Plant Magic - Oldtimer Organic PK 4-8 - Certified Organic Flowering Booster
Best for: organic growers who want a certified-organic PK boost during flower without switching to a mineral booster.
Our thoughts
Most PK boosters on the market are mineral-based, so a genuinely certified-organic option matters if you're trying to keep the whole feeding schedule organic through to harvest. Oldtimer Organic PK 4-8 gives you the phosphorus and potassium push flowering plants need without breaking that organic chain.
Plant Magic Oldtimer Organic PK 4-8 supplies the phosphorus and potassium plants need during flowering to increase weight and improve essential oil content, but unlike most PK boosters on the market, it's made using certified organic materials - containing over 95% organic components in line with EU organic regulations. Its NPK figures are 4% phosphorus pentoxide (P2O5, around 1.7% elemental P) and 8% potassium oxide (K2O, around 6.6% elemental K), giving it its "4-8" name.
As part of the wider Oldtimer range, it also supports beneficial microbial activity in the root zone, which contributes to healthier roots and, in turn, greater yield with sweeter, more abundant flowers - rather than just delivering a raw PK hit.
How it compares
PK boosters are almost universally mineral-based, which makes the organic angle here a genuine point of difference rather than just marketing language.
- Compared with Canna PK 13/14, a mineral PK booster with a stronger raw NPK figure, Oldtimer Organic PK 4-8 trades some peak potency for a fully organic-compliant formula.
- Compared with BioBizz Top Max, another organic-leaning bloom booster, the two sit in a similar space for organic growers wanting a PK-style boost.
- Compared with Plant Magic's own mineral Platinum PK 9-18, this Oldtimer version is the clear choice if maintaining full organic certification through to harvest matters to you.
If you need the strongest possible PK spike, a mineral booster will out-perform this on paper - but for organic growers, this is one of the few genuinely certified options available.
Usage guidance
Oldtimer Organic PK 4-8 is used during the flowering stage, dosed at a low rate.
Dosing
Use at a dilution rate of roughly 1-2ml per litre of nutrient solution during the flowering stage.
Timing
Introduce once plants are established in flower, continuing through the bulk of the bloom phase for weight and oil development.
Pairing
Works alongside the rest of the Oldtimer organic range, including Oldtimer Organic Grow used earlier in the vegetative stage.
Technical specifications
- NPK figures: 4% P2O5 (approx. 1.7% P), 8% K2O (approx. 6.6% K)
- Organic content: over 95% organic materials, EU-compliant
- Type: certified organic flowering (PK) booster
- Dosage: approx. 1-2ml per litre
- Suitable medium: soil (organic)
- Sizes available: 1 litre, 5 litre and 10 litre
- Brand: Plant Magic
Who this is for
- Organic growers who want a certified-organic PK boost rather than a mineral one
- Growers already running the Oldtimer Organic range who want to complete the schedule
- Anyone prioritising flavour, aroma and oil content over maximum raw yield
- Growers maintaining organic certification through to harvest
Our take
Genuinely organic PK boosters are hard to come by, and this one does the job without compromising on the certification that matters to organic growers.
Worth picking up if organic integrity matters to your grow as much as the yield itself.
