Tuesday 16 January 2018

Bog blog. Love your wet soil

Make the most of wet soil

It's not so much about this
It's more about this....
....and  flowers that love wet soil
New reader Carol has a very wet garden which receives drainage water from all directions. I was concerned she would want to know what to grow. A very good question but a devil to answer.
To my relief her comment column query arose from her realisation that the very best way to prepare a wet site is not to damage wet soil by cultivation but to eliminate weed by glyphosate spray.
She was worried that there was a stream over the wall in the neighbour’s garden and would she be a cause of its pollution. Although we might have a conversation about spraying vegetation alongside a running stream I was able to reassure her that in her case there was no danger whatsoever. Indeed around isolated water really difficult invasive bog weeds can be quickly, effectively and safely controlled - to the huge benefit of a surrounding ecology.

This post is intended to say how Carol’s problem site might very well be an opportunity to have a wonderful garden. This post is not so such about making a pond with an attendant bog garden or a treatise on how to improve drainage. It is just about making the best of a wet site.
As to a post about drainage. I have done that before before - and my pearls glugged down the drain.

The nature of soil wetness
In simplistic gardening literature moisture loving plants are either aquatic, bog or like ‘well drained moisture’ - whatever that means. By contrast in nature there is a complete gradation from free water all the way to severe drought and where for example iris on the water’s edge grows out into the water or the aquatic water bean scrambles onto the embankment or where the swamp cypress on the bank can have root appendages called pneumatophores growing out of a lake. (Apparently in this case nothing to do with acquiring oxygen as do genuine aerating pneumatophores)

This corner floods in wet weather
Often soil wetness varies with season. Nature - and gardeners - have to cope with Winter wet and Summer dry. 
I sometimes see garden centres selling those bog plants that love the wet water’s edge under the guise of aquatics. They survive in the water dying only slowly in Summer and failing to get through the Winter. Things like thuggish mimulus and expensive osmunda fern and zantedeschia lily just fade away in the water.

Not in the water but on the edge
And yet I know fantastic zantedeschias thriving all year round in very shallow  slow moving steams, osmundas on only slightly elevated embankments or water islands and mounds, and mimulus taking over gardens that are more  under water than they are dry

Because the water is moving it is aerated and zantedeschias thrive
My point is that nature is ever so subtle in the gradations from wet to dry.

Plant root's need for oxygen
Every plant cell needs oxygen to survive. Normal plants growing in waterlogged soil, or worse completely ‘saturated’ soil die for lack of root oxygen. In such conditions most or all of the soil air is displaced by water. In addition gaseous natural toxins fail to disperse.
Aquatic plant roots growing in open water extract dissolved oxygen from the water. Rain is also charged with oxygen which might give waterlogged susceptible plants a temporary respite. Unfortunately water in long term bog has zero dissolved oxygen.
There is huge variation in plant’s tolerance to very wet  conditions and there is huge variation in soil water absorption and duration of wetting. What is death for one plant is heaven for another. Huge opportunities for a good gardener. Some of the very best gardens are wet ones!

Site preparation

I have created undulating soil levels and in this case have sunk a small rigid plastic pond
I call this an up and down pond - sometimes wet - sometimes dry
Site preparation might be doing nothing at all and if the ground is not level to keep natural contours to maintain natural drainage patterns and to retain dips and mounds that give different planting opportunities. Keep soil movement to a minimum but it might be appropriate to either enhance soil height variation or to create slightly raised borders perhaps surrounded by lawn. Importing extra top soil might work very well but beware that soils of different textures frequently inhibit natural drainage when they lie together.
It might be appropriate to dig out a pond and use the extra soil to raise levels and at the same time create low boggy areas. Best use a spade than heavy machinery which might destroy soil structure.

The oval border with the birches and beyond is the really wet part. Now in mid January you can just make out water standing on the grass
Half an acre of my own garden is naturally a metre or more lower than the high parts and as I will explain later it can lie wet for extended periods. I have frivolously presented my posts about burying newspaper and (separately) burying woody prunings and hedge trimmings but I am deadly serious about the planting opportunities it has given me when I have raised soil levels. Only now after nye on twenty years of burying wood, newspaper and stones have I ceased -  citing ano domini. As a none digger such buried materials will not be disturbed!
Wood enhances soil fertility and in due course improves soil structure. Paper lasts an extremely long time and and charged with Winter water preserves a buried water resource to provide moisture in the dry of the Summer.

I am not enamoured to lining a site with plastic to create boggy conditions. It is fine at the edge of a pond if the pond liner is so folded that soil capillary contact is retained with the water even when pond levels fall in dry weather. If not the lining can easily create a barrier to roots going deep in the soil to find water when the surface becomes dry.

The raised edge lies over the plastic entity of the pond and water wicks up as long as the water level is high
The plants
Not only are wet sites very diverse in their nature so are the plants that have evolved in such boggy conditions. For instance monarda which likes wet - but short of boggy - always fails for me although my wet conditions are reasonably well drained. It’s best to experiment and grow what likes you and give up on the rest.

Now in a very wet January these daffodils are sprouting in the grass and have been flooded for two weeks. I am confident they will look like this in April
Many plants are generalists and have evolved to survive in a wide range of conditions. Often garden plants are hybrids and combine genes from plants with very diverse natures. Many gardeners have drainage problems and many popular plants have been unwittingly selected to survive wet conditions! My point is that many plants not promoted as bog plants will stand - and enjoy - varying degrees of wetness. Most daffodils and snowdrops do very well in wet sometimes flooded places. Fritillaria meleagris has evolved in marshland conditions where it naturally thrives. Phlox paniculata loves summer moisture and so does agapanthus which in its native habitat is often to be found on stream banks.
The boot is on the other foot with certain so called bog plants that given well drained moist conditions do even better than in waterlogged soil. Astilbes for example must have summer moisture but invariably fail if they stand in winter water.
For the rest of this chapter I will let the pictures of the plants do the talking

Although only an idiot would plant hellebors in bog all my best ones are in well drained moist soil which is sometimes flooded
Many large ornamental grasses like water meadow conditions
Gunnera survives winter wet with this huge overground food store. Its shallow roots at that time make it easy to divide!
Two vigorous thugs that love boggy conditions
Good for bog at the edge of the pond
Dwarf bulrush grows as an aquatic in my 'formal' pond. I have been dividing it to try some pieces at the base of my up and down pond
Hostas are very versatile and love wet or dry
Birch and dogwoods do well where it is wet
The soil habitat changes with level
The planting around the pond in the dry part of my garden are just normal plants
The background story of my own wet garden
You would not recognise the wet lower half of my garden as a bog garden. Just like the rest it is island borders and features set in lawn. Near the very bottom there is a 300 sq. metre oval(ish) area which only by dint of a narrow mown grass path at its rear is an island border at all. In this area and the raised strip beyond, the water table rises and falls like a yo yo for most of the year! The other borders have varying patterns of wetness in which ‘normal plants grow. I have just had to learn by dint of many failures what will grow where!
Similarly with trees. Those that don’t die grow very well.
In truth I am really lucky. My deep sandy soil lies on a basin of clay that is more than two metres down. My lower garden receives drainage water from all directions. When heavy rain falls on distant hard surfaces it finds it way to me. This is wonderful in summer but not so good in winter.
My saviour is that a single ancient huge agricultural drain - its bore is 14 inches - runs into the slope of my garden and takes much of the surplus water away. At the bottom it is two foot down and where it hits and goes under the road at the top is seven foot below the soil surface. Beyond the road the land dips away to a distant ditch. When water temporary stands in my garden after really heavy rain I can discern surface flow towards the drain and hear gurgling. After a few days most of my soil returns to drained normality and aeration. But not all! 
When we moved in I dug out two adjacent huge ponds and removed 200 barrowloads of sandy soil which over a period of nearly six months I deposited round the wetter parts of the garden creating raised areas. We designated our new e-mail address twin ponds!  
In the lower half of the garden the two lined ponds were deliberately located where water does not stand. I did not want my fish, tadpoles and crested newts swimming away during temporary flooding. I did create a narrow edge of raised soil coming out of the water which is always well wetted by capillary action. Brenda is a stickler for keeping the ponds full of water. 
My ponds are effectively borders surrounded by lawn.

Most of the rest of the story is a chequered history of discovery. In the really wet large oval border I created a series of small ponds and a stream. I called them ‘up and down ponds’ as they rose and fell with the water table. The idea was that they would take the brunt of temporary flooding, create new niches of wetness and dry and look rather nice. Unfortunately they were dry more than they were wet and I lined their bases with plastic held by landscape staples. It looked rather like an inverted skull cap. Mainly due to my incompetence they looked rather ugly. Another failure.

My up and down stream two years ago before I filled it, lining and all, to make an up and down bog!
For two ponds I removed the plastic liner. The lined stream I merely filled in with soil and so called compost from the local waste disposal plant! The stream is now a very fine bog!

My efforts burying wood
Readers thought me crazy burying great wodges of newspaper
I tried here to explain some scientific principles about soil water. It fell on deaf ears despite Cathi telling me it was too risqué to publish
Someone might be interested in my crested newts


  1. Maybe you could advise me on this . . .
    The house we have moved into is part of a late nineteenth century, stone-built terrace (1885). The house next door is empty and the guttering is blocked so water just runs straight down its front. At the point closest to our house there'a kind of stone plinth - perhaps the lintel to a vanished door that once led to a cellar. Water that hits this runs onto a small patch of earth against our house. I have dug some of it away as part of trying to reduce the amount of damp going into our basement but don't want to take it away completely because the earth catches some of the water that lands there and some of this evaporates instead of all of it sapping its way into the stonework.
    I've been wondering about putting a plant there to help suck up the water. It would need to be greedy for water but its roots would not need to go down too deep, nor be too strong. I think previous owners put earth on top of what is a paved over area in front of other houses in the terrace.
    It faces East so the sun shines on it only in the morning but trees, when in leaf, shield that patch from its full glare/ warmth. In the summer, assuming we have less rain, it will go dry (also assuming the earth does not go deep) and I don't want to water the plant too much because the idea is to reduce the moisture, not add to it!
    Any ideas?

    1. Hello Lucy
      I am not too enamoured about using plants to dry out soil. They dry the soil in Summer but not much in winter - albeit evergreens are best.
      On some sites however if the soil at depth goes into the winter very dry it keeps excessive wetness at bay as it soaks up the rain.
      Unfortunately water hungry plants usually have deep roots!
      I wonder about a dwarf bamboo or a dogwood that you can cut back every spring. Willows dehydrate the soil very well and a coloured stem one also cut back every spring might do the job.

    2. I might know a bit about this, as I did a lot of reading up on roots and foundations before I planted some trees near our house. In a modern house with concrete foundations and cement mortar blockwork, the roots can't usually penetrate. But in an old house it will be lime mortar, and it's soft enough for roots to penetrate. So you could just make the situation worse. I'd be more inclined to get the gutters cleaned!

    3. Thanks for this help Sarah. As to roots in old mortar Peter Williams had a query how to get rid of Romneya coulterii recently.Planted in a herbaceous border its root had got under an old property and was going berserk even pushing through the kitchen floor.
      Its a plant all of my life I have been unable to grow. Strangely enough I think it was in Halifax!
      Lucy I wondered if an evergreen herbaceous plant might be useful. My ophiopogon has made a huge clump and likes moisture

    4. Thanks for the suggestions Roger and Sarah.
      Re. roots. Definitely don't want roots pushing into the building!
      As for guttering. Ours is completely new - and the roof has was re-slated in the summer too. The trouble is that the building adjoining ours seems to have been more-or-less abandoned. When we bought our house is was a shop but by the time we moved in that had closed and we don't know who owns it. The guttering is choc-full so the rain falls down the roof and onto the ground as a sheet and some of this flows back onto our small patch of ground. To make it worse, our (new) guttering leads into their guttering. The people who sorted our roof said (perfectly reasonably) that they couldn't clear a neighbour's guttering without permission and as we don't know who that is . . . we are stuck. (Possibly worse still, we can hear something - either water or fine rubble - falling between the walls which join our houses.) We'll be contacting the Land Registry to find out who owns it but in the meantime we've got problems! And even then, it may well be that the owner can't afford the repairs. Otherwise why would they leave it like this?
      I have a bamboo (the kind whose leaves are delicate and whose roots grow as a ball) in a pot. I'm mulling over whether to put that there, still in its pot.
      Re. Ophiopogon. That might work - but does it take up much moisture in winter? Winter being the time when we would most need it to?

    5. My you do have a problem!
      I don't think a small bamboo in a pot will make any difference and for that matter any small plant including my ophiopogon will not evaporate water quicker than will the wet soil itself at its surface. A small plant only transpires more water than a soil surface when the soil surface is dry!
      Is there any possibility of a small rubble drain to take the water away to a more acceptable place? They can be every effective even with only a slight fall

  2. It’s interesting to see how your garden looks in January compared to how we have viewed it in September.

  3. This is really helpful to me at the moment! While we had a digger on site for the terracing work, they dug a pond. It's finished with a liner and then a clay lining over the liner. I'm not completely sure why it's like this, but I'm guessing it's for the reasons you give....so it will wick water to the surrounding soil. However I am nervous about planting into the pond itself as anything invasive will be impossible to remove. Any suggestions for well behaved plants that I can plant directly into the clay below the water line? I need to get as much as possible in there asap, as it's going to be nutrient rich in the water and I'm anticipating a green slime swamp as soon as things warm up!

    1. If you were nearer you could have had some of my dwarf bullrush.
      Aquatics by their very nature are often spreading and sometimes my menyanthes gets a splash of glyphosate. Glyphosate is very good for vigorous aquatic and bog weeds I did not mention in my article the wild pond in the farm field adjacent to my wet garden -thats up and down too. I have mentioned before some of my plants have found their way there! Invasive glyceria and flag iris and invading aquatic grasses and couch are easily set back by a spray so don't worry too much about invasive aquatics. One of the evil alien banned oxygenators - I forget its name - is also easily controlled when it comes over the water line.
      I gave a handful of hippurus to a friend recently Now that has a very bad name but looks gorgeous. Be sure to have some water lilies and water soldiers but these are also vigorous - the latter periodically need hooking out with a plastic scarifier. Most aquatic irisd will fit your bill

  4. That's a whole new level of spraying for me! How would you tackle bogbean if the water is too deep to wade in? Water level would be up to my armpits at the deep end. And how does it work....if you spray the edge of the clump does it just kill those ones? What happens to the spray that gets into the pond? I also wonder how on earth it would be possible to spray in congested conditions, like the first photo above.

    1. Just spray the bogbean scrambling onto the edge Sarah and use the length of your lance to lean over the edge. Can you imagine me going in the water! Direct your spray at the target and the other thugs won't turn a hair. Any spray alighting on the water is hugely diluted and does no harm. Promise!

  5. Wet soil gives me soothing feeling in this season, it's a great resource for growing your vegetables. Tomatoes needs more water.


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