Does Seed Size Matter? (We Investigate)

seed size

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Does seed size matter?  One would think that the bigger the seed, the better it is in germination and seedling growth.

The truth is actually not so simple.

Large seeds have higher germination success and develop into stronger seedlings with more vigorous roots and a higher chance to survive.  However, small seeds germinate faster, making them more adaptable to stress in the growing environment. 

In this article, we will show you how seed size affects germination success, germination time, seedling growth and survival, and adaptation to different habitats.

1. Germination time

A study shows that small seeds require only 29 days and large seeds took 42 days to germinate (Souza & Fagundes, 2014). 

Small seeds require shorter germination time because they have a thinner seed coat and a larger surface to absorb water to break seed dormancy.

A shorter germination period helps small seeds to germinate quickly in unstable environments with changes in water, light, and nutrients.  Small seeds are actually more adapted to grow in such environments than larger seeds.

The other factor to note is the seedling phase.

The faster germination time of a small seed does not guarantee a swift seedling phase, so you must wait longer before you can actually repot it. In the case of large seeds, the seedlings may develop later, but the subsequent growth is swifter and stronger.    

2. Germination success

Large seeds have more success in germination.

A study using the seeds of coffee senna (Senna occidental) shows that there is a much higher germination success with large seeds (96.6%) compared to small seeds (73.4%) (Saeed & Shaukat, 2000). 

Another study using the seeds of sweet chestnut (Castanea sativa Mill.) also confirms more success when germinating large seeds (98.8%) compared to small seeds (91.3%) (Cicek & Tilki, 2007):

3. Seedling development

Seedlings from larger seeds develop more vigorous shoots and roots. This is because they have a large reserve of nutrients stored, and do not need to depend on getting nutrients from the soil.  Although larger seeds have more reserves stored, they take more time to incorporate their nutrients in seedling tissues. 

Small seeds focus the energy on developing seedlings with more roots than foliage.  This is because of the poor nutrient reserves in the small seeds where the focus is put on root development rather than foliage development to absorb nutrients from the growing substrate.  

4. Seedling establishment

Large seeds produce more promising seedlings than smaller ones because of the higher storage of resources, which serve as the foundation for vigorous seedlings.

Also, longer germination time allows the seedlings to develop more than those emanating from small seeds. This means that the stronger seedling establishment ensures better survival and growth.

5. Seedling growth

Seedlings of large seeds grow stronger roots and shoots.

Although smaller seeds can germinate faster, the seedlings aren’t fully developed due to the short time. The nutrients in small seeds aren’t fully matured.

Large seeds may take longer to germinate but once they are germinated, they are more resilient in stressful environments where water is scarce or where there is high salinity because of more reserves.  Larger seedlings develop bigger roots that can dig deeper and wider to access water.

6. Plant etiolation response

Large seeds and their seedlings have a stronger response to etiolation, which rests on the nutrients in large seeds.

Small seeds don’t have sufficient reserves to respond to the inevitable etiolation in many circumstances. However, etiolation isn’t a concern if you have optimum light.

7. Dry matter accumulation

Large seedlings have substantially greater dry matter accumulation than smaller ones. So, if the growing conditions are optimum or preferable, large seedlings are likely to have much faster growth and better development (Steiner et al., 2019).

8. Seed survival

Seed dispersal and predation are pertinent issues in the wild, but less so for home gardens, and are often a nonstarter for greenhouses, laboratories, etc.

In general, all seeds are vulnerable to drought stress, irrespective of their size.

But in general, seedlings from large seeds have the highest survival.

Even though large seeds take longer to germinate and are susceptible to predators, they endure the attacks of many predators. Besides, larger seeds have more reserves than smaller ones to survive predation to produce seedlings.

How seed size affects germination

Germination isn’t solely about the seed size. The growing conditions have to be optimum for any seed size to germinate quickly and properly. However, large seeds are likely to perform better in suitable and some suboptimal conditions due to a few reasons, including:

  • Nutrients reserve
  • Number of cotyledons
  • Germination percentage

Small seeds don’t do well in salt-stress conditions. 

In contrast, large seeds or their seedlings can endure salt stress or soil salinity to varying extents. Also, large seeds tend to be a bit more resilient against water stress. However, all seeds are vulnerable to drought stress, irrespective of their size. 

The other factor to note is the seedling phase. 

The faster germination time of a small seed does not guarantee a swift seedling phase, so you must wait longer before you can actually repot it. In the case of large seeds, the seedlings may develop later, but the subsequent growth is swifter and stronger.    

How seed size affects plant growth

Large seeds have more vigorous seedlings that develop better root systems and taller shoots. So, the seedlings or plants growing from large seeds have deeper roots, making them less vulnerable to water stress. The taller shoots also enable them to overcome shades.

One study found that nascent seedlings from small seeds don’t survive in 99% shade, but large seedlings can endure such a condition. Also, large seedlings grow significantly longer in about 6 weeks than smaller ones in 95% shade (Leishman & Westoby, 1994).

These factors, combined with the nutrient reserve and greater dry matter accumulation, make large seedlings or young plants counter etiolation. Therefore, you will have better growth from large seeds and their seedlings in both shaded and optimum light conditions. 

Having said that, the stem elongation and better root system growing from large seeds aren’t indicative of any specific ratio. The root-and-shoot ratio doesn’t depend much on the seed size. Instead, the growing conditions and surrounding factors determine these characteristics.

 

Related

How Long Do Seeds Last? (And How to Store Them)

Difficult Seeds To Germinate: 3 Types (Explained)

Does Freezing Affect Seeds? (Here’s How)

Sources

Souza, M. & Fagundes, M. (2014). Seed Size as Key Factor in Germination and Seedling Development of Copaifera langsdorffii (Fabaceae)

Cicek, M. & Tilki, F. Seed Size Effects on Germination, Survival and Seedling Growth of Castanea sativa Mill.

Steiner, F., Zuffo, A. M., Busch, A. (2019). Does seed size affect the germination rate and seedling growth of peanut under salinity and water stress?

Mack, A. L. (1997). An Advantage of Large Seed Size: Tolerating Rather than Succumbing to Seed Predators

Kołodziejek, J. (2017). Effect of seed position and soil nutrients on seed mass, germination and seedling growth in Peucedanum oreoselinum (Apiaceae)

Murray et al. (1994). Etiolation

Saeed, S. & Shaukat, S. S. (2000). Effect of Seed Size on Germination, Emergence, Growth and Seedling Survival of Senna occidentalis. Pakistan Journal of Biological Sciences, 3: 292-295. https://scialert.net/fulltext/?doi=pjbs.2000.292.295

Chauhan et al. Seed Predation

Liu, Y. & Deng, M. (2020). Dry Matter Accumulation

Carol loves to garden and research to help others grow their green thumb.

She is working towards her dream of living close to nature.

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