Managing and shifting soil pH is one of the more technical skills you need to learn as a gardener. We have a great article about making the soil more alkaline, but what if you only need to shift the pH by 1? Sometimes only a small shift is necessary. In this article, I’ll teach you how much lime is needed to raise pH by just 1 point.
Shifting pH is not the most glamorous or instagramable part of gardening, but it’s one of the most important. Keep reading to learn how much lime you’ll need, different factors that will affect this amount, and how long it will take to work.
Lime is used as an alkaline garden amendment to shift the pH up. You would need to add lime to your soil if the pH is too low for what you want to grow.
Balancing the ph of your soil is important for plant nutrient uptake. If the pH is too high or too low, certain nutrients won’t be available for the plant or will be too available. In soil that is too acidic, for example, nutrients won’t be available to the plants while aluminum can reach toxic levels.
Certain diseases can also become a problem if the soil pH is off. Clubroot in brassicas, for example, is most often associated with an acidic pH. Something that can easily be solved with a bit of lime before planting.
Depending on the type of lime you use, it might even have secondary benefits to your garden. But I’ll cover more on the differences between liming materials below.
How much lime it takes to raise soil pH 1 point will vary in each situation. The exact amount of lime you’ll need depends on your soil type and the type of liming ingredient you’re using. In general, it should take about 2 tablespoons of lime per square foot to shift your soil 1 pH point.
Keep in mind that different liming materials are not equally effective. The quantities referenced above work for ground limestone. But should you use hydrated lime, I’d recommend using ¾ the amount of limestone you’d use.
Your soil type will also affect how effective your liming material will be. Keep reading to the next section to learn more.
Soil type definitely affects how much lime you need to add. The more dense the soil is, the more lime you’ll need to add. This means that clay soil will need more lime than sandy soil to achieve the same shift in pH. For every ounce of liming material, you would use on sandy soil, use 3 times that amount on loamy soil, and four times the amount on clay.
So, let’s say that you need 2 tablespoons of gardeners lime to shift the pH 1 point in a loamy soil. That means you’d need less than one tablespoon for sandy soil and 3 tablespoons for clay soil.
If you don’t know what type of soil you have, start by doing a soil test. You can easily do a soil test at home. Alternatively, call a local soil expert. They’ll provide a full report on the condition of your soil and will be able to recommend exact lime amounts.
To know how much lime you need, you need to know the pH of your soil, the type of lime you’ll use, and your soil type.
First, you’ll need a baseline for your soil pH. This will tell you how much pH change you need to meet your growing requirements. You might find that you don’t even need to change the pH at all!
The second thing you’ll need to consider is the type of lime you’ll use. Different materials will be more or less efficient, so you need to adjust.
The last consideration is your soil type. Clay soil will need more lime than sandy soil to accomplish the same change. Go through each of these factors to calculate how much lime you need to raise pH 1 point.
There are three main categories of liming substances that can be used to raise the pH of your soil. These are garden lime, dolomite lime, and hydrated lime.
Garden lime is the most common form of lime and it’s sourced from ground limestone, calcified seaweed, and ground chalk. All three of these substances have calcium carbonate as the main ingredient.
Dolomite lime is also derived from ground limestone. The difference is that this limestone is rich in magnesium carbonate in addition to calcium carbonate. Dolomite lime help raise the pH and adds magnesium to the soil. So if your soil also needs magnesium, dolomite lime will do two jobs in one.
The last option is called hydrated lime (also goes by calcium hydroxide). It is commonly used in construction, but as a natural dyer, I know it from making indigo vats. Hydrated lime is a fine white powder, so if you choose to use this material wear gloves, glasses, and a dust mask. Hydrated lime can be irritating to the skin, lungs, and eyes if care isn’t taken.
Each of these materials has an NV (neutralizing value) number attached to them, which references their effectiveness. Ground limestone and chalk have an NV between 50 and 55 while calcified seaweed has NV 44. Dolomite lime has an NV of about 56 and hydrated lime has the highest NV of 70.
These numbers will give insight into how much of each material you need to use. For example, you’ll need much less hydrated lime to achieve the same result as calcified seaweed.
What type of lime you choose to use will depend on your soil needs and what is available to you. If you can only source one form of lime, don’t stress and use that type. If you have options, make the choice based on your needs.
In situations where the only thing you need to change is the soil pH, I recommend using gardeners lime. It’s affordable, easy to find at gardening centers, and it’s safe to handle.
If you need a fast-acting material, use hydrated lime. It has a neutralizing value of 70, which means a small amount will go a long way. The powder is also finer than the other liming materials, making it dissolve faster in the soil.
The big downside to hydrated lime (besides it being more dangerous to work with) is that it kills earthworms. In my garden, protecting soil life is the most important thing. For this reason, I never use hydrated lime to change the pH.
My favorite source of lime is actually dolomite lime because it has secondary benefits. Dolomite lime also introduces micronutrients to the soil like calcium and magnesium. These micronutrients can be hard to find in large amounts in most fertilizers.
Lime simply shifts soil pH when it is combined into the ground and improves soil structure.
Gardeners use lime to counteract the acidity of the soil. This is because nutrients that are already present in the soil only become available to plants in more alkaline conditions. This is the main reason why gardeners make the effort to introduce lime in their gardens.
However, adding lime to the soil can also affect the soil structure by encouraging microbial life. When the soil pH is slightly alkaline, the conditions are perfect for nutrient availability and soil microbes can thrive. As we talked about in our article on soil microbes, healthy soil life has a huge effect on soil health.
For annual crops, apply lime to your soil in the early winter when you take away the fall vegetables. Garden beds aren’t usually plants during winter, so adding lime during this time prevents any damage to young plants.
The lime will work its pH-changing magic in the soil over the winter. By the time spring comes, the soil will be ready to plant. Choose a period without rain so the lime has a chance to work its way into the soil instead of washing away.
For perennial areas, we need a different strategy since there are always plants in the ground. A planted bed can’t be worked the way empty beds can, making it impossible to fully incorporate the lime.
Instead of applying lime once when amending the soil, you’ll need to periodically test the soil twice a year. I like to do it in the spring and fall when I’m doing other garden maintenance. and add a small amount of lime at a time.
If you can, add lime to the soil when you go to plant your perennials. This will set you up for success for years to come. If your perennials are already in the ground, liming will happen gradually by spreading liming material on the surface. With time, the effects of the lime will change the pH of the soil. But this can take a few years.
How long it takes for lime to work depends on what type of lime you’re using and your soil type. In general, it only takes a couple of months for lime to start working and the effects will last 2 to 3 years.
In its powdered state, lime begins to shift the pH almost immediately. Hydrated lime faster than gardeners lime, but you’ll still notice changes in just a few weeks. Over the next couple of years, the liming material will slowly dissolve and continue to affect the soil pH.
Managing soil pH can be a sensitive business and your best tool is constant testing. I start and end every season by testing the soil pH to understand what is happening. The biggest thing to keep in mind is that it can take a while for lime to fully work.
I recommend adding a little bit of lime at a time and monitoring the effects for a season. You can always add more liming material, but there’s nothing you can do but wait a few years if you add too much.
Controlling the pH of your soil is tricky, but it’s one of the most important things you can do for your garden’s health. The difference between a garden that’s surviving and one that is thriving can be a matter of pH. How much lime you’ll need to raise pH 1 point, however, will depend on your conditions.
Depending on the initial soil pH, the soil structure, and what type of liming material you use you’ll have to adjust. As a general rule, add 2 tablespoons of gardeners lime to each square foot of loamy soil. Then work it into the top 6 inches of soil by using a broadfork or hand-tiller.
Repeat lime application every year or every two years to keep your soil slightly alkaline year after year.