Autoflower Week 4: What to Expect and How to Care
Quick answer: By week 4, most autoflowers are finishing vegetative growth and starting early flowering, you will often see pre-flowers and white pistils, a growth spurt (stretch), and rising nutrient demand. Keep temperatures around 68-78°F (20-26°C) and humidity near 50%, begin transitioning toward bloom nutrients, and avoid heavy training now, since autoflowers have little time to recover. Week 4 sets up the whole flowering stage, so steady, stress-free care matters.
Week 4 is a turning point for most autoflowers. Having spent the first few weeks building roots and leaves, around now they begin the switch from vegetative growth into early flowering, so you will typically spot the first pre-flowers and white pistils and a noticeable ‘stretch’ as the plant gains height. Because autoflowers run on a fixed, fast clock, what you do this week directly shapes the harvest.
Recommended Strains
Mazar
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THC | 20% (Medium) |
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Type | Feminized |
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Yield | Medium |
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Phenotype | 90% Indica / 10% Sativa |
Mazar Auto
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THC | 8% - 10% (Low) |
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Type | Autoflowering |
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Yield | High |
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Phenotype | 65% Indica / 35% Sativa |
This guide covers what to expect in week 4, how to feed and set the environment, and the common problems to head off. Keep in mind that autoflower timelines vary a little by strain and conditions, so treat ‘week 4’ as a stage (late veg into early flower) rather than an exact date. Gentle, consistent care beats any dramatic intervention at this point.
| Autoflower week 4 | What to expect |
|---|---|
| Stage | Late veg transitioning into early flowering (pre-flower/pistils) |
| Size | Growing fast; stretch often begins |
| Feeding | Rising demand; transition toward bloom nutrients |
| Environment | Around 68-78°F (20-26°C), humidity ~50% |
Growth Expectations in Week 4
In week 4, expect rapid change. Many autoflowers put on their biggest growth spurt now, stretching upward as they transition, and begin showing sex with white pistils at the nodes, the first sign of flowering. Leaves should be healthy and green, and the plant noticeably bigger each day. Some faster strains may already be entering early bloom, while slower ones are still finishing veg; both are normal.
This stretch is why week 4 is the moment to finalise any gentle canopy management (like light LST) before flowering locks the structure in, heavy training later risks stressing a plant with no time to recover. Give it strong light at the correct intensity and watch the height, especially indoors, so the canopy does not grow too close to the lamp. For light levels on young autoflowers, see our guide on PPFD for autoflowers.
Promos & Deals
Feeding in Week 4
Nutrient demand climbs in week 4 as the plant grows fast and prepares to flower. If you have been feeding light, now is the time to step it up, but gradually: autoflowers are easy to overfeed, so increase strength in small increments and watch for burnt tips. As flowering begins, start shifting from nitrogen-heavy grow nutrients toward phosphorus- and potassium-rich bloom nutrients to support bud development.
Keep the environment dialled in, around 68-78°F (20-26°C) and roughly 50% humidity, and maintain a stable light schedule (many autoflower growers run 18-20 hours throughout). Check pH and feed strength so the plant can actually use what you give it. This is the beginning of the series’ flowering phase; for how plants look a few weeks on, see autoflower week 7.
Common Week 4 Problems
A few issues tend to show up around week 4. Overfeeding is common as growers ramp nutrients too fast, watch for clawed, dark leaves and burnt tips, and dilute if you see them. Light stress can appear during the stretch if the canopy gets too close to the lamp (bleaching or curling up top), fixed by raising or dimming the light. Minor nutrient deficiencies (pale lower leaves) can mean it is time to feed a little more, once pH is confirmed correct.
Avoid the temptation to fix problems with big interventions: autoflowers cannot afford major stress or recovery time now. Make small, measured adjustments, keep conditions stable, and resist topping or heavy defoliation at this stage. If the plant is green, growing and showing healthy pistils, you are on track for a strong flowering phase. To grow more autoflowers, browse our autoflowering seeds.
Watering and Light in Week 4
Watering matters more now that the plant is bigger and drinking harder. Water when the top few centimetres of the medium are dry rather than on a fixed schedule, and water thoroughly so a little drains from the bottom, then let it dry back, this wet-then-dry cycle builds strong roots and avoids the overwatering that stunts fast-growing autoflowers. Larger week-4 plants in small pots can dry out quickly, so check daily.
Light should be strong and consistent. Most autoflower growers keep an 18-20 hour light schedule throughout, and week 4’s stretch is the time to watch the distance between canopy and lamp so the tops do not get too close and bleach. If using a dimmable LED, you can raise intensity as the plant bulks up. Stable light, sensible watering and a steady environment are what carry an autoflower cleanly from week 4 into full flowering.
FAQs About Autoflower Week 4
What should an autoflower look like at week 4?
By week 4, most autoflowers are finishing veg and starting early flowering: expect healthy green growth, a height ‘stretch’, and the first pre-flowers and white pistils at the nodes. Some fast strains may already be in early bloom. Keep conditions stable (around 68-78°F, ~50% humidity) and begin transitioning toward bloom nutrients.
Should I still train autoflowers at week 4?
Only gently, if at all. Week 4 is usually the last moment for light low-stress training (bending) before flowering locks in the structure. Avoid topping or heavy defoliation now, autoflowers run on a fixed clock and have little time to recover from major stress. Small, careful adjustments are safer than big interventions.
When do autoflowers start flowering?
Most autoflowers begin showing early flowering signs (pre-flowers and white pistils) around weeks 4-5 from sprout, though it varies by strain and conditions. Week 4 is often the transition from vegetative growth into bloom, marked by a stretch. From there they fill out buds over the following weeks toward harvest around weeks 8-10.
How often should I water an autoflower in week 4?
Water when the top few centimetres of medium feel dry rather than on a fixed schedule, then water thoroughly until a little drains out and let it dry back. Bigger week-4 plants drink more and small pots dry fast, so check daily. Avoid constant wet soil, overwatering easily stunts fast-growing autoflowers.
