Emerald Harvest Cal-Mag – Quart

Emerald Harvest Cal-Mag is a liquid calcium and magnesium supplement designed to keep crops productive throughout the vegetative and flowering stages. Available here in a convenient quart size, it addresses one of the most common nutrient deficiencies in controlled-environment growing — particularly in media like coco coir that naturally lock out or deplete calcium and magnesium. Add it alongside any base nutrient program to support strong cell walls, chlorophyll production, and a heavier end yield.

Emerald Harvest Cal-Mag Specifications

Specification	Value
Brand	Emerald Harvest (Hawthorne Garden Company)
Product Type	Calcium & Magnesium Supplement (liquid concentrate)
Container Size	1 Quart (approx. 946 mL / 0.95 L)
Net Weight (shipping)	4.31 lb
Primary Nutrient Elements	Calcium (Ca), Magnesium (Mg)
Application Method	Add to reservoir or nutrient solution
Supplier SKU	HGC723950

Why Choose Emerald Harvest Cal-Mag

Calcium and magnesium deficiencies are among the most common and disruptive problems in indoor and controlled-environment gardens. Symptoms — yellowing leaves, tip burn, stunted growth — can set back a crop quickly, especially during the flowering window when plants have little tolerance for nutrient stress. Emerald Harvest Cal-Mag is formulated specifically to close that gap.

• Addresses coco-specific calcium lockout: Coco coir has a naturally high cation exchange capacity that binds calcium and magnesium ions. Cal-Mag provides a concentrated supplemental dose designed to overcome that buffering effect so roots receive what the media would otherwise withhold.
• Supports abundant flowering and yield: The canonical product description notes that adequate calcium and magnesium create the right conditions for heavy flowering. Calcium contributes to cell wall integrity during rapid bud development; magnesium is the central atom of the chlorophyll molecule and directly affects photosynthetic efficiency.
• Compatible with any base nutrient series: Cal-Mag is positioned as a universal supplement rather than a line-specific additive. It pairs with two-part, three-part, and single-bottle programs from any brand without altering EC targets in a way that requires reformulation of the base program.
• Convenient quart size for small to mid-scale grows: A quart bottle is a practical starting point for growers running a single tent or a small multi-site system. It reduces waste from bulk purchasing while still delivering enough volume to run through a full crop cycle at standard dosing rates.

Best Uses for Emerald Harvest Cal-Mag

Cal-Mag is categorized under Growth & Bloom Boosters within the Nutrients & Additives line. Its core application is as a corrective and preventive calcium-magnesium supplement. The following use cases reflect what the canonical product description identifies as the product’s primary value.

• Coco coir systems: This is the most critical application. Coco coir buffers calcium and magnesium and routinely under-delivers these ions to the root zone compared to run-to-waste or DWC systems on the same nutrient schedule. Cal-Mag is the standard corrective tool in coco grows.
• Hydroponic reservoirs (DWC, RDWC, ebb-and-flow, NFT): RO-filtered or soft source water is low in calcium and magnesium by definition. Any hydroponic system using purified water will show a calcium-magnesium gap versus what most base nutrient formulas assume. Cal-Mag fills that gap directly.
• Flowering and fruiting crops: Heavy-yielding varieties draw heavily on calcium for cell wall development during the blossom-to-harvest period. A mid-cycle Cal-Mag addition helps prevent blossom-end rot, tip burn, and similar calcium-deficiency symptoms at the most critical stage.
• Vegetative stage maintenance: Consistent magnesium supply during veg keeps chlorophyll production stable and leaf color healthy. Dropping Cal-Mag after transplant rather than waiting for symptoms is standard practice in professional production settings.
• Any grow where base nutrients alone leave a Ca/Mg shortfall: Even in soil or perlite/rockwool mixes, if the source water is soft or the base formula is Cal-free, this supplement closes the gap without requiring a full nutrient system switch. It pairs naturally with dedicated root inoculants like Advanced Nutrients Tarantula in builds where the grower wants to strengthen both nutrient uptake and root health simultaneously.

Compatibility

Emerald Harvest Cal-Mag is designed as a supplement to — not a replacement for — a complete base nutrient program. The product description explicitly states it should be used alongside a base nutrient series. No specific pH or EC ranges are published in the canonical product record, but standard practice for calcium-magnesium supplements in hydroponic growing applies:

• Growing media: Compatible with coco coir (primary application), rockwool, perlite, soil, and hydroponic reservoir-based systems. The canonical description notes that coco coir is the most important use case, but states that any garden can benefit.
• Nutrient program compatibility: Formulated to supplement any base nutrient series without line-specific restrictions. Works alongside two-part, three-part, and all-in-one nutrient programs from other manufacturers.
• Water source: Most beneficial when used with reverse-osmosis or soft source water, where baseline calcium and magnesium are lowest. In hard-water regions, confirm source water calcium and magnesium levels before supplementing to avoid over-application.
• Growth stage: Suitable for use across both vegetative and flowering stages. The canonical description identifies flowering and heavy yield as primary benefit targets, indicating this supplement is particularly valuable from mid-veg through late bloom.

For growers building a full supplement stack in a nutrient-dense program, Cal-Mag pairs naturally with organic root-feeding additives. See Earth Juice Hi-Brix Molasses for an example of a complementary carbon-source additive that supports microbial activity in the root zone alongside calcium-magnesium supplementation.

Dosing Guidelines

Specific dose rates per gallon or litre are not included in the canonical product record for this listing. The product description advises using Cal-Mag as a supplement to a base nutrient series. The following general guidelines reflect standard industry practice for liquid calcium-magnesium supplements in hydroponic and coco coir growing:

1. Shake the bottle well before measuring. Liquid Cal-Mag concentrates can settle or stratify during storage.
2. Mix Cal-Mag into plain or RO water first, before adding base nutrients or pH adjustment products. This prevents precipitation reactions that reduce nutrient availability.
3. Refer to the Emerald Harvest feed chart (available on the brand’s website at hawthornegc.com) for dose rates matched to the full Emerald Harvest nutrient system and growth stage.
4. After adding Cal-Mag and base nutrients, check EC to confirm your target range for the growth stage. Cal-Mag contributes to total EC and should be accounted for in that calculation.
5. Adjust the dose week over week based on plant response. Visible signs of calcium deficiency (brown leaf tips, blossom-end softening) indicate underdosing; dark-green clawing leaves in late veg may indicate overfeeding. Dial in based on what the plants show.

Sources & Further Reading