When To Switch From Veg To Flower? Get All the Answers from Kyle Kushman

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When to Swich from Veg to Flower
Author avatar By Kyle Kushman
November 18, 2021
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The flowering stage of your growth is a super-exciting time.

Your plant changes dramatically, developing sticky buds and colas, piling on the pounds, and stinking out the tent (in the most amazing way possible).

Unless you’re growing autos, it’s up to you to know when to switch from veg to flower. Known in trade as flipping.

I’ll show you when and how to flip your plants, how to adjust the feeding and plan for the stretch, how to get it all right.

The point at which you flip has a massive bearing on final yield, and knowing when to flower your own marijuana plants can be the difference between an average or super-heavy harvest.

So get yourself comfortable, kick off your shoes and relax. In 10 mins you’ll know exactly how and when to switch from veg to flower.

I got you. Let’s roll.

Cannabis in early flower
Cannabis in early flower

What is the veg to flower transition?

Your cannabis plant has four growth stages: 

  • germination (3-10 days); 
  • seedling (2-3 weeks); 1-3
  • vegetative (3-16 weeks); 1-10
  • flowering stage (7-11 weeks).

During the vegetative phase, the plant grows new shoots and develops its root system. 

The change to flowering represents sexual maturity, when the plant is ready to produce buds or pollen sacs.

Plants know when to switch to flowering because the sun tells them. They sense the shortening days and know they need to reproduce before the end of their life.

Indoor growers replicate nature by mimicking the light schedule, flipping from 16 hours to 12 hours of continuous light. Continuous darkness of 12 hrs is what makes them flower.

Knowing how to grow cannabis indoors is knowing how and when to do this.

I’m going to explain it all here, but I want you to check out my flipping video first.

See you in five minutes!

When to switch from veg to flower

Okay, let’s get into it. How big is your tent? How much vertical space do you have? This is crucial information, the most important factor in determining when to start flowering. 

Your plants can double or triple in height after flipping and you don’t want them to outgrow the tent. Nor do you want to waste the space and produce smaller yields than you had to.

You should measure from the base of your plant to around 12 inches below your lights. When your vegging plants reach about one third of this height, you can flip into flower.

Did you know? If growing outdoors or in a greenhouse, you can use light-deprivation techniques to cause your plants to flip. 

Cannabis plant
Cannabis plant

How to transition from vegetative to flowering, step by easy step

Step 1: Switch off lights for 12 hours per day, uninterrupted

When you start flowering, you need to switch your lighting from 16–20 hours (depending on strain) during the vegetative stage to 12/12 to induce flowering.

12/12 means your plant should receive an equal amount of continuous light and darkness each day.

Step 2: Focus on the climate

Reduce the relative humidity from 50–70% in veg to between 40–60% when you start flowering.

This can help prevent mold, mildew and other problems.

Increase Co2 beyond standard atmospheric conditions using a Co2 kit or increasing the air exchange rate.

Stay within the optimal flowering temperature range of 68–82°F.

Temperature measurement device
Temperature measurement device

Step 3: Protect your plants

It’s far easier to deal with pests and diseases during the vegetative stage. Check for problems before you flip into flowering, they’ll be harder to treat in full flower!

Step 4: Adjust the nutrients

When you start flowering cannabis, don’t feel you have to overfeed.

You need to start adjusting the feeds to include more magnesium and phosphorus, while reducing the amount of nitrogen.

Tip: make sure you slowly switch the nutrients to avoid stressing the plant.

Kyle feeding weed plant
Kyle feeding weed plant

Other stuff to think about

Knowing when to start flowering cannabis plants 

Commercial growers keep their plants in the vegetative stage for around 60 days. For you, it will be determined by the space you have in the tent / room.

If you’ve transplanted recently, give your cannabis plant at least two weeks to recover before making the veg to flower transition.

After low or high-stress training, give your indoor plant time to heal, grow more shoots, and get used to the environment you’ve placed it in.

A happy and settled plant is also a productive plant!

Cannabis in veg
Cannabis in veg

Plant height: this is vital!

If you’re lacking in vertical space, you’ll need to make the veg to flower transition much earlier.

Most cannabis plants double or triple in size when flowering, with the most dramatic changes happening during the first three to four weeks.

Make sure there’s enough space overhead (at least 12 inches) from the top bud to the lights. 

Did you know? Some lights run cooler (LEDs, for example) so you can grow the plants a little closer. 

Genetics (indica, sativa, or hybrid)

Your plants might be short indicas / indica-doms or taller sativas / sativa-doms.

Generally, when you start flowering you can expect indicas to double in height, sativas can stretch up to three times the pre-flip height. This is only a general guide, not a hard and fast rule. Most modern strains are hybrids and you should confirm the final height / stretch with your supplier.

If you’re only just learning how to flower cannabis, you’ll want a nice, uniform set of plants.

This means keeping your canopy even through trimming and training, and growing plants of the same cultivar.

Growing techniques

Growing techniques promote even light distribution to the budding sites.

Let’s look at when to start flowering cannabis in conjunction with some basic training techniques.

Sea of green (SOG)

You flower earlier with a SOG, a technique more suited to indica / indica-dominant cultivars.

Knowing when to start flowering weed in a Sea of Green is plant and set-up dependant, but you’re generally going to flip when the plants are about a foot tall.

Cannabis SOG
Cannabis SOG

Screen of green (ScrOG)

The veg to flower transition happens later with a ScrOG, once your plant has spread out nicely and is happy in the weave.

As the plant stretches post-flip, your focus will be on maximizing the number of bud sites that receive light.

Weed Screen of green
Weed Screen of green

Lollipopping

Lollipopping marijuana means cutting off lower growth so energy for the top chunky buds isn’t wasted below. 

Flipping when lollipopping depends on your plant’s height. Knowing when to switch from veg to flower in lollipopped strains is crucial. 

You should switch sativas early because they usually double (sometimes even triple) in height during flowering.

Switch “lollipopped indicas a little later.

Supper cropping weed
Supper cropping weed

What to expect after you start the veg to flower transition

You’ll notice rapid growth in the first 2–3 weeks of flowering, as the plants beef up to support the growing buds.

During the veg to flower transition, you’ll see tiny pistils that stack in the thousands to form buds. The buds then join to form colas.

The female plant then starts producing huge amounts of sticky and clear resin on leaves and buds. This resin contains the most significant quantity of THC and CBD. Use a lighted loupe or a magnifying glass to amplify your view of that glorious, delicious, sumptuous resin.

Depending on the strain, the buds might become so heavy they’ll need support.

Key Takeaways about when to flower cannabis

Cannabis is an incredible plant. It has lots of quirks that set it apart from its cousins; the key among them is the veg to flower transition. 

Let’s recap:

  • Change your light schedule to 12 hrs or more to switch from veg to flower.
  • It’s not all about the lighting—the climate and nutrients need to change as well.
  • Never put a stressed plant into flower.
  • Consider the space for your particular strain.
  • Outdoor growers rely on the seasons and don’t have much control as indoor growers.
  • Autoflowering plants switch to flowering no matter the amount of light they get—such varieties usually flower after 3 to 4 weeks in veg.
Marijuana early flower
Marijuana early flower

How tall should the plant be before switching to flower?

It depends on the genetics of the plant (tall sativas / bushy indicas) and your grow area. Use the height of your grow tent as a reference showing when to switch from veg to flowering. 

Should I flush before switching to flower?

Don’t flush before flowering unless there are lockout issues due to toxicity. 

Plants need nutrients, especially in early flowering, as they bulk up for the buds. Depriving the plant of nutrients at this stage only hurts your final yields. 

Flush a week or two before harvest for a smoother smoke. The first week of flowering should be treated as your last week of veg.

How many nodes should I have before flowering?

The number of nodes you have depends on genetics, meaning you can’t rely on this figure for making the switch.

You just need to ensure the top buds receive maximum light in relation to your surface area.

Maybe you did a SOG or ScrOG, which can offer you a different number of nodes every time before any veg to flower transition.

Does longer veg time increase yields?

Most definitely! If space isn’t an issue for you, let your plant stay in the veg stage as long as possible.

If you live in a climate that allows you to start growing in the spring and harvest in the fall, take advantage of it, since some strains could easily reach for the sky with a long vegetative stage!

Can you veg and flower in the same room?

No—unless all your plants are autos. 

Note that the veg to flower transition requires different environments as well. For example, flowering plants need slightly lower temperatures and humidity.

Do plants need more water during flowering?

Like any fruit, the buds are full of water, so cannabis needs more water than ever after the veg to flower transition.

You’ll notice more demand for water as the pistils and calyxes grow larger, with the roots absorbing more water that goes straight to the succulent buds.

Kyle with flowering cannabis
Kyle with flowering cannabis

Flipping into flower

It can be confusing when switching from veg to flower, hopefully, this article and my video will have helped!

You should now know what to consider before making your decision, the best times to transition, and why you’d want to make the switch late or early. Check out our other blogs here at Homegrown Cannabis Co. for a whole host of tips and tricks for getting the most out of your plants.


About the Author: Kyle Kushman

Kyle Kushman is a legend in the cannabis community. He is the modern-day polymath of pot: cultivator, breeder, activist, writer, and educator. After winning no less than 13 Cannabis Cups, there’s nothing this guy doesn’t know about indoor growing – he’s been there, done it, and is still doing it to this day!