Wednesday, 29 January 2014

My hydrophobic sandy soil


My sandy soil has an unusual property

Brenda says I agreed to move to Boundary Cottage because of the sandy soil. Rather unconvincingly I deny it and claim to not have even dug an inspection hole to see what I was getting. She says I had clients in the area and I knew!
I did know that the sandy soil would  increase my portfolio of plants, adding acid lovers and borderline tender subjects and those needing excellent drainage. I did envisage a huge range of new opportunities but not new constraints! 

I can now grow acid loving Wych Hazel
Sandy soil is reputed to be well drained, have low water holding capacity, have naturally low organic content and be subject to leaching. Mine did not tick all the boxes and because the particles of sand are very fine it is pleasingly water retentive when wet. The significance of this proviso will become apparent. Although I describe my soil as sandy - and if you dig down a couple of spits it is pure sand - there is actually some local dispute as to whether it is sand or silt. It depends on what diagnostic system you use. Is it fine sand or is it coarse silt? We speak of nothing else! The local soil certainly makes excellent agricultural land and much of the nation’s turf is produced in this area.

I have mentioned before that my minimum cultivation techniques have less advantages on sandy soil than on clay and I did have some unwelcome discoveries. It is amazing what surprises you get when you move form one garden to another. Some plants that are superb on one soil, will hardly grow on another. Different nutritional values make such a difference. Although lovely here at Seaton Ross, my Autumn anemones will only grow two foot high, whereas at Bolton Percy they make a magnificent six foot tall. ‘Easy’ monarda, achillea, hepatica, hakonechloa and skimmia hardly grow at all. You have to adjust your techniques in a new garden, What works in one garden is less successful in another. 

Japanese anemones in Bolton Percy soil.
My less welcome surprises included finding a small part of the garden was a natural podsol with a hard iron pan. (Well,in truth, for a mad horticulturist, it actually was quite crunchy and a fascinating horticultural challenge). The worse surprise was that my lovely water retentive soil when very dry would not easily wet.

How I made the discovery
I planted some one year asparagus crowns alongside my vegetable garden. It is slightly raised from the path. Not the fashionable raised bed that looks like a timber yard and ironically had it been one, the wooden lip would have prevented water being cast off. I have never seen young asparagus grow so well and I was starting to envisage only two years of establishment before I could crop. Disaster, hardly a shoot emerged the following year. I dug up a plant, the soil was dust dry. Not just dehydrated, like at the end of the season, it was as dry as a bone. There had been no wetting up by the heavy winter rain. No water at all!
I had already noticed that when my soil surface was dry I could not  easily water-in newly planted plants as the water ran horizontally away. I had started to plant in small holes to enable  establishment-watering to soak in. 
I then noticed in a late Spring following a very wet Winter that the shallow fall in level of the lawn - where the higher part of my garden gently slopes down - looked rather brown. An inspection hole revealed completely dehydrated soil. I recalled a former client in York who had had exactly the same problem. 

Soil hydrophobia is when fine particles of silt or sand refuse to admit water between their dry surfaces. Depending where it occurs it might be mild repulsion overcome by steady rain or in severe circumstances it needs  incorporation of bulky organic matter and dare I say loosening by cultivation to let in water! (This was to be a post in my ‘why gardeners dig’ series but I do not want to give gardeners too many excuses to dig, they invent enough for themselves!). I mentioned  adding organic matter but if this is also bone dry ‘from the bag’ it can be hydrophobic too. 
I checked on the net before writing this post and noticed people reporting hydrophobia on clay. I think they are probably wrong and they merely have compaction! When I water my none dug, beautifully structured, clay soil in my Bolton Percy garden water instantly soaks in. Pure joy.

Living with hydrophobic soil

I do not want to suggest I have a serious problem, more of a minor inconvenience to be overcome. Three quarters of my garden is low lying, receives ample drainage water from higher ground and the natural sub irrigation from my ‘perched’ and active water table ensures that even in Summer it does not become seriously dry. 

As long as I avoid small areas of elevated soil in the upper parts of the garden everything is fine. In this part of my garden established shrubs and perennials have deep roots and have followed the water table down. My trees grow particularly well. In Summer the ground water is perhaps six foot down.

The  metre wide slope on a small section of the lawn required special attention. I stripped away what pretended to be turf to reveal two foot of dust! It certainly took some wetting by repeatedly filling my holes with water and ‘working it in’ with my small border spade. As it started to wet up I added ‘water absorbent gel’ and crushed bark to ensure the problem would not reoccur. I re-sowed the surface with a fescue/bent fine grass mixture.
A grass path on the same slope was even worse. It gave Brenda a fine excuse to lay a lovely stone path. Her very successful avoidance ruse.

The slope on my lawn and Brenda’s fine path
Much of my upper garden is well mulched with bark and gravel and most surfaces therefore do not have the opportunity to become hydrophobically dry. The garden is rich in organic matter and stays moist. I never had a problem in my vegetable garden anyway, but now that I regularly spread my own lumpy biochar I do not even need to plant in holes!  I do find that my ferns do best where I have buried newspaper!

By ferns grow their very best in tubs of my sandy soil.
My sandy soil creates an unusual opportunity.
As mentioned earlier, when wet, my soil holds a lot of water and yet is well aerated. If used in tubs and containers and even pots and seed trays it does wet up as water soaks through.The water can go no where else as it is retained by the rim!  Unlike peat based composts  - which are hydrophobic when dry and making matters worse, shrink - water does not run through my sandy soil until it is at full moisture holding capacity. My soil in containers holds as much water as most regular seed and potting composts.
I have discussed this theme before in ‘Breaking the Rules’ where I tentatively suggested that skilled gardeners can use soil in large tubs and planters rather than compost. I plan to be bolder in a future post soon


13 comments:

  1. I have a small patch on the East Yorkshire Coast which is very sandy. I have two raised beds with potting compost which do well, bulbs are fine too and hostas don't get eaten by snails Any other suggestions for small shrubs or perennials would be appreciated.

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    1. Hello L!
      If you are on the coast you will have problems with salt and wind but the small advantage of being able to grow less hardy plants - but in East Yorks nothing to get excited about. We frequently cross the E.Yorkshire Wolds to get plants at Reighton Nurseries- wonderful. Fuchsia, hebe, cistus and phlomis spring to mind. Really it is best to walk round your locality and see what grows well. You can also use a search engine to find sites like RHS that publish lists for special sites. I am not a great believer in asking so called experts to give off the cuff advice what to plant. It is a kind of proof of virility to impress audiences that one can think of something!

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  2. Ours is just the opposite hydrophilic? Too hydrophilic at the moment.

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    1. I looked it up Sue to see if I could manage a cheeky reply but failed. Alcohol is quite hydrophilic so I gave you and Martyn a metaphorical 'cheers' as I had a last drink before I returned from my exotic holiday that will be the subject of my next few posts!

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  3. I can relate to the surprises the soil of a new garden can offer. The problem I now have is that in winter the water table is very high. That is a plus in the rest of the year but in winter it causes problems. My old garden had 5 foot of top soil in places (it was a former river bed) my new one has very shallow soil. But as you say it is a challenge and new conditions bring new opportunities.

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    1. Our sand is an ancient alluvial river deposit from the river Derwent and eight foot of sand overlies clay!
      I have read on your blog about your own positive attitude to drainage!

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  4. My soil is sandy too. It dries out far too rapidly for my liking. I have added lots of organic matter to it over the years, but it hasn't really altered the soil properties that much. At least it seldom gets waterlogged, which is a distinct advantage in current weather conditions!

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  5. Yes Mark, most sandy soils are coarser grained than mine and hold very little water. I have not seen my garden for over two weeks but am about to return to cold wet UK!

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  6. Interesting post as usual Roger, I have clay soil but there are bands of "sand" running through it which certainly do not add to its drainage properties. I loved your remark about raised beds looking like a timber yard, it really gets my goat when Don is waffling on about his raised beds in front of his brand new state of the art glass house which together will have cost a fortune. To me the use of raised beds implies that you are unable to manage your soil so you place a giant wooden plant pot full of expensive medium on top of it in which to grow your astronomically expensive vegetables, hardly the way to encourage beginners to join the gardening fraternity without them being probably terminally disillusioned. You are making me work hard here Roger, I had to look up podsol but this is not too surprising as I was looking through some of my old college books the other day and would swear that I had never seen some of the words used in my life!

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  7. When my own college notes mentioned podsols I then thought they were of academic interest only. It was only when I discovered a true iron pan in my Auntie Doris's garden in Huddersfield forty years ago did I know they were real. With my own students I concentrated more on compaction pans which are much more common in gardens (not in nature)

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    1. Very diplomatic Roger. In agriculture the biggest problem was the use of heavy machinery plus the depth of cultivation which would always create a pan, hence the use of subsoilers or in America "sod busters" which as you know were great big "hooks" that broke up the compacted sub-soil. The cereal growers here in the UK used a minimum depth for ploughing to create a tilth in which seed can be sown, unfortunately this used to give about 4" maximum, usually less, which eventually created a pan and negative results despite heavy fertilisation. Today these things seem to be handled in a better manner but still with a minimum of cultivation.

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