Best Cal Mag For Orchids: Compare 10 Plant Supplements

#1 · Best Overall

1. GS Plant Foods Cal-Mag 420

• Form: Powder

Best for: High-yield powder mix users.

Why it ranks #1: Its brand history explicitly traces the first formula to orchids, and the water-soluble powder makes 420 gallons for irrigation or foliar use.

A water-soluble powder stated to make 420 gallons of nutrient solution gives GS Plant Foods Cal-Mag 420 a defined high-yield mixing profile. It can be mixed into water for irrigation or used as a foliar spray, offering two listed application routes across growth cycles.

The powder lists 11% total nitrogen, 13% calcium, 4% sulfur, and 3% magnesium, giving growers a stated nutrient breakdown to consider alongside other feeds. Its water solubility supports mixing for irrigation, while the foliar-spray option offers another application method. The product is described as beneficial throughout all growth cycles, and the stated 420-gallon yield helps growers understand its solution-making capacity. Because it is a powder, users must mix it with water before either listed use.

Skip it if you prefer a liquid supplement that avoids dissolving powder; General Hydroponics CALiMAGic is a concentrated liquid blend.

For orchid growers comfortable mixing a powder, this offers a stated 420-gallon solution yield and both irrigation and foliar uses. Its listed nitrogen and sulfur should be considered alongside the rest of your feeding program.

Listed on Amazon as: GS Plant Foods Cal-Mag 420 Dry Super Concentrate, Makes 420 Gallons of Nutrient Solution, 18 Ounces, Calcium/Magnesium Fertilizer

#2 · Broad Media Use

2. Botanicare Cal-Mag Plus

• Weight: 8 oz
• Form: Liquid

Best for: Foliar and container growers.

Why it ranks #2: This 2-0-0 liquid adds iron and lists use in soil, coco, containers, and hydro gardens, giving growers several media options.

Calcium, magnesium, and iron in one supplement distinguish Botanicare Cal-Mag Plus from two-nutrient formulas. It can be mixed with water for every-watering use as needed or applied as a foliar spray, giving growers two stated ways to add it to container, coco, soil, or hydroponic routines.

The 2-0-0 formula adds nitrogen alongside calcium, magnesium, and iron, so growers can account for those nutrients when supplementing an existing program. The directions say to mix well and use with every watering as needed, while also allowing foliar application. That choice can suit a routine based on watering or spraying leaves. Listed settings include containers, coco, hydrogardens, and soil; the product description also names reverse-osmosis water and soilless media.

Skip it if you want a powder with a stated total solution yield; GS Plant Foods Cal-Mag 420 specifies 420 gallons per container.

For orchid growers who want calcium, magnesium, and iron with both watering and foliar options, this is a flexible supplement. Account for its nitrogen contribution, and choose it only if those application methods fit your routine.

Listed on Amazon as: Botanicare Cal-Mag Plus, A Calcium, Magnesium, And Iron Plant Supplement, Corrects Common Plant Deficiencies, Add To Water Or Use As A Spray, 2-0-0 NPK, Quart

#3 · Multi-System Liquid

3. General Hydroponics CALiMAGic

• Weight: 2.8 lb
• Form: Spray

Best for: Hydroponic drip-system growers.

Why it ranks #3: The concentrated calcium-magnesium liquid is listed for hydroponics, soil, and coco, with reservoir compatibility and spray-line use noted.

A concentrated calcium-magnesium blend that will not clog spray lines or drip emitters gives hydroponic growers a way to add these nutrients to reservoir-based feeding. CALiMAGic is also listed for soil and coco blends, so its use is not limited to water-based systems.

The 1-0-0 formula supplies readily available calcium and magnesium, making this a targeted supplement for fast-growing plants when secondary nutrient deficiencies are a concern. Its compatibility with reservoirs and its stated resistance to clogging spray lines or drip emitters can fit an existing hydroponic irrigation workflow. The product is also identified for soil and coco blends in continuous liquid feed programs. Monitor and manage pH in hydroponic growing, as the supplied facts specifically call for pH management.

Skip it if you want a powder measured for irrigation; GS Plant Foods Cal-Mag 420 is a water-soluble powder with a stated 420-gallon yield.

For orchid growers already using liquid feed through hydroponic reservoirs, drip lines, or soil and coco programs, this offers a concentrated calcium-magnesium addition. Its 1-0-0 nitrogen content and the need to manage hydroponic pH are relevant feeding considerations.

Listed on Amazon as: General Hydroponics CALiMAGic Quart

#4 · OMRI-Listed Option

4. FoxFarm Bush Doctor Cal Mag

• Weight: 16 oz
• Form: Liquid

Best for: Organic gardening liquid feeders.

Why it ranks #4: Its product title identifies it as OMRI Listed for organic gardening, and the label gives a weekly mixing direction of one teaspoon per gallon.

OMRI listing for organic gardening distinguishes FoxFarm Bush Doctor Cal Mag for growers seeking a cal-mag supplement with that designation. The liquid supplies 3% calcium and 0.9% magnesium, with directions to mix one teaspoon per gallon and apply weekly as needed.

FoxFarm identifies this liquid as a 1-0-0 supplement for calcium and magnesium deficiencies, with the supplied description connecting those nutrients to cell-wall strength and fruit development. Its directions call for one teaspoon, or 5 mL, per gallon of water, applied weekly starting before bud development and continuing as needed. That defined dilution and schedule give growers a repeatable mixing routine. The listing also identifies it as OMRI Listed for Organic Gardening, a useful distinction when choosing a product for an organic gardening approach.

Skip it if you want a foliar-spray option explicitly listed alongside watering; Botanicare Cal-Mag Plus is labeled for both uses.

For orchid growers looking for an OMRI-listed liquid and a stated weekly dilution routine, FoxFarm provides specific application directions. Its schedule is weekly, so consider whether that cadence fits your established feeding practices.

Listed on Amazon as: FoxFarm Bush Doctor Cal Mag for Plants -OMRI Listed for Organic Gardening – 1-0-0, 3% Calcium, 0.9% Magnesium – 1-Pint

#5

5. Athena Cal-Mag Classic

• Weight: 2.5 lb
• Form: Liquid

Best for: Calcium-magnesium-iron formula seekers.

Why it ranks #5: This 32-ounce liquid supplement lists calcium, magnesium, and iron, with hydro, coco, and soil named as compatible growing setups.

Athena Cal-Mag Classic combines calcium, magnesium, and iron in a liquid 2-0-0 supplement, a specific nutrient profile for growers seeking those three elements together. Its title identifies hydro, coco, and soil as compatible growing settings, spanning several common cultivation approaches.

The title identifies a 32-ounce container and a 2-0-0 NPK formula, so the supplement brings nitrogen along with calcium, magnesium, and iron. It also names hydro, coco, and soil, allowing growers to consider the same listed product across those media. The supplied facts do not provide mixing rates or a frequency, so they do not establish a precise orchid feeding schedule. Buyers should weigh the nutrient profile and media compatibility against how much application guidance they require.

Skip it if you need grow- and bloom-phase dilution directions; Bloom City Ultra Pure Cal-Mag lists rates for both phases.

For orchid growers seeking a liquid calcium-magnesium-iron formula compatible with hydro, coco, or soil, Athena’s listed profile covers those media. The supplied details do not establish a dilution rate or schedule, an important boundary for precise feeding.

Listed on Amazon as: Athena Cal-Mag Classic | Calcium, Magnesium & Iron Supplement for Plants | Cal Mag Fertilizer | NPK 2-0-0 | Hydro, Coco & Soil | 32 Ounce

#6

6. Gardenera Cal-Mag Plus

• Weight: 8 oz
• Form: Liquid

Best for: Foliar deficiency-support users.

Why it ranks #6: The 8-ounce liquid combines calcium, magnesium, iron, and micronutrients, and its listed guidance gives a 1–2 mL-per-gallon rate.

Direct spraying on leaves and stems is a stated application method for Gardenera Cal-Mag Plus, which combines calcium, magnesium, iron, and micronutrients. The listing gives a 1–2 mL-per-gallon rate and describes use across growth stages, offering a defined starting point for mixing.

The 9-0-0 formula includes substantial listed nitrogen alongside calcium, magnesium, iron, and micronutrients, a profile to factor into an existing orchid feeding program. The stated 1–2 mL per gallon rate supports measured dilution, while direct application to leaves and stems provides a foliar route. The description positions the supplement as a way to address common deficiencies and support stalk and leaf health through growth stages. Its liquid form can fit a routine that already includes measured liquid supplements.

Skip it if you want a powder with a stated solution yield; GS Plant Foods Cal-Mag 420 is a water-soluble powder stated to make 420 gallons.

For orchid growers who want a measured liquid rate and a direct foliar option, Gardenera lists both along with a broad nutrient mix. Consider its 9-0-0 nitrogen contribution when fitting it into an existing feeding routine.

Listed on Amazon as: PROFESSIONAL Grade Organic Cal-Mag Plus Growing Fertilizer Concentrate: Calcium, Magnesium, Iron & Micronutrients Supplement for Plant Deficiencies (9-0-0 NPK) – 8oz Bottle

#7

7. VIVOSUN Cal+Mag+Iron

• Weight: 2.6 lb
• Form: Liquid

Best for: Multi-nutrient liquid feeding.

Why it ranks #7: This 32-ounce, 2-0-0 liquid combines calcium, magnesium, and iron; the supplied facts also say it can be combined with other nutrient systems.

Calcium, magnesium, iron, and nitrogen are combined in VIVOSUN Cal+Mag+Iron, a 2-0-0 liquid supplement. The listing says it can be used with other nutrient systems and identifies several deficiency symptoms it aims to address, giving growers a defined role for the formula.

The product names blossom end rot, interveinal chlorosis, stunted growth, leaf curling or cupping, and leaf brittleness among the issues it aims to prevent or correct. Its calcium, magnesium, iron, and nitrogen blend can be combined with other nutrient systems, according to the supplied facts, so it can accompany an existing program. The 2-0-0 NPK indicates nitrogen is part of that addition. Handling directions call for protective clothing, gloves, and eye or face protection during application.

Skip it if you need a stated dilution rate for mixing; FoxFarm Bush Doctor Cal Mag specifies one teaspoon per gallon of water.

For orchid growers adding a multi-nutrient liquid to an existing system, VIVOSUN lists compatibility with other nutrient products and names several deficiency-related concerns. Account for its nitrogen contribution and required protective gear when handling it.

Listed on Amazon as: VIVOSUN Cal+Mag+Iron (2-0-0), 32oz Calcium, Magnesium & Iron Supplement

#8

8. TPS Nutrients Cal Mag

• Weight: 8 oz
• Form: Liquid

Best for: Indoor and hydroponic growers.

Why it ranks #8: The 8-ounce liquid includes iron and micros and is listed for soil, hydroponic, and container growing, though no orchid-specific direction is supplied.

Calcium, magnesium, iron, and micros together give this TPS Nutrients liquid a broader stated nutrient set than a calcium-magnesium-only formula. Its listed compatibility with soil, hydroponic, and container systems makes it a candidate for growers moving among indoor plants and garden setups.

The product description links calcium and magnesium with plant growth, nutrient absorption, and overall strength, while its features say the formula supports sturdy structure and steady development. That positions it as a general supplement for balanced feeding rather than a product with an orchid-specific claim. Compatibility with soil, hydroponic, and container systems lets growers use the same stated product type across those setups. The instructions require dilution before use, an important step to include in the mixing routine.

Skip it if you need published stage-specific mixing rates; Bloom City Ultra Pure Cal-Mag provides separate grow- and bloom-phase directions.

For orchid growers who want a liquid listing calcium, magnesium, iron, and micros across soil, containers, or hydroponics, this offers broad setup compatibility. Plan to dilute it before use; the supplied information does not give an application rate.

Listed on Amazon as: Cal Mag for Plants – Calcium and Magnesium Plus Iron and Micros, 8 oz

#9

9. Bloom City Ultra Pure Cal-Mag

• Weight: 8 oz
• Form: Liquid

Best for: Phase-based watering routines.

Why it ranks #9: This liquid lists soil and hydroponic use plus watering-can and foliar applications, with separate 2–4 and 3–5 mL-per-gallon rates.

Separate mixing ranges for grow and bloom phases make Bloom City Ultra Pure Cal-Mag a fit for growers who adjust feeding by plant stage. The directions also allow use with every watering, precise application from a watering can, and larger-area treatment with a hose-end sprayer.

For the grow phase, the listed rate is 2–4 mL per gallon; during bloom, it is 3–5 mL per gallon. Those stage-specific ranges help organize mixing around the plant’s phase, while the every-watering direction supports a regular routine. A watering can is specified for precision nutrition in pots, and a hose-end sprayer is listed for larger areas at a 1:100 or 1:200 ratio, applied one or two times monthly. Use is listed for soil and hydroponic systems.

Skip it if you need an OMRI-listed cal-mag product; FoxFarm Bush Doctor Cal Mag is identified as OMRI Listed for Organic Gardening.

For orchid growers who adjust liquid feeding by grow or bloom phase, Bloom City supplies stage-specific rates and multiple application methods. The hose-end directions use a separate monthly cadence, so match the method to the intended growing area.

Listed on Amazon as: Bloom City Professional Grade Ultra Pure Cal-Mag Fertilizer, (8 oz)

#10

10. TPS Nutrients Organic Cal-Mag OAC

• Weight: 2 lb
• Form: Liquid

Best for: Large-volume liquid supplement users.

Why it ranks #10: The quart-size liquid is described for soil and hydroponics, but the supplied details provide less nutrient-profile and application specificity for orchid selection.

A one-quart liquid supply sets this TPS Nutrients Organic Cal-Mag OAC apart for growers seeking a larger container of supplement. Its listed use spans indoor plants, gardens, and hydroponic systems, while the directions say to apply CalMag at every stage.

TPS Nutrients describes this formula as supporting plant strength and development and helping nutrient absorption. Those stated aims make it a general cal-mag supplement for a range of growing settings, rather than a formula with orchid-specific directions. The product is identified for both soil and hydroponic growing, so it can serve different listed setups. Directions call for application at every stage, but the supplied details do not give a dilution rate; growers will need to account for that when planning a mixing routine.

Skip it if you need a stated per-gallon dilution rate; Bloom City Ultra Pure Cal-Mag lists separate grow- and bloom-phase rates.

For orchid growers seeking a larger liquid supply for soil or hydroponic use across growth stages, this matches the listed application scope. The supplied directions lack a dilution rate, so it may not suit growers who need precise mixing guidance.

Listed on Amazon as: TPS Nutrients Organic Cal-Mag OAC Plant Supplement, 1 Quart (32 oz)