Marijuana plants are annuals. A plant lives out its whole life in a single growing season and does not return from its roots the next spring. Unlike some annuals, such as a bean, though, cannabis doesn’t die on a fixed schedule; it finishes because shortening days tell it to flower. Growers who control the light can keep one plant going far longer than nature intends.
What Makes Cannabis an Annual
Botanists classify cannabis as an annual herb, a plant that completes its life in one year.1Frontiers in Plant Science. Architecture and Florogenesis in Female Cannabis sativa Plants Hemp, the same species grown for fiber and seed, usually finishes in about 60 to 120 days from planting, depending on variety and conditions.2Kind Seed Co. Cannabis And Hops: How These Plant Cousins Compare Individual cannabis plants are also usually either male or female, though some types carry both.3University of Guelph Atrium. Optimizing Floral Reversion Based Micropropagation in Cannabis sativa L. An outdoor plant’s job each year is to produce seed before winter, and once it has, it is spent.
Over one outdoor season, a seedling appears in spring and grows leafy and fast through summer. Buds form as days shorten in late summer and fall. After harvest or seed set, the leaves yellow and the plant declines. A female that is never pollinated keeps making flowers for weeks, so buds keep swelling until harvest.
Hops, cannabis’s closest cultivated relative, are perennials that come back every year.4Kind Seed Co. Cannabis And Hops: How These Plant Cousins Compare They keep a living underground rhizome and root system that sends up new shoots, reaching about 20 feet before fall.5Kind Seed Co. Cannabis And Hops: How These Plant Cousins Compare Cannabis has no such underground storage organ, so a dead stalk will not resprout in spring.
Cannabis has a taproot and fibrous roots, but they aren’t storage organs the way a perennial’s crown or rhizome is, so they hold no reserves to restart growth. Once the stalk is cut or dies back, the roots break down over winter. You can safely pull the root ball from a pot and compost it.
One thing can fool people. Seeds dropped by the old plant may sprout the next spring nearby, and these look like regrowth. They are new plants, and because they come from seed, they may differ from the parent.
Why Shorter Days Tell Cannabis to Flower and Finish
Most cannabis is a photoperiod plant: it grows leaves first, then flowers in autumn as days shorten.6The Biochemist. Timing is everything: the genetics of flowering time in <i>Cannabis sativa</i> It starts its reproductive phase once daylight drops below a critical length.7Journal of Natural Fibers. Review of Flowering Control in Industrial Hemp Young plants ignore day length, and only older plants respond to it.8PubMed Central. Photoperiodic Flowering Response of Essential Oil, Grain, and Fiber Hemp (Cannabis sativa L.) Cultivars The response is sensitive. In some varieties, a difference of only about 15 minutes of daylight noticeably changed when flowers began.9PubMed Central. Photoperiodic Flowering Response of Essential Oil, Grain, and Fiber Hemp (Cannabis sativa L.) Cultivars
Outdoors, this is why plants finish on a similar calendar. Nights reach the trigger length at a time set by how far north or south you live, so a given yard hits the switch at roughly the same time each year. A plant sown in April and one sown in June will usually both begin flowering around the same point in late summer, because both respond to the same lengthening nights. The late-sown plant has had less leafy growing time, so it flowers at a smaller size and gives a smaller harvest.
Indoors, growers typically trigger flowering by moving lights to 12 hours on and 12 off.10Sensi Seeds. How to regenerate cannabis plants Keeping lights at 18 hours or more holds the plant in leafy growth.11Sensi Seeds. How to regenerate cannabis plants
Flowering depends on a long, unbroken dark period, so a porch light, a streetlight, or opening a tent with a lamp on during the dark hours can disrupt it. A plant with interrupted nights may be slow to start flowering, may stall, and in some cases can drift back toward leafy growth. If flowering seems stuck, sit inside the dark tent or room for a few minutes with the lights off and look for slivers of light at zippers, vents and doors.
Autoflowering Plants Run on an Even Shorter Clock
Autoflowering varieties inherit genes from a wild type called ruderalis and start flowering about 2 to 3 weeks after sprouting.12PubMed. Autoflowering cannabis An autoflower flowers on its own timetable, whatever the light is doing. Many are ready to harvest less than 10 weeks from seed.13PubMed. Autoflowering cannabis Their short life fits places with short, cool summers.14PubMed. Autoflowering cannabis Switching to long days cannot hold an autoflower in leafy growth, so they are the most strictly annual cannabis plants.
To tell whether your plant is one, start with the seed pack or breeder’s label, which will say whether the strain is auto or photoperiod. If a plant shows flower parts within a few weeks of sprouting while it still gets long days, that points to an autoflower. A photoperiod plant under the same long days stays leafy and keeps growing until the light schedule or the season changes.
An autoflower suits a first-timer or a place with a short summer, because it finishes quickly and doesn’t depend on the season’s light. A photoperiod plant gives more control, since it can be kept growing as long as you like and can be regrown or cut for cuttings.
Can a Plant Regrow After Harvest
A harvested photoperiod plant does not have to die if some green growth is left on it.15THCFarmer. Do Weed Plants Regrow After Harvest? How to Reveg Cannabis Putting it back under long days usually makes it push new shoots, a process growers call revegging.16THCFarmer. Do Weed Plants Regrow After Harvest? How to Reveg Cannabis The usual light schedule for this is 18 to 24 hours a day.17Gamut Packaging. Can a Marijuana Plant Regrow After Harvest? Growers commonly switch back to leafy-growth feeds, with extra nitrogen right after harvest.18Sensi Seeds. How to regenerate cannabis plants After about two weeks, new growth is usually established and the plant can be flowered again.19Sensi Seeds. How to regenerate cannabis plants
It starts at harvest. A grower who wants to reveg leaves some lower branches with their leaves, and often a few small buds, rather than stripping the plant bare. Those leaves let the plant make energy and push new growth. A plant cut down to bare stalks with no green is much less likely to recover.
Afterward, the plant goes back under long days to signal that it is time for leafy growth instead of flowers. Water carefully at first. A plant with little foliage uses much less water, and soil that stays wet can lead to root problems.
The first new leaves often look odd, such as single-bladed, rounded or twisted ones. That is normal and doesn’t mean the plant has failed. Regrowth can take a week or more to show, so don’t give up after a few days of nothing. Normal-looking leaves return as the plant settles into leafy growth, and then you can decide whether to flower it again.
Outdoors this is much harder. Fall days keep shortening, so a harvested plant gets no long-day signal to regrow. Revegging is practical mainly indoors or with plants brought under lights. Even then, revegging extends one life rather than making cannabis a perennial.
Keeping One Plant Going for Years With Clones
Keeping a female plant permanently under long days holds it in leafy growth, which lets growers take cuttings for years. This works because flowering only begins when days shorten. The plant kept for cuttings is called a mother plant, and each cutting is a clone, a copy of the parent grown from a snipped piece of it.
A mother needs regular feeding, a pot big enough for its roots, and trimming to keep it a manageable size. Pests such as spider mites or fungus gnats can build up on a plant kept for years, so checking leaves often matters more than with a short-lived plant. Cuttings should come from healthy, vigorous new growth rather than old, woody or weak shoots. A cutting needs to be kept humid and rooted before it is treated as a plant of its own, and a healthy mother gives better ones.
Copies are not perfectly stable, though. Clones copied over and over gradually build up DNA changes, and clones that look identical may slowly drift in traits like potency or vigor.20cannabisworkforce.org. Are Marijuana Plants Annuals or Perennials? Experienced growers report that clone vigor fades over time without good nutrition and plant health.21cannabisworkforce.org. Are Marijuana Plants Annuals or Perennials?22PubMed Central. Effect of Explant Source on Phenotypic Changes of In Vitro Grown Cannabis Plantlets over Multiple Subcultures23Leafly. Does cloning ruin cannabis strains over time? A cutting carries the parent’s accumulated changes, while a seed starts a new plant with its own fresh mix of genes.
If cuttings begin rooting slowly, growing weakly or giving smaller yields, the line may be losing vigor. You can restart from seed or from a fresh mother of the same strain rather than relying on cuttings indefinitely. Labeling each generation with a date or number makes it easier to notice when decline begins.
Can Cannabis Survive Frost or Winter Outdoors
Mature hemp plants can handle light frost of 29 to 32°F.24Pest&Crop newsletter. Frost And Hemp, Should Growers Worry? A moderate freeze of 25 to 28°F can damage some leaves and buds.25Pest&Crop newsletter. Frost And Hemp, Should Growers Worry? At 24°F or colder, heavy damage is possible.26Pest&Crop newsletter. Frost And Hemp, Should Growers Worry?
When frost is forecast near harvest, overnight lows matter more than daytime highs, since damage happens in the cold hours before dawn. A brief light frost is usually survivable for a mature plant, but a forecast of 28°F or lower is a good reason to harvest. Check the forecast low for your own area in the days before, instead of guessing from the season.
A plant that isn’t ready yet can sometimes be protected. A potted plant can be moved indoors or into a garage for the night. A plant in the ground can be covered overnight with a cloth, but that only helps on mild frosty nights, not hard freezes.
Bringing a plant inside to overwinter only works with indoor lights giving long days. A window in winter gives short days, which triggers flowering. Expect pests to come indoors with it.