Veg Duration Estimator
Two calculators in one. Plan mode recommends how long to veg based on training method, strain, tent height, and pot size — including stretch math so you know exactly how much headroom you'll have after flip. Check mode answers the daily question: is my plant ready to flip right now? Input current height and SCROG fill and get a clear verdict.
Plan your veg or check flip readiness
About this mode
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Pick a mode above.
Common veg timing mistakes
- Flipping based on weeks, not readiness. "Week 4" doesn't mean anything without knowing training method, plant size, and ceiling height. The calendar is a rough guide — your plant's state is what matters.
- Underestimating flower stretch. Plants typically double in height after flip. Sativas can triple. Flip at 24" in a 5ft tent and you'll be bending plant tops away from the light by week 4 of flower.
- Flipping SCROG before the net is ready. The whole point of SCROG is canopy fill. Flip at 50% fill and you wasted the training — flip when 70–80% of net squares are covered.
- Assuming sativas need shorter veg. They grow faster per week, so they reach flip height faster — but that's not the same as needing less time. Sativas also need more height clearance for aggressive post-flip stretch.
Recommended veg
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weeks
Flip height
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inches
Final height est.
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inches
Headroom
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inches left
Stretch multiplier
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×
Rationale
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Space note
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Plan before you start, check while you grow
Use Plan mode at grow start
Before planting or taking clones, set your training method, strain type, tent height, plant count, footprint, and pot size. The tool returns a recommended veg duration range plus stretch math — the estimated final height after flip and how much headroom you'll have below the lights. This is the "does my plan actually fit the tent?" check. If the stretch math shows negative headroom, adjust flip height or switch to a training method with better height control before you start.
Switch to Check mode during veg
Starting at week 3 of veg, check every 3–5 days. Measure plant height from soil surface to the tallest tip, enter it in Check mode. The tool tells you where you stand: too-early, approaching, ready, overdue, or ceiling-risk. Each verdict includes the stretch math at your current height so you can see what the final plant will look like if you flip right now. For SCROG, enter net fill percentage — the flip decision for SCROG is fill-based, not height-based.
Respond to the verdict
Too early: keep vegging, check back in 3–5 days. Approaching: start preparing your flowering environment (calibrate meters, verify VPD targets, get nutrients transitioned). Ready: flip now or within the next few days. Overdue: flip immediately — further delay means more aggressive stretch and increasing ceiling risk. Ceiling-risk: flip now and consider top-bending or super-cropping to prevent the plant from burning the light.
For SCROG: check fill percentage, not height
SCROG plants are intentionally kept short — height isn't the right metric. The flip decision is net fill: you want 70–80% of the net squares filled with tucked branches before you flip. Under-filled means an incomplete canopy and sub-optimal yield; over-filled means unmanageable density in flower. Measure fill visually from above — count squares with a branch under them vs empty squares. Check mode's SCROG output shows fill state (empty / partial / mostly-filled / full) and guidance.
Why the sativa modifier reduces veg time (not increases it)
The legacy veg calculator had this backwards. Sativa-dominant strains grow faster per week in veg — they reach the target flip height in fewer days than indica-dominant strains, which grow bushy and slow. But sativas also stretch 1.8–3× after flip (vs 1.3–1.6× for indicas), so you actually need more height clearance, not less. The tool accounts for both: shorter veg recommendation (they get there faster) plus aggressive stretch math (they grow a lot after flip). If you're running a true sativa in a 6ft tent, either keep the flip height under 18" or plan to bend/tie canopy away from lights in early flower.
Stretch factors, pot constraints, and why training method is the dominant variable
Veg duration isn't an input you choose from a fixed menu — it's the output of several interacting constraints. Training method sets the structural target. Strain type modifies growth rate. Pot size caps maximum plant size via root volume. Tent ceiling sets the hard physical limit via post-flip stretch. Most existing veg calculators ignore training method entirely (the biggest variable) and use a simple weeks × strain modifier — which produces answers that are wrong by 2–6 weeks for non-trivial training setups. The Growing Overview covers the basics; this section covers the biology and physics behind the timing math.
±6 wks
Training method swing
SOG flips at 1–3 weeks. SCROG needs 6–10 weeks to fill the net. Same strain, same tent, entirely different veg duration — training method is the primary driver.
1.3–3×
Post-flip stretch range
Plants grow significantly after 12/12 flip. Indicas 1.3–1.6×. Hybrids 1.5–2×. Sativas 1.8–3×. Your flip height × multiplier = final plant height. This number must fit under your lights.
14"
Minimum lights clearance
LED lights need 12–18" clearance from canopy. HPS/CMH needs 18–24". The tool uses 14" as a conservative LED default — subtract this from tent height for actual plant headroom.
Why training method dominates
The purpose of veg is to build the canopy structure you intend to flower. Different training methods require different canopy states before flower is productive:
| Method | Flip trigger | Typical veg | Why this timing |
|---|---|---|---|
| SOG | 6–12" height reached | 1–3 weeks | Many small plants, each with one main cola. Speed of cycle is the strategy — high density compensates for individual plant size. |
| LST | 12–20" with spread branches | 3–6 weeks | Need enough branch development to tie horizontally and create a wide, flat canopy. Flip too early and there's not enough to work with. |
| Untrained | 14–24" height | 4–6 weeks | Standard growth. Flip height calibrates to tent size and expected stretch — taller tent allows taller flip height. |
| Topped | 16–28" with multiple tops | 5–7 weeks | Topping requires 7–10 day recovery before nodes resume growth. Need time for multiple tops to develop evenly before the flip. |
| SCROG | 70–80% net fill | 6–10 weeks | Flip decision is canopy fill, not height or weeks. Under-filled = incomplete canopy = wasted net. Over-filled = unmanageable density in flower. |
Post-flip stretch — the physics
The "stretch" after 12/12 flip is a hormonal response. When photoperiod drops to 12 hours, the plant detects shortening days and triggers reproductive mode. During the first 2–3 weeks of 12/12 (the transition phase), significant gibberellin production drives internode elongation — the same hormonal mechanism that causes vegetative stems to stretch in spring for outdoor plants. This stretch typically continues for 1–3 weeks after flip, then stops as flower development dominates the plant's resources.
Indica-dominant strains carry Cannabis indica genetics, which evolved in highland climates with short, intense summers. Their stretch is compact (1.3–1.6×) because their native environment didn't reward tall vertical growth. Sativa-dominant strains evolved in equatorial climates where tall, leggy growth was adaptive — their stretch response is aggressive (1.8–3×) because the genetic programming says "grow tall fast." These aren't arbitrary multipliers — they're emergent phenotypes from distinct evolutionary pressures.
Why pot size constrains veg duration
Root volume limits canopy volume. A plant's root system mirrors its canopy — to support a large aerial structure, a plant needs a proportionally large root mass. When roots fill the pot (rootbound), the plant hits a hard wall: nutrient uptake decreases, water stress increases, and growth rate stalls. For a 3-gallon pot, the root wall typically arrives after 3–4 weeks of active vegetative growth. For a 10-gallon pot, 7–8 weeks of veg is sustainable before rootbound becomes a limiting factor.
The practical consequence: if your training method recommends 6–8 weeks of veg but you're in 3-gallon pots, the pot will rootbound before the net fills. Either upsize to 5–7 gallon minimum for SCROG, or shift to a training method compatible with smaller containers (LST or topped in 3-gallon works; SCROG in 3-gallon doesn't).
Where the numbers come from
Training method veg duration ranges derived from consensus grow community data (Rollitup, GrowersNetwork, IC Mag growing guides) cross-referenced against multiple published cultivation references. Stretch multipliers (indica 1.3–1.6×, hybrid 1.5–2.0×, sativa 1.8–3.0×) are empirical population medians from published phenotype variance data and grow community reports — individual strains vary significantly within these ranges. Pot size constraints based on root-to-shoot ratio research from horticultural literature (general container horticulture, applied to cannabis context). Lights clearance (14") is the LED manufacturer minimum recommendation; HPS/CMH requires 18–24".
Common veg timing questions
How do I know when my plant is actually ready to flip?
For photoperiod plants, the answer depends on your training method. Untrained/LST/topped: check height against the flip range for your method and verify the stretch math fits your tent. SCROG: check net fill — 70–80% of squares covered is the flip trigger. In all cases, the plant should also show vigorous growth (not stressed), healthy internode spacing, and no signs of pest or deficiency issues before flip. A stressed plant carries its problems into flower — better to address issues in veg than flip into a problem grow.
What happens if I flip too early?
The plant flowers at whatever size it is at flip — no more vegetative growth happens. Early flip produces smaller plants with less surface area for bud sites, lower yield potential, and (for SCROG) an underfilled net that defeats the purpose of the training. The one scenario where early flip is intentional: SOG. That's literally the strategy — many small plants flipped early, high density compensating for individual size. For any other training method, early flip is usually a mistake.
What if my plant outgrows my tent before the flip window?
Flip immediately — that's the ceiling-risk verdict. The post-flip stretch will be on top of current height, not instead of it. If the plant is already 30" and will double in a 6ft tent, you have a serious problem waiting to happen. Options: flip now and accept the early flip tradeoff, super-crop or top to reduce main cola height (requires recovery time), or LST the tallest branches horizontal to manage canopy height in flower. For future grows, reduce flip height: plan for the final stretched height to be tent height minus 14" (lights clearance), then back-calculate the flip height by dividing by the strain's stretch multiplier.
Can I veg under 12/12 light to keep a plant small?
No — photoperiod plants flower under 12/12. Starting a photoperiod strain under 12/12 will trigger flowering from the seedling stage, producing tiny plants with minimal yield. For small plants with fast cycles, use autoflowers (they flower regardless of light cycle) or run 18/6 for veg and flip at a shorter height. Some growers run 14/10 or 13/11 as a "faster flowering" veg schedule but this can cause some strains to begin pre-flowering early — not recommended without knowing your strain's photoperiod sensitivity.
Why does the tool show different veg times for sativa vs indica when the training method is the same?
Growth rate in veg. Sativa-dominant strains grow faster vertically per week — they reach the training method's target flip height in fewer days than indica-dominant strains, which grow bushier and slower. The tool applies a -7 day modifier for sativas (they reach flip height sooner) and a +7 day modifier for indicas (they take longer). This is different from flower time or post-flip stretch — it's specifically about how quickly the plant builds the canopy structure needed for the chosen training method in veg.
How much does topping affect veg time?
Topping adds 7–14 days to veg compared to untrained. After you top (or FIM), the plant goes into a recovery mode — the wound response redirects growth hormones, slowing height gain while the plant develops two (or more) new growing tips. This recovery takes 7–10 days. You need those new tops to develop some size before they're worth flowering, which adds another week. Multiple-topping strategies (topping the new tops as well) add another recovery cycle each time. The rule of thumb: each topping event adds roughly one week to veg time.
Is there a maximum veg time beyond which the plant suffers?
Not from veg time alone, but from the constraints that come with long veg. The practical limits are: pot size (rootbound risk increases with time in the same container), available space (plant eventually outgrows the tent), and nutrient buildup (salt accumulation in soil over many weeks). If you're repotting and have the space, plants can veg for months — commercial mother plants are kept in veg indefinitely via light-schedule control and regular repotting. For home grows in a fixed container and tent, the pot-size constraint is usually the binding limit.
Does the Veg Duration Estimator work for autoflowers?
Not meaningfully. Autoflowers begin flowering on their own schedule (typically 3–5 weeks from sprout) regardless of light cycle. The "veg duration" for an auto is fixed by genetics, not by the grower's flip decision. Selecting autoflower in this tool fires a warning because the concept of a controlled flip doesn't apply. For autoflower timing, use the Germination Calendar which handles auto lifecycles correctly without a flip event. The stretch math is still relevant for autos (they also stretch after pre-flowering begins), but the flip readiness check is not applicable.
Training gear and veg supplies
The training method you choose determines your veg duration, plant structure, and ultimately yield ceiling. Most training gear is cheap; what matters is choosing the right method for your space and committing to it. SCROG nets are the highest-ROI training investment if you have the patience for 6–10 week veg.
SCROG nets & frames
Trellis nets for 4×4 and 5×5 ($15–30), adjustable frame systems ($40–80), net clips. SCROG produces the most even canopy and highest yield per sq ft of any training method. Requires 6–10 week veg commitment. 5cm squares are standard for most photoperiod strains.
LST wire, clips & ties
Plant training wire ($8–15), soft-tie velcro ($6), bending clips for stems, bamboo stakes. LST is the lowest-stress, most beginner-friendly training method. Start bending branches outward from week 2 of veg. Cheap and effective for a single-plant setup.
Fabric pots & containers
3-gallon (SOG), 5-gallon (standard), 7-gallon (SCROG/topped), 10-gallon (large single plant). Fabric pots allow air pruning of roots, preventing rootbound and extending viable veg time vs plastic. Match pot size to training method — SCROG needs 5–7 gal minimum.
Measuring tools
Retractable tape measures, plant height markers, canopy rulers. Checking height every 3–5 days is the core habit that makes Check mode useful. A basic tape measure works; some growers use a stick marked with their flip height target so it's a one-second visual check.
Veg nutrients
High-nitrogen veg formulas, Cal-Mag for coco and RO water, root stimulators for early veg. During veg, nitrogen drives vegetative growth — plants need 3:1:2 N:P:K ratio approximately. Pair with the Nutrient Schedule Generator for a full feeding plan aligned with your veg timeline.
Veg lights
Full-spectrum LED panels for veg (300–600W), T5 fluorescent bars for low-heat veg ($40–100), CMH for combined veg/flower. Veg lighting target: 300–600 PPFD at canopy, 18/6 schedule. PPFD/DLI Calculator helps verify your specific setup hits target.