Autoflower Showdown: Which Autos Grow Fastest—and Which Grow Biggest?
For homegrowers who want speed… or size… and need to know exactly which genetics deliver.
Autoflowers have come a long way from their early days as small, low-yielding, “beginner-only” plants. Today’s autos are powerful, high-producing genetics capable of rivaling the quality and potency of many photoperiod strains. But every grower eventually faces one big question:
Do you want the fastest grow… or the biggest plant?
Because with autoflowers, those two traits rarely come packaged together.
This guide puts the most popular autos head-to-head—so you know exactly which strains race to harvest, and which ones bulk up like champions if you give them time, training, and space.
Understanding Speed vs. Size in Autoflowers
Before comparing strains, it’s important to understand what drives their performance:
Fast Autos Tend To:
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Finish in 55–70 days from seed
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Stay shorter (18–30 inches tall)
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Focus energy on flower production rather than long vegetative growth
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Thrive in tight spaces, micro-grows, closets, and 2×2 tents
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Require consistent light and minimal stress—anything slows them down
Big Autos Tend To:
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Take 75–100+ days from seed
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Grow large, bushy structures with long side branches
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Respond extremely well to LST, topping (when skilled), and wide fabric pots
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Produce Cola Forests™—multiple top-heavy buds
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Need more root space, more training, stronger airflow, and more nutrients
Fastest Autoflowers on the Market
Perfect for growers who want speed, stealth, or a fast turnover.
1. FastBuds—Lemon Pie Auto (Seed-to-Harvest: ~60 days)
If you want a sprinting strain, this is a proven speed demon.
Traits:
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20–24% THC
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Citrus-forward terpenes
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Compact plants ideal for micro spaces
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Minimal stretch
Why It’s Fast:
Its genetic structure prioritizes rapid flower onset. Expect pistils by day 18–22 from sprout.
2. Royal Queen Seeds—Quick One Auto (Seed-to-Harvest: 55–65 days)
One of the earliest “quick” autos ever created.
Traits:
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13% THC (lower potency but extremely reliable)
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Stays short and manageable
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Very beginner-friendly
Why It’s Fast:
Selective breeding cut the veg phase extremely short—often < 14 days.
3. Mephisto Genetics—Ripley's OG Auto (Seed-to-Harvest: 65–70 days)
A boutique-quality autoflower with speed and heavy frost.
Traits:
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20% THC
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Dense, gassy buds
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Medium-height plants
Why It’s Fast:
Highly optimized autoflower lineage that flips early and stacks quickly.
4. FastBuds—Gorilla Glue Auto (Seed-to-Harvest: 65–70 days)
A fast-finishing powerhouse with resin production that rivals photoperiods.
Traits:
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22–26% THC
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Sticky, pungent colas
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Usually finishes a few days early in hydro
Why It’s Fast:
Genetics trigger extremely early trichome development.
Fast Autos Summary Chart
Biggest Autoflowers on the Market
The strains that prove autos can be absolute monsters.
If size is the priority—and you want to pull half-pound harvests from a single autoflower—these genetics are the heavy hitters.
1. Humboldt Seed Company—Magic Melon Auto (75–90+ days)
This is a giant when given root space and strong lighting.
Traits:
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20–25% THC
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Sweet melon terps
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Can exceed 4 feet with LST
Why It Gets Big:
Late transition into flower + vigorous early veg.
2. Barney’s Farm—Zkittlez Auto (75–95 days)
One of the most consistent big-yielding autos.
Traits:
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20% THC
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Known for resin and bud density
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Huge lateral branching
Why It Gets Big:
Dominant hybrid genetics favor extended veg growth early on.
3. Dutch Passion—Auto Ultimate (90–105 days)
The biggest autoflower many growers will ever see indoors.
Traits:
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20–24% THC
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Massive yields (350–600g/plant in ideal setups)
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Loves heavy feeding
Why It Gets Big:
Longest veg time of almost any auto on the market.
4. Mephisto Genetics—Sour Stomper Auto (75–90 days)
A cult classic known for exploding in size under strong LEDs.
Traits:
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18–22% THC
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Grape, berry, fuel terps
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Excellent for SCROG setups
Why It Gets Big:
Responds extremely well to training, unlike many autos.
Big Autos Summary Chart
Fast vs. Big: Who Wins?
The answer depends on your goals:
✔ If you want rapid turnover:
Choose Lemon Pie, Quick One, or Ripley’s OG.
✔ If you want tent-filling beasts:
Choose Magic Melon, Auto Ultimate, or Zkittlez Auto.
✔ If you want the “in-between” balanced performer:
FastBuds Gorilla Glue Auto is a perfect middle-ground strain:
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Not the fastest
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Not the biggest
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But consistently strong, frosty, and easy to grow
Factors That Determine Whether an Auto Grows Fast or Big
Not all results are genetic—your setup plays a major role. The same strain can finish in 65 days in one tent, and 90 days in another.
Here’s why:
1. Light Intensity
Autos under 150W tend to stay small and finish quicker.
Autos under 300–500W tend to stretch and bulk up.
2. Pot Size
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1–2 gallon → fast finish, small plant
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3–5 gallon → balanced growth
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7+ gallon → monster autos
Root space = plant size.
3. Training Style
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No training → smaller, faster
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LST → wider, more colas
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Topping (for advanced growers) → biggest plants
4. Stress Levels
Autos hate stress.
Anything that slows growth—transplant shock, overwatering, pH swings—reduces size AND delays finish.
5. Nutrient Load
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Light feeding → small but fast
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Full feeding → big and slow(er) but heavy yields
Autos that grow big need more nitrogen early and more potassium late.
What Should You Grow?
Grow Fast Autos If You Want:
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Quick personal supply
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Small tents or stealth setups
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Uncomplicated growing
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Predictable timelines
Grow Big Autos If You Want:
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The highest possible yield per plant
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A full tent canopy
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A long veg period without switching light cycles
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Colossal buds and monster branches
Either way, modern autoflower genetics mean you can achieve top-shelf bud quality in a fraction of the time it used to take—whether you’re racing to harvest or building a jungle in your tent.
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