In stock

Grow Gear


Containing top-quality ingredients, Emerald Harvest Cal-Mag is designed to nourish crops with extra calcium and magnesium and create the right conditions for abundant flowering and a heavy yield. This is especially important when growing in some media, such as coco coir, but any garden can benefit.

Growers use calcium-magnesium supplements to strengthen their plants and correct nutritional deficiencies inherent to some popular growing media. Calcium regulates growth and encourages plant development, while magnesium is essential for chlorophyll production, so your garden gets enough energy from light. Magnesium also activates enzymes your valuable plants need to uptake nutrients.

Use Cal-Mag as a supplement to a base nutrient series for guaranteed professional results.

Tips & tricks

  • Use as needed, rather than as part of your regular feeding schedule. For example:
  • It can feed hungry plants undergoing a rapid vegetative growth spurt, in transition or at peak flowering. During such times, plants greatly benefit from extra calcium and magnesium.
  • It can help minimize the risk of deficiencies when you use other brands’ base nutrients that may not have as many essential elements. (Emerald Harvest’s 2-part and 3-part professional base nutrient series contain the essential elements plants need to grow).
  • Soak coco coir and other soilless growing media with CalMag before planting.


  • Appearance: dark brown to black liquid.
  • Aroma: like saltwater, but a bit “funky” like the beach.
  • Texture: mildly viscous and a bit oily.
  • Spoilage: has a shelf life of 3 years or more if kept under normal conditions

Returns Policy

You may return most new, unopened items within 30 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).

If you need to return an item, simply login to your account, view the order using the 'Complete Orders' link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.


We can ship to virtually any address in the world. Note that there are restrictions on some products, and some products cannot be shipped to international destinations.

When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.

Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.

Size Chart