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On a Chalk Hillside July 2018

Constructing a pond – marginal plants  

What a month June was for the garden!  No rain at all for us here, and a long long hot spell.  After the very humid heat in May which I find particularly hard to work in the garden in, the last part of June, though much hotter, was at least fresher, and we have struggled on trying to keep pots, cuttings, and vegetables alive.  We don’t water the rest of the garden generally, and our soil is like dust.  The drought has been so severe even some of the hardy geraniums with their shallower roots are looking droopy.  Other plants are flowering but going over quickly – the Jasminum Officinale has flowered and dropped its flowers all in the last four days of June.  But the scents in the garden this month from the roses (what a great rose year this has been, very floriferous), the philadelphus, and then the honeysuckles, and then – all too briefly – the Jasmine have been accentuated by the heat and stillness.   
Perhaps it’s a good time to talk about a pond.  Let’s start with another look at the plan for the pond I showed you last month:-

The block wall at the back is the retaining wall for the patio I showed you being constructed in my article about the cowslip meadow.  This I hope shows you how much we had to dig out to make this flat surface – the blocks that step down to the left at the back retain the utility path that we remade – also shown in the article about the cowslip meadow.   As you can see there is a bog garden marked out on the right, and a double thickness block wall at the front to retain the pond about 60cm out of the ground.  The dots inside the rectangle are to represent the marginal shelf, and there is room for a hoggin path on the left far end of the pond and round the back to where the diagonal marks are which is the edge of the bog garden.  
Here is a shot of the side wall stepped down along the utility path:-

This gives you an idea of how low the side walls were to be, but also how much the patio above had to be built up to make it level.   Just as well we had to dig out an enormous hole for the pond!
To give you an idea of the size of the pond, here I am stood “in” it hand mixing mortar for the blockwork walls to be made:-

The ditch you can see is the edge of the pond where there is to be a retaining wall between the pond and the bog garden.  There is a raft of concrete at the bottom of that ditch on which the block work wall will be laid.   If you look at the following picture of the retaining walls being rendered you can see that wall completed:-

You may have noticed that so far there isn’t actually a pond – just a flat piece of ground.  As you will have guessed from the planting you could see behind the work areas in the above photos it had taken us almost 10 months to get to this point – all that preparation and construction to reach the moment on 25 June 2009 when the pond hole started to be dug.  Drum roll please:-

So, what shape, depth, features is the pond to have?  I’ve mentioned we wanted a marginal shelf, and also a shallow “beach” for wildlife.  When I researched what marginal plants I wanted, naturally some liked to be planted in a different depth of water than others.  So I took an average, and we dug a marginal shelf on two sides that was about 30cm wide and about 20 cm deep.  On the side that was shored up by the double thickness retaining wall (which I refer to as the front of the pond), whilst part of the marginal shelf was to be that depth and width, part of it, nearest to the bog garden was to be much wider, and shallower – about 50 cm wide, and only about 15cm deep.  To see what I mean, please see photo below, showing me during the digging out:-

The measurements I have given you are of where the ground is under the pond in relation to the proposed surface of water level, we had to factor in underlay, liner, and soil/pebbles to determine where the planting level for marginal might be.  Eg, Equisetum hymale likes to be in a water depth of 0-10cm, so the top of the soil on the marginal shelf needed to be as close to 10cm below the water surface level as possible, but the ground surface under the pond’s marginal shelf had to be dug out to much deeper than that to accommodate the underlay/liner and soil on top of it.  
What marginal plants did I want?  I already had the Equisetum hyemale and the Iris pseudacorus ‘Variegata’ as I mentioned last month, but I wanted to have something of interest in the winter as well as the Equisetum, so I chose Acorus gramineus ‘Variegatus’ (Variegated slender sweet flag), which was such a chunky plant when I got it I was able to divide it and place half just where the beach turned into the lower, narrower marginal shelf, and half directly opposite, with the Equisetum next to it. 
To be both easy on the eye, and attractive to wildlife I was looking for native species if possible.  Having seen the bull rushes or reedmace (Typha latifolia) along the River Avon, as below, in full seed in May this year:-

And being well aware they were far too big and invasive for my little domestic pond, on the shallow beach I planted Typha minima, the miniature reedmace.  It requires 5-10 cm water above its soil line, and I was assured would not be invasive if you took the 3cm seedheads off before they exploded into a ball of white fluff and spewed seed all round.  

I can confirm that they were WRONG.  Even taking every single reedmace seedhead off this innocent looking little plant (the leaves were less than 10cm high) it spread, within one year, not just all round the side of the pond it was planted on, but was headed for the other side too.  Very thickly growing, like a wall of thin green stems popping up in the middle of the clump of Acorus gramineus ‘Variegata’, and other marginals I mention below, and smothering the Lobelia cardinalis I planted beside it at the edge of the shallow beach by the bog garden.  That winter I pulled up every leaf I could see of it.  Trying to get its extensive roots out too.  To my surprise, I seemed to have succeeded, and it did not reappear.
Opposite the Lobelia cardinalis at the other side of the pond in the less sunny side, I put Caltha palustris, the Marsh Marigold.  This dies down in the winter under the water, but is a lovely splash of yellow in the spring.   Here it is flowering in early May:-

You can also see the Equisetum hyemale beside it, and in front of that the Acorus gramineus ‘Variegatus’.  Perhaps now would be a good moment to explain why I chose Equisetum hyemale for my first pond, and have it in this one.  I am fascinated by its “living fossil” status.  The idea that it is the only genus alive today of its class which dominated the understorey of the world’s damp forests 400 million years ago in the Devonian period really appealed to me.  Add to that the fact that dragonflies (which I wanted to attract to the pond) originated 325 million years ago, and seeing the two together in my garden is a living representation of the ancient past, it really gives me a thrill.  Here is a newly hatched Emperor Dragonfly drying its wings on the Equisetum hyemale on 22 June 2017:

The yellow of the Marsh Marigold would be followed by the variegated spikes of the Iris and then its yellow flowers.  For midsummer colour I had drooled over a beautiful pink plant at the Hampton Court Palace flower shows for several years – Butomus umbellatus, the Flowering Rush.  It has the most lovely pale pink flowers in an upturned umbrella formation in July, and I had to have it!  

The Marsh Marigold is also of interest then - here in July 13 is a shot of the seedheads of the Caltha palustris with a couple of blue damselflies:-

On the wider, shallower shelf, at the other side to the Lobelia and reedmace, and the only marginal I put in an aquatic pot, I had Bowles’ Golden Sedge – Carex elata ‘Aurea’.  Now most of the year the surface of the pot was above the water level, as this is a plant that can be put in moist soil, rather than in the pond.  I am fairly sure I had seen it at Mr Bowles’ garden at Myddleton House as a marginal beside the steps into his big pond, but it really struggled in our pond.  In the end I hoiked it out, and temporarily dumped it into a tubtrug with a spot of water and left it on the patio whilst I thought about what to do with it.  As you can see from this picture of it a couple of years later (oh, alright, FOUR years later) in May 2016, it is thriving, and has been joined by some self-sown Caltha palustris from the pond below it:-

(Why it did not like the pond but loves being in the tubtrug in almost exactly the same situation as before I cannot say, but some plants are just ornery.)
In its place in the pond I put some water mint – Mentha aquatica – also in a pot to try and contain it a little – like any mint, it took no notice of its confines and is spreading across the water, but is good for cooking, and easy to pull out.  I was particularly taken with this plant as I had seen it at the edge of many natural ponds, and it is very good for wildlife – as you can see from this shot in July 2016 with the exuvia (discarded nymph case) of a dragonfly clinging to a leaf of it – sorry I don’t remember which dragonfly it is, though it could be the Emperor Dragonfly pictured above.

And it flowers beautifully in August – the last of the marginals to do so:-

To show you how I planted the marginals here I am putting the mud I have mixed on the marginal shelf – this mud was some of the subsoil that we had excavated out of the hole for the pond, mixed with a very small amount of top soil from the hole, sieved twice at least to get all the stones/flints out of it, and then mixed with water.  Lovely job for cold October days!

 Can you see Bowles Golden Sedge sitting on the beach shelf – you may note there is a white material layer on top of the butyl which is some spare underlay I am putting the mud on so that the roots/any small particles I haven’t got out of the soil etc don’t pierce the liner.   It goes up behind the blocks that you can see under the capping bricks so they are not rubbing on the liner either.  These bricks cap all the retaining walls which you can see have been painted cream.  
Here is a shot showing the planting of the original marginals and showing the beach in place as I described above:-

Next time I will talk about completing the pond and the water plants we chose for it.

Sheila May

Posted by Sheila May

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