6 MONTH Money-Back Guarantee

10% off $250+, 15% off $1000+

Free Shipping on US Domestic orders $75+

CalMag & Iron

174 reviews
Regular price
Sale price
Regular price
Sold out
translation missing: en.products.product.unit_price_label
translation missing: en.general.accessibility.unit_price_separator 

Making Growing Simple, Exciting, and Easier to Succeed At

CalMag & Iron contains an exact balance of calcium, magnesium and iron specifically formulated to address any deficiencies that could be encountered.

Product Information

About CalMag & Iron

Give your garden exactly what it needs with our cal mag nutrients for hydroponics. This formula is specifically designed to come to the rescue of any plant with deficiencies that may be present. CalMag & Iron is a liquid calcium, magnesium, and iron supplement for plants that will not only treat a deficiency but support the growth and development of your garden.

CalMag & Iron works especially well in soil, hydroponic, and container gardens, ensuring strong and healthy yields in both. We also recommend using this formula on plants growing in coco substrate or reverse osmosis water because the absorption process becomes magnified in these conditions.
Many flowering varieties need this type of blend to flourish properly.

Order your Cal Mag & Iron today!

CalMag & Iron Feed Chart

Mixing Procedure

1) Fill your reservoir with water.  It may be filtered or tap water.  If you use filtered water you may need to add some CalMag & Iron.

2) Add HUMBOLDTS SECRET NUTRIENTS listed on the feed chart (Shake each bottle a little bit)

3) After you add your nutrients, adjust the PH so that your end mixture in your reservoir is between 5.5 and 6.5 (If needed.)

4) Can be used in Soil, Coco, Deep Water Culture (DWC) and Aeroponics.  Typically less nutrients are used in DWC. If you grow in Hydroponics it is recommended that you use  Golden Tree at a lower dose and use Plant Enzymes. We suggest you play around with the amounts of each nutrient and find out what works best for your setup as there are many variations to growing.

Additional Information

1) In order to have a successful grow growers should use at minimum Base A, Base  B & Golden Tree. 

2) For Veg: Add 1-2ml of Golden Tree per gallon to your reservoir. Then, add your base nutrient until PPM levels of the reservoir mixture reaches between 800-1000 (Hanna Scale)

For Flower: Add 2-5ml of Golden Tree, then add base nutrient into your reservoir  until your PPM levels of the reservoir mixture reaches between 1000-1300 (Hanna Scale, which is 2.0-2.6 in EC.) Remember that this is a rough estimate. Strains and growing mediums vary, some will enjoy higher PPM's and some lower.  Flushing at the end is not necessary.

Shake bottle and measure out 3-5mL per gallon of water

Shake bottle and measure out 3-5mL per gallon of water

Apply to the root zone, or use as a foliar spray. For optimal results feed with every watering as needed throughout your entire growing season.

We are confident that you will be pleased with your product and offer a 6 month 100% satisfaction guarantee.

Refer to our return policy for full terms for the satisfaction guarantee.

Frequently Asked Questions


Humboldts Secret CalMag & Iron can be used as both a soil drench and foliar spray.

Coco coir naturally draws on calcium and magnesium making it unavailable to plants. By using Humboldts Secret CalMag & Iron you can avoid any deficiencies before they happen.

CalMag & Iron help correct many common plant deficiencies, helps supplement calcium and magnesium for those using RO water, and helps increase nutrient absorption!

Customer Feedback

Don’t just take our word for it..

Rated by hundreds of happy growers

Grow bigger plants in less time without struggle

Get the Startaer Kit for only $170.77 $99.99

Each Starter Kit Includes:

  • World's Best Base Nutrient System Grow & Bloom Base A and B (1/4 Gallon of Each)
  • Golden Tree (1/8 Gallon)
  • Flower Stacker (1/4 Gallon)
  • CalMag & Iron (1/4 Gallon)
  • Plant Enzymes (8 Ounces)
Customer Reviews
4.9 Based on 174 Reviews
5 ?
4 ?
3 ?
2 ?
1 ?
Write a Review

Thank you for submitting a review!

Your input is very much appreciated. Share it with your friends so they can enjoy it too!

Filter Reviews:
Premium Concentrated Cal-Mag+Iron

Love this Brands whole line up to be honest the Part A & B , Cal-Mag and my #1 MUST Have is the (Humboldts Secret “Golden Tree”) this is a very easy to use product and every grower knows the importance of Cal-Mag and this one is one of the best and I have used AN, GH and many others so for ease of use to grow very healthy plants even a beginner can do these are for you.

earl w.
Great stuff

It works I use it every time I water if your plants are struggling get this asap and start using. Happy gardening

ralph s.
an excellent source of calcium.

Easy to use and very effective

O.G Bang Bang
how did I go so long without this amazing product

I love the results on my tomato plants no more calcium deficiency no more iron deficiency value for your money .

Donald L. Lewis
A lot for the price of the jug

This is just the boost my plants needed . The balance put plants into growing. A good mix of cal. Easy to mix and then my plants took off. I would buy this again. Humboldt is good stuff!. Like night and turn my plants around. Green plants the next day.