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Why do my seedlings stretch?

Seedling stretch is a phenomenon that occurs due to various factors influencing the growth of plants. In this article, we will explore the reasons behind seedling stretch, the role of genetics, and the impact of environmental conditions on plant growth.

Factors Contributing to Seedling Stretch​

1. Biotic and Abiotic Factors​

Seedlings stretch as a result of both biotic and abiotic factors affecting their growth. The environment in which the plants are grown can influence stretching due to nutrient deficiencies or other factors such as temperature and day length.

2. Seed Source​

The origin of the seeds plays a crucial role in seedling growth. Seeds from stable environments or from plants that have been selectively bred for certain traits may exhibit consistent growth patterns. On the other hand, seeds from hybrid plants or those grown in crowded conditions may result in a higher degree of variation and stretchy plants.

The Shade Avoidance Response Phenotype (SARP)​

When plants stretch to compete for light, it is known as the shade avoidance response phenotype (SARP). Plants can detect the proximity of their neighbors by sensing the amount of red light reflected by other plants. As the red light is absorbed by the neighboring plants' leaves, the stretching plant responds by growing taller to compete for light.

Role of Light Spectrum​

HPS (high-pressure sodium) lights, which are rich in the red spectrum, can reduce the stretching of plants grown under them. However, the overall yield may be lower with a stretched plant compared to one grown under a full-spectrum light, even if the stretched plant is larger in size.

Impact of Temperature and Photoperiod​

Temperature, photoperiod, and planting density can affect the plant's response to red light. Higher temperatures, shorter photoperiods, and dense planting make plants more sensitive to the amount of red light, thus influencing their growth pattern.

Seedling Awareness and Growth Implications​

Seedlings are aware of their surroundings and adjust their growth accordingly. While the SARP may not be affected by photoperiod in seedlings, short day-lengths can induce flowering and stretching. Elongated plants require more resources to grow, as more stem and less bud are produced. Therefore, temperature and photoperiod should be considered when planting densely to minimize stretching.

Frequently Asked Questions​

Q1: What is the shade avoidance response phenotype (SARP)?

A1: The shade avoidance response phenotype (SARP) is a phenomenon where plants stretch to compete for light when they sense the proximity of their neighbors.

Q2: How do plants detect the proximity of their neighbors?

A2: Plants can detect the proximity of their neighbors by sensing the amount of red light reflected by other plants, which is reduced as the neighboring plants' leaves absorb the red light.

Q3: Can the type of light used for growing plants affect seedling stretch?

A3: Yes, the type of light used can affect seedling stretch. HPS lights, which are rich in the red spectrum, can reduce the stretching of plants grown under them.

Q4: What factors can influence a plant's response to red light?

A4: Factors such as temperature, photoperiod, and planting density can influence a plant's response to red light, thus affecting its growth pattern.

Q5: Do elongated plants produce a higher overall yield?

A5: No, elongated plants may be larger in size, but the overall yield is usually lower compared to plants grown under a full-spectrum light, as they produce more stem and less bud.
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