Plant Magic PK 13/14 — Classic Phosphorus-Potassium Flowering Booster
Best for: Growers wanting to push flower size and weight during peak bloom without overcomplicating their feed schedule
Our thoughts
PK 13/14 is one of those formulas that's stood the test of time for good reason. It does exactly what a bloom booster should do — supplies the right ratio of phosphorus and potassium when plants need them most. The trick is timing and restraint. Use it from week 4 onwards, keep the dose measured, and stack it with a solid base feed. That's when you see the results.
Plant Magic PK 13/14 is a purpose-built phosphorus and potassium additive designed to support the flowering phase of your grow. It supplies additional P and K at precisely the point plants are stacking flowers, helping drive flower development, density, and overall yield without forcing unnatural growth or nutrient lockout.
Made at Plant Magic's UK laboratory to pharmaceutical-grade standards — tested on in-house grows and checked every batch — this is a flowering booster that does what it says without the marketing fluff. Add it to your base nutrient from week 4 of flowering onwards, and it helps plants convert energy into larger, heavier, higher-quality flowers.
How it compares
PK 13/14 occupies the middle ground of the bloom booster market — the original formula that most others were based on.
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vs Canna PK 13/14: Same ratio, similar performance, lower price with UK backing
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vs Buddha's Tree PK 9-18: Different ratio (more potassium-heavy). PK 13/14 suits mid-bloom; 9-18 leans late-bloom and higher cost
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vs Plant Magic Platinum PK 9/18: Platinum is stronger and more complex. Standard PK 13/14 is the straightforward choice for cost-conscious growers
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vs Advanced Nutrients Big Bud: Both work well. PK 13/14 integrates better into Plant Magic systems; Big Bud is more standalone
In simple terms: PK 13/14 is the tested formula that delivers reliable results without premium pricing. It's not the strongest in the range, but it's proven and it works.
Usage guidance
When to start
Introduce PK 13/14 from around week 4 of flowering, once flowers have begun to develop visibly. This is when plants shift energy into bloom and can make best use of additional phosphorus and potassium.
Dosing rates
Plant Magic recommend 1–2ml per litre of water, depending on your base nutrient and growing medium. Always start at the lower end and adjust upward if needed. Overuse is a common mistake and can actually lock out nutrients rather than improve uptake.
How to mix it in
Never add multiple nutrients in concentrated form at once. Add PK 13/14 to your water or reservoir, stir well, then add your base nutrient. Keep each addition separate until fully mixed. This prevents chemical reaction and ensures proper uptake.
Duration
Typically run PK 13/14 for 3–4 weeks during peak bloom, not the entire flowering phase. Once flowers are fully formed and starting to mature, you can taper it back.
Compatibility
Works cleanly with Plant Magic mineral feeds and most standard mineral nutrient programmes. Also stacks well with Plant Magic Ignition Boost and Silicon for broader spectrum support.
Technical specifications
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Type: PK flowering additive (phosphorus and potassium concentrate)
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Nutrient ratio: 13% phosphorus (P) / 14% potassium (K)
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Phosphorus content: Water-soluble P2O5 8.0%, elemental P 3.5%
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Potassium content: Water-soluble K2O 10.0%, elemental K 8.3%
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Added benefits: Magnesium and sulphur to prevent nutrient lockout; amino acids for improved plant structure and flavour quality
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Recommended dosage: 1–2ml per litre of water from week 4 of flowering
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Available sizes: 1L and 5L bottles
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Manufacturing: UK-formulated and tested, no plant growth regulators or artificial hormones
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Suitable for: All growing systems and media types (hydroponics, coco, soil)
Who this is for
- Growers running Plant Magic mineral nutrient systems who want a focused bloom push
- Mid-range and intermediate growers looking for proven, simple PK supplementation without premium pricing
- Cost-conscious operators managing multiple spaces where nutrient budgets add up quickly
- Anyone wanting to increase flower density, weight, and sugar content without forcing growth
- Growers who prefer tested, UK-made products with quality assurance backing
Particularly well suited to mineral-based feeding programmes where additional P and K during peak bloom translates directly into measurable yield gains.
Our take
This is a straightforward, properly made flowering booster that's been doing the same job reliably for years. It's not fancy, it doesn't claim to be. It just supplies the nutrients plants need at the right time, and when dosed sensibly alongside a solid base feed, it helps push larger, denser flowers and better yields.
If you're running a mineral system and want a cost-effective way to boost bloom without guessing whether you're buying snake oil, worth picking up. Plant Magic backs every batch on in-house grows — that's not marketing talk, that's how they work. Good time to buy while stock lasts.
