
'The most common Rhododendron in Britain, it spreads at the expense of almost all other species.
'In Argyll, it can climb the ancient oaks and block the light so essential for the lichen and moss.
'Each plant produces millions of seeds.'
Ponticum even uses chemical warfare to conquer all that surrounds it.
It releases poison from its roots that knocks out anything that dares to compete.
'The plant is host to Phytophthora, a fungus-like mould genus
'implicated in the tree disease known as Sudden Oak Death.
'Gordon Gray Stephens from Scottish Natural Woodland knows what it's like to be at the sharp end
'of this war against Rhododendron Ponticum in Argyll.'
- What proportion of the county is covered in Rhododendron? - A Forestry Commission survey three years ago,
a partial survey of Argyll,
and they came out with over 3,000 hectares of ground infected with Rhododendron.
The Rhododendron casts such a dense shade that the oak can't seed into that dense mat of Rhododendron.
In 400 or 500 years' time, we won't have an oak woodland left. We'll just have a Ponticum thicket.
In the short term, it destroys the ground layer, so there's nothing left growing on the ground.
That makes a real difference to a lot of these lower plants.
The root can be on ground that is favourable to Ponticum and the layers go away onto wet ground.
Because its main root is on dry land, it can spread into areas it otherwise wouldn't be able to get to.
It's like a Swiss army knife of a plant, I suppose. The cost of treating it is quite substantial
so this is labour-intensive hard work.
The Forestry Commission reckoned it would cost £9 million to clear Argyll of Rhododendron in 2007.
But the other dramatic figure is that by 2050, if we don't do anything,
it'll cost £50 million, so the stuff is spreading so quickly,
not doing something now means we'll have a far bigger problem later on.
'The only way to tackle the problem effectively is to gather a group of committed volunteers.'
If we could see the last 100 years of Rhododendron expanding through Scotland
it would appear as an army, advancing all the time up the hills, up the glens.
- It just gets bigger and bigger. - How would you physically attack it? - We try to get them out by the roots.
That way the plant is finished. All that might survive are seedlings coming up over the next few years.
We knock it back as hard as we can in the first pass.
You need a vigorous approach for a plant that is so vigorous.
It is a bit of a battle. You need a team, really.
One man on his own, it's a bit daunting. Even with two, you can go, "I'll start here, you start there."
The more people you've got, the bigger your army is against the army of Rhododendron.
You engage every part of your body. You get battered and scratched and bruised, but it's beautiful.
Obviously, at the end of each day you see what you've achieved. I like the idea that they don't go quietly.
No, they fight back every time! At the end of the day, you know you've been at war for a day.
- You know you've been fighting. - Here it comes.
'But again, there is more than meets the eye to our relationship with Rhoddies.
'Rhododendron Ponticum may once have flourished in Britain before the glaciers came 20,000 years ago.
'And maybe that's why it thrives here today.
'It's only our decision to classify it as an alien that leads us into battle against it.
'When something is labelled alien, an entire industry will spring up, dedicated to its destruction.
'Never was that truer than with the introduction of one very special foreign beauty.
'Introduced into Britain by Philipp von Siebold, a German biologist, in the early 19th century,
'this fast-growing plant producing big white flowers in summer quickly became a gardeners' favourite.'
I'm here amongst the strands of Japanese Knotweed and it really is like a jungle in here.
It's conquered the surrounding grounds. It's hard to believe this was a much sought after ornamental
and an expensive one at that. It was very prized in Victorian gardens. You can see why.
it's got many qualities. It's pollution-resistant, it grows in poor soil and it's fast-growing.
It can put on five foot in four weeks. Speaking as a gardener, I can understand why they prized it.
In fact, in 1879, the horticultural journal The Garden described it
as one of the most beautiful herbaceous plants in civilisation.
How reputations are lost.
'Today it's turned into the most aggressive alien weed in Britain,
'an outlaw we decided to hunt down without mercy.
'True, this is no ordinary weed.
'It out-competes everything around it.
'The plant's complex root system or, as we gardeners call it, rhizome
'spreads up to 20 feet in all directions, as well as going down 9 feet below the surface.
'And just for good measure, the roots can swell and throttle entire root systems of other species.
'And these plants don't just grow downwards.
'Above ground, they can grow over 20 feet a year and rapidly swamp any vegetation in their path.
'But there is a dirty little secret in our relationship with knotweed.'
The most amazing thing about this plant is it's never propagated by seed. Humans spread it.
Let me show you...the secret... of knotweed's success.
It's this rhizome here. If I break a piece off and take it away, I'd spread the plant.
'It can penetrate concrete and completely envelop a house.
'Japanese knotweed is now posing a problem to home owners in the UK.
'Some high street banks are refusing mortgages on properties infected with the weed.
'And removing it is difficult. Not only is there the sheer mass of plant and root to remove,
'but the soil is treated as controlled waste.
'So a giant weed control industry has grown up along with the knotweed
'and the two are now locked in mortal combat.
'It's a lucrative business worth a staggering £1.5 billion per year in the UK.
'To clear the new London Olympic site alone cost one contractor £9 million.
'Clearing building land's a big part of the knotweed removal industry.
- 'So what do you have to do to get rid of it?' - You have to erect a fence to prevent humans
from entering the area and spreading it around.
We basically apply the herbicide to the plant. It can take up to 3-5 years
and require several applications per year, if not more.
The second thing is then to cut and clear absolutely all the surface growth.
We then put it in a designated area and incinerate it, usually in a cage incinerator,
to prevent any small fragments being dispersed and potentially regenerating as new infestations.
- You deal with the soil so this is classed as a toxin? - It's classed as controlled waste
- contaminated with active Japanese knotweed rhizome. - So if you did build on it,
- people could have it in their front room? - Literally. That does happen.
- Getting rid of it is quite expensive? - Yeah, there's some horrific statistics out there.
To eradicate it all now would cost something like £2 billion.
'The thing is, we brought all this on ourselves
'by bringing in non-native species to an environment where they could spread without natural predators.
'The knotweed removal industry is here to stay, partly thanks to government tax breaks.
'But there is an arms race going on here and we're never going to win it developing bigger, better weapons.
'It's time to come up with a new plan. One man thinks he has the answer.
'Part of the reason Japanese knotweed flourishes in Britain is it has no natural enemies here.
'But in Japan where, as you might expect, the plant is common, it doesn't rage out of control,
'thanks to the insects that keep it in check.
'10 years ago, plant scientist Dick Shaw began an epic quest to find a natural way
'of controlling knotweed in the UK. His first port of call was Japan's native insects.
'He tested various bugs that fed off the weed before selecting a psyllid as the best control agent,
'a creature with an appetite for Japanese knotweed and little else.'
I'm really interested. How does it set about attacking the knotweed?
It's called a psyllid. The adult female lays up to 600 eggs
and the eggs hatch and suck the sap out of the plant, just like a bunch of aphids.
If you have a load of aphids, you know the damage they can cause.
Our psyllid attacks this plant only and causes stumpier leaves, shorter plants and, hopefully,
a less invasive species.
'After battling suspicious authorities in Britain, who quarantined them for several years,
'Dick finally got clearance last year to release them in Britain.
'This is the first time that bio-control has ever been used in Europe to fight a weed.
'This climate-controlled greenhouse is a psyllid breeding colony
'where generations of the bugs are being raised to do their duty by devouring our Japanese knotweed.'
We need an awful lot of knotweed to feed them. It's mass production.
- So this is a pantry, for all intents and purposes. - Exactly.
A pantry with only one food source.
- Are there psyllids here now? - Nothing on these plants. These are ready to be fed to the psyllids
until they've got to a suitable size.
So this is like a supermarket. I'm guessing this contraption is where our friends, the psyllids, are.
This is their dining room. They feed on the plants in here,
go through their cycle and we end up with more psyllids at the end than the beginning.
- This is about getting as many psyllids as possible to get them out. - That must be an exciting moment.
It's the culmination of a lot of work and an awful lot of scientists have been involved in this.
What you can see here, we're lucky, is a couple of adults mating here, a female and male.
There's an other interested male coming down the mid-vein. This is exactly what we want.
With any luck you can see the eggs on the surface of the leaf. The tiny white dots are the progeny.
There's three there, aren't there?
'This extra psyllid seems to have turned insect reproduction into an eight-legged Carry On film.'
- There's another one in there now. - It's like a disco dance floor with one bird and three geezers.
THEY LAUGH
She's very popular.
A very frustrated male charging around the leaf now with his bottom lip hanging out.
'Dick's return to organic methods of dealing with weeds fits with the present-day revival
'of ancient folklore about the use of weeds in herbal remedies.
'Today 10 million of us spend a total of £240 million
'on herbal cures derived from weeds.
'As a medical herbalist, Dee Atkinson knows a great deal about the medicinal qualities of weeds.'
I see this as a medicine chest. Just looking at this, I'm excited about all the medicines I can make.
Look at those nettles, wild garlic, all sorts of things.
'Herbal treatment is the oldest form of medicine in the world.
'Human use of wild plants goes back at least 70,000 years.'
There's our friend, the nettle.
So this Galium, or Sticky Willy we call it down south,
- you could combine those two together? - They're really good. Nettle, cleavers and dandelion
were the three herbs that we used as spring tonics, the idea being
that they were some of the first herbs of the early spring and after a winter of preserved meats
and no refrigeration, of course, you needed to cleanse the system.
'It was time to turn my hand to a weed tonic.'
I'm just going to use the leaves.
- If I feed them in... - And I just turn the... - Just turn the handle. - OK.
'Herbal medicine isn't just used for things like indigestion.
'The seeds of milk thistle are the only known antidote to death cap mushroom poisoning.' Some galium?
So I'm going to get up in the morning and have a cup of dandelion and nettle tea to help in which way?
- It will help with your impending arthritis... - OK!
The cleavers are good for skin problems and dandelion is a fantastic bowel herb.
A mild diuretic. It's used for joint problems, for arthritis and rheumatism.
What I'm going to do is I'm going to take the dive and see how this tastes.
Ho! I can taste the nettle and I can taste the dandelion.
It's not bad. A little bit bitter.
It's interesting you say it's bitter. That's where the aperitif came from, the idea of something bitter
- before a meal to stimulate digestion. - Interesting.
That's perfectly easy to drink.
'We had always known weeds could be useful.
'But then something happened in the 1940s that made us realise
'how unexpectedly beautiful they can be.
'The bombing of London during the Blitz had a strange side effect.
'40,000 Londoners were killed.
'One and a half million were left homeless and 600 acres of the city were reduced to rubble.
'But something else happened, too.
'On May 3rd, 1945, the Times ran a front-page story
'recording a strange consequence of the Blitz.
'At the Savoy Chapel, just off London's Strand,
'one of our most eminent botanists used a public lecture to describe this extraordinary phenomenon.
'The beautiful and unexpected growth of weeds on London's bleak bomb sites.'
Most bomb sites were awash with yellow and purple.
Imagine what an incredible sight that must have been.
This was the biggest dig over ever and the weeds wouldn't miss out.
'Weeds' ability to regenerate and bring life where there was none
'was not lost on the inhabitants of the ruins of London.
'These weeds were truly welcomed.
'One Londoner in particular was paying close attention.
'The man who delivered the lecture was Sir Edward Salisbury,
'a respected scientist who happened to be passionate about weeds.
'During the Blitz, he travelled to numerous bomb sites and identified a total
'of 127 different species of weed.
'The most common was Rosebay Willowherb.
'Native to Britain since the glaciers, it was not very common
'until the Blitz gave it an unexpected opportunity. It spread rapidly across the bomb sites
'as each plant produced about 80,000 seeds.
'They also liked burnt ground and took nutrients from the ash.
'The plant is a perfect example of how weeds bring life to otherwise desolate or damaged environments.
'They wait patiently for the right opportunity to prevail.
'Sir Edward continued his research into weeds
'when in 1943 he became Director of the most important botanical research centre in the world -
'Kew Gardens.
'He wrote a book detailing his sometimes rather strange experiments with weeds.
'It remains a touchstone for botanists to this day.'
Sir Edward Salisbury, like most plantsmen, was eccentric.
It wasn't enough for him to find, identify and log the plants.
He was fascinated by the resilience and mobility of weeds,
so he set up an experiment to find out how seeds behaved in the wind.
'I'm going to recreate one experiment to find out if the results still hold good.
'In the test, he dropped seeds from a height of nine feet to record
'how long they took to reach the ground in a windless environment.'
He collected the seeds of plants he was interested in - Rosebay Willowherb, Buddleja and Taraxacum.
He then took a ladder and would climb up to 9 feet and release them.
The time it took to get from his hand to the floor would determine how easy this seed was wafted
or spread around the city or environment it grew in.
'The longer they took to fall to earth, the further afield they could spread in the real world.'
It's Taraxacum Officinale or the dandelion.
Two, three, four,
five, six. About six seconds.
And this is Buddleja Davidii.
It's taking about three, four seconds here.
What's impressive about this plant is just the sheer numbers on the raceme.
And this one is Oxford Ragwort.
Finding out about plants like this really does bring out the eccentric in you.
I'm sure Sir Edward had a great time and I can see why, to be honest. Beautiful.
And that is taking about 16 or 17 seconds,
proving that Sir Edward's work...
..was on the money, really.
'But at the same time as Sir Edward was carrying out his painstaking experiments in the 1940s
'to put weeds on the map, other scientists were hell-bent on destroying them.
'Wartime research by the Nazis into nerve gas had a peacetime spin-off.
'The first pesticides and herbicides were based directly on research into Sarin and other toxic agents.
'Things were about to get very bad for weeds.
'In the post-war rush to maximise food production in austerity Britain,
'weeds started being destroyed on an industrial scale.'
Into battle against the foreign invader. That was the watchword of an armoured division last week...
'As a result, the weeds that had always reduced crop yields were banished.
'Before the 1940s, useless weeds sometimes amounted to a third of the total harvest in any one field.'
As this is highly inflammable, two men carrying fire extinguishers are on hand through the operation.
'Herbicides allowed wheat farming to become big business for the first time.
'And wheat turned into our leading source of vegetable protein,
'used in everything from pasta to beer.
'We thought we'd achieved the ultimate victory in our war on weeds,
'but the countryside has paid the price.
'In the last 50 years, Britain has lost 98% of its flower-rich meadows
'due to production of arable crops like wheat.
'We are only now starting to realise what we may have lost
'when we banished weeds from our fields and created a monoculture.
'Dr Jonathan Storkey has studied the unforeseen consequences of the chemical warfare revolution.'
What's happened since the 1950s
is as the production of agriculture has become more intensive, we've used more fertilisers, herbicides
and pesticides and also we're growing much less kinds of crops.
We're basically growing winter wheat and winter oilseed rape.
So we've lost the diversity and we're growing those crops more intensively.
That's contracted the available niche or the habitat space that other species can use
to grow and persist. So we now have quite a number of rare arable weeds like cornflower and corncockle
that have disappeared from fields. And the overall amount of resource for wildlife has decreased.
So we're losing species at all trophic levels.
Also it's important because some of that biodiversity does helpful things, like pollinators,
some of the natural enemies control the aphids in the crops.
We need some biodiversity in the environment. It's not good enough to have wall-to-wall crops.
'So without some weeds in fields, we lose essential insect pollinators, as Jonathan showed me.'
We've got quite a nice range of species in this quadrant.
We recognise the dandelion. What's its role here?
They provide pollen and nectar resources, particularly early in the season for pollinators.
- So bees, very important... - Bees, butterflies, yeah.
- We've got a Hogweed here. - Yeah, there's a couple of them.
There's Hogweed and Cow Parsley.
Things like hover flies like those small, white flowers
and they're important for controlling crop pests later in the season.
So they go out and help clear up the insects we don't really want?
Providing a mosaic of resources through the season.
We want the resources here at the right time to encourage natural enemies later.
So a small sacrifice for our small friends here, really.
Yeah, we're talking maybe six metres at the edge of the field with reduced herbicide, reduced fertiliser
to just provide an opportunity, some habitat for some of these species to persist and thrive.
The massive irony of this is that 'the very crop that has become a monoculture at the expense of weeds,
'wheat, was once a weed itself.
'Plant scientist Prof Nick Harberd of Oxford has researched the moment a weed became wheat.'
About half a million years ago
there was, spontaneously in the wild, nothing to do with human beings,
a cross-pollination, if you like,
between two wild grass species.
So one can imagine that humans were cultivating this wheat in a field
and, by chance, a weed was growing within that field and there was again a spontaneous hybridisation event
between the cultivated wheat and this wild grass growing there.
The whole process made a plant that was bigger and more vigorous.
And as a result of that, we ended up with the wheat crops that we all grow and feed off today.
'Nick can recreate exactly how wheat and weeds cross-bred in a lab today.'
What I'm doing here is getting an immature flower head from cultivated wheat.
So this is cultivated wheat. And down here next to it,
- that is... - This is a wild wheat species.
The idea then is to take a flower and open it so that you pull away these bloom cases,
which I'm doing now. I think that's fine now.
And now we move onto this wild flower and it's very different.
What we're looking for now are anthers shedding pollen.
Now that's an anther and then you come back to the flower where we were before and you spread the pollen
- on the female part of the flower. - So what we've done there
is recreated in a laboratory what happened 10-12,000 years ago
between our domesticated wheat and our wild grass.
- They would have cross-pollinated exactly the same way in natural conditions. - Exactly right, yeah.
'Weeds helped us out millennia ago and now scientists in the 21st century have turned to weeds
'for one of the most important discoveries in plant biology ever.
'It could save lives by creating a super wheat.
'It all took place here at the John Innes Institute in Norwich.'
Come on in, Chris. You need to sterilise your feet.
- We're not bringing in anything nasty. - Viruses or anything else.
'Dr Alison Smith is Head of Metabolic Biology here.'
- It's the first time I've dressed up to see a weed! - We look after them!
'Alison's team have been studying a small, common weed called Thale Cress,
'which is now used as the model to map the DNA of all plants on the planet.'
This weed is incredibly easy for us to work on. All plant scientists
in the world take information from this weed. Many only work on this little weed.
It's really useful because, like a lot of weeds, it goes from seed to seed really quickly,
so we can get through lots and lots of generations, which makes it easy to do genetic studies,
to understand how the weed behaves and what its genes are doing.
About 20 years ago plant scientists got together. They were working on different plants and they decided,
"Let's work on one plant together, so it becomes the model to develop our understanding of plants."
About the same time as we were sequencing the human genome, we started on this little weed.
So, in 2000, we got the entire gene sequence of this weed. All of the genes are known.
At the same time as the human genome.
- So really, then, this small weed is a blueprint for all plants. - This is the model for all plant life.
'But the sequencing of the genome is not just for the sake of it.
'Alison and her 600 colleagues are unlocking the secrets of the plant's success,
'like its speedy growth rate and its hardiness,
'and transfer those abilities to the crops that matter to us, like wheat.
'This is one of the most important discoveries in plant biology ever,
'where one of the humblest weeds could save millions of lives around the world.'
Now we've seen our magic weed
and you've got this genetic blueprint. How do you apply it to arable crops?
Well, we can start to tackle some of the real problems we have with our crops,
like disease, for example. Our crops are quite susceptible to some diseases.
We've been able to breed for that. In Arabidopsis - Arabidopsis gets diseases as well -
we can understand exactly how it's resistant to those diseases.
We know what genes it needs and we can say, "Where are they in wheat?
"Can we make sure our new wheats have the genes to resist disease?"
Another example would be how the wheat exactly makes its seeds.
This is the really important bit. This is human food.
We understand a bit about the process of how these little seeds are formed,
but in Arabidopsis we understand it in absolute molecular detail
and that helps us to understand how we'd make better seeds, bigger seeds, more nutritious seeds.
We can apply that knowledge.
I know scientists don't like to be too dramatic, but I'm going to be.
Weeds could play a big role in arable crops like wheat, or even maybe the future of humanity.
I think it was the starting point for what has to be a revolution in our crops,
a revolution in understanding how they work and making them work better, and doing that fast.
It's taken millennia to get to here. We can't afford to take millennia.
We have to do it in tens of years or less and in order to do that
the information from Arabidopsis has been the key to pushing us forward.
'It's the resilience of weeds and the insights they give us into helping crops survive
'that makes them among the most useful plants on the planet.'
Usefulness may not be just the obvious usefulness
of, "How does it do us humans good?"
Take some horehound to cure your cough.
Mint tea, good for indigestion.
It may be a much bigger ecological usefulness.
Weeds come in to disturbed ground to try to green it up.
So they're doing one of life's basic functions,
to try to turn sterile, bare earth into green vegetation.
And we should pause to think about that before we hoik them out.
'This is nature at its most fundamental.
'Greening over gaps is what weeds have done since the beginning of time,
'creating new life - a process called succession.
'Here is one place where you can see this in action.
'And no one who really observes what they do can fail to be grateful to weeds.
'Built in 1853, with money from sugar and the slave trade,
'Poltalloch is a Victorian mansion on the west coast of Scotland.
'The house was abandoned in 1958.
'Since then, it's become a perfect example of plants reclaiming the voids created by man.
'These grounds would have been tended to by ten gardeners.'
But that was a long time ago and now nature's moved in and nature's doing the gardening.
'50 years ago, weeds were the brave new pioneers,
'their rapid life cycle bringing vital nutrients and organic matter to the surroundings.'
Now these are plants whose only agenda is to set seed.
I've got a perfect little example with this Bittercress. This really is a frontline weed.
It only has one thing on its mind - to get its roots down, get its flower up, set its seed.
But it does a very important job. The life cycle's so quick, it rots down, forms organic material,
and provides a substrate of soil which you can see here on this windowsill.
This then allows other plants to move in.
'During the first winter, perennial weeds with root systems, like the bramble, would have begun
'to get the upper hand here, breaking up the ground, letting in crucial elements
'such as oxygen and carbon dioxide.
'The Rubus or bramble is a really aggressive coloniser.
'The backward-sloping spikes allow it to grow over anything in its way
'and it has a thick carpet of roots. On those roots, at their apex, is a cambium cap.'
That enables it to drill through the soil and in times of austerity, if attacked by a gardener's spade,
it's these roots that enable this weed to survive.
This plant is a very important member of the environment.
It's clover, but it belongs to the legume family.
On its roots there's a special bacteria called rhizobium, which fixes nitrogen from the atmosphere.
All the plants around it swap this nitrogen for sugars. The whole process nourishes the soil.
This plant is a highly-prized member of the process of succession.
Down here on the floor, which was once probably a beautiful room,
here we have bracken. This is a perennial that has died back over the winter
and its leaves and debris form this lovely substrate.
You can see this works because moss has moved in and, eventually, small saplings of trees start to grow.
And, finally, the long-term species move in. The kings of nature,
like the beech and the oak. This beautiful specimen is just sitting here being nursed
by these big willows, which will die out. The beech will then grow up and succession is complete.
The weeds will have done their job.
'We've waged a war on weeds because these tenacious plants have annoyed us.'
They don't fit in with our plans to confine them within the boundaries of our gardens and our fields.
Weeds don't recognise boundaries, only opportunity.
And they are engineered to be born survivors.
Some that were once welcomed with open arms are now being rebranded as alien invaders,
and condemned to extermination.
But our relationship with weeds will change again as we understand more about them.
And the more we learn about exactly how they work,
the more it becomes obvious how essential they are to the life cycle.
It might pain us to admit it, but without weeds we'd be in trouble.
Or as Gerard Manley Hopkins put it in his 1918 poem Inversnaid,
"What would the world be Once bereft of wet and of wildness?
"Let them be left O let them be left, wildness and wet
"Long live the weeds and the wilderness yet."
Subtitles by Subtext for Red Bee Media Ltd - 2011
Email subtitling@bbc.co.uk