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PSA: The Flowering Stretch

by: Sirius Fourside

Right around the time when kids go to junior high, short awkward teenagers go through puberty and turn into taller awkward teenagers. I’m sure you knew of at least one who grew so much, they looked almost as if someone grabbed them by their head and feet and just stretched them out.

When cannabis plants start to mature, they also go through a brief transitional period; a sort of cannabis-puberty if you will. And just as humans as undergo a burst of rapid growth, cannabis plants will also create a large portion of their final height in a short period of time. This explosion of vertical grow this commonly called the ‘Flowering Stretch’.

What is the Flowering Stretch?

The best way to give you an idea is with pictures. Here’s a cool animated .gif Nebula made of one of our grows.

This makes for a great example of how small or large a stretch can be. Notice that the plant on the left (818 Headband) gains only a few inches while the plant on the right almost doubles in size! And even this picture is misleading once you realize that by the end of the .gif, the plant on the left is actually an extra foot higher off the ground!

In short, the flowering stretch is potential burst of rapid growth that happens shortly after switching to the flowering phase. It can be massive, or it can be next to nothing. The important thing is to expect that it might happen and have a plan ready in case it does. Luckily, most strains you buy from a seedbank are stabilized, so it’s known if the plant will stretch a lot or a little. This allows us to not only plan for a stretch, but take advantage of it when it happens!

What to Expect

Depending on the strain you’re growing, you can expect a pretty wide range of stretching. Some strains can double their height, some can do almost nothing. If you know the name of the strain you’re growing, you can get a good idea of what might happen:

Sativas - Sativas tend to grow taller, lanky stems even when trained; inch-for-inch they tend to stretch much more than indicas.
Strain height - Many breeders and seedbanks have the average height of their strains listed. Sometimes it’s as vague as “short - medium - tall”, but even that is enough to give you an idea of its growth characteristics.
Light type - Certain light types are more conducive to stretching than others. You can use the right light color to help control growth characteristics.
Light distance - Plants also stretch when they're trying to get more light (like this plant to the right). As a result of this type of stretching, plants grow taller, but with fewer budsites. Most growers want to avoid stretching caused by not enough light.

One of the main reasons it’s so important to know about stretching is that it can rapidly reduce the amount of space you have in your grow tent/area. If you’re growing in a space with limited height, a good stretch can make it so you no longer have room to raise your lights. This leads to light/heat stress and lost buds.

I personally had a stretch where there was no longer any room to raise the lights. I used a CFL/LED combination at the time, and the LEDs absolutely cooked the buds underneath it until I got desperate and cut the stuff that was too close. I would handle that situation totally differently now, but it shows that no one is immune if they’re unaware.

Planning For the Stretch

Planning for a stretch is easy to do when you know it’s a possibility. There are two things growers can do that will give a lot of control over planning for a potential stretching situation:

Research your strain
If you know what strain you’re going to grow, you can usually find its growth characteristics online. Seedfinder.eu is a good resource of reviews on strains submitted by other growers. While it isn’t necessarily 100% accurate by its nature, it should give you a good range. Knowing the strain you’re growing gives you the power to decide how much stretch you’ll deal with. Since stretching is often accompanied by a ‘tall’ final height, you can reduce stretch by getting plants that are characterized as being ‘medium’ or ‘short’.

Plan for your lights to go higher
Many stealth growers plan out every inch of height to be used so they can make their grow spaces small and sneaky. But what happens when your light can go to a maximum of 36”, and your plants stretch to 32” tall? Training will definitely help, but having your light go up a few inches would be nice at this point, wouldn’t it? It’s always a good practice to make sure your light can go up a bit further than you think it’ll need to. Sometimes an extra 3 or 4 inches makes a world of difference.

Pre-Stretch

Post-Stretch

Reducing the Stretch

Since we know the factors that can lead to more stretching, reducing how much a plant stretches is just a matter of acting on those factors.

Genes: Indica plants tend to be shorter. If you prefer Indicas, you’re in luck. If you like Sativas, you can also find many strains that have a shorter finishing height. Again, you can usually find the heights of strains at the websites of breeders and seedbanks.

Light type - Did you know that HPS (High Pressure Sodium) lights encourage stretching? You can combat this by leaving your MH (Metal Halide) bulb in for the first 2-3 weeks of flowering, and then switch to the HPS bulb.

This also goes for CFL growers who are utilizing vegetative (6500K) and flowering (2700K) colored bulbs. You can leave the vegetative colored bulbs in for the first 2-3 weeks of flowering before switching to your flowering bulbs.

Light Distance - Keeping your lights as close as they can comfortably be will ensure that your plants don’t have to stretch to get more light. Use the ‘hand test’ to make sure your lights are as close as they can be without harming your cannabis.

Hand test: Place one of your hands right over your plant with your palms facing downward. Your hands should be less than a ¼” away from the top of your plants or lightly touching the top.
If the heat from your CFL or HPS lights is uncomfortably hot or painful to your hand, move the lights away an inch and try again.
This test does NOT work for LED lights.

Plant Training - Although training itself does nothing to slow down stretching, it does give growers a good way to manage it. For example, if branches are set to grow vertically by low-stress training, a stretch can actually be beneficial since so much of the plant will be receiving light. Plant training can come in the forms of low-stress training, mainlining, topping, fimming, and more.

Making the Stretch Your Friend

For those with larger grow spaces, such as 7'+ tents or custom made grow spaces, stretching can actually be a part of a growing plan.

Example: Let’s say you’re growing a cannabis strain with a predictable stretching pattern in DWC (Hydroponics). Let’s also say that you have 2-3 extra feet of vertical growing space to fill in your grow tent and it’s time to switch to the flowering phase.

A mainlined cannabis plant would definitely take advantage of this situation; in fact, it’s what I do! Mainlining creates a ‘manifold’, which is essentially a more efficient way for colas to grow. Once this manifold is created, the plants can grow 2-3 inches before we purposefully stretch them whilst keeping the lights close. What remains is 8 loooong colas with buds growing all the way down. In this case, we made the stretch increase our yields while utilizing more of our grow space.

With that being said, I would only advise that you purposefully stretch plants when you have intimate knowledge of their growth patterns. This doesn’t mean that you have to have grown the strain before although it helps. What it does mean is that this strategy is much easier to run successfully when you do some research into the growth patterns of the strain you’re planning to cultivate.

The ‘Flowering Stretch’ is another piece of knowledge that makes growing cannabis much more easy once you know about it. I’ll leave you with a picture of when I got blindsided by a stretch and had no idea what to do (yet again). Don’t let this happen to you, too!