PK Boosters and Bloom Boosters: PK 13/14 Doses and When to Add
A PK booster is an extra feed of phosphorus (P) and potassium (K) for flowering and fruiting. The name bloom booster covers PK boosters and bloom stimulants, which are different products; many ranges sell one of each. This guide explains the numbers on the bottle, why the makers' timings differ, and how to choose from the PK boosters and bloom stimulants we sell.
PK booster or bloom stimulant?
A base feed carries nitrogen, phosphorus and potassium throughout; a PK booster tops up the last two when plants in flower or fruit need them most. Stimulants work differently. Going by their pages, Canna Boost is a sugar stimulator, Plant Magic Boost delivers biostimulants and growth hormones, and Biobizz Top Max contains humic and fulvic acids.
Our Canna Boost page says the Boost on its own generally speeds things up, and suggests a PK booster such as Canna PK 13/14 as well. A few products do both jobs, their pages say: Dutchpro Explode and Atami Bloombastic.
What 13/14, 9/18 and 0-14-15 mean
The figures are the label's NPK numbers (see our growers' glossary): nitrogen, phosphorus and potassium, in that order. PK 13/14 gives only the last two, which the Intense PK 13/14 page spells out as 13% phosphorus and 14% potassium. Plant Magic Platinum PK 9/18 has twice as much potassium as phosphorus, which its page says is unlike most PK boosters; Buddhas Tree PK 9-18 and Plant Magic Oldtimer PK 4/8 share that ratio. Doses do not follow the numbers (the table below runs from 0.2 to 3.2 ml per litre), so go by each label.
Phosphate or phosphite? The Vitalink Buddy page says most brands use phosphate. Buddy blends phosphite with phosphate and is designed for VitaLink's own fertilisers; Mills Ultimate PK (0-7-6) contains phosphite too. Neither page gives a dose; follow the label.
PK boosters we sell compared
| PK booster | NPK on the page | Dose | When |
|---|---|---|---|
| Canna PK 13/14 | 13/14 | 1.5 ml per litre (chart) | One week, 3-4 weeks before harvest (chart) |
| Hesi PK 13/14 | 13/14 | 0.25 rising to 1.5 ml per litre (chart) | Bloom weeks 4-7 (coco chart) |
| Hesi Phosphorus Plus | – | 2.5 ml per litre (chart) | Bloom weeks 4-7, soil (chart) |
| Plant Magic PK 13/14 | 13/14 | 0.5-2 ml per litre | From about bloom week 4 |
| Plant Magic Platinum PK 9/18 | 9/18 | 0.2 rising to 0.5 ml per litre (chart) | Bloom weeks 4-7 (chart) |
| Plant Magic Oldtimer PK 4/8 | 4/8 | 1-2 ml per litre | Week 4 to the flush; soil, organic |
| Buddhas Tree PK 9-18 | 9-18 | 0.25, then 0.5 ml per litre | From week 4, for four weeks |
| Athena PK | 0-4-5 | 0.8-3.2 ml per litre | From flower week 3 |
| Atami Bloombastic | 0-14-15 | 0.5-1 ml per litre | From flowering week 3 |
| Dutchpro Explode | – | 0.5 rising to 1.5 ml per litre | Through flowering |
| FloraMax Flowering Enhancer | 0-5-3 | 2 ml per litre | Throughout flowering |
When to add it: why the makers disagree
Each maker times its PK around its own base feed; our advice is to follow the chart for yours.
- One short dose: Canna's single week; House & Garden PK 13/14 at up to 1.5 ml per litre for 3-4 days, 3 weeks before harvest; or Essentials Plus PK13/14 at 1 ml per litre in the peak flowering week, bloom week 5 or 6.
- A steady run from mid-flower: Plant Magic, Hesi and Buddhas Tree from bloom week 4, Athena from week 3. On the Athena feed chart the PK peaks in flower week 7 as Bloom A and B come down.
- Early or late PK feeds: Buddhas Tree Flowerburst (0-10-8) covers the switch into flower, at 0.25 ml per litre from the last week of growth to flowering week 3. Mills Ultimate PK is for the final 2-4 weeks. Intense Climax, mainly phosphorus and potassium, is a finishing solution for the 5-7 days before flushing, with the base feed reduced, its page says.
Bloom stimulants we sell
| Stimulant | Dose | When |
|---|---|---|
| Canna Boost | 2-4 ml per litre | W1-W9 on the Canna charts |
| Hesi Boost | 2 ml per litre (chart) | Bloom week 1, then weeks 4-7 (chart) |
| Plant Magic Boost | 2 ml per litre | From bloom week 1 (chart, as Ignition Boost) |
| Biobizz Top Max | 1 rising to 4 ml per litre (chart) | Through flowering; organic |
| Intense Wide Load | 1-2 ml per litre | From 5 days before flowering |
| Advanced Nutrients Big Bud | 2 ml per litre (chart) | Bloom weeks 2-5 (chart) |
The Advanced Nutrients Big Bud page says it provides phosphorus and potassium too. On the Advanced Nutrients feed chart, Advanced Nutrients Overdrive, which its page calls a late-stage boost, follows it in weeks 6 and 7, with no overlap.
Which should I choose?
- You use one maker's base feed. Use their PK booster, and their stimulant if the chart has one: see the Canna Coco feed chart, the Hesi feed chart or the Plant Magic feed chart.
- You mix brands. Pick one whose page says it works with any range: Plant Magic PK 13/14, Atami Bloombastic, or FloraMax, which adds calcium, magnesium and iron too. Bloombastic is strong: our note on its page is half dose, 0.5 ml per litre, for the first week or two, then full strength, and hand-watering it in once a week in AutoPots (see our AutoPot guide).
- You grow organically, in soil. Our pick is Plant Magic Oldtimer PK 4/8 with Biobizz Top Max, an organic stimulant made for soil; the Biobizz feed chart gives its weekly doses.
Whichever you pick:
- One PK booster at a time. The Mills page says not to use it alongside any other PK additive, the Bloombastic page says it replaces any PK booster, and the Advanced Nutrients Big Bud page warns against doubling up.
- Mix it in after the base feed, then check the EC and pH last. On the Canna coco chart the total EC rises from 2.0-2.4 to 2.4-2.9 in the PK week, then drops back. Check yours with a pH and EC meter (see pH and EC meters), and if leaf tips burn, see yellow leaves and leaf problems.
- Stop the PK before the flush, as all our feed charts with a PK do; see our flush products.
Quick answers
How much Canna PK 13/14 per litre?
Canna's charts give 15 ml per 10 litres (1.5 ml per litre) for one week only, 3-4 weeks before harvest: column W6 on our Canna Coco, Canna Terra and Canna Aqua feed charts.
When should I use Canna Boost?
At 2-4 ml per litre from the first signs of flowering, its page says; the Canna charts give 20 ml per 10 litres in W1 and W2, then up to 40 from W3 to W9. Add Canna PK 13/14 for its one week too.
How do I use Dutchpro Explode?
Add it to your regular feed, its page says, at a dose rising gradually from 0.5 to 1.5 ml per litre through flowering and fruiting, in soil, hydro or coco. The page calls it a bloom stimulator and PK booster in one, so our advice is not to add another PK booster.
Is a bloom booster the same as a PK booster?
Not always. Some are stimulants (Canna Boost, Hesi Boost, Top Max), some are PK feeds, and a few do both jobs (Dutchpro Explode, Atami Bloombastic, Advanced Nutrients Big Bud), so check before adding a second product.
More Growers' Guides
- Canna Coco feed chart
- Which nutrients? Soil, coco and hydro base feeds
- Hydroponics: the systems explained
Not sure what you need? Call the shop on 0117 971 3000 or pop in to the Bristol store and we'll help you pick.