Tomato plants need a variety of nutrients to grow tall, flower, and produce healthy fruit. However, this raises the question of where calcium comes in when it comes to tomato plant health.
So, do tomato plants like calcium? Tomato plants like a good dose of calcium, which they need for proper growth. Calcium helps to balance ions, improve cell wall stability, build strong roots, and transport other nutrients. Lack of calcium causes blossom end rot in fruit, necrosis of leaves, stunted growth, and poor fruit production.
Of course, a lack of calcium may occur in a tomato plant even if there is plenty of calcium in the soil. At the other extreme, it is possible to add too much calcium to the soil.
In this article, we’ll talk about why calcium is good for tomato plants and how to tell if there is a deficiency. We’ll also look at how to prevent calcium deficiency, along with ways to provide more of it if the soil is lacking.
Let’s get started.
Do Tomato Plants Like Calcium?
Tomato plants like calcium, which often comes from the calcium carbonate in limestone-rich soil. Calcium is necessary for plant growth, and a lack of it will negatively impact tomato plants and their fruit.
Does Calcium Help Tomato Plants?
Calcium does help tomato plants to grow properly. In fact, plants need calcium for several reasons.
- Balance of ions – anions (negative ions) and cations (positive ions) need to be balanced.
- Cell wall stability of fruit – without enough calcium, tomato fruit will get soft spots on the bottom (due to blossom end rot – more on this later)
- Extending roots – calcium is necessary for tomato plants to expand their main root system.
- Nutrient transport – tomato plants use calcium to help move other nutrients throughout their tissues.
When a tomato plant suffers a calcium deficiency, some or all of these processes will break down. The result is a predictable decline in the fruit quality and health of the plant.
What Does Calcium Deficiency Look Like In Tomatoes?
A tomato plant with calcium deficiency will display some or all of the following symptoms:
- Blossom End Rot
- Stunted Growth
- Poor Fruit Production
Let’s take a closer look at each of these symptoms, starting with blossom end rot.
Blossom End Rot
A common symptom of calcium deficiency in tomato plants is blossom end rot, which affects the fruit. A flat tan, brown, or black spot will appear on the bottom (blossom end) of the fruit.
These spots can provide a place where bacteria and fungi can attack the fruit, leading to more decay and soft, mushy, rotten tomatoes. Below, you can see a picture of blossom end rot on tomatoes.
Blossom end rot can also affect cucumbers, melons, peppers, and squash.
Necrosis means the death of a part of the tomato plant. Often, necrosis caused by calcium deficiency begins with newer leaves turning brown.
These leave will turn brown at the edge, and the brown color will move towards the center of the leaf. Eventually, the necrotic leaves fall off.
Without enough calcium, a tomato plant’s roots will develop poorly. This prevents the plant from absorbing nutrients and water from the soil.
New leaves may also be small or misshapen, due to weaker cell walls at the cellular level. This means that the plant will absorb less sunlight for energy (due to lower surface area of leaves).
A smaller root system and smaller leaves will lead to stunted growth of the plant.
Poor Fruit Production
A plant that lacks calcium may also drop its flowers, resulting in less fruit at harvest. The fruit that does appear may be small, misshapen, or diseased.
How Do You Fix Calcium Deficiency In Tomato Plants?
A calcium deficiency in tomato plants can have several different causes. So, the treatment for calcium deficiency will depend on the cause.
Some common causes of calcium deficiency in tomato plants include:
- Lack of calcium in soil – this is rare, especially in soil with lots of lime. However, it is possible.
- Improper pH – a soil pH that is too low or too high can prevent a tomato plant from absorbing calcium through its roots (even in calcium-rich soil).
- Excessive nutrients – too much nitrogen, potassium, magnesium, or sodium can interfere with calcium uptake by a tomato plant’s roots. According to the University of Minnesota Extension, too much potassium, magnesium, ammonium, and sodium can decrease calcium availability.
- Root injury – damaged roots may not be able to absorb enough calcium to allow all of the fruit to fully develop (even if the calcium, pH, and other nutrient levels are balanced).
- Uneven watering – roots need water to absorb calcium, so dry soil can prevent calcium uptake. Wet soil can also damage roots and lead to root rot, which will also harm plants.
Remember that calcium is an immobile nutrient in plants. This means that a plant cannot easily move calcium through its tissues.
Therefore, a tomato plant needs a steady supply of calcium to prevent blossom end rot in the fruit.
Treating Calcium Deficiency In Tomatoes
To treat calcium deficiency in tomato plants, there are a few important steps to take.
Get A Soil Test
A soil test from a lab will reveal a lot about your soil, including:
- Calcium levels
- Levels of other nutrients (including nitrogen and potassium)
- Soil pH (a pH level that is too low can prevent roots from absorbing calcium, as you can see in this chart from Research Gate).
If the soil test reveals a pH that is too low (acidic), you can add lime (calcium carbonate) to the soil to raise the pH. If the soil test reveals that pH is too high (basic or alkaline), you can add sulfur to the soil to lower the pH.
If the soil test reveals excessive nitrogen, you can scale back the use of nitrogen fertilizers for your tomato plants. Another possibility is to try one of these low-nitrogen fertilizers.
If the soil test reveals that calcium levels are low, you can provide calcium by adding lime, dolomitic lime, or other sources (more on this later).
If the soil test reveals that pH and nutrient levels are fine, then look to root injury or improper watering as causes of calcium deficiency in tomato plants.
The table below summarizes the soil test result and the action you can take.
|Soil Test |
|Low pH |
|Add lime |
|High pH |
|Add sulfur |
|High N |
|Use low |
|Low Ca |
|Use high |
|Normal||Check for |
soil test result and the
action you can take.
Avoid Root Injury
Damaged roots will have a hard time absorbing water and nutrients (including calcium) from the soil. Once a plant has a calcium deficiency, its roots will not be able to grow as well, leading to a vicious cycle of smaller roots, weaker growth, and nutrient deficiency.
To avoid root injury, transplant tomato plants carefully when you put them outside. Handle them carefully when repotting.
Also, keep the transplants in shade until they are ready to plant. If you take them out of their container and leave them in the sun, their roots may get burned if they have started to circle the pot.
It is also important to avoid root injury to established plants during the growing.
If you need supports (stakes, cages, etc.), install them right after you transplant the tomatoes. Otherwise, driving the stakes into the ground will damage an established root system.
Also, avoid digging too close to the tomato plants. If you need to fertilize, consider using a liquid fertilizer and watering it in, rather than using one that you have to mix into the soil.
Ensure even watering for your tomato plants. You don’t want them to be too dry or too wet.
If your soil is too dry, tomato plants will have difficulty absorbing calcium (they need water to do it). A thin layer of mulch over the soil can help to retain moisture.
If you find that dry soil is a problem for you, check out my article on how to fix dry soil.
If your soil is too wet, it will cause root rot. This will also make it difficult for plants to absorb nutrients.
How Do You Add Calcium To Soil For Tomatoes?
There are several options available if you want to add calcium to the soil for tomatoes. The following are a good source of calcium for tomato plants:
- Shells (Egg, Clam, & Oyster) – shells are an excellent source of calcium for plants, since they are 98% calcium by weight. The smaller the pieces, the faster it will work, so grind up the shells into powder for maximum effect.
- Lime – lime is also known as calcium carbonate, and it contains 37% to 40% calcium by weight. This naturally occurring substance (found in limestone) is one of the most common sources of calcium for plants. It also lowers the acidity of soil (by raising pH). You can learn more about lime for tomato plants here.
- Dolomite Lime – dolomite lime contains magnesium carbonate in addition to calcium carbonate. It is a good alternative to lime if you want to add both calcium and magnesium to your soil. Dolomite lime contains 23.5% calcium by weight and 9.5% magnesium by weight. You can learn more about dolomite lime here.
- Gypsum – gypsum is also known as calcium sulfate. It is a good alternative to lime when you want to add calcium to the soil without changing the pH. Gypsum is 20% to 23% calcium by weight. You can learn more about gypsum in my article here.
- Wood Ash – wood ash is a good alternative to garden lime, and it has a similar effect in raising soil pH. It also contains 7% to 33% calcium by weight, so it can be a pretty good source of calcium for tomato plants as well.
- Bone Meal – bone meal contains 15% to 22% calcium by weight. It also contains a good amount of phosphorus (around 15% by weight), making it a very good fertilizer for your garden.
- Calcium Nitrate – calcium nitrate adds both calcium and nitrogen to your soil. It contains 19% calcium by weight, making it about as good a source of calcium as bone meal.
When Should I Add Calcium To My Tomato Plants?
You should add calcium to your tomato plants at the beginning of the growing season, right when you transplant them. Mix a little lime (or wood ash, bone meal, or whatever source of calcium you like) right into the soil in the spot where the tomato plant will go.
If you have had trouble with blossom end rot in the past (or see it happening this year), spread some lime (or another calcium source) into the soil near your tomato plants and water it in. If you are worried about burning your plants, use gypsum for a pH-neutral effect.
It is also a good idea to add calcium (in the form of lime) to your tomato plants is when the soil becomes too acidic (low pH). Again, a soil test will help you to determine this.
Can You Put Too Much Calcium On Tomatoes?
It is possible to put too much calcium on your tomato plants. Remember that calcium and magnesium “compete” for uptake by a plant’s roots.
This is because they are chemically similar (they are in the same column on the periodic table). As a result, too much calcium in soil will prevent a plant’s roots from absorbing enough magnesium.
A lack of magnesium is a big problem for plants. As you can see in the image below, magnesium is the central atom in a chlorophyll molecule.
Without magnesium, there is no chlorophyll, no photosynthesis, and no energy production for the plant!
Now you know why tomato plants like calcium and the signs of deficiency in your plants. You also know how to provide more calcium for them.
I hope you found this article helpful. If so, please share it with someone who can use the information.