A soil test number tells you whether to lime and roughly how far to move, not how much to add. Use ground limestone, take the dose from the table below for your soil type and starting pH, and aim for pH 6.5 as an all-round target (Scottish farm advisers aim lower), and keep lime and manure apart: at least a week with manure or slurry first, or three months with lime first. The advice is for vegetable and ornamental beds, not lawns.
What your soil test number tells you
pH 6.5 is the best all-round pH for the majority of garden plants, and nutrient availability is at its highest between pH 6.1 and 7.0, when nothing usually needs adding (RHS). The RHS dose table starts at pH 6.0 and works downwards. Test with a cheap home kit, and do not retest within three months of adding lime, fertiliser or organic matter, because the test may give misleading results. For why Scottish soil is acid and how to test it, see soil pH testing and adjustment.
The target is lower in Scotland. Scottish farm advisers aim for pH 6.0 to 6.2 on mineral soil and pH 5.3 to 5.5 on peaty soil. Peat soils cover 22.5% of Scotland (Scottish Soil Framework), Acid rocks and podzols are widespread too, and the wet climate washes elements out of the soil, leaving it relatively acid and nutrient poor. If your soil really is peaty rather than just dark, do not chase the clay or loam number.
Three kinds of lime
Ground limestone (calcium carbonate) is the default, and every dose rate here is for it. Its neutralising value is 50 to 55. Ground chalk has the same value, so use it at the same rate. Dolomite lime (56) is close enough to swap in at the same rate and adds magnesium, which is worth having if a soil test shows low magnesium. Calcified seaweed is weaker, at 44, so it takes more of it for the same effect. Hydrated (builders') lime has a value of 70, so you need less of it, and it can irritate skin and eyes: wear gloves and consider safety goggles (RHS).
How much to apply
Clay holds onto acidity more stubbornly than sand, so it takes more lime to move the same distance. These are kilograms of ground limestone per square metre to reach pH 6.5 (RHS):
| Soil type | Starting pH 6.0 | Starting pH 5.5 | Starting pH 5.0 | Starting pH 4.5 |
|---|---|---|---|---|
| Clay | 0.6 kg/m² | 1.0 kg/m² | 1.4 kg/m² | 1.8 kg/m² |
| Loam | 0.5 kg/m² | 0.8 kg/m² | 1.2 kg/m² | 1.5 kg/m² |
| Sandy | 0.4 kg/m² | 0.7 kg/m² | 1.0 kg/m² | 1.3 kg/m² |
A 6m² clay bed starting at pH 5.5 needs about 6kg altogether, not the 1.0kg per square metre in that cell. When the rate is more than 0.5kg per square metre, dig half into the soil and sprinkle the rest on the surface after digging. For smaller amounts, dig it all in if practical.
The table is for pH 6.5, which is more than the Scottish mineral-soil target of 6.0 to 6.2. No rate table exists for stopping at 6.0 to 6.2, so on Scottish mineral soil add part of the table amount, retest after three months, and add more only if you are still below target. Lime acts slowly, so it is easier to add more later than to correct an overshoot. Peaty soil is not in the table, and no garden-scale dose exists for it: work towards 5.3 to 5.5 in small additions and retest.
Timing, and why lime and manure don't mix
Lime is usually added in winter for annual crops such as vegetables, just before digging. On perennial beds, surface lime can take years to have any effect, so lime first if the soil is acid and then plant (RHS).
Keep lime away from slurry and manure in time. Irish advice for farms (Teagasc) is that up to 50% of the available nitrogen in cattle slurry can be lost as ammonia when it is spread on recently limed ground. The advice is to apply slurry first and lime seven to 10 days later, or to leave three months between lime and a following slurry or urea application, which is the order to follow if the lime goes on first. That research is on slurry and urea in fields, not garden manure, so treat it as a precaution for beds: do the two jobs at different points in the year, for example lime in winter before digging and manure or compost in spring, rather than on the same weekend.
The risks of over-liming
Nutrient lockout. In alkaline soil, iron and manganese become less available to roots, and boron is less available above pH 7. The symptom is yellowing between the leaf veins: iron affects the youngest leaves most, manganese the older ones (RHS). Avoid liming soil that is already alkaline.
Acid-loving plants. Rhododendrons, camellias, heathers and blueberries are acid-lovers, and rhododendrons do not grow well in soil with appreciable calcium (RHS). Plants that cannot take up iron and manganese yellow and grow poorly. Keep lime away from their beds, and do not lime a bed you plan to use for them.
ClubrootA soil-borne fungal disease of the brassica family that swells and distorts roots, and survives in soil for years. Full definition → against potato scab. Clubroot of brassicasThe cabbage family: cabbage, kale, broccoli, cauliflower, Brussels sprouts, kohlrabi, swede, turnip and more, sharing the same pests, diseases and rotation rules. Full definition → is less prevalent in alkaline soil, but common scab is worse on it, so liming to prevent clubroot predisposes potatoes to scab. The RHS advice is to apply lime only after potatoes in your rotationMoving each crop family to different ground each year, on a multi-year cycle, so pests and diseases that build up in soil don't get a repeat host. Full definition →, so put it on ahead of the brassicas, not on a fixed yearly schedule.
Common questions
Will liming harm blueberries, rhododendrons or other acid-loving plants nearby?
Yes, potentially. Rhododendrons grow best at pH 4.5 to 6.0 and do not grow well in soil with appreciable calcium, and camellias, heathers and blueberries are also acid-lovers (RHS). Lime-induced yellowing (chlorosis) is the plant failing to take up iron and manganese. Keep them in their own bed or a container away from any area you are liming.
How long after liming can I plant?
Lime is usually added in winter for annual crops such as vegetables, just before digging, so it has done its work before spring planting (RHS). Surface-applied lime on established plantings can take years to have any effect.
How often do I need to lime?
There is no fixed yearly schedule, so retest instead of liming by the calendar. Wait three months after adding lime, fertiliser or organic matter, because a test sooner than that can mislead (RHS).
What if I don't know whether my soil is clay, loam or sand?
Clay is sticky when wet and rolls into a long thin sausage that smooths to a shiny finish. Sandy soil feels gritty, falls through your fingers and cannot be rolled into a sausage. Loam is a mixture of clay, sand and silt that avoids the extremes of both (RHS).
Is peaty soil treated the same as the rest?
No. Scottish advisers aim for pH 5.3 to 5.5 on peaty soil, against 6.0 to 6.2 on mineral soil. No garden-scale dose is published for peaty soil, so add lime in small amounts and retest rather than borrowing a mineral-soil rate.
Sources
Show the 12 sources
- RHS: Lime and liming: The pH 6.5 all-round target, the dose table by soil type and starting pH, lime types and neutralising values (ground limestone and chalk 50 to 55, dolomite 56, calcified seaweed 44, hydrated lime 70), splitting doses over 0.5kg per square metre, winter application before digging, surface lime taking years to work, the three-month retest caveat, clubroot being less prevalent in alkaline soil, and gloves and goggles for hydrated lime
- RHS: Soil pH and testing: Home test kits, pH 6.5 as the best general-purpose pH, nutrient availability being highest at pH 6.1 to 7.0, iron and manganese becoming less available at 7.1 to 8.0, and nothing usually being needed at 6.1 to 7.0
- RHS: Potato scabs: Common scab being worse on alkaline soil, liming for clubroot predisposing potatoes to it, and applying lime only after potatoes in the rotation
- RHS: Nutrient deficiencies: Yellowing between leaf veins, iron affecting the youngest leaves and manganese older ones, boron being less available above pH 7, and avoiding liming already alkaline soil
- RHS: Rhododendrons on alkaline soils: Rhododendrons growing best at pH 4.5 to 6.0, not growing well with appreciable calcium, and chlorosis being failure to take up iron and manganese
- RHS: Acidifying soil: Rhododendrons, camellias, heathers and blueberries as acid-loving plants
- RHS: Soil types: Telling clay, sandy and loam soil apart by feel
- FAS Scotland (SAC Consulting/SRUC): Best use of limited supplies, lime: Target pH of 6.0 to 6.2 on Scottish mineral soil and 5.3 to 5.5 on peaty soil (a farm advisory source)
- gov.scot: The Scottish Soil Framework: Peat soils covering 22.5% of Scotland and acid rocks and podzols being widespread
- Scotland's Soils (Scottish Government soils portal): Scotland's wet climate washing elements out of soils and leaving them relatively acid and nutrient poor
- Teagasc: The lime, silage and slurry quandary: Up to 50% of available slurry nitrogen lost when cattle slurry is spread on recently limed fields, and applying slurry first and lime seven to 10 days later (Irish farm advice)
- Teagasc: Lime, the forgotten fertiliser: Leaving three months between lime and a following urea or slurry application, and seven days between urea or slurry and a following lime application (Irish farm advice)