Soil pH

Soil pH tells you how acidic or alkaline your soil is. It runs on a scale from 0 to 14: anything below 7 is acidic, 7 is neutral, and above 7 is alkaline. It matters because pH controls how easily plants can take up nutrients from the soil. Even a well-fed bed can leave plants struggling if the pH is wrong, because the nutrients get locked up where roots can't reach them.

The good news is that most vegetables are relaxed about it. Aim for a slightly acidic to neutral pH of about 6.0 to 7.0 and the great majority of crops will be perfectly happy. Only a handful of plants are genuinely fussy, and those are the ones worth knowing about.

Testing your soil

You don't need anything expensive. A simple pH testing kit from any UK garden centre or Amazon costs a few pounds and uses a colour chart to give you a reading. Mix a small soil sample with the supplied solution, compare the colour, and you have your answer in minutes. Test a few spots around the plot, as pH can vary across a single garden. Digital pH meters exist too, though the cheap ones can be unreliable, so the colour kits are often the safer bet for beginners.

What different crops want

Most veg sits comfortably in that 6.0 to 7.0 band. Two groups are worth singling out:

• Brassicas (cabbage, kale, broccoli, sprouts) prefer the higher end, around pH 6.5 to 7.5. A slightly limier soil also helps deter clubroot, a disease that thrives in acidic ground.
• Blueberries are the classic acid-lover. They need a properly acidic soil of around pH 4.5 to 5.5 and will simply sulk, yellow and fail in ordinary ground. This is why blueberries are nearly always grown in pots of ericaceous (acidic) compost rather than in a border.

When the pH is too high for an acid-loving plant, you often see chlorosis — yellowing leaves with green veins — as iron and other nutrients become unavailable.

Nudging the pH

You can shift pH, but it's a slow business, so don't expect overnight change. To make soil more alkaline (raise the pH), add garden lime in autumn or winter, following the rates on the bag. This is the traditional move before a brassica bed. To make soil more acidic (lower the pH), it's far easier to grow in containers of ericaceous compost than to fight an alkaline garden, but you can also dig in plenty of well-rotted organic matter and use sulphur chips to gently nudge things down over a season.

For most beginners, the simplest approach is to test once, then choose crops that suit what you've got. Working with your soil beats endlessly battling it.