Topic: understanding P.H.

[settler]

i have been making alot of enquiries about my p.h.in the soil now the thing i can`t get my head around is does the p.h. stay at the level required all the the time after you have done the business with manure and lime or do we have to keep checking this and how often


can anyone help

cheers john

[Palustris]

That is hard to answer. The basic .ph of your soil is determined by the underlying geology and and changes you make are limited. The length of time the alteration you make will last, depends on the type of soil you have. A heavy clay will retain the lime for longer than a free draining sand. Also as you add organic material, the bacteria in it use up the lime and convert the soil back to an acid type.
No doubt the more chemically wise types will answer you in greater detail and with more accuracy, but we have found here on a moisture retentive, but free draining, neutral silt, that to raise the .ph enough to grow brassicas we have to add lime about every 3 years. This means we do tend to check the soil every time we are about to use that section for brassicas. Hope this helps.

[settler]

thanks very much this should help alot
and good luck in your lottie next season

[tim]

When we first came here, I thought it clever to lime, & did so for a year or two - blindly.
Gave up 20-30 years ago & we still grow great brassica with a steady pH6.5 on test. = Tim

[djbrenton]

As a sidenote, when I first tested my soil, I also decided to check my water butts. All the ones that were fed from greenhouse roofs and were used most commonly, had PH's of between 6.5 and 7. The butts that stood alone and weren't in as much use had PH's below 6. Without a check, I could easily have been using relatively acid water on seedlings.

[Palustris]

I dug a test pit when we first started in this garden and took .ph samples from the different layers. The top was slightly acid (mainly plant debris, leaf mould etc) the next layer was neutral and so on down. The acidity decreased to slightly alkaline as you went down. However in places the ph was very different, very alakline. Guess where?
All those places with old lime mortar and brick rubble had a much higher .ph.

[Hugh_Jones]

The first point in understanding pH is to understand what the expression  indicates.  pH is an abbreviation for potential Hydrogen ions, and the scale of numbers is in fact the inverse logarithm of the proportion of such ions present in the soil. So taking the scale from neutral downwards, the proportion of hydrogen ions is as follows:-
7 (Neutral)              = 1
6 (Moderately acid) = 10
5 (Much more acid) = 100
Etc.
Hydrogen is, of course, an acid gas, but is neutralised by any alkaline substance, and the level of potential Hydrogen ions is therefore governed by the amount of alkaline substances either naturally in, or subsequently added to, the soil. A prime example of the latter is Eric`s reference to lime, plaster and brick & mortar rubble.

Topsoils naturally derived from leafmould and plant debris tend to acidity, as does clay (which naturally contains no lime), while calcareous soils of marl and limestone are obviously alkaline.

However, farmers and gardeners have been tinkering with the soil for centuries, and so while truly alkaline soils can very rarely be made acid, originally acid soils can have been made neutral or even alkaline, and neutral soils can have been altered in either direction.

It is quite common for any given plot of land to contain soils of varying pH level, and the only way to ascertain (and if necessary correct) this is to make numerous tests.

Garden composts and manures such as cow and horse are all slightly acidic in nature and repeated use will gradually lower the pH level (although not to any great extent), and this can also be done by the use of sulphur in either powdered (flowers) form or as chippings.

[Sarah-b]

I have never tested mine, but on the basis of what you say can I be fairly sure that it is alkaline?
Mine is sandy, flinty, stony, and I suppose a bit chalky too.

Sarah

[aquilegia]

I haven't done mine either. But as it's heavy clay, it must be acid. I must get some lime for my sprouts next year.

[Sarah-b]

And presumably for your cavelo nero too aqui?? ;)

[aquilegia]

Oh yes - thanks. I forgot that's also a brassica.

[Hugh_Jones]

Ladies, please don`t bank on your soil having a certain pH level simply because of its type, because you just don`t know what a previous occupant has been doing to it. Test it before you start adding lime (except for brassicas, which love it).  If you have the patch where an adjoining tenant washed out the cement mixer or mortar bucket when he was building his shed base then your soil will have an entirely different pH level to that of the surrounding plots, whatever the soil type.

One question of settler`s which I didn`t clarify is as to whether it is necessary to keep checking the pH after treatment with lime, manure etc.  Let me emphasise this, that the slightly acidic effect of manure or compost is not cumulative below a pH level of about 6.5 (which is the usual pH level of decent compost or well rotted manure).  Once this level is reached adding more of the same cannot lower the level further.  The alkaline effect of lime is to neutralise the potential Hydrogen ions, and to keep adding this indiscriminately will result in the pH level of the soil rising to a point where many plants are uncomfortable, essential trace elements are `locked`, and potatoes are covered in scab. Most vegetables are happiest at a pH of between 6.5 and 7, and once you are satisfied that your soil is within these parameters (and assuming that you practice a normal 4 year rotation) it should only be necessary to lime for your brassicas each year.

Many gardening books will tell you that lime is an important fertilizer. It is, but only when it is necessary and used properly.

Personally, I check each of my vegetable beds every year, and would certainly never add lime without checking.

[aquilegia]

It's my garden, I don't have an allotment and I know that until I started, the garden hadn't been cultivated in years. I doubt it's ever seen a vegetable patch before! But I will add PH tester kit to my christmas list!

[Hugh_Jones]

House gardens can be even worse.  I have a roughly circular area where the rhododendrons all died.  Digging down 3 feet I found the original lime pit in which all the lime mortar and plaster used in building the house had been mixed.  Depite days of effort in breaking up and removing the `pan` I still have an area which is highly unsafe for calcifuges.

[Sarah-b]

So Hugh,  let's get this straight: for brassicas, add lime no matter what?
What exactly is the effect of lime on brassicas?

Do need to know all this because OH is madly double digging brassica bed and adding lord knows how much manure. Think he will be very sad if fab brassicas are not forthcoming!!

sb

[Hugh_Jones]

Just, as you say, for keeping the record straight, Sarah, brassicas will stand quite heavy liming, but even they have their limits, and you should bear in mind that the effects of very heavy liming will only only slowly diminish over the following three years.  Too much lime for the brassicas means that there will still be too much for the potatoes (which don`t like it) 3 years later, so you have to try and strike a balance.

However, your posting raises another problem - manure and lime simply do not get on together.  You should never apply them both in the same season, and if OH is madly digging in manure now you shouldn`t apply lime before next autumn.  Grow the brassicas somewhere else next spring where he hasn`t manured and you can lime, there are plenty of other things you can grow on manured ground - and tell him if he keeps on double digging he`ll do his back in sooner or later.

[tim]

Is there one more problem there?? With such enthusiastic double-digging, might not the soil be so loose that some brassica will fail to  heart well?? = Tim

[Hugh_Jones]

Quite right, tim.  As I don`t believe in digging anyway, and can`t grow brassicas for club root, I overlooked that point.  Another good reason to tell OH not to waste his energy on double digging.

[Sarah-b]

 But he seemed to be enjoying himself so much.
How about we give it a really good pressing down in the Spring?

Sarah.