Soil sulfur calculator: how much sulfur to lower pH
Enter the area and soil-test pH to get the elemental sulfur you need. On established grass, spread no more than 5 lb per 1,000 sq ft at a time.
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More options: S % · Max per go · Acres …
- Bags to buy
- 2 bags
- Applications
- 2 applications
- Each application
- 25 lb
- Spreader rate each time
- 5 lb per 1,000 sq ft
NDSU table, loam soil, pH 7.5 → 6.5: 18 lb per 1,000 sq ft of sulfur (S)
Established lawn: ÷ 2 = 9 lb per 1,000 sq ft
÷ 90% sulfur in the product = 10 lb per 1,000 sq ft of product
10 lb × 5,000 sq ft ÷ 1,000 = 50 lb → 2 bags of 25 lb
10 lb per 1,000 sq ft ÷ 5 lb per 1,000 sq ft max per go = 2 applications of 25 lb each
- At pH 7.5 or higher, check for free lime first: NDSU suggests stirring a tablespoon of soil into two tablespoons of vinegar. If it fizzes, the soil holds a lot of calcium carbonate and NDSU advises against sulfur.
- Spread it as 2 applications of about 5 lb per 1,000 sq ft. NDSU advises spring or fall, with core aeration, and a retest before each new round.
- Sulfur works slowly — soil bacteria convert it to acid over months, faster in warm, moist soil. Retest before adding more.
Sulfur product by starting pH (soil type, area and lawn as above)
| Soil pH now | Sulfur product to buy | Applications | Each application | Bags to buy |
|---|---|---|---|---|
| pH 7.0 → 6.5 | 11.1 lb | 1 application | 11.1 lb | 1 bag |
| pH 7.5 → 6.5 | 50 lb | 2 applications | 25 lb | 2 bags |
| pH 8.0 → 6.5 | 94.4 lb | 4 applications | 23.6 lb | 4 bags |
| pH 8.5 → 6.5 | 158 lb | 7 applications | 22.6 lb | 7 bags |
Lime raises pH; elemental sulfur lowers it. Soil bacteria turn the sulfur into acid over months, and heavier soils need more to move the same distance. The amounts here come from NDSU Extension’s table for bringing lawn soil down to pH 6.5. On established grass the rate is halved and split into smaller doses, because heavier doses can injure it.
How much sulfur lowers soil pH
Sulfur lowers pH through soil bacteria, which oxidize it into sulfuric acid. How far a pound moves the pH depends mostly on texture: clay and organic soils resist change, sandy soils move quickly. NDSU Extension’s turfgrass soil-test guide gives these approximate amounts of elemental sulfur for bringing soil down to pH 6.5:
| Change in pH | Sand | Loam | Clay |
|---|---|---|---|
| 7.0 → 6.5 | 2 lb | 4 lb | 7 lb |
| 7.5 → 6.5 | 11 lb | 18 lb | 23 lb |
| 8.0 → 6.5 | 28 lb | 34 lb | 46 lb |
| 8.5 → 6.5 | 46 lb | 57 lb | 69 lb |
sulfur (S) per 1,000 sq ft = table amount (÷ 2 on an established lawn) product = sulfur ÷ (S% on the bag ÷ 100) applications = product per 1,000 sq ft ÷ 5 lb (round up)
Example: loam at pH 7.5 under an established lawn. The table says 18 lb, halved to 9 lb of sulfur per 1,000 sq ft; with a 90% sulfur product that is 10 lb of product per 1,000 sq ft, or 50 lb for 5,000 sq ft — two applications of 25 lb at 5 lb per 1,000 sq ft each.
Why the lawn dose is so small
Heavy doses of sulfur spread on top of an established lawn can injure the grass. NDSU’s advice for established turf is to use half the table amount, apply it only in spring or fall with core aeration, and put down no more than 5 lb per 1,000 sq ft at any one time (2 lb on bentgrass putting greens). On a new lawn the whole amount can be mixed into the top 6 in before planting.
That makes lowering a lawn’s pH a project of a year or more, not a weekend. Retest between rounds: the table is approximate, and your soil’s real response is the only reliable guide.
When sulfur won’t work
- Free lime. Soils formed on limestone or full of shell fragments contain calcium carbonate that neutralizes the acid as fast as the bacteria make it. NDSU’s vinegar test: if a spoonful of soil fizzes in vinegar, don’t use sulfur.
- Alkaline irrigation water keeps pushing the pH back up. If your water is hard, expect the effect to fade.
- Aluminum sulfate and iron sulfate are different products with different rates. This calculator is for elemental sulfur only; follow the label for anything else.
Going the other way — pH too low? The lawn lime calculator converts a lab rate, or a pH and buffer pH, into bags. For the feeding that follows, the lawn fertilizer calculator works from the numbers on the bag.
What you’ll need
- Handheld spreaderBudget price
A hand-crank spreader for seed and fertilizer on small lawns and patches.
See options on Amazon (opens in a new tab) - Broadcast spreaderMid-range price
Spreads seed and granular fertilizer evenly. Use the setting on the product label, then check it on a measured area.
See options on Amazon (opens in a new tab) - Soil test kitBudget price
A quick read on pH and nutrients. For detailed results, many state extension labs offer inexpensive mail-in tests.
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Frequently asked questions
How much sulfur to lower lawn pH by one point?
It depends on soil type. NDSU Extension’s table gives about 11 lb (sand), 18 lb (loam) or 23 lb (clay) of elemental sulfur per 1,000 sq ft to bring soil from pH 7.5 to 6.5 when mixed in. On an established lawn, use half and spread it no more than 5 lb per 1,000 sq ft at a time.
How much sulfur can I put on established grass at once?
No more than 5 lb per 1,000 sq ft at any one time, according to NDSU Extension (2 lb on bentgrass greens), in spring or fall with core aeration. Larger doses risk injuring the grass.
How long does sulfur take to lower soil pH?
Months. Soil bacteria have to convert elemental sulfur to acid, which goes faster in warm, moist soil and slows almost to a stop in cold soil. Retest before adding more.
Why is my soil pH still high after adding sulfur?
The usual culprits are free lime (calcium carbonate) in the soil, hard irrigation water, or simply not enough time. Try NDSU’s vinegar fizz test on a spoonful of soil; if it fizzes, sulfur is not worth adding.
Sources
- NDSU Extension H1824: Interpreting the NDSU Soil Test Analysis for Managing Turfgrass (Zuk & McGinnis, 2023) (opens in a new tab) — Elemental sulfur to lower pH to 6.5 by texture; established turf: half rate, spring or fall with core aeration, ≤5 lb per 1,000 sq ft at a time (2 lb bentgrass greens); new lawns: incorporate 6 in; vinegar test for calcium carbonate at pH ≥ 7.5; ideal turf pH 6.5
- Clemson Cooperative Extension HGIC: How to change soil pH (opens in a new tab) — Sulfur rates by present and desired pH; less for sandy soils, more for clay; sulfur works gradually