how to keep marijuana plants short

What To Do When Your Cannabis Plants Grow Too Tall

Everybody loves big cannabis plants, but sometimes they can get too tall. This is bad news in a restricted space or for the stealth outdoor grower. Find out how to control your overeager marijuana plants with this informative blog from Royal Queen Seeds.


When marijuana is exposed to prime growing conditions, it should fulfill its genetic potential. Sometimes, this means your plants will grow too tall. This can easily happen with sativas that stretch substantially or Kush varieties that tend to have generous distances between nodes. Some species of cannabis stretch notoriously when they enter the flowering phase, even doubling their vegetative height in some cases. Although the whole idea is to get the largest of plants with the heaviest yields of mature flowers possible, depending on the situation, plants that are too tall can be inconvenient.

Often, space is limited indoors and plants that are too tall can exceed the height of the grow space. If the grow room is a multi-strain grow, raising the lights to suit the taller plants can deprive shorter plants of sufficient lighting. Outdoors, especially in stealth grows, plants that are too tall can attract unwanted attention. Controlling the height of your marijuana plants is not very difficult and can be done in a number of ways. Here are a few techniques that can keep the height of your marijuana under control.


If you are well aware that the strain you are growing is going to be tall, then height control starts in the early vegetative phase. Alternatively, the size of your grow space may require height control no matter the strain. Topping or fimming when plants are young encourages a shorter, but bushier plant. Grow room space still needs to be considered, however, as you are exchanging height for floor area.

Air circulation is a priority when plants become bushier in tight quarters. Controlling the height of your crop, only to suffer from mould or fungus due to lack of circulation is definitely a no-no. Lollipopping your plants will guarantee good air circulation below the canopy, preventing pathogens from taking hold. This also has the added bonus of chunkier and weightier colas come harvest, with less unwanted popcorn buds.


LST or low stress training is the art of gently tying the branches of your plants to grow more horizontally. Either the main stem is tied down, encouraging the side branches to be dominant, after which the side branches are also tied down; or the plants are topped a number of times and the new growth is tied down in the mainlining style. LST and mainlining have the benefit of exposing more of the plant to light, therefore encouraging weightier flowers all over.

What’s great about these techniques is an even canopy instead of one main cola. The extreme of this style is ScrOGging, in which the whole plant is encouraged to grow horizontally. A screen of netting is used to hold down all new growth until the plants form a mat. Appropriately called “screen of green,” one or two plants may fill an entire grow space.


Letting your plants grow untouched during the vegetative phase, then topping just prior to flowering also controls height. When your plants are about to enter the flowering stage, top all branches. This has the effect of reining in the flower stretch. The plants are urged to produce new flower growth instead of focussing energy on stretching out.

Occasionally, pre-flower topping needs to be a full pre-flower pruning. If your plants fill the grow space during the vegetative phase, there is no way there will be enough room for flowering. It is time to get drastic. Aggressively prune the plants to half their size and switch lights to the 12/12 flower cycle. Don’t worry, cannabis is very hardy and can even recover from being reduced to a stalk with only one or two leaves remaining. Try not to beat yourself up about the loss of time and reduced final yields. All lessons are good lessons on the way to becoming a weed growing expert.


Cannabis plants transpire a substantial amount of water. Marijuana prefers a relative humidity (RH) of 50-65%. When they get too big, humidity can become a problem as the plants constantly release water vapor into the air. Water then gathers on leaves and other surfaces in the grow room, potentially causing mould and other issues. If humidity is becoming a problem, the use of a dehumidifier or increasing exhaust fan power can help. Defoliating can also increase airflow to control humidity. Remove lower and mid-level fan leaves only. This has the added benefit of increasing light penetration to the lower flowering branches.


As with humidity, when plants get too big, temperature in the grow-op can rise. Reduced airflow and excessive height can drive up temperature and position plants too close to grow lights. Cannabis thrives when the temperature averages 25°C. When temps exceed this, plants are more likely to stretch. High temperatures can also affect leaf and flower formations, as well as final bud flavours and potency.


If your plants are getting too tall or too hot and you have the room, simply raise the grow lights as high as possible. Remember, lights that are too far from the tops of your plants can also cause stretching, so make sure to achieve the ideal light positioning.

Light intensity can be adjusted as a method for controlling growth speed and height. Some grow lights have adjustable outputs. If your plants are getting unruly, reduce the intensity. If you are using more than one lamp, simply turn some off.

During the flowering phase, growth can be controlled by reducing the photoperiod – but only if your plants have been flowering for at least six weeks. Reducing leaf production and stem stretching can be achieved by reducing the “lights-on” period from 12 hours to 11 or 10 hours.


Appropriate strain choice can help avoid height issues before they even arise. If you have limited space, your dreams of cultivating a classic sativa will need to remain just that, dreams. Stout indicas and hybrids or autoflowering genetics can keep heights under control. Many autoflowering strains are ideal for indoor growing as they have relatively no vegetative period. Some strains will not grow taller than 50cm, but will still provide excellent yields per m².


With a little bit of consideration and forethought, height need not be an issue when growing marijuana. Some research into strain characteristics is the first, very important step. Then, appropriate growing techniques will make sure you get lots of yummy buds with no drama. Happy growing!

Cannabis is a hardy plant that can grow too tall for your grow space if you just let it go. Sometimes you need to take charge to keep things under control.

How To Top / Trim A Marijuana Plant To Keep It “Short”

Looking for the terminal bud on a sativa-dominant marijuana plant.

One of the problems faced by home growers is the daunting prognostication of the height your plants may reach! If you have chosen a Sativa strain (or even a sativa mix), you may be looking at the potential for the plant to reach 6 to 8 feet in height (growing conditions permitting) by the end of your grow. Yipes! That’s just a teeny bit bigger than my grow cabinet…

Autoflowering strain growers take note: Don’t top/trim your plants – they won’t like it, and don’t need it. They’re on a tight growth schedule, and most varieties won’t reach more than 3-4 feet tall.

The particularly tricky part is that the plants will often let you believe that they’ll stay nice and manageable in height. Even by the 4th week of vegetative growth, they may remain squat and bushy, reaching only a foot-and-a-half in height (taller is possible under higher wattage lamps). Then, when flowering begins, they start reaching for the sky – they’ll surge up a couple of inches overnight, and continue stretching as they flower and buds form. By that point, it’s too late to trim without seriously sacrificing harvest yield.

They key is to plan ahead. Top your plants (again, only the non-autoflowering varieties!) while they still have 1-2 weeks to grow in the vegetative phase. This will give the plants time to recover from the minor trauma of “topping” and extend axillary buds from lower nodes of the plant up towards the light. During flowering, these new “stems” will both (the plant will usually respond to topping by extending two lower buds) become flower-, and later, calyx-coated masterpieces of marijuana growing glory.

So here’s what you need to do – it’s rather simple:

First, look for the terminal bud of the plant. Please don’t confuse the term “bud”, which in plant anatomy refers to a an actively leaf-growing appendage of the plant with the slang term “bud” for the mature flower pods (calyxes) of the marijuana plant.

You need to carefully trim only this terminal bud – don’t damage lower leaves or the stem. The idea is to “re-route” the plants energies into growing two lower buds upwards and outwards, therefore maintaing the bulk of the plant, but controlling it’s height:

Looking for the terminal bud (aka “shoot tip” or “apical bud”).

Don’t be afraid to gently pull downward on the leaves at the top of the plant – they will not break too easily. When you have found the terminal bud, you should trim it cleanly using a small set of shears (I prefer nail scissors for smaller plants, such as those in this 100 Watt grow). Better to trim twice than trim too much and cut into the stem – so have a close look and be cautious.

Trimming the top of the terminal bud without cutting into the stem below.

To alleviate your fears, I should note that even if you were to lop off the top of your plant with garden shears, it will more than likely make a full recovery – cannabis plants are famously resilient. I’ve revived the stump of a failed grafting experiment to full growth and harvested several ounces of perfect buds from the final plant. The only thing you will lose is time – a harder pruning means that the plant will first need to gather resources and produce more of those all-important light-gathering vegetative leaves at the top of the plant.

A note about topping plants, and what you can expect: The most wily of sativa plants may indeed require a second top trim to keep them withing vertical confines of a small grow room. Some growers refer to continued topping during vegetative growth as a “screen of green” (discussed in our ebook), where you additionally support the many vertical stems with a metal screen or series of wires. You can trim and continue to vegetate your plants to your heart’s content – they won’t flower until you switch the light schedule (again, autoflowering varieties excluded). You can also expect to harvest more great-looking “colas” (Spanish for “tails”) of finished marijuana flower buds from topped plants. You may even increase your final yield this way – light exposure tends to be more even this way when using overhead lights.

The devil is in the details when it comes to successfully growing your own marijuana. Avoid pests, heat- and nutrient-burn, overwatering, root problems, and all the strength-sapping problems that can occur along the way, and you’ll have your own top-shelf medical marijuana growing in the privacy of your home. Grow organic quality, with fine aromas, and the assurance that you had a hand in production from start to finish – check out the links below for our ebook “How To Grow Cannabis At Home: A Guide To Indoor Medical Marijuana”.

[Author and Medical Marijuana Grower Glenn Panik’s “How To Grow Cannabis At Home: A Guide To Indoor Medical Marijuana Growing”, is available on iTunes (iBooks) here on the Amazon Kindle, and also available as a ‘stealth title’ for the Kindle here. Protect your privacy!

One of the problems faced by home growers is the daunting prognostication of the height your plants may reach! If you have chosen a Sativa strain (or even a sativa mix), you may be looking at the potential for the plant to reach 6 to 8 feet in height (growing conditions permitting) by the end…