PK additives are concentrated bloom boosters that deliver extra phosphorus (P) and potassium (K) during the critical flowering and fruiting stages. These two elements drive flower density, weight, and essential oil production, helping plants reach their full potential. Our range includes trusted PK boosters, PK 13/14 formulas, PK 9/18 blends, and bloom stimulators designed for use in hydroponics, coco, soil and rockwool.
Why Use PK Additives?
Phosphorus (P): Fuels flower development, energy transfer, and root support.
Results in denser flowers, heavier harvests, and stronger overall performance.
When to Apply PK Boosters
PK additives are typically applied mid to late bloom, once flowers and fruit set have begun. Exact timing depends on the crop and feeding schedule. Overdosing too early can unbalance nutrition, so always follow the manufacturer’s feed chart.
PK 13/14 vs PK 9/18
PK 13/14 has been the long-standing standard in bloom boosters, offering a well-balanced ratio of phosphorus (13%) to potassium (14%). PK 9/18, on the other hand, increases potassium levels (18%) relative to phosphorus (9%).
PK 13/14: Balanced formula, widely trusted, effective in most setups and plant types.
PK 9/18: Higher potassium ratio, preferred by some growers during later flower stages to help harden and bulk up flowers.
Both blends work well — some growers stick with the classic 13/14 because it’s consistent and proven, while others prefer 9/18 for its potassium-heavy push during finishing. Choice often comes down to crop type, feeding style, and personal experience.
Types of PK Additives
Classic PK 13/14: Balanced phosphorus & potassium in a ratio long trusted by growers.
PK 9/18: Higher potassium ratio, popular for finishing phases in bloom.
High-intensity PK boosters: Extra-strong blends for short bloom windows.
Enhanced bloom stimulators: PK combined with trace minerals, amino acids, or biostimulants for added impact.
Choosing the Best PK Additive
The right booster depends on your setup and crop:
Hydroponics / DWC: Clean, soluble PK 13/14 for compatibility with pumps and drippers.
Coco & soil: Balanced PK formulas with added calcium or magnesium support.
Advanced systems: Enhanced boosters with bio-stimulants for maximum terpene and essential oil development.
PK Additives FAQs
What does PK 13/14 mean?
It refers to the ratio of phosphorus (13%) to potassium (14%) in the additive. This classic blend is proven to support heavy bloom phases.
What about PK 9/18?
PK 9/18 increases the potassium ratio compared to phosphorus. Some growers prefer it in late bloom for helping flowers pack on weight and density.
When should I start using a PK booster?
Generally from week 3–4 of bloom until late flower. Always check the product’s feed chart for precise timings.
Can I use PK boosters in coco and soil?
Yes — PK additives work in any medium. Just ensure your base nutrient isn’t already heavily supplemented with P & K to avoid overfeeding.
Are PK additives essential?
While not mandatory, they’re widely used because they reliably increase flower weight and quality compared with base nutrients alone.
Shop our full range of PK additives and bloom boosters — from trusted PK 13/14 and 9/18 formulas to advanced bloom stimulators. The Hydro Bros ship fast, discreet, and worldwide 🌍.
