Watermelon Auto is a Royal Queen Seeds autoflower built for speed, flavor, and a relaxing high. From Watermelon x OG Kush Auto, it is a compact, indica-dominant plant at 19-20% THC with a sweet, tropical watermelon taste. Its standout feature is how fast it finishes: ready in just 8-9 weeks from seed, with a flowering stage as short as 6-7 weeks, so it is one of the quickest strains you can grow.
This is an autoflower, so it flowers on age rather than a change in the light cycle, which keeps the grow simple. Note it is a different strain from Watermelon Zkittlez and the photoperiod Watermelon. The figures below are Royal Queen Seeds breeder values; check your own pack for the exact numbers.
Recommended Strains
Watermelon Auto
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THC | 19% - 20% (Medium) |
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Lineage | Watermelon x OG Kush Auto |
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Type | Autoflowering |
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Height | 3.61 ft | 1.1 m |
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Yield | High |
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Yield Indoor | 1.47 - 1.64 oz/ft² | 450 - 500 g/m² |
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Yield Outdoor | 1.76 - 3.17 oz/plant | 50 - 90 g/plant |
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Life Cycle | 6 - 7 weeks |
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Phenotype | 75% Indica / 20% Sativa / 5% Ruderalis |
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Effects | Calming |
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Flavors | Fruity, Melon |
Watermelon
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THC | 21% - 22% (Medium) |
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Lineage | Watermelon OG S1 |
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Type | Feminized |
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Height | 5.91 ft | 1.8 m |
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Yield | High |
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Yield Indoor | 1.47 - 1.64 oz/ft² | 450 - 500 g/m² |
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Yield Outdoor | 15.87 - 17.64 oz/plant | 450 - 500 g/plant |
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Flowering Time | 7 - 8 weeks |
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Phenotype | 80% Indica / 20% Sativa |
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Effects | Calming, Relaxed |
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Flavors | Fruity, Melon |
Watermelon Auto Grow Info
| Trait | Watermelon Auto (Royal Queen Seeds) |
| Genetics | Watermelon x OG Kush Auto |
| Seed type | Autoflowering |
| Genetic profile | 75% indica / 20% sativa / 5% ruderalis |
| THC | 19-20% (medium) |
| Flowering time | 6-7 weeks (full cycle 8-9 weeks) |
| Height | Around 1.1 m (70-110 cm indoors) |
| Indoor yield | High, up to 450-500 g/m² |
| Outdoor yield | Around 50-90 g per plant |
| Effects | Calming, relaxing |
| Flavor | Sweet watermelon, fruity, tropical |
These are Royal Queen Seeds’ published figures for the Watermelon Auto line at Growlantis. When you need an exact THC percentage, height, or yield, check the specification on your own Watermelon Auto seed pack.
What Makes Watermelon Auto Worth Growing
Speed and flavor are the pitch. Watermelon Auto finishes a full cycle in 8-9 weeks, which is about as fast as cannabis gets, and it still delivers a strong indoor yield of 450-500 g/m². For a quick turnaround or several runs in a season, few strains keep pace.
The taste lives up to the name: sweet, juicy, tropical watermelon over a fruity base. The effect is calming and relaxing, an indica-led body stone with a moderate CBD content that keeps it smooth, so it works best as an evening unwind. Compact size and easy care round out a strain that is friendly for beginners and efficient for experienced growers.
Is Watermelon Auto Indica or Sativa?
Watermelon Auto is strongly indica dominant, listed at 75% indica, 20% sativa, and 5% ruderalis. The indica side leads clearly.
That shows in both the plant and the high. The plant is short, compact, and easy to manage, while the effect is a relaxing, soothing body stone that calms both body and mind. It is a nighttime and evening strain more than a daytime one, good for winding down.
Flowering Time vs Full Grow Time
Autoflowers confuse a lot of growers on timing, and this strain publishes both numbers, so the distinction is clear.
- Flowering time: 6-7 weeks. This is the bloom stage, where the buds form and ripen, and it is unusually short.
- Full grow time (seed to harvest): about 8-9 weeks. This covers the whole cycle, with flowering happening inside it rather than after a separate long veg period.
The takeaway: the 6-7 week figure is flowering only, while 8-9 weeks is the complete seed-to-harvest cycle. Plan around the full cycle, and enjoy one of the fastest finishes in cannabis.
Does Watermelon Auto Need a 12/12 Light Cycle?
No. Watermelon Auto flowers on age, not day length, so it never needs a 12/12 photoperiod to bloom.
Indoors you can hold a longer schedule like 18/6 or 20/4 from seedling to harvest. Dropping to 12/12 once flowering starts only cuts daily light and costs you yield. Keep the longer schedule and strong light intensity instead.
Watermelon Auto Grow Timeline, Week by Week
Treat this as a development pattern, not a fixed schedule, and remember this strain runs fast, so the windows are tight.
- Weeks 1-2: germination and seedling. The taproot and first leaves establish. Keep water light and conditions stable, since there is no time to recover from a bad start.
- Week 3: vegetative growth. The plant builds a compact frame quickly and may start to preflower. Begin gentle low stress training now.
- Weeks 4-5: stretch and bud set. Vertical growth slows and flower sites fill in fast.
- Weeks 6-7: main flower development. Dense, resinous buds build and the sweet watermelon aroma gets strong.
- Weeks 8-9: maturation and harvest. Most plants finish here. Judge ripeness by the trichomes, not the day count.
Choosing Your Setup: Space, Light and Pots
Watermelon Auto is made for small spaces. At around 1.1 m (70-110 cm indoors) it fits a compact tent, and low stress training keeps it even shorter and more even.
Light drives the yield, so give it a strong source from day one, since the fast cycle leaves no time to make up for weak light. A full-spectrum LED at 25-35 watts per square foot on an 18-20 hour schedule keeps the buds dense. Add an inline exhaust fan and a carbon filter for the fruity aroma.
Plant straight into the final 3-5 gallon fabric pot and skip transplanting, which autos dislike, especially on a strain this quick. Fabric pots air-prune the roots and keep the root zone healthy.
Germinating and Raising Seedlings
The paper towel method is the easy, reliable start. Soak the seeds for 12-24 hours, then set them between damp paper towels on a covered plate, kept dark and warm at 70-85°F (21-29°C). A taproot usually shows in two to three days.
When the taproot reaches about 1-2 cm, plant it root-down a knuckle deep in a light mix and keep the surface moist until the seedling breaks ground. A clean, strong start matters even more on a fast auto. New to germination? Our beginner growing guides walk through it step by step.
The Vegetative Stage and Low Stress Training
Veg is very short on this fast auto, so start training early. Keep nitrogen available, hold temperatures in the low to mid 70s°F, and begin low stress training as soon as the branches bend.
Low stress training is the technique that pays off here. Tying the main branches outward opens the compact canopy and gets light to the lower buds, which adds weight. Skip topping and other high-stress cuts entirely, since this strain has even less recovery time than a typical autoflower.
Feeding and Watering Watermelon Auto
Keep feeding light. Autos run smaller root systems, so start nutrients at about half the label strength and build up only if the plant asks. Use a nitrogen-forward base through the short veg, then move to a bloom formula higher in phosphorus and potassium as flowering sets in, watching the leaves for burn.
Water by root-zone moisture, not a timetable. A young plant needs very little, and soaking the whole medium starves the roots of oxygen. As the plant grows, demand climbs, so increase water gradually by pot weight and how fast the top layer dries.
Flowering and Knowing When to Harvest
Flowering begins on its own around week three or four, with a short stretch and the first pistils, then dense, resinous buds build fast over the 6-7 week bloom. The sweet watermelon aroma develops quickly, so keep air moving and run a carbon filter indoors.
As the 8-9 week finish approaches, let the plant decide. Check trichomes under a loupe and harvest when most are cloudy with a few amber for the fullest calming effect. After the cut, hang the branches in the dark at about 60°F (15-16°C) and 55-60% humidity for 7-14 days, then cure in jars, burping daily for the first weeks to protect the fruity flavor.
Growing Indoors vs Outdoors
Indoors is where Watermelon Auto is at its best. Hold 18/6 the whole way, keep a lightly trained canopy under strong light, and the 450-500 g/m² indoor yield is well within reach in a small tent.
Outdoors, the autoflower trait and short cycle let you plant after the last frost and harvest in about two months, fitting several runs into a long summer. Outdoor yields are modest at around 50-90 g per plant, so this strain earns its keep indoors. Give outdoor plants full sun and well-draining soil.
How Tall and How Much? Height and Yield
Height is easy to plan for. Watermelon Auto stays around 1.1 m, or 70-110 cm indoors, compact enough for small tents, and low stress training keeps it shorter and even.
On yield, it is a high indoor producer: up to 450-500 g/m² indoors under strong light, and around 50-90 g per plant outdoors. Strong light from the start and an open, lightly trained canopy are the main ways to hit the top of the indoor range on such a fast cycle.
Best US Climates for Watermelon Auto
As a compact, very fast autoflower, Watermelon Auto is flexible. Growers in California and the warm West get easy outdoor runs, and the quick cycle suits the Pacific Northwest and northern states, where an 8-9 week finish beats the fall rains with room to spare.
In the humid Southeast, keep airflow up around the dense buds. The short cycle and small size also make it a strong indoor choice anywhere, which is where it yields best. For other varieties, browse our full how-to-grow library.
Common Problems When Growing Watermelon Auto
A few predictable issues are easy to avoid on a fast auto.
Weak light early on
The fast cycle leaves no time to recover from a slow start. Give it strong light from the seedling stage so it builds a good frame before the quick flip to flower.
Expecting big outdoor yields
Outdoor returns are modest at around 50-90 g per plant. The high yield is an indoor figure, so lean on indoor light if weight is the goal.
Overfeeding or overwatering a small auto
The compact auto root system burns and drowns easily. Start nutrients at half strength, increase only on demand, and water to root-zone moisture rather than a schedule.
Harvesting by the calendar
The 8-9 week window is a reference, not a cutting date. Read the trichomes and flower maturity before you cut, since phenotype and environment shift the finish.
Making the Most of Your Harvest
Do not waste the trim. The resinous sugar leaves make good bubble hash, dry sift, or infused oil that keeps the sweet watermelon flavor. The stems, roots, and fan leaves compost well and feed your next grow.
Is Watermelon Auto Right for You?
If you want a fast, compact autoflower with a sweet watermelon flavor and a calming effect, yes. It is one of the quickest strains around, friendly for beginners, and productive indoors. Just set outdoor yield expectations modestly. For another sweet, fast auto, our Guava x Gelato 41 Auto grow guide is a good next read.
Frequently Asked Questions
Is Watermelon Auto indica or sativa?
Watermelon Auto is strongly indica dominant, listed at 75% indica, 20% sativa, and 5% ruderalis. It grows short and compact, and the effect is a relaxing, soothing body stone that calms both body and mind, helped by a moderate CBD content. It is best suited to evening and nighttime use.
Does Watermelon Auto need a 12/12 light cycle?
No. Watermelon Auto flowers automatically with age, not day length, so it never needs a 12/12 schedule. Indoors you can hold a longer photoperiod like 18/6 or 20/4 from seedling to harvest. Reducing the light once flowering starts only lowers your daily light and costs yield.
How long does Watermelon Auto take to grow?
Watermelon Auto is very fast, with a flowering stage of just 6 to 7 weeks and a full seed-to-harvest cycle of about 8 to 9 weeks. The flowering figure is the bloom stage only, which sits inside the full cycle. Judge the finish by trichome maturity rather than the day count.
How much does Watermelon Auto yield?
Watermelon Auto is a high indoor yielder, at up to 450 to 500 g/m2 under strong light, and around 50 to 90 g per plant outdoors. It performs best indoors. Strong light from the start and an open, lightly trained canopy are the main ways to push the indoor figure toward the top of its range.
How tall does Watermelon Auto grow?
Watermelon Auto stays compact at around 1.1 m, or 70 to 110 cm indoors, which makes it easy to fit in a small tent. Low stress training keeps it shorter and more even, and it needs no topping. Most of its height comes during the quick stretch in the early flowering weeks.
How strong is Watermelon Auto?
Watermelon Auto tests at a medium 19 to 20% THC with a moderate CBD content that smooths the experience. The effect is calming and relaxing rather than overwhelming, which makes it an approachable evening strain and a comfortable choice for less experienced users who want a gentle body stone.
Can you clone Watermelon Auto?
Not usefully. As an autoflower, a cutting keeps the mother’s age, so it tries to flower straight away as a tiny plant and yields almost nothing, especially on a strain this fast. If you want more plants, germinate more seeds. Cloning only makes sense with photoperiod strains.
