How To Control the Stretch of Cannabis Plants

If you’ve ever grown cannabis, you’ve probably witnessed its ability to double in height seemingly overnight. While it’s perfectly normal for cannabis plants to stretch, especially during flowering, it can become problematic if they grow too tall. To help you get the best results from your grow, we will discuss why plants stretch and how to control the stretching of cannabis plants.

What Is Stretching and Why Is It Bad?

Stretching refers to the rapid vertical growth of cannabis plants. A variety of factors, including genetics, growth stage, light intensity, temperature, and environmental stressors, can cause plants to stretch.

Most strains of cannabis will stretch at some point during their lifecycle. Vertical growth, in moderation, is a good thing. It provides space for the flowers to develop and increases light penetration within the canopy; however, if the plants stretch too much, it can create many problems in the garden.

For indoor growers with limited space, excessive vertical growth can cause the plants to grow too close to the light. When this happens, the tops of the colas can become burnt, reducing the quality and yield of the flowers.

Stretching can also cause plants to become weak and spindly. As the buds increase in size, the stems may not be able to support the weight and will fold over or snap. Additionally, thin stems won’t be able to transport enough water and nutrients to the flowers, which can lead to diminished yields.

Lastly, and perhaps least importantly, stretching can detract from the visual appeal of the plants. Most growers aspire to cultivate big, fat, photo-worthy colas; however, if the plants stretch excessively, you’ll be left with sparse buds with too much internodal spacing.

What Causes Cannabis Plants to Stretch?

The first step in controlling the stretching of cannabis plants is to understand what causes excessive vertical growth in plants. A wide range of factors can affect the structure and development of cannabis.

Growth Stage

Cannabis plants typically display the most vertical growth during the early flowering period. When plants experience a drop in daylight hours, they undergo hormonal changes which result in stretching and bud formation. This is a natural occurrence that allows the plants to absorb as much light as possible to form large, healthy buds. Depending on the plants’ genetics and the environmental conditions they are exposed to, it’s common for them to double or even triple in height during the first few weeks of flowering.

Genetics

Genetics plays a significant role in how much cannabis plants stretch. Typically, Sativa strains display more vertical growth than Indica or Ruderalis strains. This is likely because Sativas originate from the thick jungles of Central America and Southeast Asia, where they must compete with the surrounding foliage for sunlight.

In contrast, Indicas hail from the arid regions of the Middle East, where there is plenty of direct sunlight and little surrounding foliage. As a result, these plants typically remain short and compact throughout the vegetative and flowering periods.

Even within one strain, height can vary among plants. This is especially true with hybrids that have not been inbred for stability. One phenotype can display vastly different traits than another despite having the same genotype.

Light Intensity

Light exposure is another important factor that can impact the growth of a plant. As mentioned above, plants will try to soak in as much light as possible by outgrowing the surrounding canopy. When flowering plants aren’t exposed to enough sunlight, etiolation may occur. This process often causes thin, weak stems, small leaves, and chlorosis.

For indoor growers, stretching could indicate that your light is too weak or too far away from the plant canopy. In outdoor gardens, direct sunlight could be obstructed by surrounding trees, bushes, fences, or buildings.

Temperature

Prolonged exposure to high temperatures can cause cannabis plants to stretch. This is because the plants will attempt to cool off by increasing their surface area and thereby raising the transpiration rate. As the transpiration rate rises, leaf temperature decreases via evaporative cooling. When this happens, you’ll have to water the plants more frequently to keep them healthy.

Limited Space

Cannabis plants need sufficient space to branch out, soak up the sunlight, and form flowers. If they don’t have enough room to form lateral branches, the plants may compensate by growing taller rather than wider.

Crowding the plants together also can result in decreased airflow throughout the canopy. Exposure to wind causes the stems and stalks of plants to thicken. So, if the plants aren’t sufficiently spaced apart, they may grow weak and spindly due to insufficient airflow.

How To Stop the Stretching of Cannabis Plants

Now that you understand why cannabis plants stretch, let’s take a look at the various ways to prevent them from doing so.

Choose the Right Strain

The most effective way to limit stretching in cannabis plants is to choose the right genetics. For indoor growers or those with limited vertical height, Sativa strains may not be ideal. Instead, opt for a hybrid, Indica, or autoflowering variety, as these tend to be much shorter. Most reputable seed banks will list the average height of their strains, so make sure to reference this if you have concerns.

More Light

If you find that your plants are stretching during the seedling or vegetative period, it’s probably a sign to increase the amount of light the plants are exposed to. For indoor growers, you can either use a more powerful grow light or lower the light to be closer to the canopy. How close you place it to the canopy depends on the wattage of the light. Below is the general rule of thumb for light distance with respect to wattage; however, these values may vary depending on the genetics and growth stage of the plants.

  • 150 watts: 8 to 12 inches from the canopy
  • 400 watts: 12 to 24 inches from the canopy
  • 1000 watts: 16 to 30 inches from the canopy

More Space

If your plants continue to stretch after increasing the light intensity, consider spacing them farther apart. In general, cannabis plants should be spaced between 6 and 12 inches apart from the lateral branches. This will provide them enough space to grow outward rather than upward.

Control the Environment

Another way to control the stretching of cannabis plants is to optimize the temperature and humidity of the grow room. The most accurate way to do this is to calculate the vapor pressure deficit (VPD). By dialing in the environmental conditions, you’ll be able to keep transpiration rates in check and regulate plant growth.

Shorter Vegetative Period

The longer you allow a plant to veg, the bigger it will grow during the flowering period. Therefore, if you’re cultivating a strain that is known to be tall in height, consider reducing the vegetative growth period.

Most indoor growers veg their plants for four to eight weeks; however, some bypass the vegetative growth period altogether and provide the plants with 12 hours of light from seed to harvest. While this will reduce the plants’ height, it may also result in diminished yields.

How To Fix Stretched Cannabis Plants

Once your plants have become stretched, there’s no way to reverse it; however, there are some techniques you can use to support the plants and encourage them to become thicker and more robust.

Bury the Stalk

If your plants become weak and stretched, one way of offering support is to plant them deeper into the medium. If you are using containers, you can transplant the plants into taller pots to provide additional support. If you’re growing in-ground, remove the plants and dig deeper holes for them. Just be sure to handle the plants delicately to avoid damaging the root balls.

Increase Ventilation

One easy way to increase the thickness of the stems is to increase airflow in the room. Ensure the fans are blowing on the plants enough to shake the leaves gently. Doing so will provide just enough stress to encourage the stems to grow stronger. Just don’t crank up the fans too high, or you risk subjecting the plants to wind burn.

Plant Training

Growers can use various plant training methods to prevent stretching while supporting the stems of the plants. Some popular ways to limit vertical growth include topping, fimming, and super cropping.

Growers should use these techniques only during the vegetative and pre-flowering periods. Attempting to use high-stress training methods during flowering may result in diminished yields.

If your plants become weak and spindly during the flowering phase, you can support them with a trellis net or stakes. These will help to prevent the branches from sagging or snapping without stunting the growth of the plants.

How To Control the Stretching of Cannabis Plants: Conclusion

A little stretching is natural and beneficial for cannabis plants. After all, the taller a plant is, the more bud sites it can form. But too much of a good thing always turns bad. If your plants become too stretched, you may face light burns, broken stems, reduced yields, and other problems.

Ultimately, controlling plant growth boils down to picking the right genetics, regulating your environment, and training your plants. By following these steps, not only will you reduce stretching, but you’ll also maximize the yield and quality of your buds.

What are your top tips for controlling stretching? Please share your advice in the comment section below. While you’re here, don’t forget to shop our collection of regular, feminized, and autoflower cannabis seeds.

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