Marijuana plants stretch for a variety of reasons. Genetics is the most obvious reason.
Some plants are programmed to produce long stems no matter how much you try to prevent
it. Sativa strains that grow tall outside will do the same when indoors. Excluding genetic
factors, there are some things that gardeners can do to decrease stem length between leaves.
Strong air circulation can create stem and leaf movement that strengthens and
widens the stem while also slowing its vertical growth. Winds will bend the stem,
creating infinitesimal tears in the plant’s tissue. The plant will then quickly
mend these small tears by growing new tissue. Simply brushing or bending the leaves
and stem can mimic the benefits provided by air circulation and, thus, widen and
strengthen the stem. Download my free marijuana grow bible and learn more about
The light spectrum can also serve a purpose when it comes to controlling height.
Blue light will promote shorter, sturdier stems while red and orange light will
stimulate longer, skinnier stems. If exposed to metal halide lamps during vegetative
growth, plants will have shorter stems. If exposed to high-pressure sodium lamps,
they will have longer stems.
Infrared light, which is invisible to human eyes, can also be used to help maintain
plant height. It is used when the lights are off and is produced by heat lamps
(which also emit some red light). A black cotton cloth will cover the heat lamp
reflector, allowing the infrared rays to produce the desired effect while also
capturing red light to avoid negating the effect. Even so, infrared light can
also induce flowering and should really only be used during flowering.
Heat can also affect stem growth. As the temperature rises, marijuana plants will
naturally grow longer stems. At around 60F (15C), plant growth slows down and the
stems tend to be thicker. At 80F (27C) you’ll notice that both buds and lower stems
will start to stretch.
Buds that extend too close to a light might become airy or lanky. Some growers
will mistakenly associate this phenomenon with “light burn.” But, this isn’t the
real problem. What really happens is that the lamp’s heat creates an unsustainably
hot atmosphere in the bud zone. Some solutions include using an air-cooled lamp that
will prevent a large part of the meat from even entering the room. Likewise,
water-cooled lamps will capture virtually all of the lamp heat so that buds can
be very close to the light without the chance of burning.
Commercial greenhouses also use a method called temperature inversion.
This basically entails keeping the temperature higher during dark periods
and lower during light periods. Maintaining a temperature in the low 70’s
(21-23C) during the light period and increasing that temperature to around
80F (27*C) at night will slow vertical growth and will not affect
Lack of adequate light will cause stem elongation. Seedlings will grow long,
thin stems in an attempt to reach more light. To prevent this, supply a much
more intense light regimen or at least put the seedling closer to the light
source. If the seedlings have already stretched, try to support them using
wooden skewers. After providing much more intense supply of light, the stems
will fill out and will be able to support themselves on their own. Older
plants will also stretch toward the light source if they are suffering from
Light deprivation. In this case, buds grow airy, they won’t tighten up, and
they also have scant trichome coverage. Adding extra bulbs or moving the light
closer to the plants can prove beneficial.
Welcome to ILGM
We all here at ILGM hope that you join our community.
I hope this helps
Pruning can also be utilized to decrease stem length. Excising the very top
of the main stem forces the surrounding branch to grow. These ancillary
branches will not grow as long or as tall as the main stem. You can also
just bend the top branch until it snaps and hangs lower.
All top quality marijuana seeds are available in my marijuana seed shop.
We ship seeds to the US, CA and many other countries. For any growing related
question please visit the marijuana support page. Make sure to download my
free grow guide.