When considering the question of how tall do weed plants grow, the answer is really as long as a piece of string – or perhaps a joint of weed! There is an enormous variation between different strains of cannabis – from compact bushes to leggy giants – and how they are grown can also make a difference to the overall height. Let’s look at the heights you can expect a typical weed plant to achieve when grown indoors or outside, and the impact various techniques can have on height.
Sativas, Indicas and Ruderalis
These are two main strains of cannabis, although there are many hybrids which combine genetics from both. There are many visual differences between Sativas and Indicas, and one of the most obvious is height. Sativas can grow extremely tall, to twenty feet and is slower to grow and reach harvest. Indicas are compact, bushy plants that typically reach heights of between three to six feet. Hybrids vary enormously; we recommend reading information about the strain before your purchase to find out whether Satia or Indica is dominant when it comes to potential growth. The other strain of cannabis is Ruderalis, whose genetics are often found in autoflowers, and this is also a short plant similar in size and shape to Indica.
Cannabis height when grown outside
If you were to leave a Cannabis Ruderalis strain to grow outdoors in favourable conditions completely unchecked, a single plant could easily achieve heights of 20 feet and a breadth of two to three feet. The only limitations are the amount of root space in the soil and the number of hours light in a day. If you have the space and inclination, it is easily possible to grow a forest of truly gigantic weed plants.
Cannabis propensity to grow means that its height needs to be carefully controlled by you, the grower, without affecting the health of the plants and the quality of the yield.
The optimal height for weed grown indoors
If you cultivate your cannabis plants indoors, their final height is in your hands. Although it may seem contrary, it is not worthwhile allowing your plants to get past a certain height, unless you have enough grow space. There are several reasons for this:
- The largest buds are found at the top of the plant nearest the light source. Buds get progressively smaller down the plant. To maximize yields, you need to ensure that light can penetrate as much of the plant as possible, which is where the various training methods come in.
- Extra growth results in a long, lanky plant without any extra yield, which is really a waste of time, money and electricity!
- Plants that are too tall can attract unwanted attention when grown outdoors or if there is limited indoor space.
There are several methods you can use to control the height of your weed plants:
LST is an easy and inexpensive method of training that simply involves bending the growing stems in the direction you want them to grow and gently tieing them in place. LST enables light to reach more buds by creating a more even canopy.
ScroG works similarly to LST but involves a screen, net or trellis against which the cannabis plant is encouraged to grow horizontally. This method also creates more budding sites by stretching out branches to expose more nodes to the light.
Topping a type of pruning that takes place just before the plants enter the flowering phase. Get some pruning shears and top all the branches to rein in the stretch that takes place during the flowering phase. This might sound drastic but will encourage the plants to focus their energies on producing flower heads rather than wasting energy on growing upwards.
Follow these tips to prune safely:
- Wait for a minimum of 3 layers of leaves before cutting;
- Always use a pair of clean, sharp scissors or secateurs;
- After cutting, there should always be enough leaves left to allow the plant to breathe and photosynthesize;
- Don’t worry if the new growth turns light green after cutting; this is normal!
There really isn’t an optimal height for cannabis, it depends on your personal preference, space and growing set up. Ultimately, if you want to maximise your yields, it pays to learn as much about the strain as possible, and this includes expected height.