How much lime to raise soil pH
Sandy soil needs about 25 lb of pelletized lime per 1,000 sq ft to move pH half a point, loam about 40 lb and clay about 60 lb — here is the full table, the material adjustment, and the cap on how much you can put down at once.
How much lime, by soil texture
The honest answer is that soil texture decides it, not the pH number on its own. Clay and peat buffer two to three times harder than sand, so the same 0.5-point move costs 25 lb per 1,000 sq ft on sand and 60 lb on clay.
| Soil texture | To raise pH 0.5 | To raise pH 1.0 | Why |
|---|---|---|---|
| Sandy | 25 lb | 50 lb | Drains fast, little buffering — moves with less lime. |
| Loam | 40 lb | 80 lb | The middle case, and the reference for these figures. |
| Clay or peat | 60 lb | 120 lb | Buffers hardest; needs roughly twice what sand needs. |
Pounds of pelletized calcitic lime per 1,000 sq ft, worked into the top ~6–8 in.
Per square foot: divide by 1,000. Sand needs about 0.025 lb per sq ft for a half-point, loam about 0.04 lb, clay about 0.06 lb — which is why lime is always quoted per 1,000 sq ft or per acre. A 4×8 raised bed is 32 sq ft: on loam that is roughly 1.3 lb of lime to move it half a point, not a bag.
The cap nobody mentions
Do not put down more than 50 lb per 1,000 sq ft in one application. Above that, split it — half now, half in six months to a year — and till the first half in. Lime reacts where it touches soil; a heavy surface dump mostly sits there, and on a bed already near target it can overshoot into the range where phosphorus and micronutrients lock up.
Choosing the material
| Material | CCE | Multiply the rate by | Notes |
|---|---|---|---|
| Pelletized calcitic lime | 100% | 1× | The common garden-centre bag. Calcium carbonate, pelletized to spread cleanly. |
| Dolomitic lime | 109% | 0.92× | Carries magnesium as well as calcium. Pick it only if the report shows magnesium low. |
| Ground agricultural limestone | 90% | 1.11× | Coarser and cheaper; slower to react than pelletized. |
| Hydrated lime | 136% | 0.74× | Fast and caustic. Easy to overshoot and it burns skin and eyes — most gardens do not need it. |
| Oyster shell lime | 95% | 1.05× | Slow release, common in organic systems. |
| Wood ash | 50% | 2× | Varies widely by what was burned. Also adds potash — check K on the report before using it as lime. |
CCE = calcium carbonate equivalent. The table above is quoted for a 100% CCE pelletized lime; a material with a lower CCE needs proportionally more.
If your report has a buffer pH, use that instead
A texture estimate is a fallback. If your lab printed a buffer pH (sometimes "SMP buffer", "Adams-Evans", "Mehlich" or "Moore-Sikora"), that number already measures your soil's reserve acidity, which is the thing texture is only a proxy for. The University of Kentucky figure is about 1,000 lb per acre of 60% ECCE agricultural lime for every 0.1 of buffer pH below 7.0, toward a target of pH 6.5 in the top 7 inches. Divide by 43,560 to get pounds per square foot, or by 43.56 for pounds per 1,000 sq ft.
And if the report printed an actual lime rate, use it as printed. Your own lab's recommendation wins. Loam converts what the report already says into what your bed and your bag need — it does not set rates.
When to spread it
Lime is slow. Pelletized material worked into moist soil moves the pH over about three to six months; ground agricultural limestone takes longer still. Autumn application ahead of a spring planting is the standard advice for exactly that reason. Re-test before you lime again — the common failure is a second application laid down before the first one has finished working.
FAQ
How much lime do I need to raise soil pH by 1 point?
On a loam, roughly 80 lb of pelletized calcitic lime per 1,000 sq ft raises pH about a full point. Sandy soil needs around 50 lb and clay or peat around 120 lb, because heavier soils buffer harder. Never apply more than 50 lb per 1,000 sq ft at once — split larger amounts across two applications six months to a year apart.
How much lime per square foot?
About 0.04 lb per square foot moves a loam half a pH point — which is why the figure is normally quoted per 1,000 sq ft instead. For a 4×8 ft raised bed (32 sq ft) on loam that is roughly 1.3 lb.
How long does lime take to raise pH?
Three to six months for pelletized lime worked into moist soil, and longer for coarse ground limestone. Re-test before applying again rather than assuming the first application failed.
Is dolomitic or calcitic lime better?
Calcitic is the default. Choose dolomitic lime only when the soil test shows magnesium low — it carries magnesium as well as calcium, and adding magnesium a soil does not need can push calcium and potassium out of balance.
Can I use wood ash instead of lime?
You can, but it is roughly half as strong as pelletized lime by weight and it varies widely with what was burned. It also adds potassium, so check the K figure on your report before using it as a liming material.
What you need to do this properly
You cannot lime by eye — the whole rate depends on a starting pH and, ideally, a buffer pH.
- A home soil test kit gives you a starting pH in minutes; a mail-in lab test gives you the buffer pH and the actual recommendation, which is the number worth having.
- Pelletized calcitic lime is the default material — it spreads cleanly and the figures on this page are quoted for it.
- Elemental sulfur is what you want if the report says the pH is too high — liming is the wrong direction there.
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Sources
Texture figures are typical published values for a 6–8 in incorporation depth and are an estimate; a measured buffer pH from your own lab beats them, and a printed lab recommendation beats both.