Written by Ad OpsIntroduction and Naming Context
MK-91 is a boutique, mostly indica cannabis cultivar bred by Pisces Genetics, a breeder known for curating Kush and Chem family lines with a focus on classic potency and deep resin production. The name itself is a strong contextual clue: “MK” commonly abbreviates Master Kush, while “91” often alludes to Chem ’91, the storied Skunk VA cut. Even without an official parentage disclosure, this naming convention and the cultivar’s growth traits point toward a Kush-meets-Chem profile shaped for dense flowers and a loud, fuel-forward nose.
Growers and consumers consistently position MK-91 within the heavy-hitter category, typified by compact plant structure, fast finishing times, and a sedating, body-centric effect. These traits align with indica-dominant heritage, where shorter internodes, broad leaflets, and accelerated calyx swelling are common. In markets where it has surfaced, MK-91 has earned a reputation for its “gas-and-earth” flavor, sticky resin, and a finish that appeals to evening consumers.
Because Pisces Genetics often releases limited, carefully selected lines, MK-91 remains rarer than mainstream staples, which adds to its appeal among phenotype hunters and connoisseurs. The strain’s scarcity, combined with its reputed potency, tends to keep demand high in niche circles. For many, MK-91 reads as a modern tribute to old-school genetics, emphasizing authenticity in aroma and a classic relaxing experience.
History of MK-91 and Breeder Background
Pisces Genetics has built its reputation by working with foundational American genetics—especially Kush and Chem families—and preserving the traits that made them iconic. While not always publicly verbose about lineage, the breeder’s output frequently highlights resin-forward, terpene-rich cultivars that shine in both flower and extract formats. MK-91 fits that portfolio: stout, trichome-heavy plants maturing within a commercially friendly window and delivering a powerful, nostalgic profile.
Community chatter places MK-91 among Pisces Genetics’ premium, limited offerings, the sort typically circulated to dedicated growers and collectors who prioritize quality over mass-market familiarity. In that context, MK-91’s “mostly indica” descriptor is more than a marketing line; it predicts the cultivar’s garden behavior and end-user effects with notable accuracy. The project underscores Pisces’ ongoing focus on faithful expressions of legacy terpene chemotypes—earthy kush, chemmy fuel, and rounded spice.
Although exact release dates are not widely documented, MK-91’s emergence aligns with a broader industry resurgence of circa-1990s chemotypes and Afghani-Kush derivatives. Over the last several years, consumer demand for “gas” and “hashy incense” profiles has surged, with survey data from legal markets indicating steady interest in terpene packages anchored by myrcene, caryophyllene, and limonene. MK-91’s trajectory mirrors this trend, offering a concentrated version of those traits in a modern, grower-friendly frame.
Genetic Lineage and Inferred Parentage
Pisces Genetics lists MK-91 as mostly indica, and the label’s construction strongly implies lineage influenced by Master Kush and Chem ’91. Master Kush, historically associated with Afghani and Hindu Kush roots, contributes broad-leaf morphology, dense resin, and a grounding, earthy-spicy base. Chem ’91, the Skunk VA cut, is often credited with unmistakable petroleum-and-sour aromatics that can dominate a room at low concentrations.
While official parent records for MK-91 remain sparse, the Master Kush × Chem ’91 hypothesis is consistent with both breeder patterns and reported phenotype outcomes. Indica-leaning growth, abbreviated flowering time, and compact stature fit well with Kush ancestry. The heavy fuel character, sharp top notes, and lingering sourness align with Chem ’91’s well-known sensory fingerprint.
Genetically, such a pairing would likely produce a hybrid with significant indica behavior—shorter nodes, high calyx-to-leaf ratios, and robust trichome density—while preserving Chem-style vigor and terpene punch. This also predicts chemotypes dominated by myrcene, caryophyllene, and limonene, with occasional pinene or humulene accents. The result is a cultivar capable of both contemplative, couch-ready effects and an assertive aroma that cuts through competing scents in mixed rooms.
Appearance and Plant Morphology
MK-91 typically presents as a compact, sturdy plant with broad, dark green leaflets and a strong apical cola supported by several productive laterals. Internodal spacing often falls in the 3–5 cm range in optimized indoor conditions, driving tight bud stacking and high calyx density. Under high-intensity lighting, leaf blades can develop a waxy sheen, and the canopy holds a uniform, even silhouette.
In flower, the cultivar builds dense, golf-ball to torpedo-shaped buds with a high calyx-to-leaf ratio that makes trimming efficient. Pistils range from tangerine to deep rust, often curling into the bract clusters as they mature. Trichome coverage is generous, with bulbous heads that cloud from clear to milky rapidly in late bloom before a measured shift to amber.
Color expression is predominantly forest to jade green, but cooler night temperatures (a 3–5°C drop) can coax subtle anthocyanin flares in sugar leaves. This tends to show as a faint plum tint rather than full-on purple flowers, unless genetics skew toward a particularly pigmented phenotype. The finished appearance leans boutique: sticky, granular resin across tight, heavy nuggets that weigh more than their footprint suggests.
Aroma and Bouquet
The nose on MK-91 is best described as kush earth layered with chem fuel, followed by accents of pepper, citrus rind, and faint incense. The initial impression is often “gas-first,” with a penetrating solvent-like sharpness typical of Chem ’91-leaning offspring. As the jar breathes, deeper tones appear—loamy soil, black pepper, and a sweet, hashy warmth reminiscent of classic Afghani resin.
From a chemistry standpoint, myrcene’s musky, herbal character likely forms the base, while beta-caryophyllene contributes the peppery bite and limonene adds bright, citrusy lift. Supporting terpenes such as humulene and alpha-pinene can lend woody and pine-needle nuances that emerge on a second or third whiff. In some phenotypes, faint floral-lavender hints suggest linalool in minor quantities.
At room temperature, the bouquet is loud and lingering, and it intensifies markedly when broken up. Anecdotally, users report that a 0.5–1.0 g grind can perfume a medium-sized room for 20–30 minutes, an indicator of high terpene volatility. The overall aromatic experience is assertive and unmistakably “old-school gas” layered onto a cushioned kush backdrop.
Flavor and Consumption Experience
On the palate, MK-91 delivers immediate fuel-and-earth flavors, with a sour edge that nods to its Chem influence. The inhale tends to be clean but robust, showing lemon peel and cracked pepper over a dark, musky base. The exhale deepens into incense, wet stone, and a buttery hash finish that lingers for several minutes.
Combustion in a joint or bowl often spotlights the earthy-kushy core and pepper-spice, while vaporization (180–195°C) accentuates citrus and pine notes with less throat bite. At slightly higher vape temps (200–205°C), the gas and spice push forward, and the mouthfeel becomes oilier, signifying more complete volatilization of heavier terpenes. Users who prefer concentrates report that live resin and rosin captures push the diesel profile to the forefront, sometimes eclipsing the subtler herbal layers.
Aftertaste is persistent, commonly described as a clean fuel slick over sweet, resinous hash. Palate fatigue can set in with repeated hits due to intensity, but water or mild snacks reset perception quickly. For those sensitive to heavy “gas” profiles, cooler vaporizer temperatures or pairing with a citrus beverage can soften the edges without losing character.
Cannabinoid Profile and Potency Expectations
As a mostly indica cultivar with Kush and Chem influences, MK-91 is generally positioned in the high-THC category. In legal markets, comparable indica-dominant Kush/Chem hybrids commonly test between 18–26% THC by dry weight, with occasional outliers exceeding 28% under optimized conditions. CBD is typically low (<1%), while minor cannabinoids like CBG can appear in the 0.2–0.6% range, and THCV remains trace.
Total active cannabinoids (TAC) for well-grown phenotypes often fall in the 20–30% range, aligning with contemporary premium flower benchmarks. Industry analyses of large retail datasets in North America have reported median flower THC levels clustering around 19–21% in recent years, placing MK-91 squarely in the competitive tier when cultivated properly. Resin density and extract yield are commonly strong, making the cultivar attractive for hash and rosin production.
Consumers should expect a fast onset with inhalation—noticeable within 2–5 minutes—peaking by 15–25 minutes and sustaining for 60–120 minutes depending on tolerance. Oral formats shift the curve, with onset in 30–90 minutes, a 2–4 hour plateau, and gradual taper over several more hours. Potency perception is amplified by terpenes; high-myrcene, high-caryophyllene chemotypes can feel stronger than THC percentage alone would predict due to synergistic effects.
Terpene Profile and Aroma Chemistry
MK-91’s terpene spectrum is expected to be myrcene-dominant, followed by beta-caryophyllene and limonene as consistent secondary drivers. Typical total terpene content in top-shelf indica-dominant flowers ranges from 1.5–3.0% by weight, with standouts surpassing 3.5% under ideal cultivation and curing. Within that band, myrcene often occupies 0.8–1.8 mg/g, caryophyllene 0.5–1.2 mg/g, and limonene 0.4–1.0 mg/g, with variability tied to environment and phenotype.
Supporting terpenes frequently include humulene (woody, herbal), alpha- and beta-pinene (pine, resin), ocimene (green, slightly sweet), and linalool (floral). These minors usually appear in the 0.1–0.4 mg/g range each, but their perceptual impact can be significant due to synergistic effects and low sensory thresholds. In chemically “gassy” phenotypes, sulfur-containing compounds (thiols) present in parts-per-billion may contribute a skunky, petrol-like edge far out of proportion to their concentration.
From a functional standpoint, caryophyllene’s interaction with CB2 receptors is frequently cited for potential anti-inflammatory action, while myrcene is associated with sedative, muscle-relaxing qualities in user reports. Limonene may add mood-brightening and anti-stress undertones, which can balance the otherwise heavy body feel. Together, this terpene triad helps explain MK-91’s ability to be both deeply relaxing and psychologically soothing without muddiness when dosed moderately.
Experiential Effects and Onset/Durability
MK-91’s effects can be summarized as fast-settling body relaxation coupled with calm, steady mental drift, especially at moderate doses. Early in the session, many users note shoulder and neck tension easing within 10–15 minutes of inhalation, followed by a heavier, full-body calm. Cognitive impact often remains clear enough for conversation at low doses, but escalates to a drowsy, introspective state with additional consumption.
Duration depends on route and tolerance, but a standard inhaled session commonly delivers 60–90 minutes of primary effects with a soft afterglow for another hour. Those with lower tolerance may find the peak more pronounced and the taper slower, particularly if the terpene profile leans heavily myrcene. A small subset of consumers sensitive to high-THC indica profiles can experience short-lived head pressure or increased heart rate during onset, which typically subsides within 10–20 minutes.
Side effects mirror the category norm: dry mouth and dry eyes are the most frequent, reported in roughly 25–40% of users across indica-dominant strains in general consumer surveys. Occasional light dizziness or grogginess can occur at higher doses, especially when combined with alcohol or sedatives. Anxiety or unease appears less common than with high-limonene sativa-leaning cultivars, but can still occur in 5–10% of users if dosing overshoots comfort.
Potential Medical Uses and Dosing Considerations
MK-91’s indica-leaning effects and terpene ensemble suggest utility for stress reduction, muscle tension, and sleep initiation. The caryophyllene-forward spice points to potential anti-inflammatory support, while myrcene’s sedative associations align with nighttime use for mild insomnia. Users with chronic pain sometimes report short-term relief, particularly when tight muscles or spasms are a component of the discomfort.
For anxiety and mood support, the combination of limonene and linalool in trace to moderate levels can add a gentle lift without energetic overstimulation. That said, dose discipline is important; smaller inhaled servings (1–2 small puffs) or oral microdoses (1–3 mg THC) can provide relaxation without heavy sedation. For sleep, many patients find 5–10 mg THC effective, with some increasing to 10–20 mg under medical guidance if tolerance and prior experience warrant it.
Medical consumers should consider timing and interactions. Using MK-91 60–90 minutes before bed allows the peak to align with sleep onset when using oral formats; vaping closer to bedtime can work within a shorter window. Patients taking sedative medications, benzodiazepines, or consuming alcohol should consult a clinician due to additive CNS depressant effects and the potential for next-morning grogginess.
Comprehensive Cultivation Guide: From Seed to Jar
MK-91 grows like a classic indica-dominant hybrid: compact, vigorous, and resin-forward with a relatively short flowering window. Indoors, expect a final plant height of 0.8–1.2 m in 8–10 L containers with moderate veg time; outdoors, plants can reach 1.5–2.0 m in rich soil with full sun. A typical indoor flowering duration is 56–65 days (8–9 weeks), though select phenotypes may push to 70 days to maximize resin maturity.
Germination is straightforward at 24–26°C with 90–100% RH in a domed environment, often yielding 90%+ success using fresh seed and standard methods. Once rooted, maintain veg temperatures of 24–26°C by day and 20–22°C by night, with relative humidity around 60–70% and a VPD target of 0.8–1.2 kPa. In veg, feed to an EC of 1.2–1.6 mS/cm in hydro/coco or moderate organic inputs in soil; maintain pH at 5.8–6.2 (hydro/coco) or 6.3–6.7 (soil).
Training responds best to topping at the 4th–5th node followed by low-stress training and a single-layer trellis or SCROG. Internodes are naturally short, so aggressive supercropping is optional rather than required; gentle shaping to open the canopy improves airflow and light penetration. Defoliate lightly at pre-flower and again at day 21 of bloom, removing large fans that shade inner sites while preserving enough foliage to power robust bud swell.
During flower, target day temperatures of 22–25°C and night drops of 3–5°C to firm up buds and encourage resin. Keep RH at 50–55% in early bloom and 42–48% in late bloom, with VPD rising to 1.2–1.5 kPa to deter botrytis in dense colas. Increase EC to 1.6–2.1 mS/cm as flowers develop, with balanced macro ratios and ample calcium and magnesium to support rapid calyx production.
Lighting intensity can move from 600–900 µmol·m⁻²·s⁻¹ PPFD in late veg to 900–1,200 µmol·m⁻²·s⁻¹ in mid-to-late flower. With added CO₂ enrichment to 1,000–1,200 ppm, MK-91 tolerates the higher end of that PPFD range, improving bud density and resin output. Daily Light Integral (DLI) targets of 35–45 mol·m⁻²·day⁻¹ in flower are generally well tolerated when environmental parameters are dialed.
Watering frequency in coco/hydro may be daily to multiple times per day in smaller containers, aiming for 10–20% runoff to avoid salt buildup. In soil, irrigate thoroughly and allow the top 2–3 cm to dry before repeating, typically every 2–4 days depending on pot size and VPD. Avoid overwatering; MK-91’s dense root ball prefers oxygenated media with good drainage.
Integrated Pest Management (IPM) should begin in veg with weekly scouting and the use of beneficials like Amblyseius swirskii or cucumeris for thrips and mites, and Bacillus subtilis-based foliar products for preventative pathogen pressure. Cease foliar applications after week 2 of flower to protect resin heads and prevent moisture-related issues. Keep intake air filtered, maintain negative room pressure when possible, and sanitize tools between plant contacts.
Phenotypically, expect 2–3 main expressions: a Kush-leaning pheno with heavier earth and shorter flowering, a Chem-forward pheno with louder fuel and a hair more stretch, and a balanced middle ground. The Kush-leaner often finishes by day 56–60 and stacks extremely dense buds; the Chem-leaner may prefer day 63–67 to fully mature volatile compounds. For commercial production, the balanced pheno offers the best intersection of yield, potency, and terp intensity.
Yield potential is strong for a compact plant: indoors, 450–600 g/m² is a realistic range with dialed inputs, while skilled growers with CO₂ and optimized SCROG may push 600–700 g/m². Outdoors in temperate, low-humidity climates, 500–900 g per plant is achievable in 40–75 L containers or in-ground beds with rich organic amendments. Resin production is a highlight, with wet trim hash yields that routinely satisfy rosin makers who prefer tight, greasy heads.
For nutrient management, maintain a nitrogen-forward feed in early veg before tapering N and increasing P/K in weeks 3–7 of bloom. Supplement magnesium at 50–75 ppm equivalent when using high-intensity LEDs to prevent interveinal chlorosis. Keep an eye on calcium under fast growth; tip burn usually signals EC excess rather than a true Ca deficiency in this cultivar.
Harvest timing is best judged with trichome color: many cultivators target 5–10% amber for a balanced but potent effect, while those seeking maximum sedation push to 15–20% amber. Aromatics will be most vivid in the last 7–10 days as volatile terpenes crest; consider a gentle nutrient taper or water-only finish for 7–10 days in soil to sharpen flavor. In hydro/coco, a 5–7 day low-EC finishing period helps reduce residual salts without starving the plant prematurely.
Dry at 18–20°C and 55–60% RH for 10–14 days, aiming for a slow, even moisture release to preserve terpene integrity. Stems should bend and just begin to snap before trimming and jarring to a target internal humidity of 58–62% with two-way humidification packs if needed. Cure for a minimum of 14 days, burping jars daily in week one and every 2–3 days thereafter; a 4–8 week cure materially improves smoothness and depth of flavor.
Storage should be in airtight, opaque containers at 16–20°C away from light, with minimal headspace to slow terpene evaporation. Avoid refrigeration and freezing for cured flower, as condensation and trichome brittleness can compromise quality; if freezing is necessary for fresh-frozen extract material, vacuum-seal immediately post-harvest. Under proper storage, terpene content and sensory quality remain stable for several months, with gradual decline thereafter.
For cloning, MK-91 roots readily within 10–14 days at 24–26°C and 80–95% RH under low PPFD (100–200 µmol·m⁻²·s⁻¹). Selecting mother stock from the most aromatic, structurally sound phenotype ensures uniform production runs and consistent end-product quality. Rotate mothers every 6–9 months to maintain vigor, and track phenotypes with detailed notes on internode spacing, aroma intensity, and finishing time for ongoing improvement.
