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Why seedlings Stretch

Apr 13, 2020
Lighting Problems

Identifying and Treating Stretched Cannabis Plants

Cannabis growers face many obstacles, but stretchy and elongated stems are one of the most problematic.


A stretched-out stem doesn’t provide much of a base for a fragile seedling, which may affect future growth. To eliminate the problem and reduce disproportionate growth, seedlings must be replanted.


In this guide, cannabis growers will learn how to diagnose and treat stem stretching in their plants. Whether you plan to grow the five alive strain, or something exotic like amnesia blue headband, this information will apply to your newly budding seeds.

Why Do Cannabis Seedlings Stretch?

These plants stretch for a few reasons, and not all can be prevented. Some problems are based on biology and some are not; however, all affect plants’ growth. Here are a few of the most common reasons for plant stretching.

Plant genetics are another concern. If a plant’s parents were grown indoors in a crowded room, the process of natural selection may keep this trait in future seeds’ genotype. However, if these seeds were made by crossing hybrid plants, it may be difficult to predict the outcome. It’s important to remember that some plants will grow taller than others do. For instance, landrace Sativa strains grow very tall whether they’re cultivated indoors or outdoors.

Stretchy Plants Are Starved for Sunlight

Though cannabis plants need light, some may like it a bit too much. SARP or shade avoidance response phenotype is a term commonly used among cannabis growers. In SARP, plants stretch to reach the light that’s being blocked by neighboring plants.

Marijuana plants can tell when their neighbors are close by because less red light is reflected. These plants are less likely to exhibit stretching behaviors when red-spectrum HPS lighting is used because they’re already getting enough red light. Room temperature and growth cycle timing also play a role, so the environment largely determines whether SARP behaviors are exhibited.

Other factors that increase the likelihood of stretching include:

  • The amount of space between neighboring plants
  • The grow room’s high temperature
  • Insufficient lighting
  • The distance between the plants and the grow room’s lighting

Growers should keep in mind that SARP isn’t all about lighting; it’s due to other factors that affect light quality. Lighting levels aren’t as much of a concern when plants don’t feel threatened by the proximity of their neighbors. However, when cannabis plants don’t get enough light for a prolonged period, they become sensitive to the red-light spectrums necessary for growth. When there’s enough light exposure, the spectrum isn’t as important.

When plant stretching isn’t due to SARP, it may happen because the plants aren’t getting enough intense light. In grow rooms, problems may occur when lamps are placed too far away. Though crowding isn’t the issue in these situations, stretching may still cause problems because these plants may be more likely to flower prematurely.

Why is Stretching Such a Problem in Cannabis Crops?

Cannabis plant’s stems may stretch whether they’re grown outdoors or indoors. The problem may be hard to detect simply because a stretched plant may still grow quite large; however, its yield will be substantially less.

A stretched plant is costlier to grow because elongated stems require more energy, which could instead be devoted to bud growth. In an indoor garden, a decrease in yield may occur because of lighting difficulties. Plant stretching creates fragile stems, which means that these plants are more likely to fall over. In rooms with low ceilings, stretching is a big concern. Thankfully, there are a few ways to reduce the risk or prevent it altogether.

How to Keep Plants from Stretching

In this section, we’ll show you how to prevent stretching in cannabis plants.

  • Proper circulation: When there’s good airflow throughout the grow room, the plants’ leaves and stems will get stronger and thicker while growth height is reduced. Effective air circulation creates leaf and stem movement that widens and strengthens stems while diminishing vertical growth. The wind bends stems, creating microscopic tears in plant tissues. In areas where airflow is a concern, growers can brush their plants’ leaves to create a similar effect.
  • Lighting: The kind of light a grower uses plays a crucial role in how tall the plants’ stems grow. Red and orange lights yield thin and tall stems, while blue lights typically yield short and thick stems. When metal halide lights are used during the vegetative phase, stems typically grow shorter.
  • Infrared light: This is another simple way to control plant height. Infrared lights are used when the regular grow lights are turned off. Cover the heat lamp reflector with a black cloth to allow the infrared rays to do their job.
  • Lighting distance may also cause plant stretching. To prevent the issue, be sure your seedlings are getting enough light. In an indoor garden, put the plants under CFL bulbs (at least three watts for every seedling). The distance between the bulb and the plants should be approximately two inches. When using HPS bulbs, keep the lights about 20 inches away (for vegetating plants) or 40 inches away (for seedlings). The temperature should not exceed 77 degrees Fahrenheit.

In outdoor gardens, most of these factors are irrelevant. However, the quality and quantity of sunlight play a crucial role. It’s important to grow cannabis according to the region in which it’s cultivated. In some instances, shorter daylight hours may cause stretching no matter how much sun the plants get during the day. Even in tropical climates, outdoor cannabis plants may need supplemental lighting to minimize the risk of stretching.

How Heat Affects Stem Growth

External temperatures affect the growth of cannabis plant stems. The higher the grow room’s temperature goes, the longer the plants’ stems will be. They will widen and growth will slow down at a temperature of about 60 degrees. When the temperature increases to approximately 80 degrees, buds and stems will stretch.

If the plants’ buds get too close to the grow lights, they’ll become thin and tall. Many growers mistake this for light burn, but that’s not the case. The heat from a grow lamp may create intolerable conditions for buds. An air-cooled lamp will keep much of the heat from dissipating into the room.

Keep Plants Properly Spaced

In large-scale, close-quarters cannabis cultivation efforts, stretching is a significant concern. As plants grow, their leaves may become quite close to those of nearby plants. With time, this proximity leads to discoloration of lower leaves, and the condition of the sub-canopy may suffer. When plants are properly spaced, though, they’re more likely to get the light they need.

Resolving Stretching in Cannabis Plants

If your marijuana plants have already begun to stretch, the problem may be reversible if it’s caught early on. When plants stretch during the vegetative phase or the first part of the flowering phase, blue lights may minimize the issue. Whether you’ve sprouted regular or autoflower marijuana seeds, they should have the same response to blue light.

It’s important to remember that a bit of stretching may not be detrimental. Some growers prefer a slight stretch as it may prevent bud rot in a few strains. However, stem stretching is undesirable in most cases.

If your plants are stretching, avoid giving them excess nitrogen. Instead, use a 2-2-2 fertilizer at the start of the flowering phase to regulate nitrogen levels. Feed the plants gradually, as a sudden shift to a flowering fertilizer may cause the leaves to turn yellow. Indoor growers should use oscillating fans to keep air moving over the stems and leaves.

Emergency Care for Seriously Stretched Plants

If your cannabis plants are severely stretched, it may be possible to bring them back to good health with these strategies.

  • Burying the plant: Giving your plants a firm base will help them stand up straighter as the stems regain their strength. Create a strong foundation by re-potting your plants. Be sure the soil is completely dry. Roots may cling together in wet soil, and it’s important to prevent damage. Use a deep pot and bury the stem so that the cotyledon leaves are barely visible. Afterward, give the plant a bit of water to get things growing again. As long as the process is done carefully, the plant won’t be unduly stressed.
  • Staking is another good way to reinforce plants. Use yarn or fabric to weave a lattice around stretched and weak stems. This works well in greenhouses where growers can tie plants up to keep them standing. In other cases, growers use stakes made of wood or plastic, tying weakened plants to them for additional support. If you’re using ties or stakes, take care not to harm the plants’ stems. Staking is supposed to support the plants, not stress them.

With these methods, it may be possible to revitalize and strengthen stretched cannabis plant stems. However, both approaches should be used with caution to reduce the chances of plant stress.


Stem stretching can affect a plant from its roots to its leaves. Plants with stretchy stems won’t yield as many buds as healthier plants do. With early detection, prompt treatment, and high-quality seeds from, growers can minimize the effects of stem stretching and end up with more plentiful crops. Now that you are an expert on stretching in marijuana seedlings, the only question that remains is “where can I buy marijuana seeds?”. The only sensible answer is the place with the most cannabis seeds for sale USA, seedbank #1 the i49 superhighway!

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