9 Simple Ways to Add Calcium to Soil

A nutrient deficiency is a big problem in your garden, and if your plants show signs that they lack calcium, you have to know how to add calcium to soil.

Years ago, I didn’t understand that soil loses its nutrients over time, especially as you plant in it, and plants absorb the vitamins. I had no idea that your soil needs and loses calcium over time, but it’s true, and you have to add calcium to the soil to help your plants grow.

Gardening is a learning experience.

Adding calcium to the soil prevents one of the most dreaded garden problems – blossom end rot. I lost so many tomatoes to blossom end rot, and it’s totally preventable if you make sure your plants have access to ample calcium.

Related: 11 Natural Nitrogen Sources All Gardeners Need to Know

The Signs of a Calcium Deficiency in Plants

This is blossom end rot, a common sign that you have a deficiency in your soil.

Plants show us particular signs when they have a calcium deficiency, so you need to know how to spot this problem.

Here are a few of the common signs of calcium deficiency in plants.

  • Stunted growth
  • Brown spots on the edges of the leaves that move towards the center of the leaves.
  • Blossom end rot in tomatoes and peppers
  • Internal tip burn in cabbages

When looking for a calcium deficiency, start by examining the older leaves on the plant first towards the bottom of the plant. It often doesn’t start on the bottom-most leaves but the set above those.

Look for leaves with yellow and brown spots, and the outer edges might turn brown.

Next, look at the top leaves, the newest growth on the plant. You might also notice signs of a calcium deficiency on the new leaves. They could be stunted, smaller than average, or have a crinkled appearance.

You might also find a slimy black or brown mess when taking the plant from the ground or container. A calcium deficiency causes serious problems for the plant because it prevents the roots from absorbing the nutrients and water needed.

Let’s not forget the most common sign of a calcium deficiency – blossom end rot.

Blossom end rot is one of the most common signs. It happens when the soil lacks the needed amount of calcium for the fruits to develop properly. Then, the fruits develop a black, wet-looking lesion on the end opposite the stem, where the blossom was original.

Related: How to Fix Blossom End Rot: 7 Tricks to Try

Before You Start Fertilizing…

Fixing a nutrient deficiency is a bit different than fertilizing, and I always recommend a soil test. Not all soil tests check calcium, so make sure you read the directions to make sure it does.

One of my favorite THOROUGH soil testing kits is My Soil – Soil Test Kit.

It tests 13 nutrients, including calcium, and you send the soil test to a laboratory and receive your results within one week. The results come on an app and they even give fertilizer recommendations.

I would use this at the beginning of the season to get an overall picture of the health and nutrient levels in your garden.

When to Add Calcium to Soil

Garden fertilizers contain the three major macronutrients that all plants need to grow:

  • Nitrogen
  • Phosphorus
  • Potassium

Plants need these nutrients in larger quantities, but make sure you read the directions and labels because not all fertilizers contain the nutrients your plants need like calcium or magnesium.

Calcium is actually a macronutrient, but since plants require less of it, some refer to it as the forgotten macronutrient. However, it’s important to remember that it is necessary for your plants’ health because it creates the proper cell walls needed for fruit production.

Plants require calcium all the time because it’s needed in many different processes. The best time to add calcium is all the time – honestly.

Now, you really can’t add it all the time; that’s an easy way to end up with too much calcium in your soil. You need to add it when it will make the most difference to your plant.

The problem is that some calcium fertilizers take a long time to break down and work in your soil; these are great for providing a long-term supply of calcium. Other types provide your plants with immediate access to calcium. Using both is ideal!

    How to Add Calcium to Soil

    When I plant tomatoes, I always add eggshells to help increase the calcium in the soil.

    If you know that your soil needs calcium, there are a few ways to add calcium to the soil. You can buy soil amendments that will add more calcium over time to the soil and help your plants, or you can buy foliar sprays for a quick boost of calcium.

    Before using a granular calcium fertilizer, remember that many of them also contain other nutrients. Testing your soil helps you determine if your soil lacks other nutrients or not.

    Remember, too much of a good thing is often a bad thing.

    You might think that giving your plant more nitrogen, even if it doesn’t need more, is a good idea, but it’s not. Excess nitrogen damages your plant or leads to excess foliage growth with few fruits.

    1. Use a Calcium Fertilizer

    If you discover early in the gardening season that you have a calcium problem, a calcium fertilizer is a great option. They take time to work into the soil and provide your plants with the nutrients, but they also last the longest.

    2. Add Lime in the Fall

    The easiest way to add calcium to soil is by applying lime to the soil in the fall. Calcium carbonate is found in most garden and farm stores; it’s made from crushed limestone and comes in powder form.

    The problem with using lime is that it does affect the pH range, creating alkaline soil if you don’t use it properly.

    I suggest getting your soil tested to determine your pH range before using lime. Lime provides a great amount of calcium to your plants, so it’s an awesome way to increase it, but if your soil is already too close to being neutral, you won’t want to use it.

    However, if your soil is too acidic and needs calcium, lime is the perfect choice for you!

    If your soil lacks magnesium and calcium, try applying dolomite lime to the soil. It contains both, but it will also increase the pH of your soil.

    You’ll find plenty of garden lime choices. I like anything by Jobe’s Organics; their garden lime comes in an easy-to-pour bag at an affordable price. It will increase the soil pH range.

    Another option is the Down to Earth Organic Garden Lime. It comes in 5lb boxes and is listed with the OMRI for organic use.

    3. Use Eggshells

    Eggshells are an organic source of calcium, and if you have a flock of chickens, I bet you have plenty of eggshells to use.

    It’s safe to add eggshells to your compost, boosting the calcium in your pile. Another option is to put eggshells into the hole where you plant tomato seedlings to prevent blossom end rot.

    I did that this year, and for the first time in two years, none of my tomatoes this year have had blossom end rot.

    4. Foliar Applications

    If you know for sure that your plants lack calcium, try using foliar applications; this causes the leaves to absorb the calcium. Foliar sprays, such as calcium acetate, calcium nitrate, or calcium chloride, are great options because you’re putting the nutrients right where your plant needs them the most.

    Foliar sprays are ideal if you want to prevent blossom end rot because the calcium goes into the top of the plant where blossoms develop. Another reason that gardeners use foliar sprays is that they won’t affect the soil’s pH range like granular fertilizers will.

    Spray your plant with a solution of 1/2 to 1 ounce of calcium chloride or calcium nitrate to one gallon of water.

    My preferred option is Rot-Stop by Bonide. It comes in a concentrate and a ready-to-use spray. It works quickly to give your plants a boost of calcium. Another option is the Southern AG Stop Blossom End Rot concentrate. You get a huge amount in the container; it’ll last for a long time.

    5. Apply Gypsum – Calcium Sulfate

    If you don’t want to bother your soil’s pH range, adding gypsum is an excellent option. Gypsum is a naturally occurring mineral that is a fast-acting calcium source that also breaks up and loosens up the soil.

    Gypsum comes with many benefits for a garden.

    It prevents the crusting of soil, water erosion, and helps young plants grow easier. At the same time, gypsum removes salt from the soil that might cause problems with plant growth. That’s exactly what you need if you live in a coastal area with high salt content.

    Garden gypsum is easy to find and readily available at most garden stores.

    6. Use Ground Oyster Shells – Calcium Carbonate

    If you have chickens as I do, chances are you already have oyster shells, known as calcium carbonate, around your homestead. Oyster shells for chickens are a supplement for laying hens that help your flock produce eggs with stronger shells.

    It’s possible to use oyster shells in your garden, but since it’s similar to the same calcium as lime, it will increase the pH range of the soil.

    The good thing is that oyster shells don’t increase the pH range as fast as lime; it takes years to break down entirely. That also means it won’t help you as much as you would help.

    7. Wood Ash – Calcium Carbonate

    Another way to increase the calcium in your soil is to use wood ash from your fireplace or fire pit. Hardwood ashes provide half the amount of calcium as lime; ashes from softwoods are harmful to plants.

    When you add wood ash to your garden, it also includes potassium, boron, and phosphorus.

    Using this source of calcium has pros and cons. It’s free and a natural source of calcium to your soil. However, it increases the pH of your soil, so you shouldn’t use it if your soil is neutral or borderline alkaline.

    You’ll need twice as much wood ashes as you would lime. Make sure it doesn’t touch the plants; make a ring around your plants because wood ash is caustic and will burn plants.

    8. Bone Meal

    Organic gardeners love bone meal, myself included. It’s made from the ground-up bones of animals, and since bones are made of calcium, this is a great source. It contains nitrogen and phosphorus as well, so it’s considered a more balanced fertilizer.

    However, it does raise the pH range of the soil, so it shouldn’t be used on alkaline soil.

    Bone meal releases calcium into the soil for up to four months. If you add it at the beginning of the growing season, it should be sufficient for the entire growing season.

    The great thing is that bone meal is great for all plants, not just vegetable plants. Use it on flowering plants, bulbs, and root crops.

    Bone meal is available at most garden stores and farm supply stores. It’s something all gardeners should have on hand. I typically use the Down to Earth Organic Bone Meal; one container lasts me at least two gardening seasons.

    Another option is Burpee Organic Bone Meal. It comes in a 3lb bag; that should last you quite a while, and the price is perfect for those gardening on a budget.

    9. Collodial Phosphate – Calcium Oxide

    Colloidal phosphate is typically called soft rock or rock phosphate, and it’s a source of calcium that doesn’t contain as much as other options on the list. It also won’t increase your pH range as much as lime or other amendments.

    One thing to consider is that colloidal phosphate slowly releases calcium, slower than lime or gypsum. It contains large amounts of phosphorus as well.

    You can find two types: hard and soft phosphate. If you want to use it as a fertilizer, go with soft rock phosphate because it breaks down faster, so your plants have access to the nutrients faster. However, it’s not recommended for soils with a pH range higher than 5.5 since it only breaks down in acidic soil.

    I recommend trying the Down to Earth Organic Rock Phosphate. It comes in a 5lb box and contains 18% calcium. Plus, for being organic, the price is great!

    How Calcium Affects Plants

    Garden soil contains many different vitamins and minerals needed for plants to grow, including calcium. Plants need calcium to build strong cell walls to keep them upright, and it helps transport other minerals throughout your plant.

    Calcium is required in large amounts, and it’s immobile in the soil and plant tissue. Plants need to have a constant supply available for access. It’s only xylem mobile, so it only moves up the plant and stays in place. That means young tissue and fruiting bodies are most affected when the reserves run out.

    1. Creates Healthy Soil

    Having proper amounts of calcium in the soil leads to a healthy soil structure. This nutrient regulates the pH range of your soil and increases aeration, opening up the soil and allowing water to absorb better.

    2. Brings Nutrients Up the Plant

    While calcium itself is xylem mobile, it’s like the trucker of all nutrients; it takes the other nutrients up the plant to wherever it needs to go.

    Calcium enters the plant through the roots (or leaves) and moves the nutrients through the water to the leaves or wherever else it needs to go. That’s why more calcium leads to stronger plants.

    3. Helps with Early Season Growth

    Having the right ratio of calcium in the soil leads to a larger, healthier root mass and faster growth in the spring. You’ll also notice uniformity amongst your plants.

    4. Creates Healthy Plant Tissue

    This nutrient is a necessary component of cell walls, responsible for cell division, the permeability of cell membranes, and nitrogen utilization.

    5. Increases The Yield Size

    All of these benefits lead to one major benefit – a larger yield size. It’s a great way to increase the harvest size in your garden.

    Calcium is a necessary secondary nutrient that your garden soil and plants need. Don’t let a calcium deficiency ruin your plants; it’s so easy to add calcium to soil!

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