Probing roots

Roots absorbing water and nutrients.

Any gardening encyclopedia will tell you that the function of roots is to absorb water and nutrients, provide anchorage and sometimes store food. The first two are my subject today.

Root spread

Years ago I would present my gardening article to the editor of the village magazine in my own ineligible hand. In a piece about roots I wrote that roots might penetrate down to as much as five feet. The editor, in her wisdom, printed ‘five inches’. Just what people think when they yank a plant out of the ground and imagine what they see is all there is!

Although this bog plant may have less extensive roots when growing near water, here in a drier part of my garden I expect its roots will go as deep as two meters

In suitable conditions it is not uncommon for herbaceous plants to have roots two meters down. It is well known that the horizontal spread of tree roots is frequently the height of the tree and sometimes very much more. Perhaps not unsurprisingly people imagine that the bulk of a mature tree’s roots are deeper than they actually are. In exceptional circumstance they may be as shallow as 400mm but perhaps more routinely between one and two meters. The thing to appreciate about tree and shrub roots is the huge distances they grow horizontally.

Even in the severest of droughts the deep roots of my vine enable it to grow luxuriantly (too luxuriantly for my liking!)

Taking trees as an example, their woody roots are only the actual tip of the iceberg. Fine feeding roots develop in all directions and might penetrate deeply. The life of these delicate roots might be as little as a few days but the volume of soil reached may be quite enormous. Mycorrhizal links between fungal hyphae enable tree roots to exploit an even greater soil profile and to extract water and nutrients from every crack and crevice.

The root systems of large plants are huge because they need massive amounts of water and they need to explore a long way to find nutrients. I am not aware that they have any special mechanism to find nutrients, they just grow towards water and well aerated moist soil. 2107 update Apparently they do!

Perhaps I should mention that all the soil’s water is not completely available to plants. As the plant extracts water the remaining amounts are more tightly held by capillarity. A clay soil for example has an extremely high water holding capacity with a great deal of available water and yet as it dehydrates to the point that the plant can ‘suck out’ no more, it might retain almost 50% of its original capacity.

The bog iris has the capacity to grow in boggy soil and sometimes actually in the water. The floating aquatic plant’s roots are exclusively in water

Although roots grow towards wet soil rather than to dry, typical plant roots do not survive in saturated conditions. Indeed in very wet weather when water tables rise to saturate the soil and displace oxygen, roots cease to function and eventually die. This puzzles some gardeners as they observe roots of aquatic plants thriving in water! The difference is that open water contains a much greater amount of dissolved oxygen absorbed from the air or produced by the photosynthesis of aquatic plants. Soil water lacks sufficient dissolved oxygen although rain itself is well oxygenated but is rapidly depleted. Root death due to lack of oxygen is swifter when temperatures are high. Flooding is more serious in Summer but fortunately less common.

My scientist friend Peter reminds me of a more subtle point about root death due to waterlogging. Ethylene is a gas produced by plants as a natural hormone. Surplus cannot freely escape from waterlogged soil and the build up is toxic to plants and this prevents them from absorbing both water and nutrients. Think of this when the houseplant you left standing in water wilts and dies!

In heavy rain excess sub-surface water runs down the sandy field at the bottom of our garden. Look at the effect on the farmer’s wheat! In contrast see how the aquatic grasses near the pond thrive!

The perched water table was extremely high in Winter 2012/2013 and only surface roots survived. A severe drought in Summer 2013 consequently caused very severe dieback. Now in 2014 our catalpa is starting to recover.

Uptake of nutrients

Any gardening book will tell you that plants require nitrogen, phosphorus and potassium and significant amounts of sulphur, calcium and magnesium. Plants also require smaller amounts of trace elements. These are copper, molybdenum, boron, zinc, manganese and very significantly iron. A few more are sometimes listed as some plants can use extra trace elements such as sodium, silicon and chlorine. In nature all plant nutrients are normally absorbed direct from the soil.

1. A farmer’s list of trace elements is longer than that of the gardener. Absorbed elements such as cobalt and selenium are essential to his livestock. Such nutrients passively absorbed by the plants are of interest to fruit and vegetable growers’ customers too.

2. Nutrients are only absorbed by the plant when they are dissolved in water. They are usually absorbed in very simple inorganic forms although dissolved complex molecules such as natural chelates supply nutrients that otherwise might be unavailable. The fact that systemic pesticides can be absorbed show that certain manufactured chemicals can be taken up too. With the aid of mycorrhiza organic molecules are also exchanged.

3. It used to be thought that absorption of nutrients was exclusively passive. In fact plants have a measure of control over the nutrients they absorb as long as they are available in soluble form.

4. Too few nutrients lead to plant nutrient deficiencies. Too much of certain elements can be toxic to plants and  much more rarely to consumers too. Toxicity might occur if plants are grown on polluted ground.

Some interesting facts from the recent scientific press.

Toxicity from industrial pollution, especially in the form of heavy metals such as nickel and lead, can render soil completely inhospitable to normal plants. Fortunately the pool of genetic variability in populations of native plants can mean that natural selection within surprisingly few generations can lead to resistant forms. Peter Williams showed me remarkable data showing how natural vegetation down-wind from former lead mines in Wales grows healthily, whereas exactly the same species transferred to the polluted ground from elsewhere die.

Patents regarding exploiting plants ability to extract heavy metals through their roots are about to run out and release for commercial use this exciting technology. There is potential to grow certain plants that have an astounding capacity to take up heavy metals and if cropped and disposed of can be used to clean up polluted sites. A variation of this technology is to grow such plants in mineral rich soils, to harvest the plants and extract useful metals such as nickel from them. A new kind of mining! Perhaps not a good thing?

Another remarkable fact is that many plants have the ability to passively absorb soluble metal ions and thereby indicate the presence of metals below. Apparently eucalyptus trees have directed miners to nickel deposits one hundred meters down. Don’t ask me if the roots get so deep!

How knowledge of root action can be helpful to the gardener

1. The volume of soil in a container is tiny compared to what roots can explore in the ground. Apart from considerations of water retentive compost and enriched nutrient supply, the frequency of watering needs to be more often than for the same plants in the ground. Except in really wet periods, the amount of water supplied by rain to containerised plants is not nearly enough. Last year I wrote how my bougainvillea in my conservatory needed oodles of water and was hyper-sensitive to drought. In a post about Madeira, luxuriant bougainvillea scrambled over the cliffs for many months without rain!

Where watering is skilled, frequent and includes liquid feeding it is actually quite amazing how healthy large plants will grow in very small pots.  Growing in excessively small pots is not recommended!

2. When new plants are planted into dry ground, establishment watering might be needed. Once root growth is underway plants will frequently not need watering ever again. Other than generous watering in I almost never water my own vegetable garden.

3. It is important to avoid severe compaction such as rotavator pans that might prevent roots penetrating deeply.

4. Too frequent watering encourages roots to grow at the surface rather than deeply. This is fine as long as watering continues but it is a heck of a bind to need to water bedding plants every day. My bedding plants in the open ground, once established, are almost never watered.

5. Because deep roots of perennials might die in waterlogged ground, especially in winter, surface roots surviving in more oxygenated surface soil should not be cut away by digging!

6. Because nutrients might leach out of containers, extra nutrition such as liquid feeding is usually needed whereas the same plants in the ground may need no fertilizer at all.

7. Beware planting delicate plants near where aggressive tree or hedge roots roots will severely dehydrate the ground. Sometimes in such conditions planting plants in a tub might be a good tactic. This keeps any watering exclusive to your plants and shade from the trees will reduce evaporation.

In the Summer drought of 2013 our wedding cake tree suddenly showed extreme stress. We needed to leave the hose pipe running for more than an hour over about four square meters to save it!

 8. Sometimes newly planted trees and shrubs will thrive for many years as they grow. As they get bigger their water demand hugely increases and they compete with each other for limited supplies of water. Roots can explore extensively but if they eventually reach already dehydrated soil or depleted water reserves under tarmac or buildings they will suffer in dry periods. Often the weakest trees or shrubs will die.

9. Sometimes an established plant might die for no apparent reason. A very rare occurrence that I have sometimes witnessed and recently personally experienced was something toxic buried deep in the ground. Most of us do not know the long term history of our garden. Goodness knows what might have been buried down there and roots can go very deep.

Oh dear, I have found another reason for digging!

The roots of the royal fern next to the pond do not have far to go to find water

The large fern in a large pot has a good reserve of water…..The osmunda must not dry out…. The gesneriad will lose water very quickly when it is a metre high….The Scots flame must not be watered if still very wet….

All to be considered when I go round with my hosepipe!

Links to previous posts 

Shrub death

Do not use too many different fertilisers

Nice looking soil

My soil surface is extremely scruffy

Miscellaneous scruffiness

I have a problem. It lies deep in my personality. I am not tidy. When it comes to the soil my natural scruffiness, my laziness and my fundamental belief in the benefits of nature’s recycling of organic matter coincide! It is best for the soil if organic matter created by plants is directly returned. It is natures way. My soil is more organic and black with higher levels of organic matter than any garden regularly top dressed with stuff from the garden centre. I decry gardens whose borders are dug and otherwise regularly stirred. Photosynthesis of green leaves creates in situ, far more organic matter than a gardener can easily add to his plot. Most gardeners destroy natural organic matter by repeated cultivation and physical removal! Worse, some gardeners even pull out large weeds with attached rich fertile soil and put it in the bin!

I am adamant that weeds should be killed and left on the surface to recycle their organic matter and nutrients. I argue that frequent soil cultivation oxidises soil organic matter away. I won’t bore you again with all the benefits of minimum cultivation. The problem I want to address today is that recycling bulky vegetation larger than my small weeds is not tidy and is therefore unacceptable to most gardeners.

For me In my cemetery gardens and on the village plot it is easy. I merely shred dead herbaceous tops with my hedge trimmer and leave them to decay. All leaves from the trees can lie there as a beneficial mulch. I never pull out overgrown plants and take them away. If unwanted, I spray large herbaceous perennials with glyphosate and leave them to  decay. If I had established perennials weeds such as bindweed I would kill them with glyphosate and let their remains enrich my soil. One year old woody prunings, I usually shred. Larger woody prunings, I burn on a bonfire but extinguish the embers with water to make my own version of biochar. 

All the tops of my uneaten vegetables are directly returned to the soil. I top and tail the leeks and clean up the sprouts before bringing them inside. Trimmings from cabbages and cauliflower, pods from the peas and beans are immediately returned from the kitchen and scattered on the vegetable garden surface. For me it is a fundamental part of no dig vegetable gardening. Let plants in life and death benefit the soil.

I recently described shredding the haulm of my broad beans and leaving them on the surface. A step too far for some of my readers. My very dear friend Rowena, gently reprimanded me and delicately mentioned  that when she tried it, it took a long time to decay. Most gardeners think my methods as unhygienic, untidy and completely out of order. I must confess to my own pathological obstinacy when it comes to these things. For most gardeners there needs to be another way!

In my own garden at Boundary Cottage I am not the complete master. Brenda insists that in the ‘less wild’ parts of the garden I cut down herbaceous perennial tops and take them away to compost. I did get away with it this year when she was not looking and shredded six foot high tops and further reduced them to a mulch with my rotary mower. I am completely beyond the pale. One last salvo, before you have a go at me for encouraging the slugs. I deny my slug damage will be greater than in the conventional tidy garden. Indeed I argue that it will be very much less. I also insist that my methods grow healthy plants that are generally free of pest and disease.

Liverwort and Moss

Oh dear, I have yet more thing to confess. My uncultivated soil surface in some places grows liverwort and moss. Brenda’s sister Joyce who has ecological interests, without any irony, recently admired my liverwort. Most people, and I include my dear friend Peter Williams, cannot stand this weed. Peter says that that he greatly admires my garden and he recently observed that for two show gardens, our two philosophies could not be more different. I think he was being kind.

Elaine’s method

I have played bridge with Elaine for the past forty years. She fluffs up her soil! Despite my protestations and explanations she says she likes it that way. In a small garden it is easy to keep her soil looking like sand on a beach by repeated gentle cultivations which she  says she enjoys. She does not actually dig and thereby chop up the roots of her plants, thank goodness, it would be too much like work. She understands that she is not aerating the roots, I have told her that so often. She has no interest that she is oxidising organic matter away when she can buy some more at the garden centre. I am pretty sure her garden debris goes straight in the green bin!

She is only too happy that she cannot plant and sow when it is wet, she is a fair-weather gardener. No one would dare walk on her soil and compress it. Her grandchildren are too old or wise to disfigure it by riding bicycles over it. Visitors like me who are disposed to walk on the soil to examine the plants are unable to do so. There is actually no need as  the borders are narrow and the plants common. I go too far, I gave her most of them! In its own way her garden is pretty. UK soils are amazingly resilient to gardener’s abuse!

Elaine has no hang-ups about glyphosate but is incapable of using it. Had her new garden several years ago been full of perennial weeds she would have had no inhibitions about calling me in!

I am rude to Elaine very often - but not about her bridge. She has a thick skin and never reads my blog. I mischievously forewarned her of this piece I was writing when we were at the bridge table last night. She told me I was a cyber-bully and later trumped my ace! She does not seem to be free next week!

(Bridge officiendos will be aware that trumping partner’s winner can sometimes be the correct play).

I don’t want to disturb my soil to show visitors that it has beautiful structure. Here the moles have insisted. If I scatter this soil over my borders they will look like Elaine’s!

Elaine is not alone. I visited a superb very small garden in Northumberland last week. The soil was fluffed up and it looked very nice.

Is there a better way?

Nobody actually tells me that my soil surface lacks a certain je ne sais quoi  Not to my face! The nearest a garden visitor came to it was saying he felt ‘comfortable’ in my garden because the soil resembled his own.

Of course a none dug soil can be tidy! Peter’s soil surface is always immaculate, cohesive, well structured, free of debris and has a tidy profile. Provided you do not stand on his self-sown trilliums you can walk on it too. He does not call himself a no dig gardener but like all quality gardeners his soil is minimally disturbed.

Like most gardeners he removes his unwanted bulky debris away to a compost heap. Unlike many gardeners he actually returns this compost, this most wonderful of materials, back to the soil as a mulch or sometimes in the form of his home made potting compost when he plants. He is quite prepared if doing some serious replanting to use a rake, fork or spade to re-establish a level and no doubt incorporate compost. When I saw the numerous tools in his barrow recently he looked like a real gardener. I can pay him no greater compliment!

Like my own, Peter’s weeds are killed when they are small and our methods and timing of weed control enables them to be left to shrivel and die on the soil surface. In Peter’s garden there is not a liverwort in sight! Liverwort can be controlled by the hoe on our sandy soils and easily raked away. Regular readers will remember I do approve of hoeing and often hoe the weed in my vegetable garden and sometimes in my ornamental borders. I hoe the weed by severing the weed at ground level without disturbing the rest of the soil. As a none digger with a no-letting-weeds-seed policy, this is easy, as unlike those who constantly bring buried weed seed to the surface by deep cultivation, my weeds are sparse. If weed seedlings are dense as in most gardens it will be best to hoe the complete area - but keep it shallow.

Although Peter leaves small Autumn leaves on the surface of his woodland garden, he rakes larger unsightly ones away. He composts them 50/50 with his accumulated lawn mowings to make some marvellous material.

There are many variations on how gardeners manage their soil surface in their perennial borders. Only the deep diggers are beyond the pale!

My giant herbaceous border in Winter are particularly scruffy. But in a few weeks now no soil will be visible at all.

A nice looking garden

Much of the above is written tongue in cheek and you might be wondering by now how anyone like me can have a beautiful garden.

Much of the answer lies in garden  design. I want the observer to look at my garden in soft focus and look at the overall view. I don’t want visitors to look at the soil. I want them to look at the plants. The layout should lead the eye to beauty and horticultural interest. Hard surfaces and sweeps of turf and grass access paths in my own garden help.

Overall in soft focus

I don’t want people to look at vast tracts of soil. I don’t want visitors to say what a good job of maintenance I have done today and how I have transformed a weedy patch. I don’t want anyone to notice I have done any maintenance at all! I want my garden always to be weed free and by my own low standards, trim.

Miscellaneous mulches

There are two significant methods of ensuring the soil surface is beautiful. One is to cover it with a suitable mulch. You can have most of the advantages of minimum cultivation and a whole array of further advantages too.

The best method of all is to cover the soil with plants. I don’t just mean  conventional ground cover that just fills a space, but how plants are used and how they mingle together. Both are beyond the scope of my article today!

link to gravel mulch and ground cover

Tips on planting and sowing

The best practical gardener I know

My own methods  of gardening are somewhat unconventional and my none digging policy negates the need for much standard advice such as not working on wet soil and the need to undertake detailed soil preparation. I thought today for a change I might adopt a different tone and provide information generally useful to more orthodox gardeners. I have known in my life many wonderful gardeners and I hope that some of their knowledge has rubbed off.

In the vegetable garden

Gardeners dig their allotments in Autumn for many reasons but not least to break up the soil by exposure to Winter cold. To this end, having thoroughly buried weed, debris and bulky manures they leave the surface covered with unbroken clods over Winter.

a) Do NOT dig the soil again in Spring. Do not bury again all that beautiful frost-mould made by the winter cold. If necessary gently fork through. A further reason not to invert the soil again is if the soil is dry at the surface and you bring up wet soil  you will lose precious moisture by evaporation.

b) Do NOT make a seedbed if the soil is very wet after heavy rain. Nor when it’s too dry!

c)Your boot is the most useful tool to create a suitable seedbed. A few well aimed kicks and shuffles will knock down the clods and carefully treading will ensure it is suitably firm. Gentle forking will usually be sufficient but with stubborn soils you may need an occasional thwack!

d) Most gardeners make their seedbeds too fine. If you must use a rake at all, do not work the soil excessively. Many soil textures are prone after heavy rain and subsequent drying to ‘cap’. This is the formation of a very thin layer of hardened surface soil which seedlings cannot penetrate. A slightly lumpy seed bed is not necessarily a bad thing. Do not be afraid to tread down your seedbed after you have sown.

e) My own sandy soil can become quite dry at the surface. We get persistent dry de-hydrating Spring winds. I frequently heavily water my seed drill or planting hole a few minutes before sowing or planting. I might use several cans of water carefully directed to my drills or holes on my patch.

f) All soils are different. Gardening tips are only given for guidance. If you find your own methods are better than mine in your own garden please ignore me and carry on!

I normally protect my young vegetables against the pigeons with fleece. This year I have tried enviro-mesh which seems to be much better. The debris on the surface is fallen blossom from my nectarine which has yet again failed to pollinate. I think it will have to go!

Permanent planting of shrubs, trees and herbaceous perennials.

It is difficult to advice on this as there are so many variables. Existing soil structure, texture, drainage, season, soil wetness, plant species, size of plant, whether the plant is container-grown or is from the open ground and many other considerations are all relevant to how to carry out the task of planting. Garden books tend to give recipes and precise instructions, experienced gardeners make it up as they go along! I am not being entirely jovial about this as each circumstance is quite different.

Many gardeners tend to work the planting-zone soil excessively. Sometimes breaking up surrounding soil may be a good thing but frequently not.

In general I am against ameliorating the soil by adding bulky materials in the immediate root zone. You expect the plant to succeed in your actual soil and not in some special concoction. Some gardeners give the new plant such wonderful planting conditions that the roots never grow beyond them.

It is not necessarily wrong to mix in planting compost, what is wrong is to put the plant entirely in a pocket of foreign material where it will be very confused! A deep planting hole exclusively filled with compost on a heavy badly drained soil might in Winter act as a sump! I despair when I see some amateurs planting in layers of dark brown or golden rubbish from the garden centre. I want to plant in real soil. Mixing in a little real compost from a compost heap is an exception!

In general I tend not to add fertiliser to the planting hole. I am afraid of scorching exposed roots. In general a new ornamental plant is not going to need extra nutrition for several weeks - if at all. If necessary, top dress with a proper general fertiliser soon after planting. Some gardeners need the crutch of adding bonemeal to the planting hole. This toy fertiliser is utterly useless but might make you feel better and will do very little harm!

1. Never let the bare roots of trees and shrubs dry out by carelessly leaving them on the surface. Even ten minutes of dry windy conditions is fatal.
2. Plant woody plants at the same root/stem/soil junction as they were planted before lifting. This includes containerised and container-grown stock. If the nurseryman has potted his container grown plant too deep, scrape some soil away. It is the same principle as not piling soil around the base of established trees, it will kill them!
3. Beware leaving string labels around the root or trunk or main branches of woody plants. They will strangle the plant in future years.
4. Often, but not always, I like to plant herbaceous plants a little deeper than before. Where I intend to leave frost tender plants such as dahlias, ‘hardy’ fuchsias and gladiolus corms in the ground overwinter, I plant really deep.

Last year I planted my Dahlia ‘Bishop of Llandaff' deeply.
It has survived the mild winter and is growing again

1. It has been recently demonstrated that if roots of woody plants have been torn or otherwise damaged it is best to cut them back cleanly to undamaged root.
2. If moving a larger established plant within a garden it often helps to reduce a portion of the top by pruning,
3. Often a container grown plant will be in very dry compost. Thoroughly wet it by soaking in a bucket of water for up to a minute before planting.
4. Not all sites are level. It may make the difference between success or failure in future years if you plant in a dip or a hollow. In very wet periods waterlogged conditions might kill your plant. Of course a depression might be the best place for a plant that likes boggy conditions!

I have planted at different levels in my bog garden to satisfy the needs of different plants

Six years ago Peter Williams gave me a large container-grown ‘Dawyck Beech’. In a wet part of my garden I planted  it on a mound. The beech has thrived but as 99% of its roots are now in the wet soil I have no idea whether its ‘good start’ made any difference!

1. Sometimes hard surfaces such as paving near a border may cast off water in heavy rain. Depending on the plant and your own conditions this might be very bad or a very good thing!
2. Where drainage is suspect consider planting on raised beds. On some wet soils I would plant on a slight mound. Not usually the latter on my own sandy soil which when very dry is difficult to rewet as rain or irrigation runs away!
3. A huge determinant of eventual success is proper management particularly with regard to watering. Container grown plants with a large top will dry out very quickly if planted in Summer. Give a well directed can-full of water in dry weather. The rule is generous but infrequent watering through the establishment period. I remember a lady who heavily watered her new hedge every night and killed her plants by saturating the soil!

My toad lily, tricyrtis was doing very well but was becoming overgrown by my hosta

Elsewhere in my garden an existing clump of toad lily needed a gap to be filled. It is a little retarded because the wet soil is cold

It was early May when I lifted some of the overgrown plant…

...and with minimal soil disturbance immediately planted it on the new site

Don’t work the soil too much

You might  expect me, as a no dig gardener to say this. I suspect many gardeners regard planting as a major operation rather than a rapid routine process. If your soil is in fine fettle the procedure involves a slit or a hole to accommodate the new plant, return of the soil and perhaps a gentle stamp to firm the plant in. For a small herbaceous plant it is the work of seconds, for a larger shrub or tree somewhat more and perhaps soaking the hole if conditions are dry. Your eventual success will depend more on putting the plant in the appropriate place and after-planting care, rather than how you stick it in!

I must confess my progress in planting is just a little slower in my two cemetery gardens. Thick tree roots and at Worsbrough soil that is 60% rubble rather slows my progress and almost breaks my wrist!

There are some pictures of my methods of planting I dare not show you.

I am reminded of a story about my dear friend and former student Alan Mason. Twenty five years ago Alan was well known for his TV programmes. A surprising number of folk remember how he was one of the first to do a garden makeover. It was at his dilapidated manoir in Porte-de-Roche, France. Ten students were invited over in their Easter vacation with their tutor, me! We were there for three weeks to completely redesign and develop the overgrown and previously neglected seven acre garden. Alan had accumulated perhaps two thousand plants that he held in his nursery. There was much work to do preparing the site and the TV crew started to fret that by the start of the last day of filming nothing was planted! Miraculously by that same evening there was a magnificent new fully planted garden! We did not take much time shoving each plant in!

On the subject of the television, I flicked to a premier gardening programme the other night. It was an accident and was between the ads on the football. A well known gardening guru was demonstrating how to plant and of course did it perfectly. As ever the BBC soil had a beautiful tilth - I wonder why they never find roots or stones? After completing the planting the gardening sage gave the plant a little shuffle. It was almost as if he was giving the plant a pat on the back as it was released into the cruel gardening world. The look on his face said ‘Good luck son’.

Such is the way of broadcasting stardom.

Between you and me that faint final flourish was not strictly necessary!