What Makes Soil Alkaline – Plants And Tips For Fixing Alkaline Soil
By: Susan Patterson, Master Gardener
Just like the human body can be alkaline or acidic, so can soil. The pH of soil is a measurement of its alkalinity or acidity and ranges from 0 to 14, with 7 being neutral. Before you begin growing anything, it is good to know where your soil stands on the scale. Most people are familiar with acidic soil, but exactly what is alkaline soil? Keep reading for information on what makes soil alkaline.
What is Alkaline Soil?
Alkaline soil is referred to by some gardeners as “sweet soil.” The pH level of alkaline soil is above 7, and it usually contains a great deal of sodium, calcium, and magnesium. Because alkaline soil is less soluble than acidic or neutral soil, availability of nutrients is often limited. Because of this, stunted growth and nutrient deficiency are common.
What Makes Soil Alkaline?
In arid or desert areas where rainfall is slim and places where there are dense forests, soil tends to be more alkaline. Soil can also become more alkaline if it is watered with hard water that contains lime.
Fixing Alkaline Soil
One of the best ways to increase acidity in soil is to add sulfur. Adding 1 to 3 ounces (28-85 g.) of ground rock sulfur per 1 square yard (1 m.) of soil will lower pH levels. If the soil is sandy or has a lot of clay, less should be used, and it needs to be mixed in very well before using.
You can also add organic matter such as peat moss, composted wood chips and sawdust to bring down the pH. Allow the material to settle for a couple of weeks before retesting.
Some people prefer to use raised beds where they can control the soil pH easily. When you use raised beds, it is still a good idea to get a home soil test kit so that you know where you stand as far as pH and other nutrients are concerned.
Plants for Sweet Soil
If fixing alkaline soil isn’t an option, then adding suitable plants for sweet soil may be the answer. There are actually a number of alkaline plants, some of which may signal the presence of sweet soil. For example, many weeds are commonly found in alkaline soils. These include:
- Queen Anne’s lace
Once you know your soil is sweet in a given area, you still have the option of growing some of your favorite plants. Vegetables and herbs for sweet soil include:
Some flowers also tolerate soil that is slightly alkaline. Try the following:
- Sweet pea
- Rock cress
- Baby’s breath
Shrubs that don’t mind alkalinity include:
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25+ Acid-Loving Plants For Your Garden
Author: Marlene Affeld // Last updated on March 15, 2021 3 Comments
Experienced gardeners know: A healthy productive garden is one in which the plants are compatible with the pH of the soil.
Not all soils are the same, and it’s important to recognize that many plants, shrubs, grasses, and trees require a specific nutrient balance. Some plants prefer a neutral soil, and others prefer a more alkaline soil. There are also a variety of acid-loving plants, too.
Some soils have a neutral pH, while others can have an acidic or alkaline pH balance. A pH balance of 7 is considered neutral, and some plants grow better in slightly acidic soil, from 5.5 to 7. Some like soil that’s even more acidic. Acid-loving plants include:
- Vegetables: sweet corn, cucumbers, beans, broccoli, turnips, squash, onions
- Fruits: cranberries, blueberries, huckleberries
- Trees: evergreen perennial, beech, willow, oak, dogwood
- Flowering plants: azaleas, rhododendrons, hydrangeas, camellias, daffodils
The pH test kits measure the amount of hydrogen ions in the the soil. The soil becomes more acidic as the hydrogen ions increase. The test levels range from 0 to 14 with 7 being the neutral number. Test results below 7 indicate an acidic or sour soil and those above 7 indicate an alkaline or sweet soil. You can change the soil pH through the application of lime or sulfur. It is best to amend the soil about three months prior to planting.
Sulfur lowers the pH level of the soil and will make it more sour. To sweeten the soured soil you must add lime. Lime comes in a variety of forms. It is available in powder form from many garden centers. Crushed oyster shells and wood ash also add lime to the soil. There are liquid applications available from nurseries and agriculture feed stores. The amount of lime needed to sweeten the soil depends upon the desired pH level. The amount of lime is generally listed as a percentage on the package and is calculated by pounds per acre or per 1,000 square feet. For instance, it takes about 60 pounds of lime for 1,000 square feet of sandy soil to increase the pH level. More lime is needed for loamy soils that are used for growing mushrooms or other plants that need a high pH.
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I need more information on field and Horticulture crops which can be grown under alkalinity of 7.5 pH to 9 pH. shell4life January 27, 2013
@DylanB – Scientists have debunked that idea, but I tend to disagree with them. I have seen improvement in my flowers after adding pine needles to the soil around them, and these were flowers that wanted an acidic soil.
Pine needles are acidic, and it seems that when water runs over them and down into the dirt, the dirt should become more acidic. Maybe this isn't a scientific fact, but it makes sense to me, and since my flowers have become so much happier, I believe it.
Either way, the needles couldn't hurt. Even if all they do is make more nutrients available to the plants by keeping weeds down, it's worth the effort of spreading them around your plants. DylanB January 26, 2013
@JackWhack – I like growing chrysanthemums in my garden. My soil is alkaline and won't support just any plant.
Chrysanthemums don't smell great, but they are beautiful. Also, they bloom from late spring until frost, so you will get flowers from them long after most blooming plants have died.
At times, I've wished for my soil to be more acidic so that I could grow a bigger variety of plants. I don't have a compost pile or peat moss, but there is a pine forest nearby. Would pine needles work to make the soil more acidic? JackWhack January 25, 2013
Gardenias smell wonderful. I have alkaline soil near my house, so I planted a couple of gardenias next to the porch. Every time I walk up the steps, I can smell their sweetness.
What are some other shrubs for alkaline soil? I like planting shrubs instead of flowers from seed, because they are easier to take care of and not very picky. Perdido January 24, 2013
Zinnias certainly aren't picky about soil. I've grown them in alkaline, acidic, and even extremely rocky soil, and they have flourished.
They have a shallow root system, but they are super sturdy. My dogs have walked across them and have even lain down on top of them without damaging them.
All they need is a little dirt, and they don't care about the pH. Since many of my other flowers do prefer acidic soil, I plant the zinnias in the alkaline soil. Fiorite November 7, 2010
@ Istria- You can also keep doctoring your soil instead of paying lots of money for professional analysis and new water systems. It might be easier to fertilize your garden area with compost, composted manure, or peat moss as well as planting a few plants that prefer soil that is more alkaline. Any of those three soil additives will increase the acidity of your soil, and adding a few plants will add variety to your garden. GiraffeEars November 7, 2010
@ Istria- Before you go out and spend a bunch of money on water softeners, filters, etc, you should have a professional come and perform a soil analysis to determine the exact problem and cause of your soil issues. Once this is done, they can probably help you determine the best solution to mitigating your alkalinity problem. istria November 7, 2010
This article was very helpful. I have alkaline soil, and it seems like nothing will fix it permanently. I live in an area that gets a decent amount of rain, so I would think that my soil would be acidic if anything. After reading this article, I found that maybe my soil is too alkaline because of the minerals in my water. How does lime get in my water, and is there any way that I can reverse this so that my water does not keep affecting my soil? My garden is small and I water it with my garden hose and a portable sprinkler, so it's not a huge area.
Alkaline soils can be amended or balanced to come back to neutral, or become more acidic, with the additions of acidic fruit compost scraps, or elemental sulfur, or peat moss.
The addition of ash or lime will make soils more alkaline if you have acidic soils.
Note that there are differing levels of alkaline soil.
Some plants for example may grow in slightly alkaline soil (just about 7), whilst some might like more alkaline soil.
You can test pH with a simple pH testing kit you can buy online or at the local gardening or home/outdoors store.
You can also get soil professionally tested.
Read more about working with and improving alkaline soil at:
Try Adding Lemon to Your Soil to Adjust pH
Another easy way to alter the pH of your soil, making it more neutral for proper plant growth, is to add lemon. In areas with slightly alkaline soils, using diluted lemon juice once a month helps keep the pH closer to 7. This can help keep the soil neutral or even slightly acidic for proper plant growth.
To use lemon juice to change soil pH, you will want to avoid pouring the juice onto the plant leaves. This can cause the leaves to shrivel and can compromise the plant’s ability to perform photosynthesis. While great for weeds in your garden, this is not ideal for plants you actually want to grow.
- To add lemon juice safely, mix a couple of tablespoons of lemon juice in one gallon of water.
- Pour this mixture directly onto the soil, and it should begin to change the pH for the plants.
- You want to do this every so often to guarantee the pH is changing as needed and continue to test the soil regularly.