Why Soil pH Deserves Your Attention

Soil pH is one of those quiet numbers that shapes almost everything else on your plot. It governs how readily your crops can take up nutrients, how well soil life thrives, and which plants will simply sulk no matter how much you water or feed them. Get it roughly right and carrots, brassicas and beans seem to look after themselves. Get it badly wrong and you can spend a fortune on fertiliser while your vegetables sit there, small and yellowing, unable to access what is already in the ground.

The good news is that pH is one of the easiest things to measure at home, and one of the most rewarding to adjust. You do not need a laboratory or a science degree — just a little patience and a willingness to test before you act.

The pH Scale in Plain English

The scale runs from 0 to 14, with 7 sitting neutral. Anything below 7 is acidic, anything above is alkaline. Most UK garden and smallholding soils fall somewhere between 4.5 and 8.5, and the majority of vegetable plots sit comfortably between 5.5 and 7.0.

Where you are in the country gives a strong clue. Sandy heathland soils in parts of Norfolk, Surrey and the New Forest tend to be naturally acidic, sometimes below pH 5. Clay and loam in the Midlands often hovers near neutral. If your land sits on chalk or limestone — think the Cotswolds, the Chilterns or the Yorkshire Wolds — you are likely working with something alkaline, occasionally above pH 7.5. Old pasture, woodland edges and long-cultivated kitchen gardens all carry their own history, so never assume.

Simple Tests You Can Do This Weekend

Start by sampling properly. Take ten to fifteen small cores from across the plot, each about 10–15cm deep, and mix them in a bucket. Test awkward corners separately — an old bonfire patch, a hedge border or a spot where lime has been tipped in the past can read very differently from the rest of the plot.

• The vinegar test: put a spoonful of soil in a jar and dribble on a little white vinegar. If it fizzes, your soil contains free lime and is alkaline.
• The bicarbonate test: mix another spoonful with a little water, then add bicarbonate of soda. Fizzing means acidic soil.
• Liquid indicator kits: cheap, reliable and far more precise than the fizz tests. Follow the instructions and compare the colour against the chart in daylight, not under a kitchen bulb.
• Electronic meters: handy for quick readings, but the inexpensive ones drift badly. Test damp soil, take three readings and trust the average rather than a single number.

For accuracy, and especially if you are planning an orchard or a serious soft fruit bed, a professional soil analysis is money well spent. It will also tell you about phosphorus, potassium and magnesium at the same time.

What Your Result Means for Crops

Most vegetables are happiest in a slightly acidic to neutral range, around pH 6.0 to 7.0. That is where nitrogen, phosphorus and potassium are most available, and where the soil bacteria and worms that keep everything cycling are at their busiest.

• Brassicas — cabbages, sprouts, kale, broccoli — want pH 6.5 to 7.5. Liming also helps suppress clubroot, which thrives in acid ground.
• Legumes — peas, beans, clover green manures — need pH 6.0 or above for their nitrogen-fixing bacteria to work properly.
• Roots — carrots, parsnips, beetroot — do well at 6.0 to 6.8.
• Onions and leeks prefer 6.0 to 7.0, and dislike freshly limed ground.
• Potatoes are the exception: they tolerate pH 5.0 to 6.0, and growing them in alkaline soil encourages scab.
• Blueberries, cranberries and rhubarb want genuinely acidic ground, pH 4.5 to 5.5, which usually means growing in containers of ericaceous compost.

If your plot reads below 5.5, expect poor results from most brassicas and legumes. Above 7.5, iron, manganese and zinc start to lock up, and you may see interveinal yellowing on raspberries and other soft fruit.

Adjusting pH Without Making a Mess

Raising pH is straightforward. Ground limestone or dolomitic lime, applied in autumn and raked into the surface, will lift it gradually. As a rough guide on a sandy loam, around 250–300g per square metre raises pH by about half a point; heavy clay may need twice that. Never apply more than 500g per square metre in one go, and always read the product label rather than guessing. Dolomitic lime also supplies magnesium, useful on light soils where that is often short.

Lowering pH is slower and harder. Flowers of sulphur, worked in over a season, will gently acidify soil, and regular dressings of composted bark, pine needles or leaf mould help over the long term. For acid-loving plants, the practical answer is usually raised beds or pots filled with ericaceous compost rather than trying to change a whole field.

Two rules worth remembering: do not lime ground you plan to plant with potatoes, and do not spread lime and manure at the same time, as the lime drives off nitrogen you would rather keep.

Retest, Record and Rotate

Keep a simple notebook or a note on your phone: the date, the reading, what you applied and where. Retest every two to three years, or annually if you are actively correcting a problem. Aim for the pH that suits the bulk of your crops rather than chasing perfection for one awkward plant, and use your rotation to put acid-tolerant potatoes before a limed brassica bed. Get the number right and the rest of your growing year becomes noticeably easier.