Mills Nutrients - C4

Mills Nutrients C4 — Bloom Stimulator for Early-to-Mid Flowering

Best for: Growers wanting a proper bloom booster that works from week 2 of flowering without breaking the budget

Mills C4 is a bloom stimulator and carbohydrate additive designed to support your plants during the critical early-to-mid flowering stage. Unlike pure PK boosters that just hammer phosphorus and potassium, C4 works differently — it delivers a sophisticated blend of sugars, amino acids, humic acids, and bio-stimulants that trigger flower production, encourage denser blooms, and boost the plant's natural essential oil output. Use it from week 2 of flowering through to week 6, and you'll see quicker fruit set, heavier yields, and noticeably better quality.

How it compares

C4 sits in the hybrid bloom booster category — neither a pure PK booster nor a late-stage hardener.

• Works alongside your base nutrients (Basis A & B) rather than replacing them — it alters the NPK ratio to favour flowering
• Early-to-mid phase focus means you'll transition to a finisher like Mills Ultimate PK from week 6 onwards
• Carbohydrate-driven approach mimics how premium brands like Advanced Nutrients work, but at significantly better value
• Organic-derived formula plays well with beneficial biologics and works across soil, coco, and hydro systems

In short: you're getting professional-grade bloom stimulation at mid-tier pricing, not premium markup.

Usage guidance

C4 is highly concentrated, so a little goes a long way. Start low, work up, and watch how your plants respond.

Standard application
Use from week 2 of flowering at 0.5 ml per litre of water, increasing gradually to 1.5 ml per litre as you move through the mid-flowering phase. Alternatively, dose at 4–8 ml per gallon from week 2 through week 6.

Integration with Mills base nutrients
C4 is designed to work alongside Mills Basis A & B. When combined, it shifts the overall NPK balance to favour flowering and fruit production. If you're running Mills as your base, C4 becomes the bloom trigger; if you're on another brand, just run it as your standalone bloom additive during this window.

Transition to finishing phase
Run C4 through week 6 of flowering, then switch to Mills Ultimate PK for the final weeks. This two-stage approach mirrors how the plant naturally shifts its priorities — early blooming, then hardening and ripening.

Compatible across all systems
Works equally well in hand-watered soil, coco drip systems, deep water culture, or NFT — no special considerations needed.

Technical specifications

• Product type: Liquid bloom stimulator and carbohydrate additive
• Composition: Macro and micronutrients, bio-stimulants, complex sugars, amino acids, humic acids, and trace minerals
• Format: Heavy-duty polyethylene jerrican with collapsible handles and dual twist-top pour/vent system
• Available sizes: 1L (hobby), 5L, 10L, 20L, 60L, 200L, and larger commercial volumes
• Concentration: Highly concentrated — only 0.5–1.5 ml per litre required
• Classification: Predominantly organic-sourced, zero biological activity
• Application window: Week 2 through week 6 of flowering
• Compatibility: All growing media and watering systems; designed to work with Mills Basis A & B

Who this is for

• Growers entering the flowering phase for the first time who want straightforward, proven results
• Experienced growers building a complete Mills nutrient regimen for consistency and synergy
• Anyone running multiple plants or rooms where bloom booster costs add up — better value than premium alternatives
• Growers running soil, coco, or hydro systems who need a universal bloom additive that plays well with biologics
• Those chasing denser, heavier blooms with richer aromatic profiles without guessing which product to use

Particularly well suited to setups where proven results and straightforward integration matter more than brand hype.

Our take

C4 is a proper bloom stimulator at a price that makes sense. Mills have been doing this for years — started in Holland, now manufactured there too — and they've dialled in a formula that works. The bio-stimulants trigger the plant to produce more essential oils and sugars, the carbohydrates support flower development, and the whole thing plays nicely with everything else you're running.

If you're planning your flowering phase and want a bloom booster that delivers without the premium markup, worth picking up while stock lasts. Does exactly what it should, week after week.