About PK Boosters
A PK booster is a flowering additive that adds extra phosphorus (P) and potassium (K) to your feed at the point in bloom when plants need more of both. It is not a complete nutrient: every booster here is made to go in alongside your normal base bloom feed, in soil, coco or hydro.
We stock the two classic ratios, PK 13/14 from Canna and Plagron and PK 9/18 from Monkey, Shogun and Buddha's Tree, plus Mills Ultimate PK, Ionic PK, House & Garden Top Booster and FoxFarm Cha Ching. Use them for flowering tomatoes, chillies, peppers, strawberries and flowers.
Free UK delivery on orders of £94.99 or more (large 19L to 25L containers have a delivery charge shown at checkout), price match on PK boosters, and Click & Collect from our West Bromwich store.
How to choose a PK booster
The two numbers on the label are the share of phosphorus and potassium. Shogun, for example, says PK Warrior 9/18 contains 9% phosphorus and 18% potassium. PK 13/14 products are usually given as a short, strong dose for a few days in peak bloom, while PK 9/18 products are used at a lower rate over several weeks. Always follow the dose on the bottle.
| Booster | P and K | When the maker says to use it | Maker's dose |
|---|---|---|---|
| Canna PK 13/14 | 13/14 | 3 to 6 days, around 3 weeks before harvest; or a low "trickle" dose from week 2 to 3 of flowering | 1.5 ml per litre; trickle 0.33 ml per litre |
| Plagron PK 13/14 | 13/14 | One week in peak flowering, around week 4 to 6 | 2 ml per litre |
| Monkey PK 9/18 | 9/18 | From week 3 to 4 of flowering until the last two weeks | 0.5 to 2 ml per litre |
| Shogun PK Warrior 9/18 | 9% P, 18% K | Weeks 4 to 8 of bloom | 0.5 to 2 ml per litre |
| Mills Ultimate PK | Phosphorus and potassium | From week 4 of bloom until harvest | 1 to 3 ml per litre |
| Ionic PK | 14:15, with iron | Through peak flowering | Rate on the label |
| House & Garden Top Booster | Phosphorus and potassium, with iron | A short boost in flowering | 1.5 ml per litre for 3 to 4 days |
| FoxFarm Cha Ching | N 9, P 50, K 10 (soluble powder) | The final weeks of flowering | See the product page |
If you already feed a brand's full range, the matching PK booster keeps things simple: Canna with Canna, Plagron with Plagron, Monkey with Monkey, Shogun with Shogun and Mills with Mills. Ionic PK works alongside any base feed.
PK booster FAQs
What is the difference between PK 13/14 and PK 9/18?
The numbers show the share of phosphorus and potassium. PK 9/18 carries more potassium than phosphorus. In practice the makers use them differently: Canna and Plagron give PK 13/14 as a short, concentrated dose, while Monkey and Shogun give PK 9/18 at 0.5 to 2 ml per litre over several weeks of flowering.
When should I add a PK booster?
It depends on the product. Plagron says one week in peak flowering, around week 4 to 6. Canna says 3 to 6 days around 3 weeks before harvest. Monkey says start at week 3 to 4, and Mills says from week 4. Our guide to reading a nutrient feed chart shows where boosters sit in a weekly schedule.
Do I still need a base nutrient?
Yes. Every PK booster on this page is an additive, not a complete feed. Use it alongside your base nutrients and check pH after mixing.
Can I use two PK boosters at once?
Canna advises against using other PK heavy boosters at the same time as PK 13/14, and Plagron says not to combine PK 13/14 with Green Sensation, which already contains PK. Pick one PK booster for the job.
Will a PK booster work in soil, coco and hydro?
Yes. Canna, Plagron, Monkey, Shogun and Mills all say their PK boosters suit soil, coco and hydroponic systems.
Looking for something else for bloom? See our bloom boosters or browse all additives and boosters.
Need advice? Visit our West Bromwich store, call 0121 553 7872 or WhatsApp our experts.