September 24, 2022

Best cal mag supplement: When and why to use them

Cal mag supplements are some of the most widely misunderstood supplements in the fertilizer market. These supplements can be very helpful, but only if your plant already has a nutrient deficiency. If you’ve correctly diagnosed your issue, then a cal mag supplement is a great way to treat your plant and also to prevent this problem in the future.

Kushteller’s number one choice cal mag supplement is the Lotus Nutrients Cal/Mag Pro Series, although there are several good alternatives as well.

Best Cal mag supplements

Kushteller recommends the following cal mag products:

  1. Lotus Nutrients Cal/Mag Pro
  2. Botanicare cal mag plus
  3. Root Organics elemental supplement
  4. FoxFarm FX17020 Bush Doctor cal-mag
  5. Advanced Nutrients 6360-12 Sensi Cal Mag Xtra

Cal mag supplement reviews – full analysis

#1. Lotus Nutrients Cal/Mag Pro

Lotus Nutrients Cal mag
Lotus nutrients cal mag supplement

The lotus Nutrients Cal/Mag Pro is our top choice for cal mag treatments. The lotus nutrients group is a team of growers, scientists, and horticulturists based out of North Carolina. Their goal is to create a full spectrum of nutrient products to support plant growth.

This product comes as a dry power that can easily be mixed into a liquid treatment. This cal mag for plants is designed to work in soil for regular grows, or coco coir for hydroponic grows. It can also be made into a foliar spray for leaf or root application.

Nutrient profile

Their cal mag product has an ideal calcium to magnesium ratio of 4:1.

Their full nutrient profile is as follows:

  • Nitrogen: 4%
  • Calcium: 11%
  • Magnesium: 3%


This product currently costs $15 for 15 oz, which is a solid value. This price is slightly less expensive most other products on this list. Furthermore, this product comes as a concentrated powder, whereas other liquid concentrates have you paying for water weight.

#2. Botanicare Cal Mag Plus

Botanicare is a very well known plant nutrient company. This company started as a hydroponics store, and eventually moved to formulating their own line of nutrient products. They have been in business for over 25 years.

This cal mag for plants comes as a liquid concentrate, and can be used for standard soil grows, or in coco coir hydroponic systems. It can also be made into a foliar spray.

The cal mag plus product is very popular, sitting at a 4.5 star rating on amazon with over 20,000 reviews at this point.

Nutrient profile

This cal mag supplement contains the calcium and magnesium needed in a standard cal mag treatment, as well as nitrogen. It also contains iron, which is another trace mineral that many plants require.

This product is a liquid concentrate rather than a dry powder, which means that it’s nutrient density is lower than the Lotus product.

The full nutrient breakdown for this product is as follows:

  • Nitrogen: 2%
  • Calcium: 3.2%
  • Magnesium: 1.2%
  • Iron: .1%


This product currently retails for around $20-$25 a quart. This is a good deal for such a readily available and well reviewed product.

#3 Root Organics Elemental Supplement

The Root Organics Elemental supplement is available from Aurora Innovations. This company has over 20 years in the business, and considers themselves a research first company. They primarily focus on products for growing cannabis.

This cal mag for plants comes as a dry power, which means that it can be mixed to create liquid supplement for leaf and root treatments.

Although a lesser known company, the product still retains 4.5 starts on amazon over nearly 200 reviews.

Nutrient profile

The root organics product contains ample amounts of both calcium nitrate and magnesium nitrate, as well a several other trace minerals.

The full nutrient breakdown for this product is as follows:

  • Nitrogen: .25%
  • Phosphorus: .01%
  • Potassium: .2%
  • Calcium: 20%
  • Magnesium: 4%
  • Sulphur: 1%
  • Iron: .1%

This formula is very well rounded, and contains several additional trace minerals that can help prevent deficiencies.


This product is currently available for $25 for a 3 Ibs bag. Given that this product comes as a dry concentrate, this should be more than enough cal mag product for multiple garden grows.

#4. FoxFarm FX17020 Bush Doctor cal-mag

Fox fam is a well known fertilizer company. They were founded almost 40 years ago in Humboldt in 1984. They are known for emphasizing high quality and organic ingredients. Their products are found all over amazon with hundreds of positive reviews.

The Bush Doctor cal mag product is a liquid concentrate that can easily be diluted with water and applied to plants in both soil and hydroponic grows.

Nutrient Profile

This product is a liquid concentrate rather than a dry powder, which means that it’s nutrient density is lower than dry power products.

The full nutrient profile is as follows:

  • Nitrogen: 1%
  • Calcium: 3%
  • Magnesium: .9%

This product has adequate levels of calcium and magnesium.


This product is available for $25-$30 for one quart. This is a lower value than some of the other cal mag products on this list, however some people might be willing to pay for the Fox Farm name.

#5. Advanced Nutrients 6360-12 Sensi Cal Mag Xtra

Advanced nutrients is another well established company, founded in 1999 by Mike Straumietis. Originally a wholesale distributer for hydroponics companies, Mike’s engineering approach convinced him that he produce better formulas for plant fertilizers.

This product is especially designed with cannabis in mind, as it contains several other nutrients and trace minerals that these plants require.

This product is available as a liquid concentrate. The growers are quite confident in their product, which has a 100% satisfaction money back guarantee.

Nutrient profile

As previously mentioned, this cal mag product has a number of nutrients included in it. They do not list the exact amounts of their proprietary formula, but it includes:

  • Calcium
  • Magnesium
  • Iron
  • Manganese
  • Zinc

This product also includes kelp extract, which can help promote healthy microbe growth within the soil. These microbes are capable of supporting a healthy and strong root system


This product costs $10-$15 for 250mL. This is the least expensive product on our listing, although it is smaller than some of the other products. It’s ideal for a grower looking for a small boost for their plants.

Why plants need cal mag supplements

Cal mag supplements always contains two very important trace minerals for plant growth. These compounds are calcium nitrate and magnesium nitrate. Calcium and magnesium are required for growth by flower bearing plants such as tomatoes or bell peppers, and are also popular with cannabis growers.

Both of these minerals, along with iron, are very important for supporting several plant functions such as:

  • Creating chlorophyll for photosynthesis
  • Metabolizing potassium and phosphorus for bud production
  • Maintaining the structure of plant cells
  • Plant tissue development
  • Absorbing carbon dioxide

When a plant is deficient in any of these minerals, it can bring growth to a halt, and start damaging leaves.

How to tell if you need a cal mag supplement

There are several symptoms for a plant going through a nutrient deficiency, although the symptoms are different for calcium and magnesium. These symptoms can be grouped as follows:

Magnesium nitrate

  • Leaves start to yellow on old growth first. This is particularly true for leaves and growth at the bottom of the plant.
  • Leaves first become light green (with brown spots and tip burn) as chlorophyll production begins to halt. Leaf veins will often remain green.
  • The color change will start at the edges of the leaves, which can also become rough to the touch
  • Leaves eventually turn yellow and begin to fold on themselves. Eventually the tip burn spreads and they begin to die (although they usually don’t fall off the plant on their own).
  • Eventually yellow leaves will spread up the entirety of the plant

Calcium nitrate

  • New growth, particularly at the top of the cannabis plant, will turn spotted and brown
  • Plant with a calcium deficiency will have their new growth completely stunted
  • New buds will be small and stop growing
  • Plant roots will also have slow growth, limiting the size of the plant

What causes a calcium and magnesium deficiency

Although calcium and magnesium are usually found in adequate amounts in standard tap water, many situations can arise where plants become deficient in these nutrients.

The most common causes are:

  • Overly filtered water (which can remove minerals), including reverse osmosis water or distilled water
  • Low ph in garden soil or potting soil, which can prevent roots from absorbing nutrients
  • Areas with soft water, which is water that has low levels of minerals
  • If growing hydroponically, coco coir is known for blocking calcium absorption

If growing hydroponically, cal mag supplements are commonly needed for plants growing in coco coir. For soil plants in regular pots or container gardens, the most common cal mag issue is low root ph.

If you low root ph, make sure to fix this issue before giving a cal mag treatment. Low root ph will block the absorption of any nutrient supplements.

How much cal mag should you feed your plants

Most cal mag supplements have their recommended feeding levels listed on the supplement label. It may be good to use levels slightly under the recommended feeding amounts, as the recommended amount is usually the maximum you want to use. Excess minerals don’t benefit the plant and can disrupt soil ph or lockout other nutrients.

Should you make homemade cal mag supplements

Some growers prefer to make their own cal mag treatments out of epsom salts or dolomite lime. These are definitely viable options for experienced home growers. However, newer growers might be better off with ready-made options. These options have been thoroughly tested formulated to fix your nutrient deficiency.


What is Cal Mag supplement used for?

A cal mag treatment can fix issues with calcium and magnesium deficiencies in your plants. Such deficiencies can be very harmful to plants.

Will Cal Mag burn plants?

In general, cal mag will not burn plants as long as you follow the instructions on the cal mag container. If in doubt, try feeding your plant slightly less than the recommended amount.

How long does Cal Mag take to work?

A cal mag can work in a little as 2-3 days. Within a couple of days, damage to the plant from a mineral deficiency should begin to completely cease.

Is Cal Mag a fertilizer?

Cal mag is not considered a complete fertilizer because it does not contain all of the basic nutrients required to support plant growth. Cal mag is a supplement that provides the trace minerals calcium and magnesium.

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