Mammoth P Explained

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What It Is

Mammoth P is a liquid microbial inoculant manufactured by Growcentia, a Colorado State University spinoff founded in 2015 ^[1]. The product contains a consortium of bacteria selected for their ability to solubilize phosphorus — the most common form is listed as containing Enterobacter cloacae, Citrobacter freundii, Pseudomonas putida, and Comamonas testosteroni ^[2].

Phosphate-solubilizing bacteria (PSB) work through a well-understood mechanism: they secrete organic acids and enzymes that convert insoluble phosphate compounds into plant-available orthophosphate Strong evidence^[3]. This same biology has been applied in agriculture for decades on wheat, rice, maize, and other crops ^[3][4].

The specific claim Growcentia makes is that its strain blend, selected from cannabis rhizospheres, delivers measurable yield and potency gains in flowering cannabis. That claim rests on much thinner evidence than the general microbiology.

Why Growers Use It

Three practical reasons drive adoption:

1. Phosphorus lockup is real in many media. In coco coir, peat moss, and even soil, phosphorus binds to calcium, iron, and aluminum at certain pH ranges and becomes unavailable to roots Strong evidence^[3]. If your growing medium has adequate total phosphorus but plants show deficiency symptoms, solubilizing bacteria can free some of that up.

2. A well-publicized yield claim. Growcentia released trial data claiming a 16% average yield increase across multiple commercial facilities ^[2]. This figure appears in grow guides, forums, and product reviews everywhere. However, it comes from the manufacturer's own internal data, not independent peer-reviewed replication Weak / limited. No published controlled study on cannabis has replicated this number.

3. Low cost and perceived safety. At roughly 0.6 mL per gallon, a small bottle lasts a long time. Many growers adopt it as "cheap insurance" — the theory being that it can't hurt. This reasoning is intuitive but lacks supporting data Weak / limited.

Real-world context: If you're growing in sterile media (fresh coco, rockwool, hydroponic systems) or running a feed program heavy in synthetic salts that suppress microbial life, an inoculant probably does something useful. If you're already growing in living soil or compost tea-amended media with established biological activity, you're likely paying for microbes you already have Weak / limited.

When to Start

The manufacturer recommends starting at the first week of flower (week 1 of the 12/12 light cycle) and continuing through harvest, skipping only the final flush week if you flush ^[2].

Some growers also dose during late vegetative growth to establish the microbial population before bloom demand spikes. There is no controlled evidence this is better than starting at week 1 of flower, but it is biologically plausible Anecdote.

Do not apply Mammoth P within 24 hours of:

• Hydrogen peroxide or oxidative products (e.g. ZeroTol)
• Strong fungicides or bactericides
• Chlorinated or chloraminated tap water (unless allowed to off-gas 24+ hours)

These will kill the inoculant before it reaches the root zone.

How to Use It

Step 1: Dechlorinate your water. Chlorine and chloramine are lethal to the bacteria in Mammoth P Strong evidence. If using municipal tap water, let it sit uncovered for at least 24 hours to allow chlorine to off-gas, or use an RO system or dechlorinator product.

Step 2: Measure the dose precisely. The standard rate is 0.6 mL per gallon (approximately 0.15 mL per liter). Use a syringe with clear graduations — eyeballing wastes product and creates inconsistency ^[2].

Step 3: Add Mammoth P last in your nutrient routine. Mix your base nutrients (nitrogen, phosphorus, potassium, and secondary nutrients) first. Adjust your pH to your target range (5.8–6.2 for hydroponic or coco systems; 6.3–6.8 for soil). Then stir in the Mammoth P. Adding it to undiluted concentrate or extreme pH conditions can damage the microbes.

Step 4: Use within 24 hours of mixing. Once mixed into a reservoir or feeding solution, the bacteria begin consuming nutrients. Do not pre-mix days in advance.

Step 5: Apply with every regular feeding or every other feeding through flower. Deliver it to the root zone via drench — soil, coco, or hydroponic drip. Foliar application is ineffective; the bacteria need root contact.

Step 6: Stop 1–2 weeks before harvest. Discontinue along with your normal flush schedule if you flush.

Step 7: Store the bottle cool and dark. Refrigeration after opening significantly extends shelf life. A bottle stored in a hot grow room may degrade rapidly.

Common Mistakes

Using it with chlorinated water. This is the most common reason growers report no effect. Chlorine and especially chloramine are persistent and microbe-lethal Strong evidence. Always dechlorinate or use RO water.

Pairing with oxidative cleaners or fungicides. Hydrogen peroxide, ZeroTol, and similar products are designed to kill microbes. They will kill your inoculant too. Space applications by at least 24–48 hours.

Overdosing. More bacteria is not better. Excess biomass can foul drip lines, create biofilm buildup, and waste product.

Expecting Mammoth P to replace phosphorus in your feed. The inoculant unlocks existing phosphorus; it doesn't add phosphorus to your system. If your base nutrient formula is chronically low in phosphorus, you still need to add more.

Treating the +16% yield claim as a guarantee. This figure comes from company-run trials in commercial facilities, many of which likely had prior nutrient inefficiencies or suboptimal management Weak / limited. A well-tuned home grow optimizing light, temperature, humidity, and nutrient balance may see zero measurable difference.

Not refrigerating an opened bottle. Live microbial products degrade over time at room temperature. Keep it cool.

Related Techniques and Alternatives

Mammoth P belongs to a broader category of microbial inoculants and biostimulants. Alternative or complementary approaches include:

Mycorrhizal inoculants (e.g. Mykos, Great White) — Fungal, not bacterial. They colonize roots directly to extend nutrient uptake networks. Different mechanism from PSB; often used together.

Compost tea and bokashi — Broad-spectrum microbial inputs made from compost or fermented organic matter. Cheaper than branded inoculants but less standardized in microbial composition.

Competing bacterial blends (e.g. Recharge, Tribus, Photosynthesis Plus) — Similar products with overlapping species. Often comparable in price and claim.

Living soil — The no-bottle approach: build a biologically active soil ecosystem once and allow it to self-regulate through multiple crop cycles. Requires more initial effort but eliminates repeat inoculant purchases.

pH Management in Cannabis Cultivation and Coco Coir Growing are relevant for understanding why phosphorus lockup occurs in specific media.

Bottom line: If you're already running a well-managed living soil or robust compost tea program, adding Mammoth P is probably redundant. If you're in sterile hydro, coco, or running heavy synthetic nutrients, it's one of the better-characterized options in its category — even though 'better characterized' still means mostly company-generated data rather than independent trials.

Sources

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