Thursday 29 January 2015

Achimenes revisited

Some posts take on a life of their own and are visited many times! I wish I knew why and I would write a few more! 
Early on I did a series that I dubbed ‘Her indoors’ to identify my little forays into how to grow house plants. There is nothing in the title ‘Her Indoors 3’ to attract attention but there have now been 18,000 visits! It had languished at about fifty ‘hits’ in the whole of its first year!
I wanted to write just a little more about this easy to grow house plant and wondered about updating my original post. But no, why should I kill the golden goose? If it’s not broke don’t fix it!

For a plant you never see at the garden centre, achimenes is very popular and has been from Victorian times. I recently read a very long list of varieties grown in an iconic Australian glasshouse in 1850.
There is a huge range of colours which vary in habit and size. Some tend to be tall and floppy, some rather insipid and others weak growing. There are however a handful of magnificent varieties that will give you for very little effort, four months of glorious colour each summer.

My rock is still purple Achimenes ’Early Arnold’ but I wanted to tell you about my fun with ‘Inferno’ last year. I have never grown ‘Ambroise Verschaffelt’ but is well recommended with it’s lilac flowers with strong purple veins and sturdy constitution. It is a heritage variety, has an award of garden merit, and has been popular for at least 150 years!
I want to grow Tarantella again as we did in my old home. I think it’s my favourite with strong pink flowers which hang from beautiful, very healthy and glossy, slightly pendulous, almost black shoots.
Go to Dibley’s site to find some beautiful named varieties. Go to google images to find lots of lovely colours but rubbish identification. 

Overwintering in our frost free porch. There is no good reason not to cut off the dead tops. Except it helps me remember what’s in the pot!

Culture of achimenes

I gave you the formula for growing achimenes in my previous post. Withhold water and let them die down to dormant tubercles in October. Keep them completely dry and frost free in Winter. 

For demonstration purposes I have divided my old plant in January. Enough tubercles for three new plants (plenty more if I feel frugal). 

Start up again in late March, usually repotting and watering thoroughly. Beware not to generously water again until they start to become dry. Over enthusiastic new gardeners tend to overwater before there are any leaves to take up water and later in summer with plenty of top growth and high temperatures they don’t water enough.

There are many variations on the above formula that might be regarded as refinements or just my own slovenly practices. In Autumn I do not remove mine from their compost until I restart them in Spring. Tidier persons than me might separate the tubercles and keep them in an envelope. On balance I think my way is better as tiny tubers can dehydrate. In Spring I just crumble-out lumps of compost containing several tubercles and repot them back into a mixture of new and old compost. I reuse all the old compost and throw nothing away! I have far more tubercles than I need and I pot up lots of extra plants to give to friends.

I lie about my use of ‘proper’ compost. Regular readers will know I am one of the lucky few whose garden soil is suitable for potting. I enrich my soil with slow release fertiliser and later on top dress with my YaraMila fertiliser. Most gardener’s will need a proper potting compost. Nothing special, but remember as to quality, you get what you pay for and these days there is a lot of rubbish around.
I read that some gardeners like to use water absorbent gel as an additive to their compost. Perhaps this is more relevant in much warmer climes than the UK when the plants  can go outside in tubs for the summer!
I recommend regular liquid feeding, perhaps fortnightly from when new growth gets going. Alternatively you might prefer to infrequently top dress with fertiliser as I do.

My plants are grown in a bright east facing conservatory and receive direct sunlight from early morning until mid day. I think they like the fairly dry atmosphere and excessive humidity can be a real difficulty in wet greenhouses. They do not like their leaves to remain wet for long periods, especially when it is cold at night. Best not to wet the leaves when you water, although I usually fail. In my old home I was not allowed to water at all!

I have sinned and wetted the leaves when the weather has been dull. It’s difficult to avoid water scorch in humid glasshouses and imagine what a garden centre would do to them!

Let the compost get dry before you give a good watering and if some water drains through into a saucer that's alright. If they had got really dry, leave them to to suck back the water which has run through. Don’t of course leave them standing in water more than a few hours.
My adventure with Achimenes ‘Inferno’.

Brenda shouted at me when I described it as orange - “it’s crimson!”

Two years ago in April, Peter gave me a small pot of tubercles. As my ‘Early Arnold’ raced away they failed to appear. Only in August they emerged and made weak pathetic growth and hardly a flower. 
I gave the stronger dormant tubercles a second chance last year. This time they did not appear until the end of September when my other achimenes were fading!
But how different from the previous year, they grew strongly and produced a continuity of magnificent scarlet flowers from late October until early January. They have been absolutely superb.
They have only now in February died down. I can’t wait to see what they do in the coming season. Should I start them later than the others? I don’t think so. They won’t clutter our conservatory whilst I wait for them as I start my plants out of the way in a warm porch.

All has been explained now I have checked out my plant on the net. It’s  actually called Achimenantha  x ‘Inferno’. It’s not a straight achimenes, it is an inter-generic hybrid, achimenes crossed with smithiantha! It looks identical to other achimenes and I guess there must have been some back crossing.

Considering  my recent posts on hybridity, it’s quite ironic really!

(I have just submitted to temptation and ordered six new varieties from Dibleys and will update this post in six months to report on their progress)

(To read my other efforts with house plants put ‘her’ in the search box at the bottom of the blog scroll)

Wednesday 21 January 2015

Is the no-dig-gardener still not digging?

A most definite yes!

For someone who posts as a no digger I have recently written very little about it. It’s just that over the last two years I have run parallel series on the detrimental effects of digging and another on why gardeners dig. The ‘why dig’ series took a broad definition of digging and included most of the legitimate (and also rather less usual) reasons why gardeners disturb the soil.

I have not changed my mind and all those writings are as relevant now as when they were written. I do not want to repeat myself (well not too much!) and will help you at the end of this epistle to find posts that you might have missed. Initially their titles did not indicate the actual content and I am starting to amend them.

Is it appropriate that a man with a spade is the house name logo on our home?

I have been a none digger nearly 45 years and my thinking has changed in one small way in recent years. Although I still shudder at the sight of fluffed up and loosened soil and cringe at the harm unnecessary soil disturbance creates, I am not as doctrinaire as I used to be when I used to think almost any soil breakup was a sin! 
Damage to soil’s structure happens. I have indicated many legitimate reasons for ‘using a spade’ such as planting, dividing, lifting root crops and burying things (not normally soft vegetation, nature does that for you).  My own soil gets loosened by the wretched rabbits and moles! I just kick it back and it sometimes looks tidier than my liverwort. Soil is actually very resilient. It has to be when you consider the dreadful things gardeners do to it!

My small, stainless steel border spade is sharp, light and easy to use

I once pondered doing a post about the legitimate uses of a spade. My small stainless steel border spade is my favourite tool – but in my own gardens never for conventional turning over! There are a myriad of operations you can do with a spade such as planting, dividing, scraping, edging, shallow hoeing, chopping out, digging holes and mixing compost. The uses are endless but I don’t want to bore you.

A recent visiting party was perplexed and could not understand what a no dig garden must be. They asked Brenda “does he rotavate?” Some gardeners never get past the false notion that soil management is only one step removed from playing with buckets and spades on the beach!

I should no longer fear that the world is against me! My informants tell me that some great TV gardening gurus have recently stated that ‘no dig’ is the future for amateur gardeners.

I am sometimes asked if no dig is so good, why do farmers plough and cultivate to smash up their soil?

My first answer is that many growers of perennial crops such as fruit don’t do much cultivation. I also point out that fewer farmers now leave their roughened soil exposed to the so called ‘beneficial’ effects of the Winter and very soon after harvesting the next crop goes in. Farmers now generally cultivate less deeply albeit interspersed with an occasional ‘deep busting’ of plough pan compaction.

My second answer is that farmers are a conservative bunch and everything in their world is built around conventional ploughing. Machinery and equipment is not geared to none cultivation.

Perhaps closer to the truth is that cultivation enables rapid turn arounds between one crop and another. Sheer brute force can be used to carry out operations at specific times when contractors are available. No matter if soil structure is destroyed by heavy equipment on wet land when harvesting. It can be broken up again by the next cultivation. It might use a great deal of energy but farming methods do work and produce very high yields. As Jethro Tull discovered all those years ago.

This cultivation needs a great deal of energy and has a huge effect on soil structure

There are certain weeds not easily controlled in farming without conventional cultivations. Direct drilling into fields of cereal stubble was once thought to be the way forward, especially facilitated by burning, but we don’t like smoke and fire. Unfortunately decaying stubble produces natural herbicide toxins - the same ones that kill algae when gardeners float barley stubble on their ponds. I have the same trouble when I have accidents with glyphosate on my lawn. Just scattering grass seed onto the fresh yellow patch does not work!

Even in farming - especially outside the UK - there is much interest in no till methods.

Our walk in the country was not ‘a walk in the park’

We have recently taken to walking local public footpaths over the fields. It has been such a nice Autumn but very wet. Some of the footpaths across fields are ploughed and cultivated and then reinstated as the law obliges. What a wet podgy mess to walk on!
Contrary to popular opinion, cultivation does not usually improve drainage - not unless severe compaction already exists and pans need loosening. Very often such compaction is the consequence of previous cultivation! 

Only lone signposts registered our way. You were actually walking on water soaked fields of newly sown cereal or grassland. Our feet sank in and caused structural soil damage and we got very muddy wellington boots. No wonder conventional gardeners are instructed to never walk on wet soil.

To me the biggest advantage  of minimum cultivation, is that you can walk and work on firm settled wet soil whenever you want to without causing any damage at all.

What a contrast when we walked on footpaths where it had been pasture for several years. It was firm and well aerated and surplus water had run rapidly away through all those un-smashed natural worm and root-made channels. 

I must qualify this statement because whether you cultivate or not, drainage only takes place if water has somewhere to drain to. Sometimes  ease of water penetration is only half of the story and land drains are needed.

The farm field next to my own garden is ploughed once a year.  
The soil has benefited by a year of none cultivation before it is due to be ploughed again
In the garden, no dig advantages come through slowly in the same way. Unlike the farmer, don’t spoil it by digging and your soil will improve year on year.

My post on mycorrhiza explained how these fungi can establish in none dug soil.
Essential in nature, I  wonder how many mycorrhiza actually  get going in a highly fertile garden soil. Even when un-dug.

How to find my previous posts on ‘reasons to dig’ and the ‘reasons why not’.
To find previous posts about digging, go to the search box at the bottom of the blog scroll. (The box at the top gives far more limited results).
Merely insert either the single words ‘reasons’ or ‘why’ to find them all!

Monday 12 January 2015

Hybridity in Evolution

How hybridity is often overlooked in evolutionary theory
Part 2

There are tens of thousands of new species that are known to have have arisen naturally from crosses between similar species and infinitely more at the plant and animal breeders’ hand.
I know of no verified cases (as opposed to assumed cases) where simple natural selection of the conventional kind has created a new species and yet conventional wisdom always states that in the absence of evidence of hybridity, that for every new species discovered, accumulation of slow small Darwinian changes in a straight line was how it evolved.

You will imagine by now that I claim hybridity leads to dramatic changes in plant and animal form. Sometimes it does and hence my comments in my previous post about abrupt new appearances into the fossil record. More usually changes are relatively small and indeed new hybrids are mainly between similar species and are of intermediate form. Such change is normally diluted when a new hybrid and its off spring repeatedly backcross with one of the parent species. An exact parallel with normal plant breeding.

The genes in this rose are of worldwide origin and have been introduced from many hybridised species 

Many naturally occurring species of rose  have contributed to modern garden forms and their breeding has continued from ancient times. In most cases the contributing species would be quite incapable of directly fertilising one another. How can it be that genes from such plants can be shared?  I will answer this vaguely but to say that frequent backcrossing and recrossing creates fertile hybrid plants where sharing of information between formally distinct forms can be made.

Hybrid lilies are frequently more fertile than their parents

Can such ‘sideways transfer’ of genetic  code be equally subtle in nature? Imagine species A can successfully, albeit rarely, hybridise with species B. And species B is able to hybridise with species C, but species A will not cross with species C. If an AB hybrid lives in a zone dominated by species B, after repeated backcrossing it is effectively subsumed into species B. Never-the-the less some genetic information has moved from species A to species B. When the modified species B hybridises with species C, genes from species A will enter the genome of species C!
This is not something from my fevered imagination, it really happens. And one might say “and so on ad infinitum”. When I wrote recently about mistletoe my title was ‘So good nature invented it five times’. I am beginning to wonder, tongue in cheek, whether nature invented it once and it was passed on!

My recent post on holly discussed how holly evolved a shared ability with other genera in ancient laurel forest  to cast off water by developing waxy and elongated leaves and pointy leaf drip tips. Convergent evolution might very well correctly explain such relatively simple modifications. But really?

A short horsey digression

At the end of the nineteenth century, a museum assembled a demonstration of purported successive fossils that demonstrated the slow evolution of the horse over tens of thousands of generations of accumulation of small changes. This sequence appears in almost every school text book that teaches evolution.

There is no doubt of the accumulation of small changes over the millenia, just doubt that the changes were in a single species, were in a continuous straight line and were not punctuated by a series of small advances as closely related species bred and created new genomes. Hybridity theory explains the evolution of the horse in a much more better way.
Most geneticists are ashamed of the claimed sequence of horse evolution and there is no certainty that all the supposed ancestors are actually linked and at least one is in the wrong order of time.
No longer on public display, this historic ‘teachers demonstration’ languishes, in disgrace in a museum dungeon!

I am NOT suggesting that the evolution of the horse is not reflected in the generalised picture painted by the fossil record. I am suggesting the progression is not in a straight line but in a series of small hybrid leaps and might be described as rather reticulate. No doubt numerous close hybridisations occurred ‘along the way’ in a similar manner when in our own ancestry, neanderthals and denisovan genes entered our genome.

Some stories of plant hybrids

Fatsia crossed with Hedera gave the interspecific hybrid Fatshedera x lizei (and subsequently a specimen ‘sported’’ to give Fatshedera x lizei aureomaculata)

If you read wikipedia you will find that  the evolution wheat is a result of a series of mutants. Clearly written by a politically correct hybrid denier!

Closer to the truth (but not exact) is the following hypothesis. Neolithic farmers grew starchy grasses. Wild einkorn Triticum boeoticum and goat grass Aegilops speltoides hybridised together to produce emmer Triticum dicoccoides. Emmer subsequently hybridised with another goat grass Aegilops squarrosa to produce durum. Several promiscuous relationships with the original parents were to produce wheat. There is of course no reason to deny that there might also also have been beneficial mutations ‘along the way’.
Conventional  opinion is that these crosses were all natural hybrids and man’s only contribution was to sow them together and opportunistically select out improved forms. Certainly true, but I wonder when ancient man, who was much closer to nature than ourselves, began to transfer pollen?

Forty years I rooted a cutting and (to my current regret) subsequently planted it.

The Leyland cypress, despite my generally snide comments makes a very fine tree. It is a bigeneric hybrid between Xanthocyparis nootkatensis and Cupressus macrocarpa. It is recorded to have naturally occurred in gardens on at least three occasions.
It produces fertile seeds albeit rarely. Not unusual for a hybrid and one wonders in the absence of man’s propagation whether it would survive in nature. Read RHS botanist James Armitage who discusses its fertility.

You might wonder where each of the fifteen known cultivars of Leyland cypress come from. One of three mechanisms will be involved - vegetatively propagated mutation (often called a ‘sport’), selected fertile seedlings or re-creation of the original cross by a plant breeder.

I can find in my garden several examples of plants that are interspecific and intergeneric hybrids. Apparently crosses as distant as between different families have been recorded although I cannot find in the literature suitable plant examples. 
There may not be any reason to think that distant crosses are more significant in evolution than an accumulation of repeated smaller hybrid ‘advances’. Distant crosses in nature are extremely rare with odds against their occurence sometimes many millions to one and odds against any such a hybrid being fertile and having selective advantages make the likelihood of survival extraordinarily small  - but not vanishingly small. On the scale of evolutionary time such events would seem likely!

I was interested to try and find references to very distant plant crosses. The strangest I found was this ‘proof of principle research’ where oenothera pollen was transferred to oryza (rice). I am afraid I did not fully understand to what extent the cross was successful and if you are interested you can read it yourself!

On further reading I discerned that this transfer of the genetically distant pollen was followed 48hours later with normal self pollination with another rice plant. The resultant seedlings showed marked differences to normal inbred rice. There was no evidence of actual transfer of distinct oenothera genes although such gene transfer is not unknown. Several generations of inbreeding were subsequently studied. In several lines there had been restructured patterns in the rice genome and significant epigenic  change. The researchers postulated that such novel hybridisation would occur in nature.

Oenothera is regarded as something of a genetic maverick that does not obey simple Mendelian rules

I have written before about that ‘alien invader’ Rhododendron x super ponticumin my post ‘Musings from York’. Peter Williams also eloquently explained in his guest post ‘A passion for rhododendrons’ how interbreeding between doubtfully hardy Iberian Rhododendron ponticum and three other introduced species created thuggish and very hardy Rhododendron x super ponticum, now described as a hybrid swarm.

Peter tells me that the chances of a plant invading the countryside is a mathematical thing and these opportunities are vastly increased when there are large numbers of seeding plants growing together. Historically the new hardy ponticums were widely planted on gentlemen’s shooting estates. Seed was very cheap and quickly scattered by unskilled labour was very fecund. There was every opportunity for the plant to become an invader.
Peter tells me that in Norway where the climate and soil is infinitely more suitable for rhododendrons, without our mass planting there is no R. x super ponticum in their countryside at all!

The term ‘hybrid swarm’ puzzled me as it suggests plurality. R. x super ponticum is regarded a single species but is highly variable and readily self and cross pollinates with itself and no doubt with garden forms. Within a large clump in the wild there may be separate seed sown clones but all are regarded as the same hybrid species.

In view of the evolution of Rhododendron x super ponticum here in the UK perhaps we should restore its good name by dubbing it native?

The interspecific hybrid Primula kewensis appeared at Kew in 1900 growing amongst Primula verticillata and Primula floribunda. Genetic analysis confirms that it is a hybrid.

  plant world seeds                              

P. kewensis is a yellow primula covered with lovely mealy white farina.
For many years it was sterile - a very common feature in new hybrids - and was propagated vegetatively by division. Several years later it produced a fertile flower and there was an increase in plant size. It had doubled its chromosomes in a vegetative mutation to create a tetraploid shoot. Described as a ‘failure of mitosis’  this has occurred on the sterile form on three separate recorded occasions. Polyploidy enables efficient pairing of genes in meiosis and is often exploited by plant breeders.

P.kewensis now prolifically produces fertile seed. The young plants show no variation other than the degree of farination. That’s very curious and indeed is a very interesting genetic story, but not for today!
As a no dig gardener I was fascinated to see that some of the early research was carried out by Miss Digby.

Senecio squalidus is native to Mount Vesuvius and was an early guest in Oxford Botanic garden. It escaped over the wall, or more accurately into the wall and then over! It is known as the Oxford ragwort.
The railway line is thought to be the agent of its spread. There is a story, probably fiction, that a botanist traveling by train observed a seed float into his carriage. At the next station it floated away onto burnt vegetation on the railway banking.
At several locations S.squalidus is known to have hybridised with the common weed groundsel Senecio vulgaris. The Scots and Welsh versions are now known as the Cambrian ragwort and are very similar. 
More recently the Oxford ragwort travelled to York, my home town, and again procreated with groundsel! This time to give a very distinct plant from its Celtic relations. Unfortunately the York Parks Department sprayed the York ragwort away where it was flourishing under Lendal bridge. Was this vandalism or a service to humanity? Fortunately the botanists have a large supply of viable seed for future investigation.

An interesting point is illustrated in the fact that the Cambrian crosses are very similar and that our York version is completely distinct. Geneticists  agree that depending on which of two hybridising species is the male or female parent, their can be a profound difference in the character of any offspring. Peter tells me that the direction of the York cross is the odd one out. Unfortunately my fount of all wisdom is now on vacation!

Animal stories

Duck billed platypus

When you have eliminated the impossible, whatever remains, however improbable must be the truth. (Conan Doyle)

If ever there was a candidate for being a hybrid it is the duck billed platypus. What a mixture of mammal and bird characteristics! It was shown in 2004 and then confirmed in 2008 when its genome was published, that at a genetic level it shares sex chromosomes of both mammals and birds.
Now I have no idea whether it really is a hybrid and must conclude I am missing something when none of the scientists involved in deciphering its genome seem to have considered that the said platypus might be of hybrid origin. Are they so indoctrinated in current theory that they give it no consideration? Do they fear they will be subject to ridicule? Are there no research grants because the idea of hybridity is so grotesque? It is apparently extraordinarily difficult to demonstrate hybridity from the map of the genome - you can see what is there but is very difficult to elucidate where the genes have come from. In the case of Duck Bill, no one seems to have tried.
It is even quite difficult to show that even a modern plant of known hybrid origin is actually a hybrid from it’s genome alone. From millions of years ago it must be virtually impossible.
Look at Eugene McCarthy’s list of bird characteristics sported by a duck billed platypus! 

The more original a discovery, the more obvious it seems afterwards. (Arthur Koestler)

Bird family tree

Another matter concerns me. An excellent huge co-operative study claims to have accurately elucidated the descent of birds from dinosaurs. There are a few surprises in the developmental Darwinian ‘tree’ but never the less it seems to fit fairly closely with expectations. It is recognised now that the dinosaur was the ancestor of birds and the bird that resembles it’s ancestor most closely is the common chicken. The hybrid history of the hen would appear to be very simple (although it probably isn’t) and it results from a hybrid cross between the grey and red jungle fowl. Both parents look very similar and such ‘close’ hybridisation in relatively recent times (several thousand years) does not challenge its certain evolution from dinosaurs (note my provocative plural). Regarding the chicken’s ancestry scratch around in friznecker’s blog and find some very juicy worms.

Is this Kafkaescue comedy or am I just cynical?

Are they throttling the black swans?

Apparently the analysis of the bird data was analysed by a process called ‘statistical binning’ This is way-way above my comprehension and I am sure that it is statistically valid although I am reminded of the phrase ‘rubbish in, rubbish out’.
Now I know statistical binning does not literally mean ‘ignoring inconvenient data’ but I really do wonder. Especially so when they are happy with the result when the previous standard method of analysis shows a much more jumbled inheritance. A jumbled result is what you would expect if ‘inconvenient’ genes had been introduced by hybridisation.

Or just strangling the chicken?

I asked Peter whether I should write these provocative words. He advised that I should not let the facts get in the way of a good story! I am concerned that the idea of the exclusivity of ‘straight line inheritance’ is held by some evolutionists with such conviction that their eyes are closed to any contradictions.

Daphne ‘Eternal Fragrance’ is an exciting new interspecific hybrid that ticks all the boxes for a fine garden plant. Mine showed it’s hybrid vigour by flowering repeatedly from the day I bought it in April right through until Christmas. (Note the ‘drip tip’)

I promised a third part to my hybridity story. Unfortunately their is so much to say about the fossil trees and other items and I am afraid there will be even more!

Link to Part Hybridity Part 1

Monday 5 January 2015

Why does a plant fail to flower?

Gardening myths discussed. “Give ‘em some potash and get ‘em to flower!

My abutilon has flowered all summer and continued up to Christmas

It’s a hoary old question on GQT and similar programs. Why does a plant fail to flower? 
Recently, after giving quite sensible advice the ‘expert’ hesitated and thinking perhaps she had not filled her time, rather unconvincingly added that you could of course give them some potash. I am not quite sure she believed it herself. When stumped by the question in front of an audience it just trips off the tongue. Shame on me I have done it myself!
I wonder how many people go out and actually apply sulphate of potash after such tosh. I am doubting today whether it will make any difference whatsoever whether a plant does or does not flower. 

Perhaps if the punter applies a high potash general fertiliser which contains a balance of nutrients, improved nutrition might very well increase the quantity of flower - but then it will often make a bigger healthier plant where all aspects of growth are improved.

I find myself thinking today that in seeking reasons why plants really fail to flower I might be promoting equally mythical gardening lore. It’s always a problem when what one assumes to be ‘a given’ is also untrue!

A little knowledge is a dangerous thing! At his Open day my friend Peter Williams was selling stunning rhododendrons in full and magnificent flower. A visiter commented that he would not touch them with a bargepole, they were destined to die! He had confused the situation where plants near to death sometimes produce a flurry of flowers in a last gasp attempt to procreate. Peter’s plants were flowering well as a result of being so healthy!

I described in a previous post that whilst I do not fear the effects of honey fungus in my garden I was suspicious that my very old lilac was showing signs of infection and would probably die. Despite Brenda’s own ominous prediction, last June it flowered absolutely magnificently. It did not make very much new growth last summer and the leaves dropped early. Brenda again predicts it’s imminent demise. My own hope is that at will again produce generous flowers. 
The strong basal shoot on the lilac is well on the way to making a new tree. (It’s not grafted, so the sucker comes ‘true’).

My lilac photographed in December. Already in January I can discern healthy buds

You can see the armillaria (honey fungus) fructification which is very close to the lilac and the Spartium junceum.

A second flowering in December, not because of stress, it is very healthy, but because of the mild autumn

Reasons for not flowering
There are very many varied and distinct reasons why plants do not flower. Most are matters of plant physiology where a plant is reacting to environmental stimuli to achieve efficient seed production.
For many perennial plants, especially shrubs and trees, there is the not so little matter of juvenility. Many woody plants have a juvenile phase when they are incapable of flowering. For some plants this period may last many years. Sometimes a gardener’s activities may prolong this phase. For example beech - not that you are bothered about flowering! Beech when grown as a hedge retains its dead leaves right through the winter and this characteristic is maintained indefinitely by regular clipping. When a beech grows as a tree it retains this character for several years but eventually achieves autumnal leaf abscission and normal leaf fall and capability to flower.

Often the mature flowering ‘adult’ form of a plant maintains its ability to flower when it is propagated by vegetative means such as cuttings or grafting. Ivy is a well known example where the difference between juvenility and maturity is very clear. The flowering tops of an old ivy will retain the ability to flower when cuttings are rooted, but not always the ability to climb. Juvenile ivy climbs remarkably well!

Adult Paddy’s Pride retains its ability to flower after propagating from cuttings. It no longer climbs but manages to scramble

The practical significance of the phenomenon of juvenility is that some seed raised  perennial plants will not flower for several years. Fear not, there are not very many of them that you are personally likely to sow. 
Wisteria is a classic example. I imagine that my first wisteria must have been a seed raised plant. It took fifteen years and when it flowered it was a huge disappointment! 
I know now I should have bought a grafted wisteria. Best to buy one in full flower at the garden centre and you can see what you are getting. Even then they are liable to sulk for a while. I would not bother with any extra potash!
Sometimes a wisteria graft fails and you buy the sprouted rootstock. That will be another fifteen years sir, to achieve inferior flowers!

For brevities sake here is a list of examples of other factors that might control flowering!
(sorry about the numbering, it's beyond my technology)
  1. Stress does not always promote flowers, sometimes the opposite. If magnolias, camelias and rhododendrons suffer drought stress in late summer and autumn they fail to make flower buds.

My camellia has made nice fat autumn buds
And so has the rhododendron 

And the Magnolia is wanting to flower in January!
  1. Some plants respond to day length. Chrysanthemums are short day plants and flower when the day length is shorter than a critical number of hours. Spinach is a long day plant and unfortunately goes to seed in the middle of the summer.
  2. Some plants require critical temperatures to flower. Early autumn chrysanthemums respond to higher temperatures rather than day length.
My pom-pom chrysanthemum flowered for ten weeks from mid August.
  1. Some plants such as campsis as are said to need ‘ripened wood’. I am not sure what this means and I fear it might be a myth. Or might it just be low temperature or even low light intensity that prevents flowering?
  2. Winter cold promotes ‘bolting’ on such as overwintered onions and too-early sown beetroot.
  3. Traditional fruit growing practices such as ring barking and root pruning may induce flowering.
  4. Inexperienced gardeners prune shrubs such as forsythia, philadelphus and weigela at the tips and in the wrong season and cut away next years flowers!

Brenda was a little over eager to tidy back the Garrya elliptica last summer. Fortunately she did not prune over most of the plant
  1. Rarely light intensity might be significant - I think!  I have never known an avocado pear flower and set fruit  in the UK although it grows very well (inside). My dipladenia failed to flower all summer in our conservatory and I concluded it was too shady. I went to Italy and in a very dark courtyard it was flowering magnificently! Wrong yet again!
  2. Actually light intensity for house plants can be very significant indeed where a plant does not photosynthesise enough to make sufficient sugar to support flowers. My Hoya carnosa merely made healthy foliage but no flowers for ten years at my previous home but now in a light position it flowers superbly.

Hoya carnosa in our east facing conservatory
  1. And what climate conditions create mast years where such as oak and beech produce prolifically. What synchronises flowering of bamboos over very wide areas?
  2. And how can you prune fruit to avoid fruit biennial bearing?

If you can add to my list, please do so in my comments column. I welcome participation!
On the subject of participation it is always me that does the spouting. Please feel free to argue!

My Aster amellus gave me an extra flower in the wrong phase.
So what about potash?
I am comfortable with the idea that high potash might promote quality of flowering and fruiting. With reservations I might even accept the notion that potash  balances excessive nitrogen that might otherwise promote excessive leafy growth. What I do doubt is that potassium ever induces flowers where they would not otherwise arise.

And a little story

‘A Woman, a dog and a walnut tree, the more you beat them the better they will be’.

Many myths surround walnuts. Real Greek and Roman ones! 
Most walnut myths seem to be about throwing sticks to knock the nuts down! This seems to have evolved into the idea of beating the bark to encourage fruiting.
(One might explain this claimed fruit promotion in terms of plant stress or translocation of sugars).

I am more inclined to believe the man who wrote on a well known gardening blog that the first two strictures did not work and he therefore doubted the third

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