Humboldts Secret CalMag & Iron | Calcium, Magnesium & Chelated Iron Nutrient Fertilizer | Hydroponic Supplies for Vegetative & Flowering Growth in Soil, Coco, Hydroponics or RO Water | 8 Ounce
Humboldts Secret CalMag & Iron | Calcium, Magnesium & Chelated Iron Nutrient Fertilizer | Hydroponic Supplies for Vegetative & Flowering Growth in Soil, Coco, Hydroponics or RO Water | 8 Ounce
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Humboldts Secret CalMag & Iron | Calcium, Magnesium & Chelated Iron Nutrient Fertilizer | Hydroponic Supplies for Vegetative & Flowering Growth in Soil, Coco, Hydroponics or RO Water | 8 Ounce

|36 ratings

Key item features

  • ‌Strength for Every Stage: Humboldts Secret supplement with cal mag for plants delivers calcium, magnesium, and chelated iron to prevent deficiencies. It fortifies stems, improves leaf color, and supports flowering and fruiting plants for vigorous, healthy growth in any type of garden.
  • Fast-Acting Plant Recovery: Our balanced formula with calmag and chelated iron targets issues caused by nutrient imbalances, helping plants recover quickly. It boosts photosynthesis, nutrient transport, and root strength in vegetables, flowers, and herbs grown indoors or outdoors.
  • Maximum Absorption Power: Using our cal-mag for plants blend with added iron improves uptake efficiency, ensuring these essential minerals are fully utilized. It supports lush vegetative growth and abundant blooms, delivering consistent results for home or commercial growers.
  • Reliable Across All Setups: Humboldts Secret cal mag fertilizer with iron works in hydroponics, soil, and container gardens. It strengthens plant structure, enhances fruit quality, and ensures balanced nutrition in indoor and outdoor systems for dependable, healthy harvests.
  • Focused on Fruiting Success: Our formula with calcium and magnesium for plants plus chelated iron benefits crops in coco coir or reverse osmosis water. It helps prevent blossom end rot, promotes firm fruit set, and improves nutrient absorption for strong, productive plants in challenging conditions

Specs

Form, LiquidProduct net content parent, 8 Fluid OuncesRec. use, Flower, Fruit, Garden, Herb, Plant, VegetablePlant category, FlowersRec location, OutdoorBrand, Humboldts Secret Supplies

About this item

Product details

Humboldts Secret CalMag & Iron Supplement is a highly effective liquid fertilizer designed to deliver essential calcium, magnesium, and chelated iron to plants in all stages of growth, from early vegetative development to heavy flowering and fruiting. Many flowering and fruiting plants require higher levels of these vital secondary nutrients to maintain optimal growth, and our balanced formula is specifically engineered to correct and prevent common deficiencies that can limit plant health and yield. Calcium helps strengthen cell walls for sturdy stems and resilient foliage, magnesium plays a key role in chlorophyll production for rich green leaves and efficient photosynthesis, while chelated iron ensures proper enzyme function and energy transfer, even in challenging pH environments. Our formula works quickly to address nutrient imbalances, improving nutrient transport and root development so plants can absorb and utilize all essential elements effectively. Suitable for use in hydroponics, soil, and container gardens, this versatile supplement delivers dependable results in both indoor and outdoor systems, whether you are a home gardener or a commercial grower. It is especially recommended for plants grown in coco coir or with reverse osmosis water, where calcium, magnesium, and iron are often depleted and supplementation becomes critical for healthy growth and fruit set. Regular use helps prevent issues such as blossom end rot, leaf yellowing, and weak stem structure, ensuring stronger, more productive plants and higher-quality harvests. Our CalMag & Iron supplement integrates seamlessly into any nutrient program and can be used alongside other fertilizers without causing nutrient lockout. For best results, use as part of your regular feeding schedule to maintain consistent nutrient levels and support the specific needs of your crops. Whether you are cultivating vegetables, herbs, flowers, or fruiting plants.
  • ‌Strength for Every Stage: Humboldts Secret supplement with cal mag for plants delivers calcium, magnesium, and chelated iron to prevent deficiencies. It fortifies stems, improves leaf color, and supports flowering and fruiting plants for vigorous, healthy growth in any type of garden.
  • Fast-Acting Plant Recovery: Our balanced formula with calmag and chelated iron targets issues caused by nutrient imbalances, helping plants recover quickly. It boosts photosynthesis, nutrient transport, and root strength in vegetables, flowers, and herbs grown indoors or outdoors.
  • Maximum Absorption Power: Using our cal-mag for plants blend with added iron improves uptake efficiency, ensuring these essential minerals are fully utilized. It supports lush vegetative growth and abundant blooms, delivering consistent results for home or commercial growers.
  • Reliable Across All Setups: Humboldts Secret cal mag fertilizer with iron works in hydroponics, soil, and container gardens. It strengthens plant structure, enhances fruit quality, and ensures balanced nutrition in indoor and outdoor systems for dependable, healthy harvests.
  • Focused on Fruiting Success: Our formula with calcium and magnesium for plants plus chelated iron benefits crops in coco coir or reverse osmosis water. It helps prevent blossom end rot, promotes firm fruit set, and improves nutrient absorption for strong, productive plants in challenging conditions
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Specifications

Form

Liquid

Product net content parent

8 Fluid Ounces

Rec. use

Flower, Fruit, Garden, Herb, Plant, Vegetable

Plant category

Flowers

Warranty

Warranty information

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Ingredients

Customer ratings & reviews

4.9 out of 5 stars
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36 ratings19 reviews
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Showing 1-3 of 19 reviews

May 19, 2026
Reviewer name: Mondragon
Top Reviewer
Item details
Size: 8 Ounce
Sold byHS SuppliesDelivered byWalmart
5 out of 5 stars
5 out of 5 stars review

Verified Purchase

Garden supplement

I was happy to see that this CalMag supplement did not have a strong odor, which is a big plus when working with plants indoors or in enclosed spaces. The bottle arrived completely full and properly sealed. I also like that the label clearly explains the purpose of the solution and what deficiencies it helps with. I purchased this to use with coco coir for my daughter's project garden since coco coir often requires additional calcium and magnesium support for healthy plant growth. It has nitrogen, magnesium, iron and calcium in it. Another thing I appreciate is that it can be used in different ways, including as a spray application, which gives more flexibility depending on the plants and gardening setup. Overall, this seems like a great supplement for gardeners looking to support healthier plants and prevent common nutrient deficiencies. I'm excited to start using it in our garden projects.

Incentivized Review
Helpful?5UDHOV22MX9F16554856423
Oct 16, 2026
Reviewer name: Venus
Top Reviewer
Item details
Size: 32 Ounce
Sold byHS SuppliesDelivered byWalmart
5 out of 5 stars
5 out of 5 stars review

Verified Purchase

This review text is styled with strikethrough formatting

The product arrived in sealed bag, with no leaks, and on time. My plants are loving it thus far.

About this review:Walmart fulfilled this order and the fulfillment issues were not the fault of the seller.
Helpful?5UDHOV22MX9F16554856423
Jun 18, 2026
Reviewer name: shopper
Top Reviewer
Item details
Size: 8 Ounce
Sold byHS SuppliesDelivered byWalmart
5 out of 5 stars
5 out of 5 stars review

Verified Purchase

hopefully, this will help my heat stressed tree!

I have had very good luck with this company's products. I'm hoping this one will help bring my very old and very heat stressed grapefruit tree back to life a bit it has 2% nitrogen, 3.2% calcium, 1.2% magnesium, and .1c % chelated iron. i'm going to both use it as a foyer spray and add some of it to my watering can.

Incentivized Review
Helpful?5UDHOV22MX9F16554856423
Current price is $13.97
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4.9 stars out of 5, based on 105 seller reviews(4.9)
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