Aptus K-Boost - Organo-Mineral Potassium Maturation Booster
Best for: Growers in the later weeks of flowering who want to push finishing weight, density, and end quality.
Our thoughts
This is a late-flower specialist rather than an all-round booster, and it earns its place precisely because it does one job well: pushing plants through maturation with a potassium-led finish. It's not a big bottle and it doesn't need to be, the dosage rates are small, so even the 150ml size goes a long way.
Aptus K-Boost is an organo-mineral maturation booster combining L-amino acids with potassium (K) and sulphur trioxide (SO3). Potassium plays a central role in a plant's late-stage development, supporting the processes that drive final bulking, density, and ripening, while the added amino acids help the plant put that potassium to use more efficiently rather than it sitting unused in the growing medium.
It's designed to be used specifically through the maturation window of flowering, aligning potassium supply with the stage where plants are finishing off rather than still building structure. Being fully water-soluble, it mixes cleanly into a nutrient tank without leaving residue that could clog drip lines or build up in the medium over time.
How it compares
Late-flower potassium boosters are a well-established category, with most premium nutrient brands offering their own version.
- Versus House & Garden's Bud-XL: Bud-XL works by moving sugars from the leaves into the fruit to build weight, while K-Boost takes a more direct organo-mineral route, feeding potassium and sulphur straight to support the same late-stage finishing goal.
- Versus Canna's PK 13/14: PK 13/14 supplies extra phosphorus and potassium together for flowering, whereas K-Boost is a potassium-focused finishing product Aptus recommends pairing with its own P-Boost or CaMg-Boost for a fuller late-flower profile.
- Versus skipping a potassium booster altogether: potassium demand rises through late flowering, so a base feed alone may not always keep pace with what heavy-finishing plants are pulling from the medium.
It's a targeted, late-stage product rather than a general-purpose feed, which is exactly what makes it useful layered on top of a standard nutrient schedule.
Usage guidance
K-Boost is used for a defined window rather than across the whole grow cycle.
Timing
Use from around the fifth week through to the seventh week of flowering, aligning with the plant's maturation and finishing phase rather than earlier bud development.
Dosage
Mix at 3 to 5ml per 10 litres of nutrient solution, adjusting within that range depending on how heavily your plants are finishing.
Pairing
Aptus recommend combining K-Boost with CaMg-Boost during this window to avoid antagonism between potassium and magnesium uptake, which can otherwise show up as a magnesium deficiency late in flower.
Mixing
Add to your nutrient tank along with your base feed and any other boosters, stirring well since it's fully water-soluble and shouldn't need pre-dissolving.
Technical specifications
- Brand: Aptus
- Type: Organo-mineral maturation booster
- Key elements: Potassium (K), Sulphur Trioxide (SO3), L-amino acids
- Sizes available: 150ml, 500ml
- Dosage: 3-5ml per 10L water
- Usage window: Week 5 to week 7 of flowering
- Solubility: 100% water-soluble, no residue
Who this is for
- Growers running heavy-finishing varieties that need extra late-flower support
- Anyone already using Aptus's Regulator or Super-PK who wants to complete the late-flower stack
- Growers chasing density and finishing weight rather than early bud size
Best suited to use alongside a full nutrient schedule during the final weeks of flowering, not as a standalone feed.
Our take
K-Boost does a specific job at a specific point in the grow, and it does it without fuss or residue buildup. Pairing it with CaMg-Boost as Aptus recommend gets the most out of it.
At a price that makes sense given how little you need per feed, this is an easy addition to a late-flower routine for anyone chasing better finish and weight.
