A little on soil pH

A little on soil pH

I decided to bite the bullet at the weekend and tackle my old Landrover which has been sitting in the shed since the gearbox packed up a couple of weeks ago. I wasn't looking forward to getting oily so was quite pleased when I discovered some blueberry plants in the back which I had forgotten about. Despite spending 2 weeks in the back of a Jeep they were all still alive so I gratefully ditched the spanners in favour of a spade and trotted off to the garden.

You probably know blueberries like an acid soil and that you should use ericaceous (acidic) compost if planting them in pots but what about planting them directly in the ground? Well, if you have an alkaline soil the answer is you can't. If, however, you have been cursing your peaty acidic garden for years then now is your time to shine!

Growgrid mat with blueberry bush

Blueberries need a low pH of 5.5 or lower to thrive but they also need reasonably well drained soil which rarely goes hand in hand. I won't bore you with any more mountain climbing exploits but wild blueberries are a common (and welcome) sight on acidic high ground where steep slopes prevent waterlogging. I have a couple of acres of acidic field so I figured it would be an ideal spot for my new blueberry farm.

My field would be very wet if it wasn't for deep drains around the perimeter so I have placed my blueberry plants close to the edge as this will be the driest ground. As you can see in the photo above I have used an old 'Growgrid' mat to keep the grass down. I dug planting holes and broke up the dark peaty soil a good deal before placing the plastic on top and planting through the pre-cut planting holes. These mats are excellent for this type of application where you want to put something in and pretty much forget about it, They are long lasting too, I have been using the same mats for the last 3 years with no deterioration whatsoever.

Acidic soil west of ireland

A brief explanation of soil pH pH means how acid or alkaline a soil is. The scale runs from 0 -14 and basically measures the amount of calcium in the soil. Neutral is in the middle (7) with lower numbers being acid and higher more alkaline. Areas of high rainfall are prone to acid soils as calcium is washed out over the years. Due to our climate most soils in the British Isles tend to be slightly acid with lower pH on peaty soils in the West.

Why does it matter? Most vegetables prefer a slightly acidic soil with a pH of approx 6.5 with some crops (like cranberries and blueberries) needing a lower, more acidic reading. The issue with acidic soil below 5.0 is that some key nutrients like phosphate can become unavailable to plants or 'locked up' while other elements like aluminium and manganese can become overly available to the extent that they become toxic. Diseases like club root in members of the brassica (cabbage) family are more likely in acid soils and can be controlled by raising the pH.

Soil bacteria

We also need to remember the micro-organisms or good bacteria in the soil which process organic matter and feed it to our plants. The more acidic the soil becomes the less active these guys are with readings below 4.5 halting them altogether. This means no more nutrients are released and the soil structure begins to break down.

As I've said most vegetables like a pH of about 6.5. Asparagus, lettuce, broccoli and mint will suffer below 6 on the scale while crops like outdoor tomatoes, rhubarb, swede and turnip are happy at about 5.5 with potatoes able to grow as low as 5.0.

Maxicro calseafeed

How do I know if my soil is too acidic and how do I fix it? Soil can be tested with an electronic soil test meter, a simple litmus type kit or if more accurate result are needed; a full lab test. As a rule of thumb if you have a good earthworm population and crops are growing well you can assume you don't have a problem. If earthworms are scarce, there is moss growing on the surface and you have acid tolerant weeds like docks. sorrel and rushes then it is worth testing your soil.

Low pH can be cured by adding calcified seaweed or lime. I prefer calcified seaweed as it also contains trace elements and you are less likely to overdo it. Lime dressings should only be added every 3rd or fourth year with lighter applications recommended and should not be added with manure or compost.

As most soils in the UK and Ireland are on the acidic side it is highly unlikely you will have a problem with high or alkaline pH.