Can I top an auto-flowering cannabis plant?

Updated May 31, 2020

by Nebula Haze

Yes, healthy auto-flowering plants respond well to being topped as long as they have at least 4-5 sets of leaves and haven’t started making buds yet. Usually around the end of week 3. Avoid topping a flowering or slow-growing plant to prevent the chance of stunting.

Diagram example - how to top an auto-flowering cannabis plant

When it comes to growing auto-flowering cannabis strains, there is a lot of controversy about whether they are compatible with the cannabis training technique known as topping (cutting off the tip of the plant while it’s young to improve plant structure and yields). This is because topping an autoflowering plant can go wrong if you don’t do it right.

Topping the right way helps keep autoflowering plants short and bushy with many buds

Two cannabis plants grown under a 315 CMH grow light, about to get trimmed!

But be careful! This autoflowering plant was slow-growing and got topped after buds started forming. As a result, it stayed small and stunted.

Autoflowering plants can produce a sea of fat buds when topped properly. This helps maximize yields under a grow light.

Example of flowering cannabis plants that were grown under a 315 LEC grow light

Autoflowering plants can still produce great yields without topping, but untopped plants are more likely to get tall and usually only grow one main bud

Example of several marijuana plants that are growing under two 300W ViparSpectra lights

Many growers say you should never top an auto-flowering plant, while others claim they can top their autos without a problem. How can there be such a big difference in results between different growers? Well, here’s the thing about topping autos….

Topping auto-flowering cannabis strains is often discouraged because plants may not recover in time. Due to their short life cycle, proper timing is crucial to success.

Auto-flowering marijuana strains have a short timeline, which is why it's usually recommended not to top them

Auto-flowering cannabis plants are on a tight schedule. Most auto-flowering strains start flowering at 3-4 weeks from germination and typically stop getting bigger by the time they’re 6-7 weeks old. After that, buds keep fattening but the plant stops growing new leaves and stems.  It’s difficult or impossible to change an autoflowering strain’s individual time schedule.

Most auto-flowering plants have achieved “full size” by the time they’re 6-7 weeks old. For example, these autos were 7 weeks old and didn’t get any bigger despite needing 4 more weeks before buds were mature enough to harvest.

The short 6-7 week grow period means that if your auto-flowering plant is shocked and stops growing for even a week or two, plants may stay dramatically smaller. A tiny cannabis plant is going to yield a lot less than a full-sized one. That’s why many growers say to never to top your autos. You want a good sized plant instead of a undersized plant to get the best yields from autoflowering cannabis plants.

For a first-time grower of autos, it can be easy to stress the plant and stunt its growth for all kinds of regular reasons. Topping just throws another factor into the equation. If an auto-flowering cannabis plant get stunted early on, it often stays tiny its whole life.

A stunted autoflower won’t produce great yields because it can’t support big buds. This plant wasn’t topped, but it suffered from deficiencies and problems during the first few weeks of life that kept it small until after buds started forming. Topping would have only stunted it more.

Even though the above grower took really great care of this plant from here on, and got pretty good yields for such a small plant, he would have harvested far better yields if the plant had gotten bigger during the first few weeks of life.

An auto that grows big can yield a lot, even if it’s untrained like this one. That’s why many growers believe topping is not worth the risk of stunting. You couldn’t yield all this bud on a small runty plant no matter what you did.

This auto-flowering cannabis plant was allowed to get much bigger, which allowed it to produce much greater yields

And you don’t need to top your plants to get multiple big buds anyway. These autos were trained with just LST/bending and they all have multiple tops. However, I will say that this took me a lot more time and effort than simply topping them.

Topping isn’t necessary to get multiple colas. There are alternatives such as LST/bending.

3 Auto-flowering marijuana plants trained to grow with multiple tops using just LST and bending - no topping!

All that being said, topping an auto usually goes great when you do it right. If you have a healthy, fast-growing young plant, topping will likely not stunt it at all.

So it’s not a matter of whether you should or shouldn’t top autos. It’s more about evaluating how your plants are growing and deciding if the reward is worth the risk in your particular situation.

When it’s Not Recommended to Top Auto-Flowering Plants

  • it’s your first grow
  • plant has deficiencies
  • plant is drooping
  • plant is growing slowly
  • plant is more than 3-4 weeks old
  • plant has started flowering (little white hairs are growing at the joints)
  • plant has less than 4 sets of leaves by the end of week 3 (that means the plant is too slow-growing)

These two plants are the same strain. The left plant was topped at the proper time, but the right plant was topped after buds had already started forming. The late topping caused it to stay small and stunted. The smaller plant still produced good buds, but yields were about half that of the full-sized plant.

Note: If you’re trying to grow really small plants (for example in a tiny grow space), you may actually want to stunt your plant’s size on purpose. If that’s the case, cutting off the top after you already see buds is a good way to do it 🙂

When You Should Top Auto-Flowering Plants

  • plant is green and healthy
  • plant is growing quickly (you’re seeing new growth every day)
  • plant has grown at least 4-5 nodes (pairs of “real” leaves) by the end of week 3; this isn’t a hard-and-fast rule, it just demonstrates that your plant is growing fast enough to handle being topped without stunting
  • plant is not flowering (no white hairs at the joints)

To actually top the auto, pinch off the top set of leaves. Try to remove as little plant as possible if you’re trying not to stunt its growth.

Only cut off the tip when topping an auto!

Diagram example - how to top an auto-flowering cannabis plant

Don’t cut off more than this when topping an auto-flowering marijuana plant

Never take off more than this when topping auto marijuana plants!

Conclusion: Topping an auto-flowering strain can be good or bad, depending on how it’s done.

There are times when topping an auto-flowering marijuana plant makes sense, and times when it doesn’t. In some situations, topping an auto may reduce yields by stunting the plant overall. But for more experienced growers, topping is a great training tactic.

Use the guidelines in this article to decide what’s right for you. When in doubt, use LST/bending instead because it can accomplish nearly the same thing without much chance of stunting your plant.

I hope this information helps guide you to make the right decision for your auto-flowering marijuana garden! Here are a few more resources you may enjoy.

 

 


 

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