is calcium bad for cannabis

Lack or excess calcium in the marijuana plant

Excess Calcium or Calcium Deficiency in Weed

Dear grower, when you decided to start growing your own cannabis, did you believe that you’d become an amateur plant scientist? This is what it takes to be proficient with growing your own high-quality marijuana. Ask any grower that’s been in the business, and they’ll tell you its takes in-depth knowledge to produce those High Times looking buds.

What’s the most challenging aspect of growing weed isn’t all the information you need to process, it’s coping with the problems you’ll eventually have. No one is perfect, and this means you’ll subsequently scan through Google searching “how to fix x.” Been there, done that, and now it’s your turn. Let’s look through one of the biggest hurdles for newbies and veterans alike: Calcium.

⚠️ What is Calcium?

Calcium is an essential secondary macronutrient. It doesn’t make the cut to hang out with nitrogen, phosphorous, and potassium; but it has a wide range of responsibilities in plant health. Its group of secondary nutrients consists of magnesium and sulfur, and these three aren’t needed in a large quantity as the primary nutrients NPK.

➕ Calcium’s Role in Cannabis Plants

Calcium’s role should never be understated. It’s responsible for keeping cell walls intact and sending messages to activate cellular activities. It’s crucial for many enzymatic processes in cannabis plants. It plays a crucial role in protecting cannabis plants from heat stress.

The list goes on and on, but we’ll leave it here for now. What we want you to understand most of all, is that calcium is an essential nutrient and is responsible for a wide host of aspects with marijuana plant.

Cell walls are responsible for keeping the body of a plant rigid and functioning. Imagine your own body, where our skin is made up of cell walls. If you suddenly managed to destroy your cell walls, then you’d immediately fall apart. The same goes for plants and its with utmost importance that they remain working.

Heat stress is a common problem in the grow room. If a plant lacks a protective measure to shield itself from the heat of an HPS or MH lamp, then it won’t survive for very long. Calcium allows for cannabis plants to regulate themselves so they may continue functioning even in hot climates.

Enzymatic functions are responsible for a plethora of activities in marijuana plants. Enzymatic functions allow for functions such as cloning, apical dominance, the creation of new shoots, and many more. Without these enzymatic functions, we wouldn’t be able to manipulate cannabis plants into growing outwards to create a SCROG setup.

Can you imagine what the cannabis industry would look like if we couldn’t clone? We owe many thanks to calcium for its critical role in the overall functions related to the production of marijuana crops.

✅ The Basics of Calcium While Growing Weed

Now that we have a basic understanding of calcium let’s take a look at what you need to know when you’re growing cannabis.

Calcium isn’t a mobile nutrient when growing cannabis. Mobility/immobility of nutrients plays a critical role in understanding how to identify a calcium deficiency or toxicity. Calcium’s immobility means that when there’s a severe lack or abundant amount, the affected leaves will be new growth at the top of the plant.

Cannabis generally uptakes a lot of calcium and depending on the substrate used, you may need more or less of it.

🔥 Calcium and Growing Medium

Calcium impacts cannabis grown in both soil and soilless mediums. Cannabis that is grown in soil generally has a natural buffer that is found in the mix. This calcium buffer is usually in the form of dolomite lime, which is powdered.

This buffer keeps the pH of the soil in check, and not allowing drastic swings toward too acidic or too basic. This necessary calcium buffer maintains the pH in the perfect range of 6.8-7.2. This is the reason why cannabis plants growing in soil generally don’t require a pH meter. This is also the reason why marijuana plants that are grown in soil usually don’t have high instances of calcium deficiency or toxicity.

On the other hand, cannabis plants growing in a soilless or hydroponic system generally has a higher instance of calcium deficiency or toxicity. The reason for this is because calcium is only available for uptake in a certain pH range. Growing in a soilless medium requires the use of a pH meter for this reason.

An especially important aspect when growing cannabis in soilless mediums is the cation exchange capacity. This chemical exchange is responsible for some of the most significant headaches growers encounter.

Cation exchange is the function of specific cations, like calcium, to be held by the medium. This means that if the cation exchange capacity of calcium is not functioning correctly due to an excess of another nutrient, the medium may hold onto the calcium ions. Calcium ions that are held by the medium will not be able to be utilized by the marijuana plant.

👾 What Does Excessive Calcium Do?

Too much calcium in your weed plants can lead to some severe consequences. The most obvious problem that you’ll see if you overdo it with a calcium additive is leaf burn. The cannabis plant is reacting to the excessive levels of calcium and is trying to push it out from the leaf tips. This causes necrosis (death) of the leaf tips, and they will be a yellow/brown color.

Besides causing leaf burn, excess calcium doesn’t actually create such drastic symptoms as a deficiency. Instead, too much calcium in your cannabis plants will actually lead to problems in other nutrients, such as magnesium and potassium. This situation presents a very frustrating problem when growing cannabis. Too much calcium will lock out magnesium or potassium, and the only way to correct the problem is by first dealing with the calcium issue.

So, although you’re experiencing potassium and magnesium related symptoms, the actual root of the problem stems from too much calcium. Dealing with an excess calcium problem doubles or triples your work by making it necessary for you to also try and fix your magnesium and potassium issues. It can also lead you astray chasing other nutrients, while the calcium problem remains active..

✨ How to Correct Excessive Calcium in Your Cannabis Garden?

Once you’ve determined that you have excess calcium in your marijuana plants, it’s time for a gentle flush. When I say gentle, I mean a low dose of a balanced nutrient mix. When growers here the word “flush,” they think pouring liters of water through the medium to flush every nutrient out. This is inadvisable because you’re suddenly depleting the cannabis plant of all of its necessary nutrients to function.

Flushing with a low dosage of nutrients allows excess nutrients to be pushed out while leaving a smaller concentration. This method allows your plants to continue taking up critical nutrients for its growth.

Alternatively, you can flush your plant with a low dose of calmag, a combination of calcium and magnesium. By flushing with calmag, you decrease your chances of suddenly locking out potassium and magnesium.

Ata Calmag one of the most effective products when your plants need an extra supply of Calcium and Magnesium…

⛳ What Does a Calcium Deficiency do?

A calcium deficiency is much more noticeable than toxicity. A calcium deficiency will always begin in new growth and the top half of the cannabis plant. The reason for this is because of calciums immobility, and this means it won’t travel to older leaf growth. So, a clear indicator of spotting a calcium deficiency is by evaluating what portion of your plant is being affected.

Visual indicators are light yellow and brown spots that look similar to rust. These spots will generally start near the edge of the leaves or near the veins. As the deficiency expands, these mottled colors will begin to envelop the entire leaf. New leaves will usually curl, and the topmost area of growth will slow down in vigor. Stems will suddenly become flimsy and fall off easily if brushed against. The overall growth of the plant will slow down drastically

A calcium deficiency in cannabis also drastically limits the plants’ ability to fight off pathogens and predators. This means that certain types of fungi and bacteria will be more likely to establish themselves in this time of weakness. Pests such as mites, whiteflies, and gnats will be readily attracted to plants that are already weak and unable to defend themselves.

Since cell walls are weak during a calcium deficiency, the overall plant’s wall structure is fragile. This makes the entire plant brittle and unable to support the weight of buds. Bud development is reduced, as well as the growth of the plant’s root system.

Also, calcium plays a significant role in helping a cannabis plant cope with heat stress. While a calcium deficiency is ongoing, a marijuana plant will be unable to cope with heat stress. This is compounded by the fact that the cell walls are already weakened.

⭐ How You Can Fix a Calcium Deficiency?

Now that you’ve spotted enough symptoms that’s lead you to believe you’re looking at a calcium deficiency, it’s time to act..

First, you’ll need to analyze the nutrients that you’ve been feeding your plants. Are you giving lower doses than what’s recommended? Are you checking pH? These should be the first questions that you answer.

If you realize that you are giving too small of a dose of nutrients, then it’s time to bump up your schedule. Start with a small increase of 10-15%. Allow 2-3 days to notice if the new leaves resume vigorous growth..

Another option is to use calmag specifically in addition to your current nutrient lineup. In this situation, it’s recommended that you cut the recommended dosage of your calmag in half. That means if your calmag bottle suggests 5mL per 4 liters, then cut it to 2.5mL per 4 liters.

If you realized you haven’t checked pH, then its time to do so. If you recognize that your pH is off in the too acidic or basic direction, then it’s time to correct your nutrient pH. You should be aiming for 6.8-7.2 in soil and 5.2-5.8 in hydro. Once you’ve adjusted your pH, then it’s time to start adding nutrients at the right level.

Of course, you won’t be seeing a change instantaneously. Patience is key in growing excellent weed, and when dealing with problems, patience is a virtue. If problems persist after 4-7 days, it’s time to increase the dosage of calmag or your base nutrient.

Infographics about Lack or excess of calcium in your marijuana plant

⚠️ Conclusion

Now you’ve learned why calcium is such an important nutrient, even though it’s called a secondary macronutrient. Calcium plays a wide amount of roles, and they are all necessary for the health and happiness of your plants. If you grow your cannabis with the objective of keeping all of these necessary nutrients in line, you’ll have a problem free grow.

Of course, having a problem free grow takes either a lot of luck or a high degree of experience. As a grower, you must keep your plant’s system well fed if you want it to produce high-grade cannabis. Having the necessary knowledge of the things that run your plant is crucial, and you’ll be a better grower for it.

For more information on growing cannabis, join us at PEV Grow to discover a wide range of topics, from nutrient issues to various growing systems.

Get the right level of calcium for your cannabis plants ⭐ Avoid excess or deficiency in your marijuana crop ⭐ Everything you need to know!

Calcium Deficiency In Cannabis Plants

Cannabis relies on the complex interaction of many compounds to ensure healthy growth. Calcium deficiency can slow vegetative and reproductive growth. Identifying and correcting issues like this is all part of becoming a master grower.


Calcium is an essential compound used to aid plant growth all throughout its life. It is necessary for proper germination and early root development, right on through to flowering and healthy maturation. Calcium helps ensure cell vitality and strong plant formation. It also helps maintain healthy root growth, protein and vitamin synthesis and the proper absorption of potassium.

Calcium is necessary for transpiration and nutrient uptake. It is a requisite for photosynthesis and helps plants resist heat stress. It guarantees the healthy functioning of hair roots and leaf stomata. Calcium is semi-fixed. It remains in the cell walls until there is extreme deficiency, in which case it becomes soluble again. This can be observed when leaves in the middle of the plant and older growth begin to be affected.

A calcium deficiency in cannabis plants is less common in outdoor soil grows than hydroponic or neutral-medium indoor grows. A calcium deficiency will:

  • Inhibit nutrient uptake at the roots. Calcium aids in the decomposition of organic matter at the root zone, facilitating nutrient absorption.
  • Impede flower growth during peak florescence. Cannabis uses extra calcium in the middle of the flowering process. Depending on species, this can be from three to six weeks into flowering.
  • Cause nutrient lockout. Poor functioning roots means poor nutrient uptake. The plant may display several types of nutrient problems when this happens.
  • Cause plants to lose vitality and wilt. Calcium is essential for general plant health and stress resistance.


Calcium acts in concert with other important compounds to ensure overall plant health and vitality. A lack of calcium can mimic other deficiencies since the plant’s ability to maintain essential biological functions is compromised.

The following represent symptoms of a calcium deficiency:

  • New growth at the top of the plant is primarily affected.
  • Young growth slows, new leaves curl. Fresh growth is twisted and dies off quickly. Young shoots are purple or yellow.
  • The root system is compromised so fewer nutrients will be absorbed. Overall growth slows and plants lose their lustre.
  • Flower growth severely affected, especially at peak florescence. Young calyces are crinkled, distorted and don’t fill out.
  • Large, light brown necrotic spots form on leaves. Leaf edges mottle and turn brown. Leaves become yellow as the problem advances.
  • Branches are weak and break easily. Stalks may become hollow and rot inside.
  • Plants do not respond well to heat.
  • Roots become brown and are susceptible to slimy root rot and other pathogens.


Growing outdoors in soil generally allows for a greater margin of error with many nutrient problems. Unmodified acidic soils like those found in pinewoods can leach calcium, but proper attention can prevent calcium issues. Modify the soil with garden lime, dolomite, powdered bones, crushed eggshells or fish meal. Good quality compost is always a must.

There is little chance of a calcium deficiency growing outdoors in pots or growbags. Contemporary soil mixes usually have a complete spectrum of vital nutrients for the life of the plant. Organic growers will have no-till winter companion plants rehabilitating the soil for the new season.

Tomatoes are another plant notorious for their calcium demands. An old gardener’s trick is to dig a hole deeper than what is needed for the transplant. Put two fish heads and a palmful of garden lime in the bottom and water in. Backfill with soil, then plant the seedling as normal. Your plants will boom, then bloom.


Soil: Avoid calcium deficiency from the outset with good soil selection. Make your own soil or buy a commercial mix with plenty of calcium for the life of the plant. If on that rare occasion a calcium deficiency is identified, there are a number of ways to rectify the problem:

  1. Add dolomitic lime or garden lime and water in. This will also help stabilise pH in the long-term.
  2. Add a commercial calcium-magnesium solution, calcium acetate or calcium-magnesium acetate for a rapid calcium boost.
  3. Add liquid calcium, liquid lime or a teaspoon of hydrated lime dissolved in four litres of water.
  4. Check pH after treatment to make sure it is still between 6.2 and 7.

Neutral mediums & hydro: Calcium problems are far more likely when variables in nutrients and the grow environment aren’t buffered by active soil. Most water contains calcium, so little is added to commercial nutrient solutions. If a deficiency develops:

  1. Make a mixture of one teaspoon hydrated lime to four litres of water and water in.
  2. Use a commercial calcium booster or liquid lime.

If your water is 150ppm (EC 0.3), then there is little risk of calcium deficiency. Using unmodified RO or distilled water can strip calcium from plants. Before making a nutrient solution, add two parts calcium to one part magnesium to the water until the ppm reading is at least 150-200 (EC 0.3-0.4).

Water is one of the most important factors when growing cannabis. Always check the water before making any decisions. Fluctuations in pH can mimic many plant deficiencies and is the primary problem where plant health is concerned. Bad pH requires flushing the plants with clean water.

Calcium deficiency in cannabis can slow growth and inhibit flowering. Find out how to identify and fix calcium deficiencies for indoor and outdoor grows.