Cal-Mag Extreme
Why Customers Love It:
✔ Fast-Acting Formula
✔ Direct from Our Facility – Always Fresh
✔ Ships Fast in 1–2 Days
Pairs well with
Cal-Mag Extreme
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Shipping Information
At GS Plant Foods, we do our best to get your order to you quickly and affordably.
We primarily ship through USPS Priority Mail, which is fast and reliable. For larger or heavier orders, we may use FedEx Ground to save you on costs while still delivering on time.
If you prefer a different shipping method, no problem — just reach out before placing your order, and we’ll do our best to accommodate your request.
Processing Time:
Most orders ship within 1–2 business days. You’ll receive a confirmation email with tracking info as soon as your order is on its way.Shipping Costs:
Shipping fees are calculated at checkout based on weight, size, and destination.Sales Tax:
We currently collect 7% sales tax on all orders shipped to addresses in Florida. If tax laws change and we’re required to collect tax in other states, we will comply accordingly. -
Return Information
We want you to be completely happy with your purchase — and your plants to be even happier.
If your product arrives damaged or defective, just send us a photo and we’ll replace it right away — free of charge. No need to return anything.
We stand behind the quality of everything we sell. If something’s not right, we’ll make it right — it’s that simple.
If you have questions about a product or need help choosing the right one, don’t hesitate to contact us before ordering. We're happy to help!
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Cal-Mag Extreme
GS Plant Foods Cal-Mag Extreme – Advanced Calcium, Magnesium & Micronutrient Supplement for Plants – Strengthens Cell Walls, Prevents Deficiencies & Promotes Vigorous Growth – For All Plants, Lawns & Gardens
Correct Deficiencies. Strengthen Growth. Supercharge Results.
GS Plant Foods Cal-Mag Extreme delivers the critical secondary and micronutrients plants need for healthy, balanced growth. Formulated with highly available sources of Calcium and Magnesium, it also includes Sulfur, Iron, Manganese, Zinc, Boron, and Molybdenum to ensure complete nutritional support.
Calcium and magnesium are often overlooked—but they are essential for building strong cell walls, maintaining chlorophyll production, and supporting the transport of nutrients throughout the plant. Deficiencies in these elements can lead to weak stems, yellow leaves, blossom end rot, and reduced yield.
Cal-Mag Extreme prevents these problems before they start—keeping your plants strong, green, and highly productive.
💪 COMPLETE NUTRIENT SUPPORT: Cal-Mag Extreme provides essential Calcium (2.5%) and Magnesium (1.0%)—plus Sulfur, Iron, Manganese, Zinc, Boron, and Molybdenum—to correct deficiencies and maximize nutrient balance in your plants.
🌿 BUILDS STRONGER PLANTS: Calcium fortifies cell walls and prevents common issues like blossom end rot, while magnesium supports chlorophyll production for lush, dark-green foliage.
⚡ OPTIMIZES NUTRIENT UPTAKE: Enhances the absorption and mobility of nitrogen, phosphorus, and potassium—making your fertilizer more effective and reducing nutrient lockout.
🌸 BOOSTS GROWTH & FLOWERING: Strengthens roots, improves nutrient flow, and promotes more consistent flowering and fruiting across all plant types.
🌎 SAFE & EASY TO USE: 100% soluble and compatible with all fertilizers, hydroponic systems, and soil types. Non-toxic, environmentally safe, and suitable for all plants, indoors and outdoors.
What is Cal Mag 420 Dry?
GS Plant Foods Cal Mag 420 Dry Super Concentrate is our Dry, powdered version. Your all-in-one solution for robust plant health and unstoppable growth! This water-soluble powder delivers a powerhouse blend of calcium (13%), magnesium (3%), and sulfur (4%)—critical secondary nutrients that fortify cell walls, boost photosynthesis, and shield plants from disease. As an effective cal mag plant food for plants, it provides essential support for healthy development. With just ¼ teaspoon per gallon, one 18-ounce jar makes 420 gallons of nutrient-rich solution, perfect for soil, hydroponics, coco coir, and container gardens. 🌿
Key Benefits
💪 Stronger Plants: Natural cal mag for plants helps strengthen cell walls with calcium and boosts chlorophyll production with magnesium for lush, vibrant growth.
🛡️ Disease Defense: Cal mag fertilizer enhances natural resistance to pests, mold, and environmental stressors.
🌞 Optimized Photosynthesis: Sulfur ensures efficient nutrient mobility and energy conversion.
🌍 Universal Compatibility: Safe for all growth stages—seedling to bloom—and all growing mediums.
💧 Zero Waste: 100% water-soluble cal-mag for plants formula leaves no residue, ensuring full nutrient absorption.
Ingredient Breakdown
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Calcium (13%): Builds robust cell structure and improves root-to-shoot nutrient flow when you add Cal-Mag for plants.
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Magnesium (3%): Core component of chlorophyll for deeper greens and higher yields.
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Sulfur (4%): Cal-Mag fertilizer supports enzyme production and amino acid synthesis.
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Guaranteed Analysis: 11% nitrate nitrogen, pH-balanced for seamless integration with any regimen.
- Derived From: Calcium nitrate and magnesium sulfate—pure, plant-ready nutrients.
What is Cal Mag 420 Dry?
GS Plant Foods Cal Mag 420 Dry Super Concentrate is our Dry, powdered version. Your all-in-one solution for robust plant health and unstoppable growth! This water-soluble powder delivers a powerhouse blend of calcium (13%), magnesium (3%), and sulfur (4%)—critical secondary nutrients that fortify cell walls, boost photosynthesis, and shield plants from disease. As an effective cal mag plant food for plants, it provides essential support for healthy development. With just ¼ teaspoon per gallon, one 18-ounce jar makes 420 gallons of nutrient-rich solution, perfect for soil, hydroponics, coco coir, and container gardens. 🌿
How to Use Cal-Mag Extreme
Simple Mix & Grow:
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Dilute: Stir ¼ teaspoon into 1 gallon of water (1 jar = 420 gallons!).
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Apply Weekly: Use as a root drench during irrigation for soil, coco, or hydroponic systems.
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Avoid Foliar Spray: Cal-mag fertilizer designed specifically for soil and root absorption only.
Pro Tip: Cal-Mag Extreme Liquid or Cal-Mag Dry 402 for plants pairs perfectly with primary nutrients for a complete feeding program!
Frequently Asked Questions:
Q: What is Cal-Mag Extreme?
A: balanced blend of Calcium, Magnesium, and essential micronutrients that strengthens plants, prevents deficiencies, and improves nutrient uptake. Safe and effective for all plants and growing systems.
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Q: What makes Cal-Mag Extreme different from other Cal-Mag products?
A: Cal-Mag Extreme contains a complete suite of micronutrients (Fe, Mn, Zn, B, Mo) in addition to calcium and magnesium—ensuring balanced nutrition, faster uptake, and superior growth compared to basic two-element blends.
Q: How do I know if my plants need Cal-Mag?
A: If you see yellowing leaves, weak stems, blossom end rot, or poor fruit development, your plants are likely deficient in calcium or magnesium. Cal-Mag Extreme restores proper nutrient balance fast.
Q: Can I mix this with my fertilizer or kelp?
A: Absolutely. Cal-Mag Extreme is 100% compatible with all GS Plant Foods fertilizers, including Liquid Fish, Liquid Kelp, and Root Ruckus. It helps your plants make better use of those nutrients.
Q: Is this safe for edible crops and hydroponics?
A: Yes—Cal-Mag Extreme is completely soluble and safe for all growing environments, including hydroponic and aquaponic systems, greenhouses, and food crops.
Q: How often should I apply it?
A: Apply every 1–2 weeks during active growth, or whenever deficiencies are suspected. Regular use promotes steady, balanced nutrition and prevents future issues.
Applying a calcium-magnesium product can benefit various types of plants, especially those that require sufficient levels of these essential minerals for their growth and development. Calcium and magnesium are both important secondary nutrients for plants, playing vital roles in various physiological processes. Plants that can benefit from the application of a calcium-magnesium product include:
Tomatoes: Tomatoes require an adequate supply of calcium to prevent disorders like blossom end rot, which can affect fruit quality.
Peppers: Peppers benefit from balanced calcium and magnesium levels for proper fruit development and resistance to stress.
Cucumbers: Cucumbers also need sufficient calcium and magnesium to support healthy fruiting and prevent issues such as bitter-tasting cucumbers.
Leafy Greens: Plants like lettuce, spinach, kale, and other leafy greens benefit from calcium and magnesium for leaf development and overall plant vigor.
Broccoli and Cauliflower: These brassica vegetables can benefit from calcium and magnesium for healthy head formation and reduced susceptibility to diseases.
Beans: Both bush and pole beans benefit from adequate calcium and magnesium for proper pod development and overall plant growth.
Apples: Apple trees require calcium and magnesium for strong cell walls, which can improve fruit quality and storage ability.
Grapes: Grapes benefit from balanced calcium and magnesium levels for improved berry development and disease resistance.
Citrus Trees: Citrus trees need calcium and magnesium for healthy fruit formation and reduced susceptibility to nutrient deficiencies.
Potatoes: Potatoes can benefit from calcium and magnesium to prevent common issues like hollow heart and improve tuber quality.
What Our Customers Are Saying
Thank you so much for Orchid Love. I bought mine on Amazon.com. I have been using it for the last five months. My orchids haven't looked better. Then I discovered a secret using your Orchid food. I have been dripping it down the old spikes of my 14 orchids not in flower for the last month. Now I have 5 of my orchids sending up new spikes that should be blooming around Christmas and 3 shooting secondary spikes off the old spikes. Even my other house plants love it. Thank you so much.
— Mary Yarwood
I received this product in a very timely manner. After the first application this seems to be working on my fall garden in zone 7. The lettuce, cauliflower, and broccoli all responded to a foliar spray of 1 Tbsp mixed in a half gallon of water. I also applied it to my tomato plants that had slowed down due to the colder weather and was surprised to see all of the plants start setting new blooms and fruit. I was at the point of actually pulling the tomato plants out for the year but look to maybe get a few more tomato's off each plant now!
— Theman
Hi, just received your kelp and humic acid per Amazon.I scoped them at 40 and 100x shortly after opening and could not believe the diversity compared to a competitor's similar products.I provide the most thorough organic lawn/soil treatments in the Gainesville Fl area, and looking forward to continuing business."Thanks for your product
— Chad Freeman
So far, my plants and microgreens seem to respond well--new growth and deeper color--to the spray I mixed with water and store in the refrigerator.
— Greenpinky
My only complaint is that the bottle could be designed better so that the liquid doesn't drip everywhere and get a little messy even when using a funnel to catch extra liquid.
It smells strong & stains, so prepare your mixture outside or on a plastic covered table.
Why Choose GS Plant Foods?
✅ Certified Organic Excellence
Every product reflects our pledge to purity, free from synthetic additives. We prioritize ingredients that nourish plants and protect ecosystems.
🔬 Innovation You Can Trust
Blending cutting-edge plant science with time-tested organic methods, we create solutions that tackle modern challenges—boosting yields, resilience, and root vitality.
🤝 Community Trusted
Decades of glowing reviews and partnerships prove our promise: reliable, transformative results, season after season.
FAQs
Please read our FAQs page to find out more.
Why do organic fertilizers like yours have lower NPK values than synthetic fertilizers?
Synthetic fertilizers artificially spike NPK levels far beyond natural amounts, much like vitamin pills overload the body with nutrients it can’t fully absorb. Organic fertilizers, however, workwithnature—enhancing plants’ ability to uptake nutrients efficiently without excess runoff. This means lower NPK numbers deliverhigher effectivenesswhile protecting ecosystems from pollution caused by synthetic waste.
How should I store your products to maximize shelf life?
Store products in a cool, dry place away from direct sunlight and extreme temperatures. Ensure lids are tightly sealed after use. While most formulas have an indefinite shelf life, always mix only what you need for immediate use to maintain potency.
Do I need to water my lawn after applying your liquid fertilizers?
No watering is required! Our liquid formulas absorb quickly into the soil. For best results, apply early in the morning to allow 2-3 hours of soaking time before rain or irrigation. This ensures maximum nutrient retention without runoff.
Is it safe to harvest vegetables right after using your products?
Yes! Most of our products have a zero-harvest interval, meaning you can pick produce immediately. However, we recommend waiting 2-3 days after application for optimal nutrient absorption and flavor development.
How do organic fertilizers reduce environmental harm compared to synthetics?
Synthetic fertilizers overload plants with nutrients they can’t fully absorb, leading to harmful runoff that pollutes waterways. Organic formulas, like ours, mimic nature—delivering balanced, bioavailable nutrients that plants use efficiently. Think of it as feeding your garden a wholesome meal instead of forcing it to “overeat” synthetic additives.