I associate soil pH values with miniature test tube kits, filled with garden soil, a mud monochrome of the model glass lighthouses you fill with multicoloured sand from Alum Bay on the Isle of Wight. But whilst lighthouses keep you off the rocks, soil testing kits will tell you what their ground down ancestors are made of. And once you know the pH of your soil you will know whether Rhododendrons planted in your garden will be a dead cert or dead shrub and if Hydrangeas will favour blue or pink.
As I don’t have enough soil to put in a test tube, let alone grow things in, my understanding beyond this, is vague. So Saturday Swot Shop today is Tomato Lover’s PDQ guide to soil pH .
What does pH actually mean ?
- Potential Hydrogen Ions.
None the wiser… How does it relate to soil ?
- Soil is either acid, alkaline or neutral. pH is measured on a scale of 1 to 14. The middle of the scale at 7, is neutral. Below 7 and it’s acid , above 7 and it’s alkaline. What’s being measured is the amount of lime (calcium ) in the soil.
Does it matter ?
- At certain levels of acidity or alkalinity some minerals cannot dissolve in water and so get ‘locked up’; held in the soil, meaning they are not available for absorption by the plant and so the plant is deprived of essential nutrients. Certain plants will thrive in one type of soil but die in another. The expression ‘lime hating’ plants covers those which grow well in acidic soil.
Can the pH value of soil be changed ?
- To make acid soil more alkaline lime is added to the soil. Increasing the acid in alkaline soil is more difficult but sulphur is used for this purpose.
What’s the normal pH range for soil and what’s the right soil for tomatoes ?
- Most soil is 4-8.5. Tomatoes grow best at 6.0 to 6.8, so slightly acid.
And why in pH is the p lower case and the H upper case ?
- pASS !
{ 7 comments… read them below or add one }
Answer to your last question: And why in pH is the p lower case and the H upper case ?
You mentioned it in the earlier part: potential Hydrogen ions.
Hydrogen’s atomic symbol is H.
Hello
Thank you for stopping by and getting in touch – and solving the mystery – the answer for which was under my nose all along! sometimes that’s the best way of learning – as once explained never forgotten!
I planted tomatoes in buckets. I just checked the soil as my tomatoes have blossom drop. It is in the alkaline level. I have a acid-alkaline tester and it is on the 8 in the alkaline level.
What do I need to do to get the right PH???
Also I water when the soil is between med to dry. I try not to over water. Also I feed them with ortho tomatoe food but not sure how much and how often.
Thanks for any help you can give me.
Charlotte
Hello. Thank you for stopping by and getting in touch.
I am sorry to hear about your flowers – very upsetting to see them blossom and then go! And you are right that 8 is not ideal for tomatoes – they would be much happier at a pH of 6.0-6.75 – at this level most nutrients plus all the major and minor trace elements will be avaliable to the plant. With an alkaline soil of 8 some of those nutrients are not going to be avaliable to the plant – they get “locked up” – a result of the alkaline soil making them insoluble – and if they are not able to travel into the plant via water – then the plant doesn’t get them – and that causes deficiencies and problems. And hence back to your problem.
To adjust soil pH to a more acid reading – so down toward the 6.0 to 6.75 range the normal approach would be to add Sulphate of Ammonia – but – and sorry not to be of more help – I dont’ want to advise you in any detail as I don’t know what the application details are. Each year I use growing compost fresh from the bag – as I don’t have any soil in my garden that I could transfer to buckets -so it wouldn’t be right to tell you how to do something I haven’t done!
And again on the feeding regime – follow the manufacturer’s instructions as each product varies. But one tip I have come across a lot and now use myself is rather than feed once a week – is to feed the weekly amount split into smaller amounts – so to feed the same overall – but to do in smaller amounts more regularly.
Sorry not to be able to solve your problems – but I hope it all works out – and that you get some nice tomatoes for the summer!
Sally
Your question and answer “What does pH actually mean ?” “Potential Hydrogen Ions” sounds good, but is wrong. pH is a scientific abbreviation standing for the negative logarithm of the hydrogen ion concentration. Thus the lower the number, the higher the acidity (higher acidity has more hydrogen ions).
Hello
Thank you for getting in touch. I get the logarithmic scale, I get that the lower the number – the higher the acidity. So I think it’s all coming together -albeit slowly!
Hi Sally,
Looks like I am a little late for this conversation but how about adding some powdered lime (calcium carbonate) as a side dressing mixed into the soil a few inches and then watered in? Of course it is better to add it in the Autumn but even then it does not have to be in too deeply. Marv