Cannabis flowering stretch master guide

01/07/2022

When a cannabis plant is ready to bloom it undergoes various hormonal changes. One effect is to cause the plant to produce a vertical growth spurt, known as cannabis flowering stretch. This often lasts for the first 2-4 weeks of bloom before the plant stops stretching and focuses on bud/bloom growth.

Depending on how the grower is cultivating plants (e.g. with the SCROG method, etc) flowering stretch can be useful. But for those growing in spaces with e.g. limited vertical headroom too much stretch can cause problems. If a plant is allowed to stretch excessively it may become lanky and weak with poor yields. Read on to find out more about cannabis flowering stretch and the techniques you can use to help control it to your advantage.

Cannabis flowering stretch meaning

Some Auto Colorado Cookies phenos show more stretch and thinner leaves

Flowering stretch simply refers to the plant elongation/growth which occurs after the plant has started bloom. When growing feminised cannabis seeds, the grower initiates bloom by reducing daily light hours to around 12. When growing autoflowering seeds, the plant genetics determines when bloom starts and not the grower.

Most cannabis strains stretch for around the first 2 weeks of flowering. Some stretchy strains will continue to stretch into the 3rd or even 4th week of bloom. Sativa strains will stretch more than indicas. A sativa may double or even triple her height during bloom whereas an indica may increase her height by 50%-100%.

What makes cannabis plants stretch in flowering?

Plant hormones are responsible for cannabis flowering stretch. Plant hormones are influenced by the number of daily light hours when growing feminised cannabis seeds. As the plant senses a reduction in daylight hours the resulting hormone changes allow greater cell division/growth and the cannabis flowering stretch will begin. Autoflower strains dictate the length of their own vegetive period according to the genetics.

The theory of plant hormones was first developed by Charles Darwin in the 1890’s when he noticed that plants would bend towards a light source, an effect known as phototropism. Plant hormones regulate growth.

There are thought to be 8 types of plant hormone – auxins, gibberellins, ethylene, cytokinins, abscisic acid, jasmonates, brassinosteroids and strigolactones. However, there are also theories that a hypothetical plant hormone known as Florigen (literally meaning ‘flowering hormone’) is responsible for triggering and/or controlling bloom in cannabis.

Growers should note that a lack of light can also cause stretch (as the plant searches for much needed light), but that shouldn’t be confused with cannabis flowering stretch.

Cannabis genetics and flowering stretch

Desfran cannabis scrog grow half pipe sativa leaves buds foxtails indoor hps organic

The genetics in your seeds play a huge role in the amount of cannabis flowering stretch. A short, bushy indica autoflower strain may finish harvest around 60cm tall and be loaded full of buds. A photoperiod feminised sativa strain may end up close to 2m tall and may require lots of LST to control her stretch.

Supercropping is a high stress training (‘HST’) technique in which the stem is crushed and bent into the horizontal position. This can be a useful technique to control a plant which has grown a little too tall for the grow room.

Other growers will top/fim their plant (removing the growing tip) during vegetive growth. This results in a bushier, shorter plant with more side branches.

Experienced growers will know which types of cannabis genetics best suit their personal grow circumstances and available grow space and choose their cannabis seeds accordingly.

A grower with limited vertical growth space may deliberately lean towards indica or indica dominant weed seeds with limited cannabis flowering stretch. Or they may prefer to stick to autoflower varieties which often tend to stay around (or below) a metre tall.

Those with a large grow area to fill, and perhaps a SCROG screen may deliberately select a highly stretchy strain such as Dutch Passion’s pure Sativa strain Desfrán.

Related:
The cannabis SCROG method

Grow environment

Indoor growers may need to control cannabis flowering stretch in order to keep as many developing buds at an optimised distance from the grow light. If a plant has stretched excessively then one option for the indoor grower is to supercrop the main bloom, laying it horizontally in the optical sweet spot. Other growers may try to lean/position a tall bloom towards a corner of the tent in such a way that it enjoys plenty of light.

Outdoor growers may have security concerns if one of their plants is showing too much cannabis flowering stretch, especially if it’s growing in a rear garden or near a neighbour’s property. Outdoor growers can also manipulate their plant height with training techniques such as super-cropping, tying-down the tallest blooms etc.

Those growing cannabis in greenhouses may also find times when they need to control cannabis flowering stretch. Remember a SCROG is also possible in a greenhouse and may be a better option than letting a particularly stretchy plant grow out of the roof vent.

Light exposure

Autoflower cannabis plant light schedule

One challenge, especially for less experienced growers, is to ensure their plant has the right amount of light at the various stages of its life. Optimised light intensity vary tremendously from seedlings, to veg growth to bloom. It helps if your grow light manufacturer lists the appropriate hanging heights/power settings at each growth stage with expected PPFD levels.

	PPFD levels (μmol/m2/s)
	Seedling stage	Vegetative stage	Flowering stage
Light cycle	18h/daily	18h/daily	12hr/daily
Minimum PPFD	100-150	300-400	600-700
Maximum PPFD	200-300	500 (up to 600)	800-1000

If too little light is given the plant will stretch as it seeks out more light. This can be dangerous for your plant, potentially causing it to become too tall and flimsy. Increasing light intensity, or bringing the light closer to the plant, will help. So too may the use of a blue dominant spectrum.

This is easy with a spectrum-adjustable LED, but better-quality grow lights (especially the LEDs) should all come with sufficient blue light to allow healthy, sturdy vegetative growth.

Specialist blue LED vegging lights are available to buy, so too are blue-dominant ceramic metal halide lights. Older HPS lights are often regarded as the type most susceptible to causing cannabis flowering stretch.

Most serious/professional growers would only consider a quality LED grow light, they inherently produce superior cannabinoid and terpene levels. LED also produces lower heat levels meaning less plant stress.

How to prepare for the flowering stretch?

Cannabis Guerrilla growing 10-step strategic plan

This can require some good grow-room management skills, especially if you’re growing several different strains with different degrees of cannabis flowering stretch.

Lesser stretching plants may be allowed to grow naturally whereas the stretchier plants may require tailored training in order to maintain a level canopy with most of the buds growing in the optical sweet spot.

If this sounds like a difficult challenge it will be useful to select cannabis seeds of strains with similar levels of stretch. Less experienced growers may prefer to avoid mixing stretchy sativa seeds with indicas.

Define and set up your grow spot

Many home growers use a 1.2m x 1.2m grow tent (4 ft x 4ft), suitable for perhaps 4-5 plants. A tent which is 2m tall (6.5ft) will be able to cope with most strains, especially if you work with short veg times on your stretchy strains.

A smaller tent with half the height would be better suited to indica strains and autoflowers, perhaps with a panel LED which would support short/small hanging distances above the canopy.

Research the best matching cannabis strain

A competent cannabis seed supplier should be able to give accurate information on the stretch characteristics, sativa/indica heritage and perhaps some real-world grow reviews.

Online grow web sites are also a good source of information. Ensure that the strains you select are matched to your grow room/grow situation. Also consider your experience using high stress and low stress training techniques. These may be required if you encounter more cannabis flowering stretch than expected.

Plan your entire grow ahead of time

You will spend several months growing your preferred strains, so spend some time reflecting and comparing the strains. It’s also worth considering your grow room. If you’re preparing for a SCROG it could be worth making a timber frame. A good mesh would be available from DIY stores, look for rolls of wire/metal fencing with 5cm square holes.

Concerned about stretch? Try these top 5 cannabis seeds for small spaces

Some more experienced growers actively seek out highly stretchy strains so they can fill a SCROG screen and aim for XXL 600g/m2 yields. But many others prefer to gain experience and confidence with cannabis cultivation by using strains that are reliably low stretch.

Auto Banana Blaze

An indica autoflower, Auto Banana Blaze is a proven, compact and low stretch strain. She is part of the Afghani Kush cannabis seed collection. These tough, bushy genetics need no special care and will suit the less experienced grower looking for a no-nonsense, easy-to-grow auto.

THC levels are officially rated as very high. One of the reasons Auto Banana Blaze sells in such quantities is the XL yield potential. Some plants will require a grow cycle of up to 12 weeks but will produce extra heavy yields and reaches a height of around 75cm, less of she is constrained by a small container.

Auto Banana Blaze cannabis seeds

Auto Blackberry Kush

Like Auto Banana Blaze, Auto Blackberry Kush is an indica autoflower strain with a compact structure.

Auto Blackberry Kush is one of Dutch Passion’s fastest autoflower strains to grow and suits the grower looking for an express harvest of potent, blue/purple buds. Some plants are ready to harvest in as little as 9 weeks after autoflower seed germination.

She tends to reach maximum heights of around 75cm with little cannabis flowering stretch. Perfect for the grower with limited space or time, but no desire to compromise the quality of their harvest! Auto Blackberry Kush uses cannabis cup winning genetics from Blueberry crossed with a dark gene bank hash plant.

Auto Blackberry Kush cannabis seeds

Kerosene Krash

Perhaps Dutch Passion’s most potent low-stretch feminised indica seeds! Kerosene Krash uses genetics from Gorilla Glue #4 x Sherbet.

Part of the USA Special cannabis seed collection, these deliver rare extreme THC levels up to and even beyond 25%. The effects are those of a stunningly powerful indica and won’t suit the casual smoker.

Bloom time on these photoperiod feminised seeds is about 8 weeks with very low levels of cannabis flowering stretch. Plants tend to reach 60-80cm tall, making them easy to manage with no stretch.

One of the other great features of Kerosene Krash, as the name suggests, is a spectacular terpene profile that smells like a fresh fuel spill.

Kerosene Krash cannabis seeds

Bubba Island Kush

Fans of compact low-stretch indica photoperiod feminised strains will find few better than Bubba Island Kush. The pure indica genetics take just 7 weeks to complete bloom and produce short, bushy and compact plants that have little cannabis flowering stretch. This makes her easy and uncomplicated to grow, and a good choice for any grower with a high value for low stretch cannabis genetics.

The sour fruity Kush aroma is rare and delicious, complementing the powerful effects which produce a deeply relaxing and enjoyable experience.

For Kush connoisseurs this is a genuine ‘must-grow’ strain. The rock hard buds are solid, they grind up and produce copious quantities of white powdery and delightfully potent herbs.

Bubba Island Kush cannabis seeds

Mokum’s Tulip

Mokum’s Tulip is a multiple cannabis cup winner using elite genetics from Gelato x Sherbet. She’s a hybrid cannabis strain with strong indica heritage and low levels of cannabis flowering stretch.

THC levels are more than sufficient for the most demanding consumer, but the pungent aroma and flavour explosion has drawn much of the attention from home growers seeking pro-level quality.

Despite some sativa heritage the growth characteristics lean more towards those of an indica with limited stretch. Anyone looking to produce genuine top-shelf buds with maximum jar-appeal will find few strains better!

Mokum’s Tulip cannabis seeds

How to prevent cannabis from stretching too much?

If your cannabis plant stretches too much it can cause numerous difficulties. In a multi-strain grow room stretch may force you to raise your grow light too far above the canopies of your smaller plants, reducing their yield as well. Stretchy plants rarely yield anywhere near their maximum. Cannabis flowering stretch can be minimised but attention has to be paid to a few different areas.

If you use light intensities that are simply too low for your grow area then you will see unhealthy stretch and a lanky, weak looking plant which will struggle to reach its full yield potential.

Plants that have lacked the care and attention when transplanting can experience stress/shock. One result of that is plant stretch, a result of significant environmental stress.

Topping your cannabis plant, or removing the growing tip forces your plant to adopt a squat, bushy structure with less stretch and vertical growth. Super cropping can achieve the same result, reducing the overall height of your plant. Tying your plant down (LST) is another option. Considering a SCROG is another proven option for strains with significant flowering stretch – this may even allow you to boost your yields.

Adequate air flow through your grow area is essential if your cannabis plants are to grow thick, healthy strong stems (rather than tall, thin & lanky stems).

Cannabis stretch frequently asked questions

Cannabis stretch during the onset of flowering can be both an advantage for some growers as well as a problem for those that perhaps didn’t prepare sufficiently for it. As with all aspects of cannabis cultivation, learning more about stretch equips the grower with the understanding and confidence to deal with it effectively.

Normally the first 2 weeks of bloom are those when you will see your plant stretching the most. But some of those strains which exhibit maximum cannabis towering stretch may continue stretching in etc 3rd or even 4th of bloom.

Once the initial hormonal changes from the onset of bloom have finished your cannabis plant should stop stretching. Usually, some 2-3 weeks after bloom began. At this point the plants biochemical energy switches and focusses on building thick blooms and plants of resin/trichomes.

Many growers, both new and old, keep a basic grow diary which records the main aspects of their grow. This may include plant height, nutrient regime, lighting levels etc. Most cannabis growers visit their plants regularly, meaning it is fairly easy to monitor how much their plant is stretching.

Cannabis flowering stretch is partly genetically determined. As a result, it may be possible that your cannabis seeds are simply doing what they should and producing a plant with high stretch. If so, you have the option to train your plant if required. One other possibility is that the grow room itself is supplying environmental conditions which exacerbate stretch. If the grow room is too hot, if light levels are too low, ventilation is poor etc then your plants may suffer unhealthy stretch.