Quick Answer

A 2-45-28 dry PK booster for the last 2 to 3 weeks of flower. Almost no nitrogen, so the plant puts its energy into density rather than new growth.
Dose at 0.3 to 0.6g per litre on top of your base nutrient. A 1kg bag treats roughly 1,600 to 3,300 litres.
Suits hydro, coco and soil growers who want harder, heavier flowers at harvest.
You'll need scales. At these doses a kitchen teaspoon isn't accurate enough.

GH KoolBloom Dry 1kg

KoolBloom Dry is General Hydroponics' powdered ripening formula. It's 2-45-28, which means it's almost all phosphorus and potassium with very little nitrogen. That's exactly what you want in the final weeks of flower, when the plant should be filling out and hardening the flowers it already has rather than putting on more leaf.

It's a finisher, not a bloom base. Run your normal bloom nutrient as usual and add KoolBloom Dry for the last 2 to 3 weeks.

What it does

Fills out late flower. The PK spike supports final swell when the plant's demand for phosphorus and potassium is at its highest.
Firmer, denser flowers. With nitrogen this low, the plant isn't pushed into new growth, so flowers finish tighter.
Dissolves cleanly. Fully soluble once mixed, so it won't clog drippers or lines in recirculating systems.
Lasts a long time. At 0.3 to 0.6g per litre, one bag covers a lot of reservoir changes.

How to use it

When: The final 2 to 3 weeks of flowering only.
Dose: 0.3 to 0.6g per litre. Start at the low end and watch the leaf tips.
Mixing: Dissolve it in a jug of water first, then add it to the reservoir after your base nutrient. Check EC and pH once everything is in.
EC: It adds to your EC. If you're already near your ceiling, drop the base nutrient slightly to make room.
Works with: DWC, NFT, recirculating systems, drain to waste, coco and soil.

Guaranteed analysis

Nitrogen (N): 2%
Phosphate (P₂O₅): 45%
Potash (K₂O): 28%
Derived from: magnesium phosphate, potassium phosphate, potassium sulfate

Product details

Size: 1kg powder
Type: Dry PK booster and ripening formula
Stage: Late flower only
Shipping: 1.38kg, so it ships free on its own to VIC, NSW, QLD, SA and ACT.

Pairs well with

JBL Digital Pocket Scales, for weighing 0.3 to 0.6g doses properly.
GT Super PK, a liquid PK booster if you'd rather pour than weigh. Use one or the other, not both.
THC Eksit, an alternative final-stage finisher for THC users.

Seeing burnt tips or clawing once you add it? PlantMDx will help you work out whether it's the booster or something else. Free, no signup.

Frequently Asked Questions

When do I start using KoolBloom Dry?

In the final 2 to 3 weeks of flowering, once flowers are well formed and swelling. It isn't a base bloom nutrient. Starting it earlier pushes a lot of phosphorus and potassium while the plant is still building structure.

How much KoolBloom Dry do I use?

0.3 to 0.6g per litre, on top of your base nutrient. Start at 0.3g and only go higher if the plants are handling it with no tip burn.

Can I use it with my base nutrient?

Yes, that's how it's designed to be used. Mix your base nutrient first, then the KoolBloom, then check EC. If your EC ends up too high, reduce the base nutrient slightly.