If you have sliced open enough tomatoes, there is a chance that you have seen one with the seeds sprouting inside. The sprouted seeds look strange, like small green and white worms, and it made me wonder exactly how it happens.
So, why do tomato seeds sprout inside a tomato? Tomato seeds sprout inside a tomato due to a lack of the hormone abscisic acid. This hormone normally keeps tomato seeds dormant until the time is right for them to sprout. The seeds inside a tomato are more likely to sprout if the tomato was exposed to prolonged cold (more than a few days below 55 degrees Fahrenheit) and then left in a warm place.
Of course, there are other factors that will contribute to tomato seeds sprouting inside the tomato. Let’s take a closer look at some of those factors. Then we’ll get into how to prevent this strange phenomenon.
Why Do Tomato Seeds Sprout Inside the Tomato?
Tomato seeds will sprout inside the tomato when there is not enough of the hormone abscisic acid. According to Wikipedia, abscisic acid is a plant hormone that plays a role in seed dormancy by inhibiting germination (or sprouting) of seeds.
- Prolonged exposure to temperatures at or below 55 degrees Fahrenheit (12.8 degrees Celsius). For example, when tomatoes experience cold weather in the early fall before harvest, or when they are shipped at cool temperatures to preserve them for grocery store shelves.
- Overripe tomatoes. For example, fruit left on the vine too long, left on grocery stores shelves too long, or left in your house too long.
- Potassium deficiency. For example, due to soil depletion during growth, or lack of fertilizer containing potassium (the K in NPK).
- Too much nitrogen. For example, over fertilization using either high-nitrogen fertilizers or “hot” manure containing lots of nitrogen.
When a tomato does not have enough abscisic acid, the seeds can sprout inside the tomato and start growing. In fact, a sprouted seed may grow so large that it breaks through the skin of the tomato and becomes an entire new plant! However, the seed must go through dormancy before this can occur.
Seed dormancy refers to the time period when a seed is not growing or developing. Instead, a seed in dormancy is saving its energy and nutrients so that it can sprout when growing conditions improve.
For example, a tomato seed will stay dormant during cold weather to avoid sprouting during the winter (since frost and freezing temperatures will kill tomato seedlings and plants!) When spring comes and brings warmer temperatures, a tomato seed will break dormancy and sprout, given the proper conditions (more on this later).
Normally, the seeds inside a tomato remain dormant throughout the fall and winter. However, a lack of abscisic acid will cause the seeds to end their dormancy early – possibly while still inside the tomato!
Note: this seed-sprouting phenomenon has a more general name, and is called “vivipary”, which is Latin for “live birth”. According to Wikipedia, vivipary is when seeds or embryos start developing before being separated from the parent. This would be akin to a chicken laying a hatched baby chick instead of an egg!
What is Needed for Tomato Seed Germination?
Now we know that tomato seeds sprout inside a tomato due to a lack of the hormone abscisic acid. However, this plant hormone is not the only factor at play. There are other requirements for a tomato seed to germinate.
Temperature is one of the most important factors for tomato seed germination. If temperatures are lower than 50 degrees Fahrenheit (10 degrees Celsius), then they will not germinate. According to the University of California, tomato seeds can take 6 weeks to germinate at this borderline temperature!
The ideal temperature range for tomato seed germination is 65 to 85 degrees Fahrenheit (18.3 to 44.2 degrees Celsius). Within this temperature range, tomato seeds will germinate in 6 to 8 days.
Note: if you want to learn more about starting your own plants, you can read all about tomato seed germination in my article here.
The internal temperature of a tomato sitting in your house could easily fall into this ideal temperature range, which would provide ideal conditions for some of the seeds to sprout. Of course, this is more likely if you bought the tomatoes from a grocery store.
Tomatoes bound for grocery stores are often kept in cold temperatures during shipping (the ideal temperature for preservation is 58 degrees Fahrenheit). This prevents the tomatoes from rotting, and it keeps them looking good for grocery store shelves.
However, this long exposure to cold might “trick” tomato seeds into thinking that they have gone into dormancy to survive the winter. A return to warmer temperatures in your house might convince them that spring has arrived and it is time to sprout!
Older tomatoes are more prone to vivipary. The longer tomatoes sit in your house at warm temperatures, the more likely this is to occur.
Tomato seeds also need plenty of moisture in order to germinate. When starting seeds indoors for growing, the soil needs to be kept constantly watered to keep seeds moist, or else they will dry out and die.
However, soil itself is not a requirement for tomato seed germination! In fact, a tomato seed can germinate in a moist paper towel!
The seedling can then be transplanted to a hydroponic system. The plant can produce ripe tomatoes without ever touching soil!
Although there is no soil inside of a tomato, there is plenty of moisture, and the tomato seeds are right in the middle of all of it! Combined with the right temperature, the seeds will have the perfect environment for sprouting – even if it happens while still inside the tomato!
Light (Do Tomato Seeds Need Light to Germinate?)
Tomato seeds do not need light to germinate, so they will have no problem sprouting while still inside a tomato. So, the seeds could still germinated inside a tomato left in a shady corner of your kitchen.
However, after a tomato seed germinates (sprouts), the young seedling does need light so that it can continue to grow. If you want to grow the sprouted seeds from inside a tomato, transplant them into soil and give them sunlight to encourage them to grow.
Just remember that the seeds from a hybrid tomato variety may not grow true to the parent type. This means you may get a different type of tomato than what the parent plant yielded!
How to Prevent Tomato Seeds from Sprouting Inside the Tomato
Vivipary in tomatoes is a rare occurrence. However, there are a few steps you can take to prevent it from happening if it really bothers you:
- Grow your own tomatoes and harvest them on time – if you grow your own tomatoes, they will not be exposed to cold (as long as you harvest them before cold weather comes in the fall!) This will prevent the seeds from being “tricked” into dormancy and then sprouting inside the tomatoes later on.
- Buy your tomatoes from a farmer’s market or CSA – if you cannot grow your own tomatoes (due to lack of space or interest), then you can buy from a local farmer’s market or CSA. Some hydroponic growers produce tomatoes all the time, and indoor farmer’s markets may surprise you with their produce. Either way, the tomatoes will not be refrigerated to keep them fresh, as they would be when shipped to grocery stores.
- Use your tomatoes promptly – after you buy or harvest your tomatoes, use them promptly. The longer they sit on your counter, the greater the chance of the seeds sprouting inside the tomato. If you tend to forget about your produce, leave them in a place where you will see them. If you cannot think of a meal to make with fresh tomatoes, then stew them to use for chili. You could also make pizza or pasta sauce.
- Store your tomatoes out of sunlight – this will keep them cooler. Tomato seeds germinate faster at warmer temperatures, so leaving them in a shaded part of the kitchen will slow down any potential sprouting.
- Do not refrigerate your tomatoes – this will prevent the “cold shock” that can trick seeds into thinking they have gone into dormancy.
Why Do Seeds Not Germinate in the Fruit?
The dormant state is what prevents seeds from germinating in the fruit. Under normal circumstances, a seed must undergo a period of exposure to cold temperatures, before it will germinate when warm temperatures return.
This helps the seeds of the fruit, including tomatoes, to survive through the winter. Otherwise, a sprouted seed could be killed by frost or freezing temperatures.
Even if it survives the cold, a young seedling could also be eaten by a hungry animal trying to survive the winter. A seed stuck in frozen soil is almost guaranteed not to be eaten by any creatures – at least until spring arrives!
When seeds do germinate inside of fruit, it usually happens at warmer temperatures. It is also more likely to happen in fruit where there is plenty of moisture, such as tomatoes, peaches, pears, or lemons.
Now you know why tomato seeds sprout inside the tomato, and how it usually happens. You also know why the conditions inside a warm tomato are perfect for tomato seeds to sprout.
I hope you found this article helpful – if so, please share it with someone who will find it interesting.