Mills Nutrients Ultimate PK — Phosphite-Based Bloom Booster for Final Weeks Flowering
Best for: Growers pushing the finishing phase and wanting denser cell structure, richer flavour, and heavier yields in the last 2-4 weeks of bloom
Our thoughts
Mills Ultimate PK does one job exceptionally well — it hardens and finishes your crop when it matters most. Phosphite-based formula means better bioavailability than standard PK products, and it won't accumulate in your medium. Proper kit for the final sprint.
Mills Nutrients Ultimate PK is a phosphite-based PK bloom booster designed specifically for the final 2-4 weeks of the flowering phase. It's a heavyweight finisher that works on top of your base feed to drive harder cell structure, richer aromatic compounds, and superior yield in the closing stages of growth. The phosphite formulation — a highly bioavailable form of phosphate — ensures your plants get exactly what they need when they need it most, without the nutrient lockup you'd risk with cheaper alternatives.
How it compares
Ultimate PK sits in the finishing booster bracket — designed for late-stage bloom, not early flowering acceleration.
- Phosphite formula offers superior bioavailability vs standard phosphate-based PK boosters
- Won't accumulate in your medium — Mills bio-mineral philosophy keeps things clean
- Narrower application window (weeks 5-8) than broad-spectrum boosters, which means more targeted results
- Mid-premium pricing with technical formulation to back it up
In short: you're paying for precision, not just a generic PK bump. Works best alongside Mills' base range (Basis A+B, C4) but compatible with any nutrient line.
Usage guidance
Ultimate PK is a supplement — it stacks on top of your regular base feed, not instead of it.
Late-stage finishing (weeks 5-8 of flowering)
Introduce at 2 ml per litre in week 5, increasing to 2.5 ml per litre from week 7 onwards. Most growers see best results starting week 5 and running through to final flush.
Integration with base nutrients
When you introduce Ultimate PK, dial back your base feed slightly to prevent nutrient burn. Mills products work as a system, so if you're running Basis A+B, reduce those slightly and add Ultimate PK to the mix. The NPK ratio (0-7-6) means zero nitrogen — it's pure phosphorus and potassium, designed to complement, not replace.
Watering method compatibility
Works seamlessly across hand watering, drip systems, and run-to-waste setups. No special prep needed. Mix into your water reservoir as normal.
Root health bonus
Phosphite also improves oxygen flow to roots and acts as a natural root cleaner, so you're getting secondary benefits beyond just the bloom finish.
Technical specifications
- NPK Ratio: 0-7-6
- Active ingredient: Phosphite (bioavailable phosphate)
- Chelated micronutrients: Yes — optimised for plant absorption
- Dosage: 2-2.5 ml per litre (weeks 5-8 of flowering)
- Alternative imperial dosing: 8 ml per gallon (weeks 2-4 of bloom phase)
- Medium compatibility: All growing mediums (coco, soil, clay pebbles, rockwool, etc.)
- Format: Liquid concentrate
- Container: Heavy-duty polyethylene jerrican with collapsible handles and dual twist tops
- Available sizes: 1L hobby to 1000L commercial
- Accumulation: Bio-mineral formula — no residual buildup in medium
Who this is for
- Late-bloom specialists who want to squeeze maximum density and flavour in the final push
- Growers already running Mills base nutrients and looking to complete the system
- Anyone running hydro or coco who needs precise nutrient timing without guesswork
- Serious home growers and commercial setups where yield and quality matter equally
- Growers who've had nutrient burn issues — Mills' reduction-compatible approach is safer
Particularly well suited to growers who understand that the last 2-4 weeks make or break the entire crop.
Our take
Ultimate PK does what a good finishing booster should do — it hardens your foliage, drives richer aromatics, and pushes yield without overcomplicating your feed schedule. The phosphite formulation is the real win here; it's a level above generic PK products and growers notice the difference.
Worth picking up if you're serious about the finishing phase. Apply it right, dial back your base feed, and let it work. Good time to buy while clearance stock lasts.
