The pH of soil refers to the acidity level and is measured by the number of Hydrogen ions present.

When the pH is too acidity we term this as low pH, if the soil is too alkaline then this is referred to as high pH.

Nutrients present in the soil become locked-up or unavailable. Correcting the pH has the same effect as applying fertilizer since it unlocks plant nutrients already present.

pH levels are based on 'powers of 10' ( Logarithmic ), therefore pH 6.0 is 10-times more acidic than pH 7.0 and pH 5.0 is 100-times more acidic than pH 7.0


For vegetables aim for a level of pH 6.5, but between pH 6 and pH 7 is good and pH 5.5 to pH 7.5 is acceptable.


Description Level

< 5.5

Strongly acid

5.5 - 5.9

Medium acid

6.0 - 6.4

Slightly acid

6.5 - 6.9

Very slightly acid



7.1 - 7.5

Very slightly alkaline

7.6 - 8.0

Slightly alkaline

8.1 - 8.5

Medium alkaline

> 8.5

Strongly alkaline


If the soil is too acidic, the pH can be adjusted by adding lime. There are different types of lime, so please ensure you read the manufacturers instructions regarding precautions, use and quantities. Never add lime at the same time as manure as this will release ammonia which can damage your plants. Allow about a month before sowing or planting after the application of lime. The spent compost from mushroom beds contain lime.

It is not as easy to lower the pH ( Alkaline ) levels though, but most organic manures are on the acidic side and can help lower the levels. Leafmould, especially from pine trees are on the acidic side.  

Soil Structure.

It is important that you maintain and improve the quality of your soil, this can not be stressed enough, to ignore the soil will result in disappointment.

The best way to improve the soil structure is by adding well rotted down vegetable waste and farmyard manures, it they are not well rotted down they will need nitrogen to complete the process and extract it from the soil. Remember the aim is to add nitrogen to your soil. Well rotted substances become odourless when the process is completed, but some may contain a strong smell of ammonia i.e. animal and bird manures whose chemicals will evaporate or be converted by the weather.

How do you incorporate it into the soil ? Dig it in, placing the manure at the bottom of your spit level, this will help to retain moisture and supply where the nutrients are needed, at the bottom where the roots are, this will result in better plants.

Top dressing can also be applied when you have already planted or where permanent plants exist, this will also act as a mulch, but ensure the soil does not contain weed seeds or you will be creating perfect conditions for them, the very thing you are trying to eradicate. Remember that when planting fruit trees or any plant that will be a permanent site to dig your manure in first as the only option left is top dressing.

Not all crops like or need to be grown in freshly  manured soil, root crops tend to fork, which indicates the soil is too rich. Therefore use soil that as been manured for a previous crop ie brassicas or add the previous autumn.

And finally working on wet soil compacts it and destroys it's structure, to avoid this use a plank of wood.

Soil Conditioners.

Farmyard manure.

Farmyard manure has two main advantages, adding bulk and nutrients to the soil. the manure comes from many forms of livestock and should be stacked for at least six months before use.

Garden compost.

We should all recycle as much as possible from our gardens. Don't use weeds that are in seed or plants that are diseased.

Green manure.

Some crops are grown just to simply dig in to improve the soil structure and add nutrients.

Do not let them flower or go to seed.

Green manure can be grown as a separate crop or between existing rows of crops ie clover can be grown amongst Cabbages, this not only gives ground cover to reduce the weeds but fixes nitrogen.

Types of Green manure.

Broad beans, Lupins, Mustard, Phacelia, red clover and Winter tare.


Leafmould takes about two years to break down and what was a large pile reduces to a small layer. It is usually acidic and used to reduce the pH of soil.