For those who save seeds, you may have been told to wait for the fruit to turn completely ripe on the plant before picking it and harvesting its seeds.
Well, that is a myth.
You can harvest fruits before they look completely ripe because seeds mature before the fruit matures by color. For tomatoes, fruits in the “mature green” ripening stage can have mature seeds, even though they do not appear red on the surface. To be safe, once the fruit shows a tinge of color change, the seeds are already ready for harvest.
In this article, we’ll look at the different stages of ripening and the science behind the delayed visual signal of maturity. You will see that it is in fact a fascinating mechanism related to survival in nature.
Let’s get started.
1. Can you save seeds from a green tomato?
You can definitely harvest seeds from tomatoes in the mature green stage, instead of having to wait until they turn completely red on the plant.
Tomatoes go through six ripening stages:
- light red,
In the immature green stage, the fruit is still growing in size. The seeds are still soft and can easily be cut by a knife. They are not yet developed and will not germinate.
In the mature-green stage, the fruit has stopped growing in size. Flavor has not fully developed yet. But the seeds are already fully developed and are covered in a clear gel, and can be harvested. In fact, store-bought tomatoes are generally picked at this stage. Since it can be hard to differentiate between the immature and mature-green stage, it would be safer for home gardeners to wait until the next stage when it starts to change color.
In the breaker stage, tomatoes start changing their color from green to a bit tannish yellow, pink or red, up to 10% of the surface of the fruit.
In the pink stage, around 30 to 60% of the fruit surface appears pink or red in color. Birds or insects may attack the tomatoes at this stage.
In the light red stage, around 60-90% of the fruit surface appears red.
In the red and final stage, over 90% of the fruit surface is red.
2. Impact of harvesting time on germination
Germination studies have shown that seeds harvested from fruits with an unripe or semi-ripe appearance can germinate well before they reach maturity by color.
An example is a study on the correlation between harvesting time and the impact on germination for papaya seeds (Urtasun, Giamminola & Viana, 2020).
In the study, seeds were collected from 5 different stages of ripening: unripe fruits with white (immature) seeds, unripe fruits with brown (mature) seeds, unripe fruits stored until full ripening, almost ripe fruits (up to 50% yellow tinge peel), ripe fruits (over 75% yellow tinge peel).
Results show that amongst the five ripening stages, it took the longest time to germinate seeds from unripe fruits with white seeds and unripe fruits that were stored until ripening.
Seedlings developed with high vigor not only from seeds from ripe fruits, but also from almost ripe fruits with brown seeds.
|Ripening stage||Germination features|
|unripe with white immature seeds||Long germination time|
|unripe and stored until ripe||Long germination time|
|unripe with brown mature seeds||Short germination time with high seedling vigor|
|almost ripe||Short germination time with high seedling vigor|
|ripe||Short germination time with high seedling vigor|
Three conclusions can be drawn from the experiment results:
- For fruits that are harvested when they are still immature with white seeds, their seeds are not fully developed. Such seeds do not germinate or take a much longer time to germinate and their seedlings have very low vigor.
- For fruits that are harvested when they are still immature with white seeds, storing them until their appearance look ripe would not improve the germination rate.
- For fruits that look unripe (like the mature-green stage of tomatoes) but with mature brown seeds, and for fruits that look almost ripe or completely ripe, their germination time is short and their seedlings have equally high vigor.
These results show that seeds can mature inside the fruit even before the fruit matures by color.
Another study on 6 wild fruit species also shows similar results (Cruz-Tejada, Acosta-Rojas & Stevenson, 2018). Seeds from fruits with a semi-ripe appearance have a high germination rate, similar to seeds from fruits with a ripe appearance.
In other words, the visual signal of fruit ripening is delayed.
3. Why fruits delay visual signs of ripening?
The phenomenon of seeds maturing before fruits appear ripe visually is known as the “delayed visual signal hypothesis”
The reasons behind this, according to plant scientists, are two-fold and are related to survival:
- to increase the chance of being dispersed by frugivores (animals that thrive on raw fruits), and
- to reduce their chance of being damaged by predators.
Fruits develop the strategy of changing fruit color (usually from a dull color to a sharp color, e.g. from green to yellow or red) in order to attract animals to disperse the seeds that are ripe and have a high chance of germination.
However, more animals are now consuming green, unripe fruits, due to food scarcity. Frugivores, such as parrots, also thrive on raw fruits. In order to increase the chance of survival, many plant species have evolved to mature their seeds much earlier than the fruit color changes. So, even when the fruits are being consumed and dispersed before they appear ripe, the seeds are already mature enough to germinate.
Also, delaying the visual cue of maturity will reduce their exposure to predators and allow the seeds more time and a higher chance to be dispersed by frugivores to other areas. This is because mature-looking fruits are attractive not only to dispersers but also to predators and pathogens such as bacteria, fungi, and certain animals.
4. Do younger seeds germinate better than older seeds?
Young seeds have a higher germination success rate than older seeds because older seeds can deplete their nutrients and lose vigor as they remain dormant.
Seeds are living entities, containing embryonic plants in a dormant phase. When the external conditions are met for optimal growth, they break the outer protective layer and germinate.
During the dormant phase, the embryonic plant slowly consumes the nutrients inside the seed, reducing the viability of the embryo.
For instance, bean seeds have a germination rate of 80 percent after one year, and 50 percent after three years.
Some plant seeds have longer longevity, such as the seeds of the Californian branched broomrape (Orobanche ramosa), which can lie dormant for decades. However, most seeds will die after 2 to 5 years.
5. How to save seeds from a tomato?
If you want to save seeds from mature-green tomatoes, you can do it successfully if you follow these steps:
- Try to bring the tomatoes inside, before the first frost. This is important because the tomatoes have to grow and ripen as much as possible naturally, before the first frost; most tomato growers suggest that you can’t save seeds from frozen green tomatoes.
- Keep in mind that tomatoes suffer during colder periods; the first chill injuries occur if exposed to a temperature of about 50 degrees Fahrenheit (10 degrees Celsius), and serious decay occurs below 40 degrees Fahrenheit (5 degrees Celsius). Try to take your tomatoes inside before the temperature drops below this temperature.
- Select a few larger tomatoes and put them in a paper bag, together with ripe fruit. This will create the gasses needed to ripen your tomatoes;
- If you have more tomatoes, ripen them in a dark room, preferably in a ventilated, open cardboard box, at room temperature. Mature green tomatoes will ripen in 15 days at 70 degrees Fahrenheit (21 degrees Celsius) and in 30 days at 55 degrees Fahrenheit (13 degrees Celsius).
- Store seeds in a dry (8 percent relative humidity or lower) and cool environment (40 degrees Fahrenheit or 5 degrees Celsius) to keep them dormant.
6. Can I grow pepper from fresh pepper seeds?
It is possible to grow a pepper from fresh pepper seeds. If the pepper comes from the store, it depends on when it was harvested. If it is picked in the “mature green” stage with fully developed seeds, the seeds are viable.
You don’t have to wait for the fruit to look completely ripe to harvest its seeds. Seeds can fully mature even before the fruit matures by color. This is called the “mature green” stage.
But to be on the safe side, wait for the fruit to break to a slightly different color (yellow or pink), even with just a slight tinge. That way, you can be sure that the seeds are fully mature and will have a very similar germination potential and vigor as seeds from fully ripe fruits.
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Burns, K. C., & Dalen, J. L. (2002). Foliage color contrasts and adaptive fruit color variation in a bird-dispersed plant community. Oikos 96:463–469.
Herrera, C. M. (1982). Defense of ripe fruit from pests: its significance in relation to plant-disperser interactions. American Naturalist 120: 218– 241.
Cruz-Tejada, D. M., Acosta-Rojas, D. C. & Stevenson, P. R. (2018). Are seeds able to germinate before fruit color ripening? Evidence from six Neotropical bird-dispersed plant species. Vol, 9 (6).
Pardo, F. & Stevenson, P. R. (2008). Conspicuousness, fruit preference and germination rate of Miconia nervosa y Miconia trinervia (Melastomataceae). Thesis. Universidad de Los Andes, Bogotá, Bogotá DC, Colombia.
Bewley, D. & M, Black. (1994). Seeds: physiology of development and germination. Plenum Press, New York, New York, USA.
Urtasun, M.M., Giamminola, E.M., Viana, M. L. (2020). Southern highland papaya (Vasconcellea quercifolia A. St.-Hil.): Do fruit ripening and harvesting time affect seed germination? Acta Scientiarum. Agronomy, vol. 42
Groot, S. & de Groot, L. (2008). Seed quality in genetic resources conservation. Centre for Genetic Resources, Netherlands.