Jack's Nutrients -- Professional Dry Fertilizer Programs
Jack's Nutrients (J.R. Peters Inc.) is one of the oldest and most established professional fertilizer brands in North American commercial horticulture, with over 70 years of production history. Originally developed for commercial greenhouse floriculture and bedding plant production, Jack's formulations have become widely adopted in commercial cannabis, vegetable CEA, and indoor growing applications -- particularly through their Jack's 321 program (the 5-12-26, 15-0-0 Calcium Nitrate, and Epsom salt combination) which offers professional-grade precision at a fraction of the cost of premium pre-packaged nutrients.
Jack's 321 Program
The Jack's 321 program uses three dry components mixed in a specific ratio: Jack's Part A (5-12-26 water-soluble fertilizer, 3.6 grams per gallon), 15-0-0 Calcium Nitrate (1.2 grams per gallon), and Epsom salt (magnesium sulfate, 1.2 grams per gallon). This ratio delivers a balanced NPK with adequate calcium and magnesium for most crops throughout the vegetative stage. For flowering, the Part A to Calcium Nitrate ratio is adjusted (increasing Part A relative to Calcium Nitrate) to shift the nutrient balance toward higher phosphorus and potassium for flower development. The 321 program produces a nutrient solution at approximately 1.7-2.0 mS/cm EC -- within the standard hydroponic range for mid-stage growing. It has become one of the most referenced cost-effective professional programs in the indoor growing community due to its verifiable performance and extremely low cost per gallon compared to premium liquid programs.
Jack's Cost Efficiency
The cost advantage of Jack's dry concentrates over premium liquid programs is significant: Jack's 321 typically costs $0.10-0.25 per gallon of final solution versus $0.50-2.00+ per gallon for premium liquid programs at equivalent EC. For commercial operations consuming hundreds of gallons of nutrient solution per day, this difference in per-gallon cost represents tens of thousands of dollars annually. Jack's formulations are the same pharmaceutical-quality dry fertilizer used in commercial fertigation programs used in commercial greenhouse production worldwide -- the cost difference reflects the absence of marketing overhead and the efficiency of dry concentrate versus liquid pre-mixed format. Browse our complete hydroponic nutrients collection to compare Jack's against other programs. Fast shipping.
Jack's Nutrients FAQ
What is the Jack's 321 program?
Jack's 321 uses three dry components: Jack's Part A (5-12-26 fertilizer at 3.6 g/gallon), 15-0-0 Calcium Nitrate (1.2 g/gallon), and Epsom salt (1.2 g/gallon). The numbers 3-2-1 originally referred to the relative mixing ratios. This combination provides balanced NPK with adequate calcium and magnesium in a single mixing recipe. For flowering, the ratio shifts to more Part A and less Calcium Nitrate (approximately 3.79 g Part A, 1.22 g Calcium Nitrate, 0.9 g Epsom salt) to increase the phosphorus-potassium load for flower development. The 321 program is notable for producing commercial-grade results at dramatically lower cost than premium nutrient brands.
How does Jack's compare to General Hydroponics FloraSeries?
Both produce professional-grade nutrient programs used in commercial production. Jack's 321 costs approximately 5-10x less per gallon of final solution than GH FloraSeries -- a substantial difference at commercial scale. GH FloraSeries has a larger community knowledge base and more grower documentation for specific crop types. Jack's is used heavily in commercial greenhouse vegetable and cannabis production where the cost advantage at scale is the primary driver. For hobby growers where cost per gallon is less significant, either program produces excellent results; for commercial operations where nutrient cost is a meaningful line item, Jack's economics are compelling.
Do I need to add Cal-Mag when using Jack's 321?
The Jack's 321 program includes calcium nitrate as a component specifically to supply calcium -- this is one of the program's design elements, providing calcium in the nitrate form that is immediately plant-available. Magnesium is supplied by the Epsom salt component. For most water sources, the 321 program provides adequate Ca and Mg without additional supplementation. For RO or very soft water users, verify the final solution's calcium and magnesium levels against crop requirements -- the Calcium Nitrate component at the 321 ratio provides approximately 150-200 ppm calcium, which is adequate for most crops but may need slight upward adjustment in pure RO water for demanding crops.
What crops grow best with Jack's Nutrients?
Jack's was developed for commercial floriculture and bedding plant production, and their formulations are verified for a wide range of crops including vegetables (tomatoes, cucumbers, peppers, lettuce, herbs), ornamentals, and indoor flowering crops. The 321 program is used commercially in cannabis, vegetable CEA, and greenhouse production across North America. Jack's also produces crop-specific formulations for strawberries, blueberries, cannabis, and other specialty crops -- these are optimized nutrient ratios for specific crop nutritional requirements rather than the general-purpose 321 program.
How do I mix Jack's 321 correctly?
Mix the three components in separate water before combining. Standard procedure: (1) add 3.6 g Jack's Part A per gallon to your reservoir water and mix until fully dissolved; (2) in a separate small container, dissolve 1.2 g Calcium Nitrate per gallon in water; (3) add the dissolved Calcium Nitrate solution to the main reservoir -- never add dry Calcium Nitrate directly to Part A solution as this can cause calcium sulfate precipitation; (4) add 1.2 g Epsom salt per gallon and mix until dissolved. Check and adjust pH to 5.8-6.2 after all components are fully dissolved. Use our Nutrient Mixing Calculator to scale the recipe for your specific reservoir volume.
