Cannabis ruderalis is a short, hardy, low-THC type of cannabis from Central Asia and Russia that flowers based on age instead of day length, and that trait is the source of every modern autoflowering seed. Breeders cross ruderalis with high-THC plants to get autoflowers that go from seed to harvest in roughly two to three months. For growers, the choice is less “indica, sativa or ruderalis” than “autoflower or photoperiod.”
This article began as an Ask Alex reader question: should a home grower pick indica, sativa or ruderalis? Alex’s original answer weighed time, space, potency and discretion. Those still matter, so this version keeps them and adds what plant scientists have since learned about the genetics behind autoflowering.
What Is Cannabis Ruderalis?
The name comes from the Russian botanist D. E. Janischewsky, who described wild cannabis growing in southern Russia in 1924. “Ruderal” means a plant that colonizes disturbed ground such as roadsides and field edges, which is where it was found. Wild ruderalis is:
- Short and sparse, with few side branches and small, airy buds.
- Low in THC, with relatively more CBD than modern drug cultivars, so it is not grown for its own effects.
- Fast, completing its life cycle within a short northern summer.
- Photoperiod insensitive, meaning it starts flowering after a few weeks of growth no matter how long the days are.
Most botanists today treat ruderalis, indica and sativa as varieties or populations within one species, Cannabis sativa, rather than three separate species. Our guide to sativa vs indica explains why those labels say little about effects.
Where the Autoflower Trait Comes From
Most cannabis is a short-day plant: it keeps growing leaves until nights get long enough, then flowers. Autoflowering plants ignore that signal. Researchers at Cornell University mapped a locus they named Autoflower1 and noted that growers have long described the trait as a simple recessive one. A 2024 study from University College Dublin and Cornell found a second, independent locus, Autoflower2, tied to a version of the flowering gene FLOWERING LOCUS T, and concluded that photoperiod insensitivity arose more than once in cannabis.
The practical meaning for breeders: because the trait behaves as recessive, a cross between an autoflower and a photoperiod plant usually produces photoperiod offspring. It takes further generations of crossing and selection to fix autoflowering into a potent strain, which is why early autoflowers were weak and modern ones are not.
Autoflower vs Photoperiod at a Glance
| Factor | Autoflower | Photoperiod |
|---|---|---|
| What starts flowering | Plant age | Long nights (12 hours of darkness indoors) |
| Seed to harvest | Roughly 8 to 12 weeks, depending on strain | Usually 3 to 5 months or more; grower controls veg time |
| Plant size | Compact, often under 4 feet | Can be kept small or grown very large |
| Yield per plant | Lower | Higher, especially with a long veg period |
| Indoor light schedule | Same schedule all the way through, often 18/6 or 20/4 | 18/6 for growth, then 12/12 to flower |
| Training | Gentle only; no time to recover from heavy stress | Tolerates topping, heavy pruning, SCROG |
| Cloning | Impractical; clones are as old as the mother | Easy; keep a mother plant indefinitely |
| Outdoors | Several harvests per season possible; good for short summers | One harvest in fall |
Who Should Grow Autoflowers
Alex’s original advice holds up: ruderalis-based plants “pretty much do their own thing” given light, water and nutrients. Autoflowers suit:
- First-time growers who want a short, forgiving project without a light-schedule change.
- Small spaces such as a closet or a 2×2-foot tent, where a compact plant fits.
- Outdoor growers in short or cool seasons, or anyone who wants a harvest before fall rains and mold.
- Growers who value discretion, since the plants stay short.
Who Should Grow Photoperiod Plants
Photoperiod plants make more sense if you want maximum yield from a limited plant count, want to keep a mother plant and take clones, or like training methods such as topping and SCROG trellising. They give you control: you decide when the plant flowers. Alex’s original point about time and space still applies here. Long-flowering sativa-leaning strains can add weeks and need headroom.
Tips for Growing Autoflowers
- Start in the final container. Transplant shock costs days an autoflower cannot get back.
- Go easy on nutrients early. Small plants burn easily; feed lighter than you would a photoperiod plant.
- Use low-stress training only. Bending and tying down is fine; skip topping late in growth and avoid heavy defoliation.
- Keep the light schedule steady. Long days work well, but avoid interruptions.
- Check yield and timing claims. Breeders list seed-to-harvest times under ideal conditions. Expect a little longer.
For the basics of starting seeds and setting up a space, see how to germinate cannabis seeds, basic marijuana growing and our pick of strains for indoor growing.
Is Home Growing Legal?
It depends on the state. In Oregon, adults 21 and over may grow up to four plants per household (see Oregon marijuana laws). In Washington, home growing is legal only for registered medical patients (see Washington marijuana laws). Autoflower plants count toward plant limits the same as any other plant.
Cannabis Ruderalis FAQ
Does ruderalis get you high?
Wild ruderalis has little THC and is not grown to smoke. Modern autoflower strains are ruderalis crossed with potent plants and can be as strong as photoperiod strains.
Are autoflowers weaker than photoperiod strains?
Early autoflowers were. Many current autoflower strains are bred to high THC levels, though yields per plant are usually lower.
How long do autoflowers take?
Most finish roughly 8 to 12 weeks from germination. Check the breeder’s listing and allow a little extra time.
What light schedule is best for autoflowers?
Many growers use 18 hours on and 6 off, or 20 on and 4 off, from seed to harvest. Autoflowers do not need a 12/12 switch.
Can you clone an autoflower?
Not usefully. A cutting is the same age as its mother and starts flowering while still tiny, so yields are very small.
Is ruderalis a separate species?
Most botanists treat it as a population or variety of Cannabis sativa, not a distinct species.
For adults 21+ in legal states. General information, not legal or medical advice. Check your state’s home-grow rules before planting.
