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)
- 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!
- 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.
- 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.
- 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?
- Winter cold promotes ‘bolting’ on such as overwintered onions and too-early sown beetroot.
- Traditional fruit growing practices such as ring barking and root pruning may induce flowering.
- 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
- 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!
- 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
- And what climate conditions create mast years where such as oak and beech produce prolifically. What synchronises flowering of bamboos over very wide areas?
- 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