How to Add Calcium to Soil

How to add calcium to soil. Adding calcium to vegetable garden soil.

Gardening is one of those things that, when you get it right, it's so much fun and rewarding.  But, there are some things that can go wrong that can make it seem like all of you hard work has been for nothing.  Plant nutrition is key to healthy plants of all kinds, especially vegetable plants that are trying to produce food for us.

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​Adding calcium to the soil can prevent one of the most common garden problems: blossom end rot.  Learn how and when to add calcium to your garden soil to keep this nutrient deficiency at bay.

When to add calcium to soil

Many garden fertilizers contain the three major macronutrients that plants need: nitrogen, phosphorus and potassium.  These are the nutrients that plants need in the largest amount.  With that being said, many of these fertilizer blends don't include other nutrients that plants need.

​Calcium is also a macronutrient, but it's not used quite as much as nitrogen, phosphorus or potassium.  Because of this, it's often referred to as the forgotten macronutrient.  It's crucial to proper plant health; it's involved with so many functions in plants from proper cell wall formation to fruit production.

adding calcium to garden soil

Plants need calcium at all times since it's used in so many processes in the plant. So, the ideal time to add calcium to the soil is, frankly, all of the time.  Of course you can't constantly add calcium to your garden soil, so the time to add it is going to depend on the way that you add calcium.

​Some calcium fertilizers take a longer amount of time to break down and can be used as a long-term calcium supply.  Other types of calcium are ready for the plant to use immediately and can be used as needed.  You can combine the two to make sure that your plants have plenty of calcium and won't run out.

Signs of Calcium Deficiency

Plants that lack in nutrients will show signs of a nutrient deficiency.  Calcium is no different.  You'll be able to see some signs that your plants need calcium if you know where to look.

One of the first places that plants will show calcium deficiency is in the leaves. Look at the older leaves on the plant.  These are the leaves towards the bottom.  You won't always see signs of calcium deficiency in the bottom-most leaves.  Instead, look at the leaves just above the bottom-most leaves.  These leaves tend to show the first signs.  There will be yellow and brown spots.  The outside of the leaf edge may be brown.

Look at the top leaves.  The leaves at the top of the plant are the newest growth.  Since calcium affects plant growth, you may see signs of a deficiency in the newer, top leaves.  These leaves may be stunted, smaller and have a crinkled appearance.

If you happen to be transplanting your plants, you might see some root damage from a calcium deficiency.  Calcium is used to help the plant's root system grow and extend.  When there isn't enough calcium, roots can become stunted.  They may look spindly and a black/brown slimy mess.  Roots that are damaged from not having enough calcium are not going to bring in proper nutrients and water for the plant.

If can be easy to confuse these signs of calcium deficiency with other plant nutrition problems.

​One of the most common signs of calcium deficiency is seen in vegetable plants.  Blossom end rot is a common issue that's easy to treat and really easy to recognize.

Blossom end rot occurs when there isn't enough calcium for the developing fruit to continue to develop properly.  The fruit develops a nasty black lesion that looks wet. This lesion develops on the end opposite of the stem, where the blossom was attached (hence the name blossom end rot).

Fruits that are damaged by blossom end rot are usually small and should be removed and tossed out.  Blossom end rot can affect any vegetable that produces a flower and then fruit, but it's more common in tomatoes, peppers, squash, melons and eggplants.

If you notice blossom end rot on your vegetables, you will need to treat them with a calcium fertilizer that acts fast.  You won't be able to save the ruined fruits, so pluck them off to prevent the plant from putting more energy into those ruined fruits.  Treating the plant will help to prevent future fruits from being damaged.

​Learn more about calcium deficiency, what causes it and how you can manage blossom end rot in the video below:

Calcium Fertilizers

There are several ways that you can add calcium to your garden soil.  You can purchase soil amendments that can be added to the soil.  There are also sprays that you can spray directly onto your plants that can provide a quick dose of calcium where the plant needs it.  You might also have a few calcium sources at home that you can add to the soil to prevent calcium deficiencies from occurring.

Calcium fertilizers come with other minerals and nutrients in them.  When you're choosing a calcium fertilizer to use, it's a good idea to determine if you have other nutrient problems in your plants.  If you do, you may be able to kill two birds with one stone by using a source of calcium that tackles both deficiencies.

​Adding calcium to the soil can also affect the soil's pH. Use calcium fertilizers that raise the soil's pH with care since they can create a soil that is too alkaline for plant growth.

Foliar Sprays (Calcium Acetate, Calcium Nitrate, Calcium Chloride)

Foliar sprays are an excellent option and something that I highly recommend having on hand at all times.

Foliar sprays are calcium fertilizers that are designed to be sprayed directly onto the foliage of the plants.  You probably know that roots are designed to bring in nutrients, but leaves are also pretty efficient at bringing in nutrients.

When you spray calcium directly onto the leaves, you'll be providing the plant with the calcium right where it's needed the most.  Foliar sprays are the ideal way to prevent blossom end rot since the calcium is being provided at the top of the plant, where the blossoms will develop.

Another benefit of foliar sprays is that it's not going into the soil and won't affect the soil's pH.

No matter how you decided to add calcium to the soil, make sure that you have a calcium foliar spray on hand to spot treat plants as needed.  Or, use it a few times over the growing season to help prevent blossom end rot.  Look for sprays or concentrates that mention blossom end rot prevention on the label.

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Lime (Calcium Carbonate and others)

Lime can be found easily in most garden and farm supply stores.  It's made from crush limestone and typically comes in a powder.

Lime is a great way to add calcium to your soil.  It does affect the pH though and can create an alkaline soil if not used carefully.  Most vegetable plants prefer to grow in a slightly acidic soil and won't produce well if the soil is alkaline.

Before adding lime to your soil, you may want to have your soil tested.  You can purchase an at-home soil test kit or you can have someone come out and test your soil for you.

Lime will provide the most calcium to your soil, but since it can raise the pH, you'll want to make sure that you don't add too much.  If your soil is too acidic, then lime may be the perfect candidate for you.

​Dolomite lime contains calcium carbonate, but also contains magnesium.  If you've had problems with magnesium deficiency in the past, or your soil test comes back and shows that your soil is low in magnesium, then add dolomite lime to correct both problems at once.  Just like other types of lime, dolomite lime will raise the pH level of your soil, so keep that in mind.

Gypsum (Calcium Sulfate)

Want to add calcium but don't want to affect the soil's pH? Then gypsum just might be your man.  Gypsum is a perfect way to add calcium to the soil without changing the pH.

Gypsum is a naturally occurring mineral.  It's not only a good source of fast-acting calcium.  Gypsum is used for more than just adding calcium to your soil.

If your soil is compact and has a lot of clay in it, one of the best ways to break up and loosen the soil is with calcium.  It also prevents crusting of the soil, water erosion and can help your young plants grow through the soil easier.

​Gypsum also removes salts from the soil that can deter plant growth.  If you live in a coastal or arid area where the soils have a high salt content, use gypsum to both add calcium to the soil and remove some of the harmful salts.

Ground Oyster Shell (Calcium Carbonate)

If you have chickens around, you probably have some oyster shell on hand.  Oyster shell is used frequently as a calcium supplement for laying hens that need extra calcium to produce eggs.  Although you can use oyster shell in the garden, it's not always the best option to add calcium.

The calcium that is found in oyster shells is the same type of calcium that is found in lime, so you may think that it's a perfect candidate for using in the garden.  Just like with lime, oyster shells can raise the pH of the soil.  The good news is that the pH isn't usually raised immediately like it is when too much lime is added to the soil.  It generally takes several months or even years for the pH to be raised when you use oyster shell.

That sounds great and all, but the reason that it takes oyster shell longer to raise the soil's pH is because it takes a really long time for the oyster shell to break down.  If you need a quick source of calcium, don't depend on oyster shell.  It can take it years to break down in your garden, which won't help you out much.

So should you add oyster shell to the garden?

​If you happen to have oyster shell on hand, it won't hurt anything to add it to your garden as a long term source of calcium.  Just don't use it and expect immediate results.

Egg Shells

You may have oyster shell on hand if you have chickens, but you likely have egg shells whether you have chickens or not.  Egg shells are composed almost entirely of calcium, which makes them a good source of the mineral.

Rather than tossing egg shells into the trash can, save them to put into the garden.  You won't be able to see immediate results from egg shells, but they can become a good source of calcium over time in your garden.  It can take several months for egg shells to break down enough for plants to get calcium from them.  You can help speed up the break down process though.

​I keep a bowl (with a lid) on my counter for egg shells.  We currently have 16 laying hens, so we go through our fair share of eggs.  Every time that I crack an egg, I give the shell a quick rinse to remove any remaining egg from the inside of the shell.  I toss the rinsed eggshell into the bowl and set the lid on it. Don't seal the lid, you want the eggshells to be able to breathe so that the water can evaporate.

adding calcium to garden soil

When my bowl gets full, I crush the shells into small pieces.  You can also grind them up with a blender or a food processor.  The smaller the pieces are, the quicker that it will break down in the garden.

​A few times a year, I add the crushed egg shells to my garden soil.  Again, this won't be a quick fix for calcium deficiencies, but it's a good way to make use of those shells that you would normally toss in the trash.  If you have a massive garden, you probably won't go through enough shells to keep the entire garden with adequate calcium, so add the calcium in the soil around where your plants are.

Wood Ash (Calcium Carbonate)

Do you have a fireplace or a frequently used fire pit?   You may have heard someone mention that using ashes in the garden is a good way to add calcium.  Using hardwood ashes will provide about half the amount of calcium to the soil as using lime.  Don't use ashes from softwoods since these can be harmful to plants.

Wood ashes can provide many of the other nutrients that plant need, including potassium, phosphorus and boron.  In fact, one of the few nutrients that wood ashes don't provide is nitrogen.

Don't use ashes that have fake logs or charcoal briquettes in them.  Only use ashes from hardwood burning.  Oak is a commonly burned wood and is a perfect candidate for using in the garden.

There are a few things that you need to keep in mind if you're using wood ashes as a source of calcium in your garden. First of all, wood ash contains the same type of calcium as lime and can therefore raise the pH of the soil.  Don't use wood ashes if your soil is already borderline alkaline or neutral.

You'll need about twice as much wood ashes as you would lime to get the same effect.  Wood ashes only contain about half the amount of calcium as lime, so you'll need more.  However, because the amount of calcium is lower, the likelihood that you'll raise your soil's pH too much is reduced.

When you put wood ashes on the garden, don't let the ashes touch the plant directly.  Put the ashes in a ring around the plant, making sure that it doesn't touch the stem or leaves. Wood ash is caustic and will burn the plant if it touches it directly. It's better to let the ashes soak slowly into the ground where the plant can take it up with their roots a little at a time.

​If you burn wood frequently, wood ashes can be a free source of calcium for your soil.

Colloidal Phosphate (Calcium Oxide)

Collodial phosphate, also called soft rock or rock phosphate, is another commonly used calcium fertilizer. It doesn't contain as much calcium as some of the other types on this list.  It also doesn't raise the pH as much as lime does. It will only cause a small change in the soil's pH.

Collodial phosphate also releases slower than lime or gypsum. Rock phosphate does have large quantities of phosphorus, a crucial plant nutrient.  For years, gardeners used rock phosphate as a fertilizer since it contained both calcium and phosphate.

There are two types of rock phosphate: hard and soft.  If you're going to use rock phosphate as a fertilizer, look for soft rock phosphate.  It breaks down quicker than hard rock phosphate, making the nutrients available to your plants quicker.

Rock phosphate isn't recommended for soils that have a pH that is over 5.5.  Rock phosphate only breaks down in acidic soil, so if your pH is too high, don't waste your time using rock phosphate as a fertilizer. If your soil isn't acidic enough, consider adding rock phosphate to your compost pile. The nutrients will break down in the compost pile and will be available when you put the compost into your garden.

​Add rock phosphate to your soil before planting.  If you haven't already added it, you can put it in the soil when you dig the holes to put plants into the garden.

Bone Meal

Bone meal is a favorite fertilizers for organic gardeners. It's produced from the ground up bones of animals.  Since bones are composed mainly of calcium, this makes bone meal an excellent source of calcium. Bone meal also contains some nitrogen and a good bit of phosphorus, making it one of the more rounded calcium fertilizers.

Bone meal can raise the pH of the soil, so make sure that your soil isn't too alkaline before adding bone meal.

Bone meal slowly releases calcium into the soil.  Most bone meal will continue to release calcium for up to four months.  If you add it at the beginning of the growing season, you may not have to add it again in the same growing season.

Bone meal isn't just good for vegetable plants.  Flowering plants, bulb and root crops will also benefit from added bone meal.

​You can add bone meal to the soil in several ways.  Sprinkle it around the base of plants, work it into the soil or put it into the bottom of the hole that you'll plant in for a boost of nutrients.

Epsom Salt (Magnesium Sulfate)

Epsom salt is a garden additive that many gardeners swear by. Although Epsom salt is a good soil additive, it doesn't actually contain calcium at all.  In fact, Epsom salt contains magnesium and sulfur, but not calcium.  You may have heard that Epsom salt can prevent blossom end rot, but this is a myth.

Epsom salt does help plants grow by providing magnesium and sulfur.  If you're having problems with calcium deficiencies, avoid using Epsom salt.  The magnesium in Epsom salt competes with calcium to get absorbed by the plant.  So, if you try to treat your plants for calcium deficiency with Epsom salt, you may actually make the problem worse.

​If you aren't having blossom end rot problems, then by all means, add Epsom salt to your garden.  It's a good fertilizer, it just doesn't prevent or treat calcium deficiencies.

What is the best source of calcium for plants?

I try to have two methods on hand.  I like to add something to the soil as a preventative when I plant.  I also like to have a spray that I can use quickly if I notice a plant that needs a little help.  Blossom end rot can pop up unexpectedly, especially on tomatoes and squash.  Having a spray on hand is nice when you spot a random case that needs to be treated ASAP.

I like to add something to the soil that can be used as a long term calcium source.  Lime will provide the most calcium, but it can cause dangerous rises in soil pH.  If pH is a concern, then use gypsum.  It may not contain as much calcium as lime, but it's a safer option since it doesn't affect pH at all.

​Of course, if you have some of the free sources of calcium on hand, like eggshells or wood ash, then incorporate those into your garden.  There's no sense in throwing them away just because they aren't the fastest source of calcium.  They can still contribute to the overall health of your soil.

​If you haven't yet, grab your FREE copy of the From Seed to Supper guide and learn how to start growing delicious, fresh vegetables and herbs!

adding calcium to your garden soil, guide to growing vegetables

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How do you add calcium to your vegetable garden soil? Let me know below!

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I'm a multigenerational homesteader, former high school and college agriculture teacher, and your guide for embracing a simpler, more traditional lifestyle. Come along as I teach you how to grow your best garden, raise chickens and other livestock, learn traditional skills and create the homesteading haven of your dreams.

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