Topic: Bad Drainage

[Paul Dee]

Hi all,

I've been lurking here for a while now, finally got round to signing up now I need some help!  ;D

I took over my allotment last May, luckily half of it had been covered in plastic, and was clear underneath so I dug over that half quickly and got going, and had a reasonably succesfull season, contrary to the best efforts of the local mice & pigeon population.

Now winter is here, I'm digging over the other half, and frankly the whole plot has turned into a swamp. Where I have dug to a spades depth the soil is now sitting in about 3" of water, and it is very heavy waterlogged clay that squelches as you dig it. It hasn't even rained that much...

One of the older plot holders  casually mentioned that my corner of the site is known to have terrible drainage, and I should consider moving to another plot. (This after watching me slog away on the current plot for about 6 months! Thanks mate!)

There are some semi-derelict plots up the other end I could take, but it pretty much means starting again.

I'm about to get a load of manure delivered, is this likely to improve the drainage a lot? Is having a soggy plot necessarily a bad thing? Will it affect my crops?

I'm loathe to leave it now I've done about 2/3rds, but don't want to waste my time on a plot that will never improve..

What to do? Any advice appreciated! Thanks.

[tim]

Haven't a clue - but keep talking!! = Tim

[john_miller]

To answer your questions in order: No, yes and yes.
Having a super saturated soil will cause many problems. If it hasn't rained that much and you still have standing water at a shallow depth then a wet summer could cause you to have very poor crops. Micro-and macro-organisms in your soil will drown or migrate resulting in interruption/cessation of many necessary processes. What nutrients do become available will be leached out in such quantities that plant growth will be compromised, this being especially true of the form of Nitrogen that plants take up. This is highly water soluble and chemically does not bind to soil particles. Excessive water will also cause the phenomenon of deflocculation where the soil particles do not form a structure conducive to good plant growth. Plants adapted to grow in wet soils have been found to have specialised cell structures that allow transport of air downwards to aid in metabolism of nutrients- most common vegetable crops do not have this adaption.
I would move if I were you, taking your manure with you. Alternatively you could build up your present plot into raised beds so that the water table and the affected soil are below the levels that crop plants typically root into. That could be equally labour intensive with no guarantee of success.

[gavin]

Hi Paul

A question - what kind of weeds do you have growing there?  If there's a lot of sedge-type "grasses", I'd move; no question, no second thoughts.

If you don't have bog-loving weeds, ask around - if you get similar responses from several people, then look at taking another plot, if only as insurance?  And perhaps over a couple of years?  You've got 2/3 of your current plot ready - use it next year, and reclaim some of your second plot?

I'd a similar problem in October - but not nearly so bad as yours sounds like.   No sedges, and I was lucky - digging a drainage channel at the lowest point across the path seems to have solved it.  But I've got my name down to take over another plot when it falls available ;-)

Good luck - Gavin

[Jesse]

Hi Paul, my garden is at the lower end of a slope and the lowest part of the garden used to look like a pond in the winter when we first moved here. The builders put in a french drain which works well (meaning we no longer have a pond) but the soil at this end of the garden is still always very damp (even although it drains away) because it constantly receives the run off from the rest of the slope. I eventually gave up trying to grow flowers in this area and have planted a small conifer hedge which is doing well and it helps to dry the soil. If your plot is anything like my garden was and the water sits without draining away quickly, if you decide to use raised beds I would still sink some sort of drain before putting the raised beds on top otherwise the soil in your beds may end up acting like a huge sponge and sucking in the moisture. Personally, I'd take Gavin's advice and spend my energy on restoring another plot without the drainage problems. What a shame after all you hard work, it's doesn't seem fair that you were not told the problems of this plot before you took it on.

[Trenchboy]

Tough luck.

Have just taken on an allotment in Kingston, Surrey, and after building a shed, composting bin and even putting in a gardstanding for my car, found one end of the site under water, and water at about aspade depth when the digging started.

No warning by the guys on the site!

Have now dug a series of connecting drainage channels - all of which are 6-8" deep in water.

My next move is to raise the beds in two ways:

1  Organically by adding soil and the underlying clay from further digging of channels to form smaller beds

2  With prejudice by digging out beds once the groundwater level goes down sufficiently, and then ordering in hard core and other solid stuff, and then putting back soil and mixed in subsoil.

From scouring the sites online, it seems I'm going to be wasting both time and effort, and should move to another plot, but it is  hard to just give up on all the work already done.

For year 1 I don't reckon I'll have more than half the site in some form of use, as the raising of the lower beds will only be feasible when the water levels have dropped.

Let me know how your plot goes...

Derek

[Palustris]

That is unfortunate. I cannot now find the article but when we started here and found a similar problem to Jesseve I read a lot about land drainage. The most important bit was that when draining land the solution is to prevent the water getting to where it can lie. So any field drains should be placed so that the flow of water into the low lying area is interrupted. If you put a soak away in to the lowest point of your land then you are just encouraging water to go to that point. When we dug a soak away it filled up with water before I even had the chance to put drains to it! Best of luck!

[gavin]

[light goes on]Of course![light goes off again]

... prevent the water getting to where it can lie ...

Now why don't any of my books have such a simple bit of common sense - grrr!  Thanks for that!  :-)

I'll go back and look at my drainage with a completely fresh eye; silly of me - I kind of knew it was daft to drain all the standing water off onto the derelict allotment across the path!

All best - Gavin 

[Paul Dee]

Blimey!

Thanks for all the advice. My weeds are almost exclusively grasses (mainly couch) grass, and lots of creeping buttercup.

I went for another squelch around the plot. Lifted some soil in the wettest area that I haven't got to yet and it has a stale pond kind of smell to it, which suggests to me its already suffering from some of the processes John described.

Thinking about all the work of trying to correct this plot with drainage pits & channels & raised beds and so on, I have deicded the best option is to move to a new plot and start afresh.

And here was me thinking it would be quite handy as I could get away with a bit less watering!  ::)

Oh well, live and learn!

I'd best get to it then!!

Thanks again...

[Palustris]

If you are getting a bad smell from the soil it would definitely be best to move. Keep the half you have done until you get the new plot up and running.

[Maverick.uk]

If it was me i would speak to whoever runs the allotment and ask if you can split your plot. As others have suggested, hopefully this will mean you still only pay for one plot size whilst trying to move to the newer plot. Hope that makes sense.

Cheers

Mav

[Paul Dee]

Thats the latest idea, I will keep what I've done already as it's not too bad, and I'll grow spuds there while I get the new one ready.

Unfortunately there is lots of unused space on the site, but at least that means there's no problem with moving around, or runnning 2 half-plots...

I don't know if John or anyone who understand this stuff will pass this way again. But did any of you understand this bit?

... the form of Nitrogen that plants take up. This is highly water soluble and chemically does not bind to soil particles.

If nitrogen is water soluble, but it doesn't bind to soil either, how does it stay in the ground? In air gaps between the soil crumbs? Is this why people talk of crumb structure? I don't get it ??? 

I realise this is a bit off-topic now, but just a bit curious....

[gavin]

Oh wow - I think I understand, but whether I've got it right is another matter.  :-(

Plants can't use the gas nitrogen itself.  There are several processes in the soil involving specialised bacteria; they convert the nitrogen into nitrates (salts of nitric acid?). 

Eg - it's not the beans which fix nitrogen, but a "friendly companion" bacteria associated with bean roots, which does the fixing - converting nitrogen into nitrates, which other plants can take in and convert into proteins (green leaves!).

The joys of being a supply teacher - you learn something (badly) every day!

All best - Gavin

[john_miller]

After reading everyone else's comments I regretted making my post so abstract and not relating my personal experience with wet ground. Now it seems I need to go further because of my imprecision. 
Plants take up about 90% of their nitrogen in the form of nitrates (-NO₃). The rest is taken up as ammonia (NH₄). Nitrate nitrogen is a a negatively charged molecule (anion). Almost all other nutrients are taken up by plants as cations, positively charged molecules. Soil particles capture nutrients on molecules that have 'exposed' atoms and are consequently also charged. Most (again, about 90%) of these exposed atoms (called cation exchange sites- CEC's) have a negative charge so retain these other nutrients. Due to their negative charge these sites repel nitrates and, due to nitrates solubility, make them easily lost into groundwater, unless they are picked up by the other 10% of exchange sites. (This is why if someone wishes to grow within certified organic constraints manure should not be applied in autumn unless you live in an area where a green manure can be grown overwinter).  My personal experience resulted in some exceedingly yellow, 'hard' (as opposed to lush), summer squash plants in a wet field even though they were only sown in June just as our typical summer drought was about to start.

[john_miller]

Hmm, replying to myself? Even if an allotmenteer doesn't want to grow within organic constraints manure should never be applied in the fall without a green manure be sown over it as nitrate N  will be lost to groundwater under either method.