[Sticky] How to Control the Stretch in a Cannabis Plant
As a cannabis plant transitions from the vegetative stage, to the flowering stage, it will go through what is known as, the “Stretch”. This is different to other types of stretch that can come from stress, or light problems. The stretch is a natural part of the cannabis plants life cycle. It is also called regenerative growth.
A cannabis plant will grow taller throughout its flowering phase, but for around 2 weeks after the "flip" the plant will show the most dramatic change in height and internodal spacing.
Most growers like to grow dense colas, rather than lots of small nugs. Because of this, the stretch isn't a desired trait in some grow rooms. Especially as height can be an issue when growing cannabis indoors.
If you have any questions about controlling the stretch, then feel free to ask for help in our cannabis growers forum
Can stretch be useful
Some growers will encourage stretch. It can be a good technique to prevent bud rot in susceptible strains with bigger flowers. Having more space between the buds will give better air circulation, and prevent mould spores from germinating.
Why stretch can be a problem
If the stems on a cannabis plant stretch too much, they will not be able to hold the weight of the flowers as they get bigger. This can cause buds to fall over, and become rotten. Also, stretched out branches will give numerous small buds, rather than big colas.
Stretch is also a problem for growers with limited height. A cannabis plant can stretch so quickly, that if not checked on regularly, the plant can grow too close to the light and suffer burn.
Reducing The Stretch
First off, you need to consider how much space you have before you buy your seeds. Indica dominant strains will not grow as tall as sativas. If you have a small space, choose an indica dominant strain, or an auto flowering haze.
Grow a Small Strain
Indicas tend to have minimal stretch growing characteristics in flower compared to tall-growing sativas. Hybrids will be a little more unpredictable if grown from seed, as the phenotype may express more tall characteristics.
Use blue spectrum light
Because the light produced by metal halide bulbs is in the white-blue spectrum, it encourages vegetative growth and "bushyness" while discouraging upward growth.
HPS bulbs are the best lighting source for flowering. However, because they have a light spectrum concentrated in the far red, and have no blue, they can encourage stretching.
It is recommended to keep a MH light for up to 2 weeks after "flipping" to 12/12. Changing to HPS when you see the first signs of flowers forming will reduce the amount your plant will stretch. Flowers forming will mean the stretch is over.
Minimise day/night temperature fluctuations
A cannabis plants internodal spacing is directly related to the difference between day and night temperatures. Tests have shown that the further apart your day cycle temps are, from your night cycle temps, the greater your internode spacing will be.
If you keep lights off temperatures within 5c of lights on temps, you will have shorter internodes.
Reduce Nitrogen after Flipping
Nitrogen is used by the cannabis plant for many things, one of which is growing leaves and stems. After the vegetative stage is over, the plant will use less nitrogen.
It is important to reduce the amount of nitrogen available to the plants during the stretch. If there is an abundance of it, the plant will keep using it to make stems, which will inturn give you longer stems.
Reduce your nitrogen in your feed by 50% as soon as you flip your lights to 12/12. This will give the plants less nitrogen, so they will make less stems and branches.
Controlling Stretch in a Cannabis Plant
Stretching can be a physiological reaction to a variety of environmental stresses (low light, high humidity, low/high temperatures, transplant shock, leaf loss, etc). Maintaining optimum growing conditions is your best defense against stretch.
The stretch can happen at anytime during the grow cycle. For better flower formation, and a better density at harvest time, apply the following techniques to reduce stretch before flowering.
- Use MH lights during vegging and the first 2 weeks of flowering (during the stretch phase) for short internodes.
- Avoid high levels of nitrogen during the stretch. Try using a nutrient that has a ratio of (1-1-1) during the early stages of flowering
- Control lights off temperatures and keep them within 5c-10c of Lights on Temperatures
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