Saturday 27 July 2019

The magic of silicon

The nutrient that isn’t - but (for the sake of the planet) ought to be

There is more silicon in this equisetum than all its other soil absorbed nutrients put together
Spoiler alert, my post today is unlikely to improve your garden one jot. It is highly unlikely your garden is deficient in silicon. Next to oxygen it is the commonest mineral on the planet and for most British soils, plants have free access to it. The mineral content of my own soil is almost all silt/sand - almost pure silica rock.

The boffin’s definition of a plant nutrient is a mineral essential for a plant to complete its life cycle and is a constituent of a least one cellular structure. (I am not sure how completely essential potassium satisfies the latter criteria)
Silicon fails both tests. Plants in hydroponic solutions grow perfectly well without it and to all appearances it appears in the plant only as elegant crystalline deposits.
One might add in most laboratory containers such as glass ones, it’s almost impossible to avoid the presence of very small quantities.
The cynic might claim that our laboratories who omit silicon in their hydroponic nutrient solutions create plant artifacts and then draw false conclusions. Such conclusions might have worldwide significance.
The undisputed truth is that grown in the soil plants absorb substantial amounts of silicon. Levels comparable to that of the major nutrients. Sometimes very much more. Ten percent dry weight of plant tissue has been recorded in certain grasses!
It was once thought that silicon merely entered and was passively dispersed in the plant with the movement of water. It is now known that like recognised nutrients it is actively absorbed. What’s more this very insoluble nutrient is within a soil’s biosphere  converted to a solubility comparable to all the main nutrients. 
This high level of solution greatly exceeds that which might stray into scientist’s glass bottles - unless soluble compounds of silicon are added as they not normally are.

Significance in the garden
So silicon is not a nutrient, not necessary for plant growth and is most unlikely to be deficient in your garden. Why does it matter?
There is a small possibility if your garden is on a highly calcareous soil or a reclaimed moss peat many miles away from a supply of wind blown siliceous erosion it just might be. 
Apparently the Everglades are deficient in silicon

You might live in the Florida Everglades or are the proud owner of a rice paddy field. Seriously, there are huge silicon-deficient zones out there in the big wide world.

What is of interest - albeit being beyond your gardening control, is that silicon although not essential for plant growth does wonderful things to enhance it.

Benefits of silicon to plant growth
Most of these are due to its hard crystalline nature and its ability to harden plant tissue. In terms of plant evolution it is much less ‘expensive’ than manufacturing lignin.

My giant miscanthus stands like a soldier without any need for staking
1. Although not essential for plant growth many plants grow better, sometimes very much better, when they have access to silicon. For some crops, yields are increased and for flowers they might be bigger and hang more erectly. 

2. Similarly leaves may present themselves more efficiently to sunshine.

3. The structure of the plant is more stable with respect to lodging down in wind and rain.

4. Silicon interacts with other elements in plant solutions and toxic effects of such as excess manganese are reduced. There are advantages in surviving in polluted or salty soils.

5. The toughening of cell walls make them more difficult to penetrate by fungi and give a much enhanced resistance or tolerance to many fungal diseases.
Similarly parasitic plants are less able to penetrate. This is of huge importance for certain world crops.

6. In a similar vein plant pests less readily chomp tissues and for world crops' breeding programmes are seeking to select for tougher and more effective silicon deposits (phytolyths)

7. Structural effects on stomata enables plants to reduce transpiration in drought conditions

8. Root growth can be increased. 

The latter two points are of huge importance in breeding plants with enhanced capacities to absorb silicon and help tolerate climate change

YESI - York Environmental Sustainability Unit
My new awareness of the benefits of silicon came when I attended a lecture at the Yorkshire Arboretum by Professor Sue Hartley from the above organisation on the subject of  sustainability of world food production.

She never mentioned bees once! Tell that to Monty - for the world’s major foods (rice,wheat maize and potatoes) bees are almost irrelevant! (That is not to say that together with wasps they don’t do wonderful things and we would not want to be without them).

The above picture is take from the YESI website and shows two micro pictures of silicon deposits on deschampsia grass. On the right extra silicon has been laid down in response to pest damage
Sue's lecture reported the benefits of silicon in world rice production where it is already applied as a fertiliser which is commercially readily available as a by product of industry. She showed wonderful micro pictures of the arrays of silicon phytoliths and showed how conventional breeding programmes (informed by gene manipulation) were being used to enhance rice silicon uptake and effective distribution of these crystalline deposits. If you were a chomping insect you would despair for your mandibles.


No shortage of silicon on this railway line
The weed variously described as horsetail or marestail is one of the very few plants that seems to require silicon for long term survival. It contains more silicon than all the other soluble nutrients added together and in almost all of its cells. So much so that one common name is  'scouring rush'. That says it all. Now I understand why it is such a noxious weed on sandy York allotments!

Equisetum hyemale
Silicon is the reason why marestail's hardened surface makes your weedkiller run off. Many gardeners bruise its leaves to increase absorption or use a very fine spray that dries on the the leaf and stem surface.
I wonder if any readers have soils that are too low in silicon for this weed to grow. Such lucky people might have an organic peat soil or one so calcareous that their sand and silt is entirely composed of calcium carbonate. I would be interested to hear. (On second thoughts perhaps I should omit 'lucky').

Silicon helps keep the tubes rigid
You can even buy the stuff
As mentioned, don’t rush out and silicon feed your plants. Silicon is even a constituent of tap water. Beware of siliceous charlatans who will seek to sell you extra.

I think it a mistake to regard silicon as a trace element. Plants use it in much more substantial amounts than that and I think many laboratories who do not add it to their solutions really might jump to suspect conclusions.

Are our own plants in the UK ever deficient? I am unaware that they ever are. I mischievously wonder if soft growth in garden centre plants grown in such as peat or other exclusively organic composts and grown dependent on extensive liquid feeding might ever be deficient. The industry seems to be becoming aware of its importance in respect of plant quality. It would be nice to buy plants that do not keel over and die as soon as we get them home.

Another straw in the wind of the benefits of tissue hardness is that one Dutch turf breeder now classes his grasses from hard to soft. Grasses are being bred and graded with varying silicon geometries.

So what about my title "for the sake of the planet?" The world's most important food crops are all grasses which contain much silicon. Some of the world's soils are deficient. 
Improved silicon uptake by either fertilisation or better absorption and utilisation as a result of plant breeding have great  potential. 
There is a perceived need for less reliance on pesticides in newly bred crops. Tough silicon tissues might fulfill some of this need
There is a need for greater plant drought resistance and tolerance to climate extremes. Stronger root systems seem to be promoted by the action of silicon. (Perhaps it is no surprise that gardeners marvel at the depth that the roots of equisetum goes to). 
There are huge crop losses due to crop's lodging over.

There is innovative research proceeding on all these fronts that involves silicon.

Better silicon nutrition might very well have a role in feeding the world 


Forgive me for demoting bees as agents of world food production. I really do love them

I rambled about hard and soft growth

I hope YESI do not mind me using their picture

My opus on controlling equisetum

Wednesday 17 July 2019

Leaving Dahlias in the ground overwinter

These dahlias have remained in the ground for five years now and.....
...  were all raised from seed
The normal way to overwinter dahlias is to lift them after the frost turns them black and to store in a cool frost free dry place. Not one for following careful instructions it has not been always successful for me. Well documented elsewhere I do not propose to describe how today!

A beacon for drivers for five months of the year
For several years now I have left my dahlias in the ground. Not always successful I do have by now strong plants that I can more or less rely on. Some have survived for up to a decade. Through the last two mild Winters I have not lost a single plant and with self seeding my stocks have increased.

Would any survive another 2010 Winter when temperatures of minus 20 centigrade persisted for six weeks or more and cold penetrated deep in the ground? They would not.
I would buy some more and start again. 
No doubt there has been some self selection of the hardier kinds. Those that have come back each year have liked my conditions. In passing I might mention their are some species of dahlia more regularly regarded as hardy. A particular favourite is Dahlia merckii.

Over the wall Dahlia merckii sets off 'wildflowers' in  the farm field
Last year this Dahlia merckii sowed itself here
If you live in colder areas than I do or have heavy poorly drained soil my methods will not be suitable for you. If you live in the balmy south-west I suspect it is the normal method.

 I would love to hear reader’s experience and receive their opinions. I don’t live in hope as other than my much loved and appreciated stalwarts most readers seem reticent to offer an opinion. I often feel I have failed and my only conciliation is that many other garden bloggers share this frustration.

How things have changed
Seed-raised from The Bishop of LLandalf

In my youth I would have considered leaving dahlias outside through the Winter as foolish. I also considered them gaudy floppy labour intensive things not for me. I now truly love them and regard them as an essential part of my summer garden totting up  almost five months of continuous flowers. (My best performance being mid June to the beginning of November).
I remember I once had a client who by neglect had failed to lift her dahlias in a very sheltered part of her York garden. I was amazed they came back every year and thought it a complete aberration! 
What has changed? Is it climate change and warmer winters? Is it just my expanded ambition? Are modern varieties tougher?
I am told that Victorian gardeners knew that if buried overwinter below the level of soil freezing they would survive in the ground

Making it work

This one is tall and floppy and needs staking
Dahlias will fail to overwinter if your drainage is poor and there is excess water at the depth of the tubers. My soil is sandy which makes it very suitable. Even so the lower parts of my garden are too wet and I have learnt by success or failure where they will happily survive.
I suggest when first planting you plant them as a green plant and quite deep a couple of inches more than normal - or even much more. I was told that way they subsequently form new  tubers deeply. I have doubts whether this is true and many of my plants are undisturbed self sown seedlings. 

They are a bit of a jumble, Brian
Reader Brian Skeys kindly sent me seeds of a lovely extra-hardy dahlia strain and the three plants I raised have now made up to a dozen - and extended their range of colour. (Brian I have forgotten their name, if you are still there perhaps you would tell me?).

The bishop spreads himself around in diverse colours
The bishop’s children (legitimate and illegitimate offspring of The Bishop of LLandalf) have established the same. I think that like the more tender varieties of alstroemerias, dahlias make ever deeper tubers as the years pass by.
Each year the plants get stronger and with multiples of growing points are less likely to need staking. One or two of my taller ones flop all over and Brenda shouts at me when she needs to put in a stake.
We frequently suffer from late spring drought. There is no problem with my dahlias, the roots are already down.

Dahlia 'Magenta Star' in Peter Williams' garden
It is quite easy of course in late Spring/early Summer to shove your spade in deeply and take out a large segment to replant as new stock. So too with a sharp knife take cuttings going deeply to a fleshy white base (not essential). Use your favourite method of rooting preferably under glass.
In early June this year I took advantage of the wet spell to transplant some young plants that had seeded in the wrong place. Young dahlias transplant very well with very little check to their growth.

There might be some merit in mulching over with such as insulating autumn leaves or straw when your dahlias die down. I half heartedly leave dead tops intertwined with Autumn leaves  that I rake over the top.
The trouble with such insulation is that continuous frost for a day or so soon penetrates through. Your own overcoat keeps you warm because there is a heat source from your body within. Heat stored at depth in the soil is very small.
My none mulched plants come through just the same.

Pest Problem

Ugh, black bean aphid (I assume)
Although I claim leaving dahlias in the ground will be more healthy than overwintering dry and will have less fungal disease such as root rots and subsequently all the perils of humid greenhouse conditions and pest presence, last year I was not immune!
I was caught out by these aphids. In the picture they are already moulting. I know you can control black aphid on broad beans by pinching them out at the tip of the shoots, thereby restoring the natural balance with hungry predators. I had to go a step further here and cut them half back. They soon made new strong growth and were as good as ever.

Back this year
Alerted this year by blogger Sue Garret who reported that she also had suffered black aphids on her dahlias I rushed out to find in mid June just one infected plant of my own. I snipped it away.

Healthy bishop children in early June

Saturday 6 July 2019

Not quite gardening without insecticides and fungicides

In Bolton Percy churchyard for forty years I never used fertiliser, fungicide or slug killer but did use an insecticide once
My college lectures were on very diverse topics to quite separate groups of students. Some thought me a green eyed ecologist and others a raving chemical lunatic. How could that be?
In forty years managing Bolton Percy cemetery garden I only sprayed once against pest or disease. In contrast the garden would have not been created from an overgrown wilderness and maintained without the herbicide glyphosate. 
Today I have been called back by the wonderful team who now maintain the churchyard garden (You must drop in and see it if you are ever in the area - it is always open and free). I had more or less hung up my boots but Jackie reported they just cannot keep on top of the weeds. Please could I come back and spray? I am going today (written in May).

You can buy iron sulphate as a fertiliser relatively cheaply. If sold as a pesticide (in this case a mosskiller) it's rather expensive
I want today to discuss whether gardeners can manage without pest and disease control chemicals. I won’t have enough time to explain why farmers and growers cannot. 
In my own garden I sometimes use slug killer and regret that proper Provado is no longer available to control meally bug on my indoor orchids. I did eliminate Cathi’s woolly aphid on her apples with 'gentle' household chemical (safety not always a given) and pruning and scrubbing.

Now four years later the woolly aphid has never returned
In my own garden of thousands of ornamentals and not inconsequential fruits and vegetables I hardly use any plant protection chemicals at all - other than herbicides, iron sulphate as a mossklller and for my greenhouse glass cleaning fluid.

You CAN control box caterpillar with a forceful caterpillar-killer spray into the bush from a knapsack sprayer if it is spotted at the very beginning
I would on the other hand chemically troubleshoot without hesitation if such as the now notorious pest box-killer caterpillar should pay me a visit. (Except I don’t grow box - it smells too much like pee).
How to manage with little pesticide usage
When you examine lists of pest and diseases for every plant you grow it is frightening. The good news is that health is the norm and most will never appear or are of little significance. When you have a large and varied mixed planting, natural balances develop between pests and their predators and for example birds and insects will devour most of the aphids. Don’t disrupt things at first sighting by plastering  with chemicals.
The flaw in this argument is that sometimes a timely intervention such as nipping out your broad bean tops, pruning away a few tips of infested shrubs or a mere squash with a finger will solve a later problem. Or even a well timed spray - you just need to know.

If you grow your plants well you will have less pest and disease. Some gardeners are natural growers. They know  how to manage their plants. They plant in the right place and at the right time, water when needed, are alert to natural stresses and avoid creating their own. It’s not just geriatric experience, some of the best gardeners are young ones. I suggest healthy plants are more resistant to pest and disease.
And yet again their are serious exceptions. Tell it to the cabbage white caterpillar or brassica whitefly, they will still suck or munch away. 

Some diseases and pests such as lupin aphid are so virulent they can destroy their host plant however well it is grown. Just don't grow them!
Although I advocate the merits of mixed planting I do not recommend formal companion planting. Often based on false assumptions or weak plant interactions they are  rarely effective.

Aster novae-angliae is resistant to powdery mildew
One of the best ways to avoid plant pathogens is to grow plants that are resistant. Take michaelmas daisies. Many are susceptible to powdery mildew and that includes some of the most tempting new ones in the garden centre - so clean, fresh and glowing under temporary fungicide protection. Aster amellus and Aster novae anglae do not get mildew at all.

I was sucked in to a purchase of this fungicide protected aster last year. This year I am not optimistic
An important plank in the complete absence of such as glasshouse white fly, red spider mite, scale insect and meally bug from my garden is zero tolerance. If it should appear or threaten on purchased plants they are thrown away! For fear of clubroot I would never plant brassica plants grown in someone else's soil. (I have not made friends this way by refusing kind offerings). It’s called isolation and works very well. 
(Nor should you accept a herbaceous perennial infested with your friend’s ground elder). 
Do not overwinter whitefly on some half dead unwanted pelergonium left in a warm corner. For me it helps that both my greenhouses are unheated and any whitefly  or glasshouse red spider mite would freeze. (I have not suffered greenhouse whitefly - as distinct from brassica whitefly - in twenty years, nor red spider mite)

Does ‘no dig’ help reduce pest and disease?
I often wonder when I hear regular cultivators so regularly holler about soil grubs and infections. Things like flee beetle I never see. I wonder how might fluffed up soil provide a suitable pest environment and how many many pest predators cultivation deters. What are the implications of all that shredded mycorrhiza? What too are the implications of roots damaged by digging?
Of course I argue that minimum cultivation makes for healthy plants.

My top ten cultural controls
Such tricks of the trade avoid use of chemicals or in a few cases make them more efficient or less of a rolling blunderbuss. I do not personally use biological controls where pest predators and parasites are bought in. It is sometimes immensely important in commercial horticulture but for many amateurs it is an expensive (and unnatural) sop. 
Don't confuse artificial predator/parasite introduction with doing everything possible to enhance natural invasion by such as ladybirds, ground beetles and hover fly. Nor those wonderful mammals and birds that gobble aphids and slugs

1. Physical barriers such as fleece. I am particularly keen on environmesh for carrots. It can be reused every year. It is not only carrots that might be protected from winged thugs and thieves. On brassicas it will keep off pigeons, cabbage white caterpillars and brassica root fly.

2. As mentioned resistant plants. Heritage tomatoes might for you be quite wonderful. Give me modern F1 hybrid tomato seed which has been bred with all manor of resistance. They taste better too if you choose such as Albenga and Sweet Million

3. Avoid creating disease prone atmospheres such as early season heating of greenhouses when light levels are poor

4. On the above theme ensure plants have sufficient light both inside and out. Optimum levels will vary with the nature of the plant

Who would believe drought stress and heat would make rhubarb vulnerable to this leaf curling pest?
5. Do not create excessive humidity by such as covering seed trays with plastic - ugh

6. You would be surprised at the rewards of skilled ventilation in growing structures

7. Sometimes aphids accumulate early around plant growing points. Just snipping the worse ones out will restore control to its natural predators.

Last year I completely halted an infection of black fly on my dahlias by snipping out several infected shoots. I looked hard this year to just find this one
8. Avoiding drought or water logging works wonders

9. In very small gardens just squash pests or hose them away

10. Many gardeners find isolation by growing in pots hides hostas away from the slugs. I find quite a few plants get started better in tubs rather than in open ground. Difficult shrubs such as cut leaf maples (watering, wind and wilts) and small hollies (rabbits love them) are good examples. Enjoy outdoor display for a year or two before popping them in.

And what about my escapade with insecticide in Bolton Percy churchyard…….?

In the early days I found drought and shade tolerant Solomon’s seal suitable for difficult corners. One evening I found a precious clump hosting the dreaded sawfly caterpillars and knew if left they would next year take over the churchyard.
There were just a hundred or so caterpillars and rather than squash them I hand pulled them and flung them far away over my shoulder. After all they would only survive on the said host.
I came back an hour later to find if I had missed any. They had all returned and some were still climbing.
I rushed home and got a hand sprayer. 
I still feel guilty at killing those itinerant caterpillars.
PS I now just live with the defoliation of Solomon's Seal by this caterpillar. Although unsightly when skeletonised I just trim them back with my strimmer. By July I have already had the pleasure of their Spring flowers and foliage. They do not suffer in their next year performance. 
I have a vague theory that it is not in their interest to defend themselves after flowering and the turning of their tough tissues to mush by devouring caterpillars recycles the nutrients.
My variegated Solomon is admired every year. Now in July I have finished off the job done by the sawfly caterpillars

I described how to use slug pellets safely

First of two posts describing my encounter with box caterpillar in France

My previous attempt at describing cultural control

My encounter with Cathi's woolly aphid

My very early posts were so different

I found this discoloration on Choisya ternata 'Sundance'. Was it die back or disease or a sport? Should I prune it out or propagate it?

I just left it alone

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