Thursday, 13 October 2016

Controlling willow herbs; rosebay willow herb and epilobiums

The epilobiums are the main problem
Look what is blowing in
If you have come here via a search engine looking for how to control willow herb you are a probably a good gardener. I take it that all regular readers are too! When you have mastered most of the common weeds in your garden epilobiums remain! Couch, ground elder, marestail and hairy bitter cress might all be things of the past for you but epilobiums keep coming back. It’s a good illustration of how nature abhors a vacuum and when one plant goes another takes over.
It’s a little ingenuous of me putting rosebay willow herb, Chamerion angustifolia, in the title to attract your attention! That’s the name that most gardeners wrongly call their epilobiums. It is true that rosebay bay willow herb can be a problem but in the right place it is really rather pretty and can enhance landscapes and roadside verges. If you search on the net you will find places to actually buy it, especially the lovely white one.

Rosebay willow herb enhances the verge
 Epilobiums – the willow herbs

These are the two main culprits

This is by far the commonest epilobium in my garden
The good news is that epilobiums are rather pretty. The bad news is that if you stop pulling them out they will completely take over. To me it is a thorough nuisance and more than fifty per cent of my weed control time is taken up by it. More bad news is that this post might do little to help you!  We can commiserate together.

As a weed it spans the two normally distinct problems ‘weeds-from-seed’ (wrongly dubbed ‘annual weeds’) and weeds that are existing perennial structures. It is both! It blows in from seed and if left alone survives as a ‘short lived perennial’ Worse if you let them seed they remain evermore. If by dint of much effort you control them they fly back next year from ‘dirty neighbours’. When the village plot flooded last year it even came in by water!

It is so sneaky! It is able to hide itself in your most vigorous dark herbaceous or woody clumps and July to October suddenly appears from ‘nowhere’! It has of course been there all the time but after each new day of pulling them out you find several more! Even after my recent Open day when the garden had meticulous attention I pulled out another half dozen the very day after!

Epilobiums are the perfect weed – botanically speaking!

As far as I know these are the same species of epilobium. One is hunkering down for Winter the other is trying to make late Autumn flower

As a weed it knows every trick in the book. Evolved alongside agriculture it has benefited from natural selection for thousands of years. It loves the disturbed soil created by man and has 'learned' to combat most of the farmers' and gardener's wiles.

These have germinated since my last month’s visit to Bolton Percy. Other than deep midwinter it germinates all the year round
Perfectly hardy young seedlings, even ever-so-small ones, lurk over-winter waiting for Spring. Larger seedlings germinated in late Summer, Autumn, and early Winter make a tight ground hugging rosette ready to sprout in late Spring and Summer. Depending on conditions in Summer it will flower and set seed at three inches to four foot high.
It gives a curious satisfaction to easily yank out a flowering epilobium. You can do so with a tight and gentle pull from close to the ground. Beware a careless break as it regenerates a tight cluster of several new shoots to either flower or if late in the season await the next year.

This would easily pull out
In this patch there are far too many. Best to use a strimmer
If undisturbed in an adjacent paddock it is truly perennial and sets seeds strongly in August and September. The air born seeds fall like snow on your garden.

More seeds arriving
Seeds in Cathi’s paddock ready for take off
As an overwintering small plant it is resistant to normal strength glyphosate. It took me years to appreciate that I was spraying the same tight rosette several times!

Has it received enough spray?
In dry Summer even when other plants are wilting epilobium never seems short of water. On the other hand it loves bogs and water and will thrive at the edge of your pond.

Its trick of appearing from the dark middle of your plant clumps in Summer is fuelled by stored energy reserves that enable it to rapidly reach for the light and to expose its flowers and seeds. It builds up its strength when your herbaceous plants have died down or your shrubs have shed their leaves. Those green ground hugging epilobium leaf clusters continue to photosynthesize and build up their strength right through the Winter.  Even under evergreens with the sun low in the Winter sky, light reaches the darkest corners to sustain it!
Control of epilobium
Hand weeding
If it intimately infiltrates your borders you just pull it out. Ever vigilant you might check every day! If not yet flowering just cast the dead top on the ground to wilt and die and return to the soil it's due.
If flowering and ready to set seed I ought to advice you to take it away. In practice mine just gets thrown on my lawn to be later shredded by the mower. Any seed has no chance in my lawn!
You have several months to hoe the rosettes through Autumn, Winter and Spring.
If it is windy and dry they soon shrivel and die. Unfortunately in Winter the weather usually does not comply!
The technique of hoeing is slightly different to that recommended in my recent post on hoeing when you attempt to cut a weed from seed at exactly ground level. In this case you need to undercut the weed perhaps a quarter an inch down. This is necessary to detach all the perennial parts but with the consequence that it might root again! In Winter when it is cold I find re-rooting happens only very slowly and normally with luck you will get a spell of windy weather – even a few weeks later - that will kill it and all the goodness can then return to the ground. If you are tidy minded just rake it off  but do not denude your garden of organic matter by throwing it in the bin!
I have been known armed with a hoe to go out on an epilobium hunt in Winter and detach my epilobium rosettes all over my acre garden. I might on that occasion ignore any other weed but as I have mentioned at that time I have very few.

Most gardeners do not spray glyphosate in their own borders as I do. Many of my posts suggest how you might do so and one post particularly recommends the merit of spraying in Winter when many perennials are dormant. Even if this is more than you dare many gardens have open spaces that are very easy to spray. Unfortunately as mentioned in the middle of Winter epilobiums are pretty resistant unless glyphosate is applied at perhaps one in forty dilution of commercial 360gm per liter product. I often prefer to use MCPA that I buy as Agritox. Note neither of these products are to be found at your local garden center.
MCPA is an ingredient of lawn weedkiller and is not suitable between delicate plants. In my own case in the large spaces of Worsbrough cemetery where huge drifts of epilobium blow in every year and it is almost my only weed I use MCPA most of the time!
The good news is that when young epilobiums are growing strongly when it is warmer in Summer, glyphosate at 1 in 50 dilution will completely kill them. Unfortunately if they are already in flower it will be too late to stop them seeding before they die! There are many months in Spring and early Summer when glyphosate works very well!
The only good thing about epilobiums is that you have nine months of the year to control the tight leafy rosettes when ignorant observers take them to be garden plants!
Please note glyphosate spraying  is completely impractical  when epilobium is flowering in the middle of your plants. Just pull them out! When epilobiums are setting seed it is too late to spray.

I have just found a white one
Rosebay willow herb 

It looks very nice in Barnsley
Chamerion is a different kettle of fish to epilobium! Just as invasive as epilobium when it comes in with flurries of air born seed it is distinctly more perennial and as a perennial plant much more aggressive. Large clumps can cover the ground and survive for forty years. Probably much more if anyone had bothered to record them.
Acutely attuned to vacant derelict sites it is famously invasive of stony neglected areas. One of its names ‘bomb site lily’ says it all.

This strong stand In Tignes has colonized neglected land previously disturbed by cultivation
In actual gardening practice I personally find rosebay willow herb no problem at all! Although it does spread in from seed, unlike epilobium  it does not seem to establish all year round.
Your problem may very well be that rosebay willow herb has been standing many years on a site you wish to reclaim. If you use glyphosate it is easy and you will be rid of it in a single season.

Quite a good time to spray it here in September
Regular readers please bear with me if I repeat the rules for eliminating well established perennial weeds.

* Do not try to dig them out! Chopping the roots creates thousands of new propagules.
* Let the weed make plenty of top.  For the first application spray close to its mature size. It might be the end of May for maximum glyphosate absorption. It is useless zapping new shoots as they emerge.
* If you can obtain 360 gm/litre commercial glyphosate – it comes under many trade names as it is now out of patent – use it at about 1 in fifty dilution and thoroughly wet the leaves short of ‘run off’’.
* Several weeks later respray shoots you might have missed and any weed regeneration. They should be strong and green. Its pretty useless repeat spraying old half dead yellow and brown stubble.
* You might need to re spray two or three times to eliminate  a previously strong stand of rosebay willow herb.

Bits and bats
Most historical references to rose bay willow herb suggest it came to the fore in the UK in about 1850. Before that it was a rare shy woodland fringe plant. I find this difficult to believe when you consider most of Europe shares this now virulent weed. There must have been plenty of genetic diversity to be shared if plants hybridised together! One reference I found says in the US their plants have twice as many genes. Scientists recognize that ‘ploidy’ occurs in this genus.
Rosebay’s historical thuggish emergence is sometimes described as a ‘genetic mystery’. I suspect no one has really tried to find out.

Rosebay willow herb is a beautiful plant. It is also host to magnificent hawk moths. 
I allow a few plants in Worsbrough cemetery where it looks rather nice. When I started there were masses holding their own against the acre of brambles! The willow herb was much easier to eliminate.

When I took early retirement and became a freelance garden trouble shooter, plants lady, nurseryman and Chelsea winning flower arranger Jacky Barber hired me to do specialist jobs in her garden. My first task was to spray out weed in her overgrown herbaceous borders. There were masses of rosebay willow herb that I diligently sprayed. Jacky later informed me it was the white one that she treasured! She knew of course that one spraying would merely reduce it to manageable proportions.

She did not sack me! There are not many garden labourers who can eliminate well established perennial weed amongst herbaceous plants! Jacky is now a very dear friend!

Wednesday, 5 October 2016

How does water get to the top of a large tree? An alternative theory

Alan Warwick’s insight 

Although this blue eucalyptus on Hawaii barely achieves fifty metres another eucalyptus, Eucalyptus regnans can achieve a hundred metres
It is quite remarkable that water can rise to the top of a large tree. There would seem to be a limit to how high it can go. The world’s tallest trees is a coastal redwood Sequoia sempervirens which has achieved 116 metres. Some scientists have suggested that 120 metres is the theoretical limit to the height of a tree.

Imagine a hundred meter sports track, turn it vertical and add some more
David Attenborough did a TV programme from up in the tree tops. Apparently he illustrated nature’s achievement by pumping up hundreds of gallons of water. A huge red fire engine was parked at the bottom. Large trees raise water this high for themselves every day. 

The tallest sequoia in the UK - in Wales - is a mere forty metres. Introduced in about 1850 we do know not high it will go! I took this picture in Oxford 
Alan Warwick was a mature student at Askham Bryan College thirty years ago. As a retired ICI executive and PhD chemist he was a joy and a challenge. It was the one year certificate craft course in horticulture. Many great gardeners and horticulturists started their careers this way. Alan now tells me that he then knew nothing about gardening but had a vision of retiring to a garden and small holding. He now spends all and every day in his horticulturally fascinating acre. That’s when he is not sunning himself for two months every midwinter at his son’s in Australia! Now at 87 it is about time to tell his story.

Philip Orton was giving his botany lecture about water movement in plants. He explained the still current theory that water is pulled upwards in plants driven by the forces of leaf transpiration as they suck up water that evaporates from the leaf surface. The key element of this theory is that a thin tube of water molecules adhere together with considerable force. Whole columns of water are dragged up from the ground.
Alan went quietly apoplectic and had a mild  and discrete tantrum (give me a little poetic licence). At the end of the lecture he took Philip to one side. Absolutely impossible! Only botanists could believe such nonsense. Any self respecting physicist would debunk it.
As an industrial chemist Alan had experience of designing industrial solutions to carrying great quantities of liquid to very large heights. He immediately offered what he thought to be a much better explanation - the Pholé lift phenomenon. He has maintained this belief for the last thirty years.
Pohlé is a patented lifting system for fluids
I met Alan again recently at a social event. I later stopped by at his garden. It’s absolutely fantastic. I offered to use my blog as a public platform for his theory. I don’t expect my readers to judge an unorthodox theory any more than I understand it myself. Never-the-less the power of the internet is huge. Who knows who might read this from a Google search! 
Alan says he does not expect to live long enough for the botanists to be shown to be wrong!
You can read the modern synthesis of tree water uptake in this series of articles in the Scientific American

Alan Warwick

Alan now spends his time not digging and winning prizes for his vegetables and flowers
He was a model Askham Bryan student. I remember on one occasion when I mentioned chalk in my lecture about lime and a student asked me whether chalk was toxic. I flamboyantly raised a great cloud as I dusted the board and declared that it did me no harm (some hope of that). Later Alan took me on one side. No, my blackboard chalk is Calcium sulphate not Calcium carbonate, horticultural lime.
Alan actually listened to my lectures! In a throwaway line I once said that a greenhouse receives sufficient water in a year that if you could collect it all it would be enough to irrigate the plants within throughout the same year. He later put this into practice ! He purchased huge used dye vats from ICI for 'half a crown', transferred them home on the roof of his car. They are still part buried alongside the length of his very large greenhouse and they work very well.                                                                                                                                                                                                                                                                                     

Plenty of water here to irrigate his tomatoes

His cacti need rather less water and he has plenty to spare
He has been applying farmyard manure to the top of his heavy clay soil for the last thirty years with no cultivation. It is in superb condition and he wins all the prizes at local vegetable  shows.

Pohlé lift theory

Alan explained to me it is the same force that when chemistry school boys using pipettes get an air bubble in the tube and get a mouth full of chemical - in the good old days! As a former victim that represents a measure my ability in this area and my competence to judge Alan’s theory. 
A further example is when you open a glass of fizzy tonic and water overflows everywhere. When you pour your morning champagne it is what makes the glass spill over.
It is the force that is released when a dissolved gas is released from pressure.
Note that although I mention bubbles this does not mean that they occur in a plant stem! There are no bubbles in a bottle of champagne until it is opened or shaken.

More about the source of upward force
A plant exerts root pressure as a result of osmosis. It is a not inconsiderable two bars strength - don’t ask. According to Alan’s adaptation of pholé theory the sap as it rises is released from pressure and dissolved air is released and propels upward movement.
Although root water contains dissolved and hugely significant oxygen Alan considers there will be greater amounts of dissolved and more-soluble nitrogen. Nitrogen release is the same when an ascending diver gets the bends.
Alan’s personal experience of pohlé is when at ICI they designed equipment to elevate large quantities of fluid in an industrial process. Twenty gallons per minute were continuously lifted about eighty feet high. The elevating force was achieved by introducing compressed air at the base of the ‘tube’.
Alan says that he could use pohlé lift to force fluid in a capillary tube to the height of St Paul’s Cathedral!

Alan explains that in a plant there will be relatively gentle upward pressures from root pressure, capillary rise and pull from replacement of evaporating liquid. As the rising sap column proceeds the pressure will reduce and increasing amounts of gas released will speed upward movement taking water a very long way. Alan claims that if anyone measured internal pressure at intervals up the height of a very tall tree the pressure would gradually reduce and provide evidence for his theory.

Alan’s efforts to promote his ideas
If I might dare say so he was a little naive. He first wrote to David Attenborough who was very interested and in a hand written letter which Alan used to cherish suggested he approach the RHS! The RHS have an excellent science department that provides excellent advice to amateurs. It is not in their brief or inclination to promote new botanical theory. I do absolve their scientists of the dodgy science frequently purveyed in the RHS journal. I think Alan submitted to the Open University too. Again the wrong place.
Rejected, Alan took his bat home. But the flame has continued to burn


My own competence only enables me to throw a few straws into the wind.
Several forces are involved and work together to power the flow of water in plants. Root pressure is derived from the osmotic pressure generated in the root and is driven largely as a result of the pull across root membranes from dissolved sugars. Capillary rise and surface tension move water into small spaces. The fabled capillary rise is unable to pull water beyond thirty foot high. And even that could only be produced from a laboratory vacuum and forces that would collapse plant cells. In actual practical botanical terms capillary rise is piddling.
And of course in the standard theory the energy comes from the power of sunshine and the pull from the leaves as water evaporates. This Alan disputes and does not accept that water molecules hold sufficiently together

The well recognised phenomenon of root pressure is actually very significant and tends to be underrated in some text books. Any gardener knows sap’s exuberant rise in a tree trunk and branches in Spring. Wounded branches spill sap from up to thirty foot high. On deciduous trees there are not yet leaves to generate the botanists’ proposed pull. I wonder if any arboricultural readers can tell me whether such bleeding goes higher. Last year I watched my pruned leafless vine bleed profusely at ten foot high for more than a day.

I wonder how the alleged pull from the leaves starts up in Spring on very tall deciduous trees?

The physical effect of gas released from pressure is a very real phenomenon. One wonders when one considers a plant’s plumbing how it could not have an effect in a stem!
I am a great believer in evolution’s ability to exploit any available solution to a ‘problem’. If the pholé lift is real and it is possible to harness it nature would have found a way.

As usual when I have a scientific problem I turn to botanist Peter Williams. He is something of an expert on water movement in plants and is fascinated by it. He ponders about the sideways movement of water in a tree trunk. He is quite comfortable with current theory - but then as Alan would say botanists are.
Peter marvels at the surging rise of sap up a tree’s xylem and reminded me that xylem is a tube of dead tissue. (He of course accepts this as a simplification). He discussed the problems of living cells extracting water from the flow. His analogy was dipping into a surging river to extract water.

In a later exquisite explanation of the air and water pressures involved - I barely understood - Peter happened to mention that sometimes an air bubble breaks the continuous flow in an ascending xylem column and the flow interrupts with an audible plop. He discerned my face falling. This took the wind out of my attempt to bring together both theories. In conciliation he has sent me these beautiful pictures of guttation!

Guttation takes place through specialist cells

It is the way that certain plants reduce internal pressures when it is too humid for speedy evaporation
Many gardeners think they have a problem.They have not although the sap can be a bit messy
Perhaps I should take Peter to see Alan’s wonderful garden and see the sparks fly.

The worlds tallest trees are all evergreens and are almost all conifers. Huge(evergreen) eucalyptus is a principle exception. As you climb higher the leaves on extremely tall trees get very much smaller.

Alan’s parting shot. If the cohesion theory is correct then the pressure at the base of a  hundred metre tree would be about ten bars. You would need very thick stainless steel containers to contain such pressure
And his theory is not about bubbles in plants! (In this respect I misinformed Peter!)

My parting shot. The world’s tallest tree Sequoia sempervirens is thought to be an ancient hybrid between metasequoia and sequoia. A wonderful example of hybrid vigour

Final statements
As ever when I have finished writing further information is forthcoming. I present it as final statements for the two sides of the discussion

Peter Williams
Water simply moves from the soil to the air, via the plant because of a gradient of water potential and the existence of a continuous body of liquid water from the surface of soil particles to the cells lining the sub-stomatal cavities in the leaves.    
Bubbles are not needed to provide a ‘helping upward push’ because the suction generated by evaporation in the leaf  is quite enough on its own.  The air has enormous drying potential as we all know from the way clothes dry on the washing line, and water evaporation from puddles, or from the sea to form clouds in weather systems.  The air is usually so dry that it ‘sucks’ water out of the leaves of even the tallest trees.  To quantify this a little, we need to consider the units of water potential. The units are usually quoted in megapascals (MPa) and 1 MPa is equivalent to 10 bars (or 10 atmospheres in obsolete terminology). 

When air is totally saturated with water vapour, its drying potential is zero. There is no suction and water cannot flow. 
When the air is 99% saturated however- very humid indeed - it has a drying potential equivalent to 1.3 MPa, and on a typical sunny day when the % saturation might be 40%, the drying potential may be well over 100 MPa or 1000 bars!
Water will only leave the soil and enter a plant if the water potential of the plant is lower than the soil.  When soils are very dry after periods of drought, their water potential may be as low as the air on a sunny day and so water does not enter the plant and it experiences severe water stress and wilts.   Usually however, the water potential of the air is much lower than the soil and water flows through the plant.  This is possible because within the plant there is a continuous body of water throughout the   conducting systems.  This continuous body has to extend to upward of 100 metres in the tallest trees and this is possible because water molecules ‘stick’ together and to solid surfaces by hydrogen bonding.   Now, bodies of water in trees are subject to gravity and the even more powerful ‘suction forces’ of dry air.  The cohesion of water molecules is very strong and has been shown experimentally to be of the order of 3 MPa or 30 bars and has been calculated theoretically to be at least 10 times this value.  The observed value is strong enough to allow the continuous body water to extend upwards of 300m metres - far in excess of the tallest trees.
When plants are under severe water stress, or physically damaged by pests or diseases, the continuous water may be challenged and may partially fail.   This damage is localized because of the modular structure of the xylem – any bubble that forms is isolated within a single cell or group of cells, because bubbles cannot cross cell walls.  This is very important because the break in the water body would prevent water from being sucked up.   Bubbles would appear to hinder water movement rather than promote it!  Plants can cope with isolated components being bubble filled because the water can flow in the cell wall and thus bypass the bubble region.
In plants, and especially the tallest trees that are generally coniferous, there are no continuous columns of water.  The conducting elements are individual cells and do not form long vessels.  Water passes through tiny pores in adjacent, ascending cell walls that are too small to allow bubble movement.  

I feel there are numerous problems with the Pohlé lift mechanism operating in plants. 
(Peter wrote more…)

Alan Warwick
Thanks for your latest email containing Peter’s comments. You are not a nuisance. I have both the time and the inclination. Perhaps I have not made it clear enough. My theory is not a true Pohlé lift in that pohlé has no suction and no dissolved gases and relies on the air bubbles injected to lift the liquid in effect reducing the average specific gravity in the tube that my theory proposes.
If cohesion theory was correct, which it cannot be, the pressure at the base of a hundred meter tree would be about 10 bar and the root pressure would have to be more than this which it cannot be as the osmotic pressure is related to the difference in concentration of solute on either side of the membrane. 
The bubbles are formed by a reducing pressure from a saturated solution of gas in your article’s analogy of tonic or champagne. Has my mention of the tonic water confused?

There must be an unbiased Professor of Botany somewhere, with the resources and the courage to discuss with fellow physicists and engineers my theory.
Do you think it worth a mention that deciduous leaves are fragile and would collapse under the vacuum proposed by the cohesion theory?
With regard to Peter’s comments
he cohesion of water molecules is very strong as I explained in an earlier email. Water in the form of H2 0 only exists in steam and although without the cohesion of liquid water life would not exist it has no relevance to the cohesion lift theory. 
How difficult is it to make water droplets in your sprayer? In my day Peter’s cohesion was and probably still is called Hydrogen Bonding.
How many zillion molecules are there in a single string 300 foot high and why does a full vacuum only lift 30 foot?     
In my theory gas passes through the stomata as water vapour. As I understand it the cohesion theory says water vapour is formed by evaporation from the stomata. In the atmosphere the two theories have the same effect.
PS It was David Attenborough himself who referred my theory to The RHS who were his programme advisors. Soon afterwards I got the brush off. 
I was told “it’s cohesion and a continuous stream, no gas, and it was then I gave up.
Regards Alan

I wanted to end by asking whether I should in enquire whether it was ‘push or pull’ but Peter and Alan told me it was inappropriate!

I would rather have questions that can’t be answered  than answers that can’t be questioned
Richard Feynman

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