Watching cannabis seeds grow into big, strong plants is likely to spark a sense of pride in any grower. The bigger the plant, the better, one might assume. Sadly, though, growing larger is no guarantee of producing the best results. If plants start to race upwards and grow tall too fast – a phenomenon called ‘stretch’ – stems turn into long, thin, and dangerously frail stalks. Stretching is an all too common sight for novice growers; and one they should aim to avoid. This blog explains why stretch occurs in cannabis plants, and what growers can do to avoid it.
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Why Cannabis Plants Stretch
Growth is a natural process in all plant species, yet not all plants do so in the same way or by the same degree. When growing cannabis, the aim should be plant growth as well as development of full flower buds. A growth spurt right before the onset of the flowering phase is a very common sight.
At this point, nearly all energy is directed at growth, which can easily make crops grow twice as tall. This is a positive thing: big plants can sustain more colas and therefore produce bigger harvests. Stretch, however, means that plants invest too much of their energy into developing long stems, which can ultimately impede bud development, or even cripple and kill young plants.
So why do cannabis plants stretch, you may wonder. Excessive stretching can occur for a number of reasons, including:
- Unstable environmental temperatures;
- Incorrect lighting schemes;
- Lack of soil nutrients;
Planting cannabis seedlings too closely together can also cause stretch. Individuals can ‘feel threatened’ by neighbours that come too close, because they can rob them of the (sun-) light they need. A quick growth spurt is an evolutionary strategy used to make a dash for the available light by outreaching the competition.
The Downsides Of Stretching
As we have seen, bigger plants are not always better plants. It’s not hard to see why. Excessive growth in the early stages of the cannabis life cycle leads to thin, fragile stems. These can easily bend or even snap. Moreover, plants that invest too much of their energy in growing lack the resources they need to develop big, healthy buds in the flowering phase.
Stretch can occur both in outdoor and indoor cannabis growing. Indoor grows can easily become problematic if they run out of space, on top of the problems mentioned above. Suffice to say, stretch is a risk any cannabis grower ought to avoid. Luckily, there are several ways to avoid it if you know what to do.
How To Counter Stretch In Cannabis Plants?
Early prevention of stretch starts with knowing the properties of the cannabis strain you want to grow. Once your plants start growing, try to keep a close eye on the pace of growth, and use the following tips to manage their development.
1. Pick The Right Strain
Generally speaking, sativa strains tend to grow larger than indicas do. Still, that doesn’t mean sativa cannabis plants are more prone to stretch. We would advise any grower to order seeds from a renowned and established seed bank, however, as this reduces the risk of undesirable genetic traits and unpredictable plant behaviour.
2. Temperature Awareness
Cannabis plants respond to heat. That makes it important to monitor temperatures, especially when growing indoors. Temperatures above 29°C can trigger stretch in cannabis.
Use a thermometer to constantly monitor temperatures in tents or other interior grow rooms. Outside, it can pay off to make clever use of shade by picking the right spot for grows. This will help keep temperatures stable and prevent growth issues before they start.
3. Plant Spacing
The spacing of individual cannabis plants is another factor in stretch prevention. If plants are too densely packed together, they will tend to try and find space by making vertical sprints. This natural tendency can easily turn into stretching if left unchecked.
Always keep plenty of space open between your plants. This will help prevent stretching as well as improve air circulation in the grow environment.
4. Improving Airflow
Cannabis plants growing outside have to cope with wind as an environmental influence. Wind can help strengthen plants by promoting development of strong stems, which automatically reduces their innate tendency to race upwards.
Indoor grows can also be improved in term of air circulation. Buying high-tech equipment is not necessary: installing a simple fan can be enough to encourage cannabis plants to develop firm stems and prevent stretch.
5. Low Stress Training Or Screen Of Green
Low Stress Training (LST) can also work wonders in limiting vertical growth. LST is a useful way of redirecting the direction of plant growth. In addition, this technique facilitates optimal use of available space, light, and oxygen.
Screen Of Green (SCRoG) is another technique that can achieve similar results by different means. SCRoG uses a grid to redirect growth rather than bending the stems directly. This encourages lateral plant growth, which can help curb the vertical ambitions of your plant.
6. Adjusting Distance To The Lights
Lighting can also affect a plant’s vertical growth. Like most other plants, cannabis grows in the direction of the light. If you want to reduce stretch, it can be helpful to reduce the distance between the lights and the cannabis plants. Depending on which bulbs you use, be careful about burning your plants with the lamp’s heat radiation, though.
Finding the right balance can be tricky. The ideal distance depends on the type and intensity of the lighting used. Always be cautious and stay below the danger threshold to avoid ruining your grow.
7. Shortening The Vegetative Stage
Another way of reducing stretch in cannabis plants is to try and shorten the growth or vegetative stage of the cannabis life cycle. If you want to keep your plants growing before the flowering stage sets in, keep a close eye on them. Determine the maximum height you want your plants to reach. Then, switch to the flowering phase before they reach half that height. This way, even if your plants double in size, they will not reach past your personal limit.
Of course, in case of outdoor grows, there isn’t much you can do when it comes to the ‘flip’ (the same goes for lighting distance; it’s hard to put plants closer to the sun), but indoor grows can definitely benefit from this technique.
8. Adjusting The Lighting Spectrum
As we’ve explained, light is one of the most important factors that determine stretch in cannabis plants. The right light spectrum can encourage growth. Using high pressure sodium lights (HPS) will increase a plant’s pace of growth. Using metal halide lamps (MH) in the initial weeks of flowering helps keep stems short before switching back to HPS.
9. Going Easy On Nutrients
A final way of limiting stretch in cannabis plants is to limit the availability of nutrients by not adding too much nutrition at the start of the flowering phase. Restricting nutes and CO2 supply will give you optimal control over stretching tendencies.
Here too, balance is key, as you don’t want to deny your plants essential nutrients. This will not improve their health, so try to steer clear of giving either too much or too little.
10. Compensating For Cannabis Seedling Stretch
After cannabis seeds have germinated, seedlings can start to stretch at an early stage. This is a very bad start of your grow, but if it does happen before you can intervene, you can simply try to bury the lower part of the stem in soil by forming a little mound around it for support. This may sound a bit too easy, but it can help your baby plant survive without snapping until it grows strong enough to support its first fan leaves.
Cannabis Stretch Prevention
As you have seen, stretch can be a big disadvantage for cannabis plants, resulting in fragile specimens with few buds, or worse. Fortunately, making a few minor adjustments can go a long way towards preventing excess vertical growth. Giving a little bit of extra care and attention can greatly increase the prospect of a bountiful harvest if you know what to do – and that’s just what we’re here for.