Acidic soil is soil with a pH below 7.0, and most garden soils sit somewhere between pH 5.5 and 7.0, so mild acidity is normal rather than a problem. It becomes a problem when pH drops below about 5.5, because at that level aluminium and manganese become soluble enough to damage roots, and essential nutrients such as phosphorus, calcium and magnesium become harder for plants to take up. Leaves yellow, growth stalls, and vegetables that should thrive instead sit small and pale. The good news is that acidic soil is manageable: test it, raise the pH gradually with lime if needed, and grow the plants that love acid ground in the meantime.
Acidic soil is common in areas with high rainfall, which washes calcium and magnesium out of the soil, and in gardens that have used a lot of ammonium-based fertilisers or conifer needles and bark over many years. Sandy soils turn acidic faster than clay because they hold fewer buffering minerals. None of that makes the soil bad — it makes it a particular kind of soil with its own strengths, including some of the most beautiful garden plants there are.
How to test for acidic soil
Start with a pH test rather than guessing. Home test kits and probe meters are cheap and give a rough reading, but a laboratory test is more accurate and also reports calcium, magnesium and nutrient levels, which matter when you choose between lime types. Take samples from several spots in the bed, at 10–15 cm deep, mix them, and test the mixture. A single reading from one corner can mislead you. Your local extension service can usually test soil for a small fee and will tell you how much lime to apply — use that service if it is available, because a test-based recommendation beats any general figure in a guide.
As a rough guide, pH 6.0–7.0 suits most vegetables, pH 5.5–6.0 is workable for many crops but worth lifting, and pH below 5.5 needs attention. Blueberries, by contrast, need pH 4.5–5.5 and will fail in neutral soil, while potatoes prefer pH 5.0–6.0 and suffer scab in alkaline ground. So "acidic" is only a problem relative to what you want to grow. See our soil pH testing guide for the full testing method, and our loamy soil guide for the broader soil picture.
What causes acidic soil
Rainfall is the main driver: rain is slightly acidic, and heavy rain leaches calcium, magnesium and potassium downwards out of reach, leaving hydrogen and aluminium behind. Removing crops also removes calcium and magnesium with every harvest. Fertilisers contribute too — ammonium sulfate, urea and other ammonium-based feeds acidify soil as soil bacteria convert ammonium to nitrate. Organic matter such as pine needles, conifer bark and oak leaves is often blamed, but its effect is modest; a thick layer of pine needles will lower pH slightly at the surface, not turn a whole bed acidic. Parent rock matters as well: soils over granite or sandstone tend acidic, while soils over limestone tend alkaline. Knowing the cause helps you choose the fix, but in practice the fix is the same whatever the cause: add calcium in the form of lime, and keep organic matter levels up.
How to raise soil pH with lime
The standard treatment is ground limestone (calcium carbonate), which raises pH and adds calcium. Dolomitic lime also adds magnesium, so choose it if your soil test shows low magnesium, and choose ordinary calcitic lime if magnesium is already adequate. Typical application rates for garden beds are roughly 100–200 g per square metre to lift pH by about half a unit in loam, and more on clay, less on sand — but these are broad ranges, and the right dose depends on your starting pH, soil texture and the lime's fineness. A laboratory recommendation should always win over a general figure.
Apply lime in autumn or winter so it has months to react before spring planting, spreading it evenly over the surface and raking or lightly forking it in. Do not apply lime and fertiliser at the same time: lime reacts with ammonium fertilisers and releases nitrogen as ammonia gas, wasting the feed. Leave at least two to four weeks between liming and fertilising, and do not lime and dig in fresh manure together for the same reason. Retest after three to six months — lime works slowly, and over-liming is harder to correct than under-liming, so raise pH in stages rather than all at once. Wood ash is a traditional alternative that also raises pH, at roughly half the strength of lime by weight, but it is variable and strongly alkaline, so use it sparingly — no more than about 100 g per square metre per year — and never on acid-loving plants.
Plants that love acidic soil
Rather than fighting your soil, grow plants that prefer it. Blueberries are the classic example and need pH 4.5–5.5; our growing blueberries guide covers them in detail. Rhododendrons, azaleas, camellias, heathers and hydrangeas all thrive in acid ground — hydrangeas famously turn blue in acidic soil and pink in alkaline soil. Potatoes, sweet potatoes, strawberries and raspberries tolerate mild acidity well. Among vegetables, potatoes prefer pH 5.0–6.0, and carrots and lettuce cope with pH down to about 5.5. If part of your garden is stubbornly acidic, make it the berry and heather bed and lime the vegetable beds instead.
Managing acidic soil without lime
If you would rather not lime, or want to hold pH steady after liming, compost is your main tool. Compost buffers pH — it nudges both acidic and alkaline soils towards neutral — and it feeds the soil life that keeps nutrients available even at lower pH. Add 5–8 cm of compost each year. Avoid ammonium-based fertilisers where possible, choosing nitrate-based or organic feeds instead. Mulch with composted bark or leaf mould rather than fresh pine needles if you are trying to raise pH. And keep the soil covered: bare acid soil loses calcium faster in heavy rain. For raised beds, you can also sidestep the problem entirely by filling beds with a neutral mix — roughly 60 per cent topsoil and 30 per cent compost — and liming only the beds that need it. Our raised bed soil mix guide gives the recipe.
Common mistakes with acidic soil
The biggest mistake is liming without testing. Many gardeners lime every year out of habit and end up with alkaline soil, which locks up iron and causes yellowing between leaf veins. Test first, lime only when the test says so, and retest before liming again. The second mistake is applying lime and fertiliser together, which wastes both. The third is expecting instant results: lime takes months to change pH, so a spring application will not fix a spring planting. The fourth is using the wrong lime — dolomitic lime on soil already high in magnesium can create imbalances, so check magnesium levels before choosing. And the fifth is trying to grow lime-loving plants such as lavender and brassicas in unimproved acid soil: lavender prefers pH 6.5–7.5, and cabbage and broccoli are prone to clubroot in acidic ground, so either lime the bed or choose different plants.
Safety notes
Wear gloves and a dust mask when spreading lime or wood ash — both are fine powders that irritate eyes, skin and lungs, and wood ash is caustic when wet. Keep lime away from children and pets until it is watered in. Do not apply lime to beds where acid-loving plants are growing. If your soil pH is below 5.0 and plants are failing, or if you are unsure how much lime to use, check your local extension service for a soil test and a written recommendation rather than guessing.
Frequently asked questions
What pH is too acidic for vegetables?
Most vegetables grow best at pH 6.0–7.0. Below pH 5.5, growth usually suffers as nutrients become less available and aluminium becomes more soluble. Potatoes are an exception, preferring pH 5.0–6.0, and blueberries need pH 4.5–5.5. If your soil is below 5.5, lime it for vegetables or grow acid-loving crops there instead.
How much lime do I need to raise soil pH?
As a broad range, roughly 100–200 g of ground limestone per square metre lifts pH by about half a unit in loam, more on clay and less on sand. But the right dose depends on your starting pH, texture and lime type, so a laboratory test recommendation should always take priority over general figures.
How long does lime take to work?
Lime works slowly — expect three to six months for a full effect, which is why autumn application is best. Retest after that period before deciding whether to apply more. Over-liming is difficult to correct, so raise pH in stages.
Can I use wood ash instead of lime?
Wood ash raises pH and adds potassium and calcium, at roughly half the strength of lime by weight, but it is variable and strongly alkaline. Use no more than about 100 g per square metre per year, keep it away from acid-loving plants, and do not mix it with nitrogen fertiliser or fresh manure.
Will pine needles make my soil acidic?
Only slightly and only at the surface. Pine needles are acidic when fresh, but as they break down their effect on soil pH is small. A mulch of pine needles will not turn neutral soil acidic, though it is still a sensible mulch to avoid if you are trying to raise pH. Compost is the better mulch choice for that job.