Just like Goldilocks choosing her bed, plants have particular qualities they look for in their soil. One key quality is soil pH: the measure of how acidic or alkaline the soil is. We’ll walk you through the steps of how to change your soil pH so it’s just right for a lush landscape.
Soil pH can impact the plants in your yard in many ways, including:
- Availability of nutrients to plants
- Plant poisoning from toxic levels of manganese
- Well-being of microorganisms in soil, which impacts plant health
By the end of this article, you’ll be prepared to adjust your soil pH.
- What is soil pH?
- How to increase your soil pH
- How to decrease your soil pH
- How to test your soil pH
- How soil type affects pH
- FAQ about soil pH
What is soil pH?
The unit pH measures the acidity or alkalinity of a substance, such as soil, and goes from 0 to 14, with 7 being neutral. The lower the number, the more acidic the substance. The higher the number, the more alkaline.
- Acidic soil: pH of 0-5.5
- Neutral soil: pH of 5.5-7.0
- Alkaline soil: pH of 7.0-14
Soil pH is affected by many factors, including:
- Mineral content
- Soil texture
The pH of your property’s soil probably falls within 3-10.
Areas with more rainfall tend to have more acidic soil conditions because the water leaches nutrients like calcium and magnesium, which are then replaced by acidic elements like aluminum and iron.
Soils in drier climates, on the other hand, are usually neutral or alkaline.
How to increase your soil pH
If your soil is too acidic, this is the section for you. Raising your soil pH will make it more alkaline. Overly acidic soil decreases the availability of nutrients, affects the process of nitrogen fixation, and makes soil more susceptible to erosion.
Organic soil amendments for raising soil pH
Wood ash is the go-to organic choice for making your soil more alkaline. The material comes from burning hard and softwood with other organic materials and contains calcium, potassium, and magnesium. Not only do these elements raise soil pH, they’re also great for plant growth.
How to apply wood ash to your lawn:
- Remove any debris.
- Water your lawn the day before applying.
- Apply the wood ash by raking the ash over the surface of your lawn with a leaf rake or regular garden rake.
- Use a shovel or garden hoe to work the ash into the top inch of the soil.
- Water your lawn after spreading it to help the ash sink in.
How much wood ash should you apply?
If you get a soil test that gives a recommendation for using lime, you can use that to determine how much wood ash to spread. Use two to four times as much ash as lime. In general, 10 to 15 pounds of wood ash per 1,000 square feet is safe for lawns, while up to 20 pounds per 1,000 square feet is recommended for gardens.
Inorganic soil amendments for raising soil pH
Limestone is the most popular way to crank your pH up. You’ll start to see benefits in a few months, but full results can take as long as two years.
Because limestone works best when mixed with the top 5 inches of the soil, you’ll get the best results when you lime your lawn before planting anything. After application, your soil pH will likely maintain itself for several years.
How to apply limestone to your lawn:
- Only apply granulated lime to a lawn that’s dry and unstressed (which means not wilted or dormant).
- Aerate with a core aerator so there’s space for the lime to make its way into the soil.
- Spread the lime with a drop or rotary spreader walking straight over your lawn, then again in a direction perpendicular to the first.
How much lime should you apply?
Your soil test results will give you an exact limestone application rate. If it’s less than 50 pounds of lime per 1,000 square feet, you can apply it all at once. Any more, and you’ll need to split it up over two applications in the spring and fall to avoid shocking your plants or lawn.
How to decrease your soil pH
If your soil is too alkaline, this is the section for you. Lowering your soil pH will make it more acidic. Alkaline soil contains a lot of sodium, magnesium, and calcium. This makes the soil less soluble which causes plants to have a harder time absorbing nutrients.
Organic soil amendments for lowering soil pH
Sphagnum peat moss: You might hear that peat moss is a great way to acidify your ground naturally, but most peat moss in garden centers isn’t acidic enough to make an impact. Only Canadian sphagnum peat moss, which you can order online, has a low enough pH to affect soil conditions. This is a better option for container gardens as opposed to whole lawns.
How to use sphagnum peat moss:
- Place the peat moss in a big container and add enough water to thoroughly moisten it.
- Wait a few minutes for the water to sink in before adding more as needed.
- Spread a 2-3 inch layer of wet peat moss with a garden fork, incorporating it with a shovel into the top foot of soil.
How much peat moss should I apply?
Peat moss isn’t an exact science. Follow the instructions on your bag, which will be specific to the pH of that particular peat moss.
Inorganic soil amendments for lowering soil pH
Elemental sulfur is the top dog when it comes to acidifying your lawn. It produces two hydrogen reactions when mixed with soil, which causes the pH to decrease. However, it can harm your grass in high amounts. That means it may take years to safely achieve your desired soil pH.
Be aware that sulfur takes three to six months of warm soil temperatures (when the soil biology is active) to affect your soil pH.
How to use sulfur:
- Spread sulfur using a drop spreader or by hand (while wearing gloves).
- Work it into the top 4-6 inches of the soil with a shovel or garden spade.
- Water the soil well.
How much sulfur should I apply?
This table from Iowa State University Horticulture and Home Pest News demonstrates the pounds of sulfur to apply to your lawn depending on your soil type (sandy loam, loam, or clay loam).
Pounds of sulfur required to decrease soil pH to a depth of 6 inches over 1,000 square feet.
|Current pH||Target pH||Sandy loam||Loam||Clay loam|
|5.0||4.5||4 pounds||13 pounds||18 pounds|
|6.0||4.5||12 pounds||38 pounds||53 pounds|
|7.0||4.5||19 pounds||65 pounds||88 pounds|
|8.0||6.0||31 pounds||44 pounds||53 pounds|
|7.0||6.5||2 pounds||4 pounds||74 pounds|
|8.0||6.5||28 pounds||27 pounds||46 pounds|
Elemental sulfur is a strong chemical that can burn grass in excess. Only apply up to 5 pounds per 1,000 square feet at a time. If you need to use more, divide it into two applications, one in spring and one in fall, so you don’t exceed 10 pounds in a single year.
Aluminum sulfate is a good option if you don’t have months to wait. It reacts fast because it’s so soluble and can change pH in a matter of days.
How to use aluminum sulfate:
- Measure out your aluminum sulfate.
- Distribute it over your soil by hand wearing gloves.
- Dig it into the top 6 inches of the soil with a shovel.
How much aluminum sulfate should I apply?
Although this is a quicker solution than sulfur, aluminum can be toxic to plants. Don’t use more than 5 pounds over 100 square feet at a time.
This chart from Clemson University’s Home & Garden Information Center details how much aluminum sulfate to use based on your desired pH. This table is specific to loam — decrease by ⅓ for sandy soils and increase by ½ for clay soils.
Pounds of aluminum sulfate per 10 square feet needed to reach your target pH.
|Current pH||Target pH|
|8.0||1.8 pounds||2.4 pounds||3.3 pounds||4.2 pounds||4.8 pounds|
|7.5||1.2 pounds||2.1 pounds||2.7 pounds||3.6 pounds||4.2 pounds|
|7.0||0.6 pounds||1.2 pounds||2.1 pounds||3.0 pounds||3.6 pounds|
|6.5||0.6 pounds||1.5 pounds||2.4 pounds||2.7 pounds|
|6.0||0.6 pounds||1.5 pounds||2.1 pounds|
How to test your soil pH
Before you start hauling out bags of limestone, you need to know your soil’s starting pH. There are two ways to do this: Send a soil sample to a lab or test the soil yourself.
Testing soil yourself is quick (you’ll get the results in 30 minutes) and cost effective. Sending a sample to a lab takes about two weeks, but you’ll get a thorough report on other qualities of your soil, too, including any nutrient deficiencies and recommendations for amendments.
To send a soil sample to a lab:
There are lots of labs that will give a full soil report. We recommend looking up the closest cooperative extension office for affordable and reliable services.
- Order a testing kit from the lab of your choice.
- Use a trowel or shovel to take a 6-inch deep slice of soil.
- Moving in a zigzag fashion, collect at least eight samples spread out evenly across your lawn.
- In a large container, mix the soil samples thoroughly.
- Place two cups of the mixture into the resealable bag that came with your kit, fill out the form (also in the kit), and send it off for testing.
To test your soil pH yourself:
You’ll need pH strips for this. You can get those at most big box stores or online.
- Follow steps 1-3 for sending a soil sample to a lab.
- Put 4 ounces of the mixture into an 8-ounce plastic cup.
- Add 4 ounces of distilled water and mix with a plastic spoon.
- Let the sample sit for 30 minutes.
- Dip a wide range pH strip into the soil solution.
- Use the color reference chart that comes with the test to determine where your soil pH falls on the scale.
How soil type affects pH
Soil type refers to the material makeup of your soil. There are three main types of soil: loam, sand, and clay. The ground in your backyard likely features one of these main soil types.
Each material responds to soil amendments differently. How easily soil will respond to pH changes is called its “buffering capacity.” Materials with a high buffering capacity can absorb a lot of acidic or basic solutions before their pH changes, whereas materials with a low buffering capacity require only a little bit of amendment solution to change.
Clay soil has a higher buffering capacity than loam, which in turn has a higher buffering capacity than sandy soil. That means you need more material to affect clay soil, a medium amount for loam, and a low amount to amend sand.
How to test your soil type
There are two common methods for figuring out what kind of soil you have. If you want a quick, rough estimate, go for the squeeze test. If you want more precise results and are willing to wait a couple days and flex your algebra skills, go for the jar test.
Grab a handful of moist (not totally wet) soil and squeeze it in your hand:
- Clay soil feels sticky and will hold its shape.
- Sandy soil feels gritty and will fall apart.
- Loamy soil is somewhere in between — it will hold its shape, but will crumble if prodded.
- Collect about 1 cup of soil from your yard.
- Sift it with a sieve or colander to remove any rocks or debris.
- Fill a jar with your sifted soil so the jar is ⅓ full, then fill the rest of the jar with water.
- Add 1 tablespoon of powdered dishwashing detergent, then shake the contents until everything is mixed.
- Place the jar on a flat surface and set a timer for one minute, then put a mark on the jar measuring the layer of coarse sand that’s settled at the bottom.
- Set a timer for two hours, then put a mark on the jar at the top of the next settled layer, which is silt.
- Leave the jar for two days, then mark the top of the next settled layer: This is clay.
- Measure the height of each layer and the total height of all three layers, then calculate the ratio of layers using the formula below.
- % sand = sand height ÷ total height x 100
- % silt = silt height ÷ total height x 100
- % clay = clay height ÷ total height x 100
- Use the soil texture graphic to find what category your soil falls into.
FAQ about soil pH
Flowers for alkaline soils:
— Bearded iris
— Black-eyed Susans
— Woodland phlox
Vines for alkaline soils:
— Virginia creeper
Shrubs for alkaline soils:
— Smooth sumac
Trees for alkaline soils:
— Common beech
— Gingko biloba
— Ornamental cherry
Most cultivated plants enjoy slightly acidic conditions (a pH of 6.5). A few (like rhododendron and blueberries) prefer a lower range of 4.5-5.5. Check the label on your plant to make sure you have the right range.
Flowers for acidic soils:
— Bleeding hearts
Vines for acidic soils:
— Trumpet vine
— Persian ivy
Shrubs for acidic soils:
— Oakleaf hydrangea
Trees for acidic soils:
— Colorado blue spruce
If you have a clay-heavy soil with a high buffering capacity, it might be hard to make a lasting change to your soil pH. The ground in Utah, for example, is highly resistant to acidification.
If you’re willing to wait a few months to make your pH changes, you can topdress your landscape with compost to make it more amenable and then add your pH altering substances.
If you want to start your garden right away, consider a raised garden bed or container planting. That way, you have total control over the soil conditions.
If you want to secure your soil’s position as a prime spot for plants, you might need to make other changes. These include soil amendments to:
— Change your soil texture
— Add nutrients
— Alter salinity
Read here for a full guide to different types of soil amendments.
To track the efficacy of your amendments, test your soil’s pH every 6 months until the desired pH is reached. After that, test it once every three years.
Get help from a lawn care pro
Correcting your soil pH is only the beginning of the work it takes to keep your lawn healthy. Once the soil is healthy and the grass is growing, you’ll need to mow the lawn regularly, keep weeds in check, and kick pests to the curb.
If this seems like too much work for a weekend to you, Lawn Love’s local lawn care professionals can help with everything from lawn mowing to gutter cleaning to seasonal yard cleanup.
Main Photo Credit: Binyamin Mellish | Pexels