How to Make Soil More Alkaline: 4 Steps

Before you adjust the composition of your soil, you need to determine its preexisting pH level and its texture: sandy, loamy, or clayey. (Poor sandy soil, peat, and muck soil are often acidic. Clay soil, meanwhile, will more often be alkaline.) 

There are three methods for testing your soil’s pH: a lab test, an at-home test, or a DIY test. Which method you should use depends on your timeline, budget, and desired accuracy of results. 

Remember that your backyard or garden may host several different soil types. Consider taking multiple soil tests if you want to plant in several locations.

Lab Test

Ordering a soil test from your local agricultural extension office will provide the most accurate evaluation of your soil. 

In addition to analyzing the pH level of soil samples, these labs can offer recommendations on how to treat soil based on the desired pH level, soil composition, and buffering capacity (the soil’s level of resistance to changing pH). A soil test from a lab can also give you information on the soil’s Nitrogen, Phosphorous, and Potassium levels.

These tests typically cost $11 – $20, not including shipping, but as the gardening aphorism goes, “It’s better to plant a $2 tree in a $25 hole than a $25 tree in a $2 hole.” 

The downside to getting lab-tested samples is that they take the most time to get results. However, this wait will yield more specific results than merely generalized information. 

At-Home Test

Using an at-home test such as a soil meter or pH test strip will give you results more quickly than sending your sample to a lab. 

If you need specific information about your soil’s nutrient makeup, you will be better off using a lab test. Some soil meters claim to identify nutrients, but they are not reliable. However, an at-home soil test will do the job if you simply need a general read of your soil’s pH (i.e., acidic, neutral, or alkaline).

You can purchase a soil meter for about $13 from your local garden center. Note: test kits at this price will not analyze your soil texture.

DIY Test

Unless you are a pro-gardener, a DIY test will not give you a specific pH level but rather a general assessment of whether your soil is on the acidic or alkaline end of the pH scale. 

Place a soil sample in a clean tub to determine if your soil is already alkaline. Then, pour vinegar on top of your sample. If your sample begins to fizz, the soil is alkaline. Conversely, check if your soil is acidic by placing the sample in baking soda. If the soil fizzes, it is acidic. 

The more severe the fizz, the farther your soil is on either end of the pH scale. 
If you’re plant-savvy, another method of determining your soil’s pH is to examine the weeds and plants already growing in the soil.

Are there weeds present that grow exclusively in alkaline soil? Then you can deduce that your soil is likely alkaline. 

If you’re not sure if your soil is more sandy, loamy, or clayey, consider doing a percolation test (essentially measuring how quickly water is absorbed).

There are several ways to make soil alkaline naturally and organically. Lime is the go-to additive for most farmers and gardeners. However, if you want to make your soil more alkaline without using lime, there are other options. 

In addition to applying an alkaline additive, it’s always a good idea to add compost. Compost has a neutral pH and acts as a buffer, allowing you to alter change-resistant soil more easily. 

Lime 

Garden lime (also known as agricultural lime) is the most common additive to raise soil pH (PDF). Its basic chemical makeup is calcium carbonate. 

You can buy this lime in various textures: pellets, powdered, or hydrated. 
The finer the lime, the more quickly it works. Powdered lime will work faster than pelletized lime, but some people prefer working with pellets as they’re less messy and easier to spread. 

Hydrated lime works the quickest of the lime options but should be used with caution. It can burn the roots of plants and is dangerous to breathe. Wear a mask and gloves if handling it. 

Dolomite lime is a naturally occurring mix of calcium carbonate + magnesium carbonate. If you don’t have dolomite lime to hand, you can use ordinary lime mixed with Epsom salt to increase your soil’s magnesium levels. Be careful not to use dolomite lime too frequently, as doing so can cause a nutrient imbalance. 

Regardless of which type you use, lime can take 2-3 months to achieve full effect. If you’re able to prepare your garden ahead of time, try mixing lime into your soil during the autumn of the previous growing season. 

Wood Ash

Wood ash contains calcium, potassium, magnesium, and phosphorus and can increase pH up to 59% when applied to the soil. Using wood ash to raise your soil’s pH is a low-cost option that recycles a material that would otherwise go to waste. 

Wood ash raises soil pH quickly; however, it doesn’t have long-lasting effects, so you will likely need to reapply ash throughout the growing season.

For more lasting results, spread a ¼ inch layer of ash on the soil surface during the winter before your growing season. Then, incorporate the ash into the soil using a till or rake at the beginning of spring. 

A few things to remember when using wood ash:

Make sure wood ash is dry before applying it to the soil. 

Don’t use ash from chemically treated wood, or these chemicals will seep into your soil.

Coal ash is not an acceptable substitute for wood ash. Applying coal ash could acidify your soil. 

Moderation is vital when using wood ash. Applying wood ash in excess can raise your soil’s pH to a very high level. It can also damage germinating seeds or plant roots when it comes into contact, so spread carefully. 

Ground Shells & Bone Meal

Eggshells, clamshells, oyster shells, and bone meal can make the soil more alkaline while supplying phosphorus and calcium. However, if these materials are not finely ground, they will likely be too coarse to be effective. 

Baking Soda

Also known as sodium bicarbonate, baking soda has a pH of 8.2 and can produce results in a few days when applied to the soil.

The effects of baking soda will not last as long as those of lime, and you will need to reapply the baking soda every few months. 

Baking soda is a cost-effective option when bought in bulk.

Plus, it’s gentle on soil, plants, and gardeners. However, applying too much baking soda could lead to the build-up of bicarbonate in your soil, which will slow plant growth. The sodium in baking soda can also burn plant roots and leaves if overapplied. 

The amount of additive you’ll need to apply depends on a few factors: the type of additive you’re using, the soil’s current pH, the desired pH, and the texture of the soil (sandy, loamy, clayey). 

Follow your additive’s packaging guidance to determine how much you’ll need to apply. 
Use a rake, shovel, or till to mix the additive through the top 6 inches of the soil. You can top-dress additives such as lime on the soil surface.

However, this low-effort method will only increase pH levels an inch or two from the top of the soil surface. 

Water well, making sure soil is saturated to at least 6 inches deep. After the initial application of your alkaline additives, do not overwater as this will contribute to soil leaching. 

Keep in mind that sandy soil drains quickly and requires more frequent re-application. 

Again, beginning this process in late autumn of the previous growing season will produce better results. 

Soil acidification occurs naturally over time, accelerated by crop production practices and rainfall. 

Retest the soil every few months or after any significant changes (abnormally heavy rainfall, fertilizer application). 

If you’re using a fast-acting but not long-lasting additive, you’ll need to test and reapply more frequently.