True calcium deficiencies in plants rarely occur in rich, fertile soils. Why? Because calcium is the 5th most abundant nutrient found on Earth, being found in forms of calcite, dolomite and gypsum.
However, that’s not to say your potted friend is getting enough of this essential ion.
Once all the calcium in your plant’s growth media has been used up, your plant has no other way of making or absorbing anymore.
But how do you really know when your plant is lacking calcium vs being overwatered vs suffering from overfertilization. After all, they all cause yellowing leaves.
In this post, you’ll gain a deeper understanding of this nutrient deficiency so you can get to the ‘root’ of the problem, and help your plant look and feel best.
You’ll learn:
- 5 telltale signs your plant has a calcium deficiency
- The science behind this vital nutrient
- A simple way to remedy the deficiency
- How to prevent it from happening again in the future
Calcium – The Forgotten Fertilizer
Calcium is far more important to a plant’s overall growth than most people give it credit for.
It’s often referred to as a secondary or micronutrient as though a plant can thrive without it. But calcium has a deeply profound effect on your plants’ unique and defining characteristics; think leaves, roots, stems and flowers.
It’s the lifeblood of your plant’s growth and even its ‘immune’ system. Calcium not only regulates enzyme activity, nitrate uptake and cell wall development, but it also protects the plant from invading pathogens, microbes and disease.
A lack of calcium increases the plant’s chances of contracting dreaded root rot or even worse, the kiss of death, known as erwinia leaf spot. Not enough calcium can also cause withering and stunted growth.
Telltale Signs Your Plants Need More Calcium
Unlike in tomatoes and peppers, where a calcium deficiency results in the obvious blossom end rot, in houseplants you’re likely to only see subtle signs first.
These are:
- Brown/yellow necrotic spots and lines on younger, newer leaves (often mistaken for fertilizer burn)
- Droopy, withering stems (a loss of turgor)
- Youngest leaves are small, misshapen
- Leaf veins appear brown
- Leaves may look crinkled and torn
- Little to no shoot, tip, bud or leaf growth (even when in growing season)
- Roots are small and very little growth has occurred
In severe cases, instead of just small roots, you’ll likely spot soft, mushy, brown roots and a foul smelling odor emitting from the base of your plant – aka the start of root death.
Overwatering vs Calcium Deficiency – What’s the Difference?
Here’s where it gets confusing for plant owners: overwatering can cause the same symptoms as a calcium deficiency at first glance. Yellowing leaves, browning patches and curling of leaf edges.
But, the key to knowing you’ve over watered your plant lies in the texture of the leaves.
If they’re slightly soggy and mushy to feel, the culprit is overwatering. If they’re crisp and dry, you’ve got a very dry and unhappy plant on your hands.
However, the main sign of a true calcium deficiency is the necrotic spots, or brown scaly patches on the lower leaves. You won’t see this when overwatering or underwatering alone is the culprit.
However, it’s entirely possible you’re dealing with both problems at once.
Overwatering can leach calcium ions out of the soil, making them less available for the plant to use. In this case, go straight to the roots.
If you’ve got root rot (brown, mushy, foul-smelling roots) combined with those necrotic spots, I’d say you’ve got both an overwatering and calcium issue.
Magnesium Deficiency vs Calcium Deficiency – How Do I Tell the Difference?
This one is a little easier to spot. In simple terms, a magnesium deficiency will cause pale leaves and an all over yellower appearance.
This yellowing generally starts at the leaf edges before making its way to the middle of the leaf in later stages.
A plant lacking in magnesium might have some brown patches, but again these are usually only spotted on the leaf edges.
Overfertilization vs Lacking Calcium – What’s the Difference?
A keen eye is often needed to tell the difference between over fertilization vs a true calcium deficiency as both can cause yellowing and browning on young, lower leaves in their initial stages.
The first sign to watch out with overfertilization is a small crust of residue developing on the soil’s surface.
This is fertilizer salts that have baked onto the soil. Overtime, these salts will change the pH of the soil leading to root, stem and leaf burn.
Unlike with a calcium deficiency, overfertilization generally causes yellowing and browning that starts at the leaf edge and works its way into the centre of the leaf.
Calcium spots are pretty random and don’t usually follow a strict pattern.
The Remedy – Fixing Calcium Deficiency in Plants
Fortunately, you’ll be glad to know that fixing a calcium deficiency in plants is fairly straightforward. Before whipping up a homemade remedy, take a look at your fertilizer.
A high quality fertilizer should already have calcium listed as one of its core ingredients (you might see this as ‘Ca’) in a 2-4% quantity.
Anymore than that, and you could overdo it. This is the simplest and most cost effective way of treating a calcium deficiency in plants.
Premium fertilizers generally use a specific type of calcium known as EDTA. This form of calcium is highly stable and is soluble, meaning it won’t react or bind with other nutrients in the soil and can be readily absorbed by the plant.
Simply dilute the fertilizer in clean, chlorine free water and feed as usual.
Another good source of calcium is gypsum. Gypsum, unlike calcitic lime or dolomite, won’t change the pH level of your soil.
It’s fast-acting and overtime does correct even the most severe of cases.
Crab meal and marine phytoplankton/seaweed based fertilizers are another fantastic source of calcium. Just note, they both contain sources of nitrogen, phosphorus and potassium so it’s best not to double up on them.
Myth Buster! Egg Shells Are a Great Source of Calcium for Plants. Sorry to disappoint but this is a down and out myth. Egg shells decompose far too slowly to be of any use to your plants. They can be used as an organic matter amendment, but that’s about it.
How to Add Calcium to The Soil the Right Way
In plants, calcium moves from the root tips upwards throughout the plant with water. This is why sufficient watering is super important after you’ve added this nutrient to your soil mix.
If you’ve opted for the fertilizer route, you’ll already have this step covered as you’ve diluted it in water to begin with.
With gypsum and crab meal, you’ll need to add water after it’s buried in the soil mix.
You’ll be glad to know that once calcium has reached the new and young tissue or tips, it will stay put, meaning you will see some of that yellow staining start to disappear.
Note, there’s not a lot you can do about browning necrotic spots other than prune the leaves and wait for new growth to come through.
But Wait? Why Did My Plants Develop a Deficiency in the First Place?
Good question! There are many causes of a calcium deficiency in plants and it doesn’t just revolve around your soil not having enough calcium to begin with.
Sometimes your soil can have more than enough calcium in it but there’s something else hindering your plant from absorbing it.
These are the most common reasons why this might happen:
- Plants are chronically underwatered (calcium can only be transported via water).
- The pH of the soil is too acidic i.e. pH 6 or below, you’ll need to raise the pH before adding calcium.
- Temperatures are too low. If your room is too cold, transpiration rates will be low which results in less calcium being taken up by the plant.
- Humidity is high, but air circulation is low. Again, this lowers transpiration rates.
How Can I Test For Calcium Deficiency in Plants?
You can test for deficiencies, but in most cases, I’d say the average plant owner doesn’t need to.
Most home testing kits only check for the top 3 – nitrogen, phosphorus and potassium.
There are other kits out there that will test for calcium but from the reviews I’ve read, they’re highly inaccurate and not worth the money. The same goes for soil pH and moisture meters too (I never, ever recommend these).
The best and most accurate way to test for deficiencies in soil is via a professional soil testing kit but do bear in mind they’re pretty pricey (think $500+ in some cases).
Unless you’re housing a commercial nursery full of extremely rare plants such as the philodendron white knight, red moon or the ring of fire, I would save your money.
Can Plants Get Too Much Calcium?
Surprisingly, yes. Whilst calcium toxicity itself rarely happens, too much calcium can indirectly kill your plant.
When in excess, calcium can bind with other minerals and ions such as magnesium and phosphorus, preventing their uptake. Not to mention, this binding process can cause the soil’s pH level to rise, making it more alkaline.
Whilst most plants can cope with a slight change in the pH of their soil, they certainly can’t handle overly drastic changes.
To prevent this, make sure your fertilizer has calcium levels of no more than 2-4%. This is standard in most high quality or premium fertilizers.
With cheap fertilizers you’re not likely to see calcium on the ingredients list at all!
Too much calcium is only usually seen after overfertilization with a pre-made fertilizer or if too much homemade remedy has been added e.g. dolomite or gypsum.
Do My Plants Have a Cal-Mag Deficiency?
You’ll often hear plant enthusiasts and growers refer to their plants as having a ‘cal-mag deficiency’.
They’re referring to their plants having both a calcium and magnesium deficiency, but I really want to stress this, it’s entirely possible to only have an issue with one of those nutrients rather than both at the same time.
I’ve seen way too many plants overdosed with magnesium or calcium because owners believe that they should always be added together.
It’s always best to double check the symptoms your plant is showing you before adding nutrients for the sake of it.
Whilst magnesium and calcium deficiencies look similar, there are some essential key differences to look out for.
Magnesium is a mobile ion, meaning it is first uptaken by older leaf tissue, not younger tissue so you’ll see deficiencies of this ion appear in older, mature tissue first.
Calcium however is immombile meaning it will be absorbed by younger tissue first, which is where deficiencies will first show up.
