Soil pH: The Gardening Topic Everyone Talks About… But Do You Really Need to Worry?

With spring just around the corner, thousands of South Africans are preparing their vegetable gardens. Compost is being spread, seedlings are being bought, seed packets are coming out of storage and garden centres are filling up with eager gardeners ready for a fresh season.

And, almost without fail, one question starts popping up everywhere…

“Should I test my soil pH?”

It’s one of the biggest debates in gardening. Some gardeners insist you need to know your pH before planting anything. Others have never tested their soil in their lives and still harvest baskets full of vegetables every season. So who’s right? The answer, like most things in gardening, lies somewhere in the middle.

What exactly is soil pH?

Soil pH is simply a measure of how acidic or alkaline your soil is. The scale runs from 0 to 14. A pH of 7 is considered neutral. Anything below 7 is acidic, while anything above 7 is alkaline. That sounds simple enough, but why does it matter? The pH of your soil doesn’t directly feed your plants. Instead, it controls how available nutrients are to the roots. Imagine you’ve prepared the perfect Sunday lunch. The food is sitting on the table, but you’ve locked the dining room door. The meal is there, but nobody can eat it.

The same thing can happen in your garden. Even if your soil contains plenty of nitrogen, phosphorus, potassium and trace elements, an unsuitable pH can make those nutrients difficult for plants to absorb. In other words, your soil may be rich in nutrients, but your plants can still show signs of deficiency because they simply can’t access them.

Does soil ever have the “wrong” pH?

Yes—but perhaps not as often as social media would have you believe. Your soil’s pH is influenced by many factors. The type of rock beneath your property, years of rainfall, irrigation water, fertilisers, compost, and even previous crops all play a role. Here in the Western Cape, for example, many soils tend to be slightly acidic due to winter rainfall, while other parts of South Africa naturally have more alkaline soils.

The good news is that most home gardens already fall within a range that vegetables are quite happy with. Most vegetables grow exceptionally well in soils with a pH between 6.0 and 7.0. That includes tomatoes, lettuce, spinach, carrots, beans, peas, onions, peppers, beetroot, cabbage and many more. This is why experienced gardeners often focus far more on improving soil health than chasing the perfect pH number.

But don’t all plants want different pH levels?

They do. Blueberries are probably the best-known example. They love acidic soil, often between pH 4.5 and 5.5. Plant them in ordinary garden soil and they’ll usually struggle, even if you fertilise them well. Potatoes also prefer slightly acidic conditions. In fact, keeping the pH a little lower can help reduce common scab on potato tubers. On the other hand, asparagus, spinach and brassicas can tolerate slightly more alkaline soils than many other vegetables. But these are the exceptions rather than the rule. If you’re growing a mixed vegetable garden, aiming for a pH of around 6.5 is ideal because it keeps most crops happy.

The mistake many gardeners make

Every spring, bags of agricultural lime fly off the shelves. Some gardeners add lime because their neighbour told them to. Others heard it “sweetens the soil.” Some do it every year because that’s what they’ve always done. Here’s the problem… Lime is not a fertiliser. It doesn’t feed your plants. Its main purpose is to raise the pH of acidic soils. If your soil already has an acceptable pH, adding lime can actually create problems. Certain nutrients—especially iron, manganese and zinc—become less available as the soil becomes more alkaline. Plants may start showing yellow leaves even though those nutrients are still present in the soil.

The opposite is also true. Some gardeners try to acidify their soil without first testing it, creating unnecessary imbalances that can take years to correct. Changing your soil’s pH without knowing where you’re starting is a bit like taking medication before you’ve been diagnosed.

So should every gardener own a pH tester?

Not necessarily. If your vegetables are healthy, your harvests are good, and your plants grow vigorously year after year, there’s probably no urgent reason to test your soil. However, if you’ve improved your watering, added compost, fertilised correctly, ensured enough sunlight, and your plants still struggle season after season, then testing your pH becomes a very sensible next step. The good news is that testing has become inexpensive. Basic home pH kits are widely available, and for those wanting a complete picture, professional soil laboratories can provide detailed analyses that include nutrient levels as well.

Here’s what many gardeners don’t realise…

Soil pH isn’t fixed forever. It changes slowly over time. Heavy rainfall can gradually make soils more acidic by washing away calcium and magnesium. Certain fertilisers, particularly those high in ammonium nitrogen, can also lower soil pH over many years. On the other hand, irrigation water rich in calcium can slowly increase pH in some areas.

That’s why commercial farmers regularly test their soils—not because they’re constantly changing the pH, but because they want to monitor what is happening beneath the surface before problems appear.

The secret ingredient isn’t pH…

It’s organic matter. This is where many beginner gardeners get caught up in numbers while experienced gardeners quietly build beautiful soil. Compost, well-rotted manure, leaf mould and mulch feed the billions of microorganisms living underground. Those microbes break down organic matter, recycle nutrients and help make them available to plants. Organic matter also acts like a buffer, reducing sudden swings in soil pH and improving the soil’s ability to hold both nutrients and water. In many cases, adding compost year after year does far more for your vegetables than trying to chase the perfect pH. Healthy soil biology often compensates for small pH imperfections.

So, what should you do this spring?

Before spending money on lime, sulphur or fancy soil additives, start with the basics. Feed your soil with compost. Keep it covered with mulch. Avoid leaving bare ground exposed to the sun. Water deeply rather than lightly. Rotate your crops and continue adding organic matter every season. Then observe your plants. They’ll often tell you far more about your soil than a number on a pH meter ever could. If problems persist despite doing all the right things, then test your soil and make changes based on real information—not gardening myths.

After all, gardening has always been about working with nature, not against it. And while soil pH certainly matters, it’s only one piece of a much bigger picture. Build healthy soil first, and more often than not, everything else starts falling into place.

Want to learn more about building healthy soil, feeding your plants correctly and growing with confidence this spring? Our monthly VanZylStead Digital Magazine ^[1] is packed with practical, seasonal advice designed specifically for South African gardeners. Let us take the guesswork out of gardening, so you can spend more time enjoying your harvest.

Happy Gardening my friends, and thank you for being here

Tash en die Familie

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