What causes tomato plants to bear large fruit?

Question

Of course I know that some tomato varieties yield bigger tomatoes than others, but on a given plant, some of the fruits are bigger and some are smaller, so I am just wondering: Besides variety, what factors determine the size of a tomato (fruit)?

E.g.: Abundant water before they start to turn color swells them up? Abundant sun makes them ripen too fast before they get big? Hot weather? Fruit late in the season bigger or maybe smaller? Too many tomatoes on the plant makes them smaller? I'm sure there are plenty other possible reasons as well.

Answer 1

This is a very open question, and I like to see other answers.

As you wrote, variety is the main driver. Cold weather and dry soil could stop the growth of a tomato.

Position is also a determinant. Usually you have several tomatoes on a stem, so the first being pollinates will have some advantage and take more resource than other tomatoes. But varieties will determines if the difference is huge or not. By removing some tomatoes, you can make the other one (often) larger. On some extend this is true also for the size on tomatoes on other stems.

A lot of water could increase quickly the size of a tomato. But then you will see it on the tomato skin, you will see scar on skin: the skin was not able to adapt so quickly.

I think also how it is pollinated could determine the size. I don't know it in tomatoes, but on other fruits, the number of seeds (so how successfully was pollinated) determines the size of fruit.

Answer 2

While much good information has been provided, some is incorrect or partially correct. Tomatoes are primarily self pollinating, and not just to the extent of pollen being transferred between flowers. Pollination can and does occur by the pollen of one flower fertilizing the ovule within the same flower and can occur prior to the actual blooming of the flower. This is why tomato cultivars can be maintained relatively reliably without extensive manual labor. Flowers can be bagged prior to blooming which prevents cross pollination as well as pollinators from assisting fertilization. Pollinators DO assist in fruit formation as they increase fertilization by vibrating ( a bee's buzzing sound) but it is not required. Fruit size is however related to level of fertilization. Unlike what was said re: " a little bit pregnant" being impossible it is in fact exactly the case in tomatoes that more fertilization yields bigger fruit. Each fruit contains many seeds. The seeds influence fruit development by altering plant growth regulators in the fruit. Evidence of this is that sterile plants (due to chromosome imbalance fruit much more poorly and fruit size is much smaller corresponding to the number of seeds. This is also why tomato bloom set chemical sprays work. They mimic the growth regulators the seeds would normally produce in otherwise poorly fertilized situations

Answer 3

In addition to Giacomo's good answer, I'd like to mention that plants need a certain amount (sum) of light and temperature. If a fruit develops when there's more light each day and the temperature is higher, it needs fewer days compared to a fruit that started to develop when the light hours each day were fewer and colder. The fruit that developed in a longer time period has the opportunity of a higher intake of water, since you can only water this much before the skin of the fruit breaks.

Fruits of different sizes on the same plant might form on allogamous species because of pollination from another plant with compatible pollen.

Different fruit size might also happen in autogamous plants because self-pollination leads to expression of recessive genes.

The tomatoes and strawberries you mention are likely to be polyploids, meaning they have more cromosomes' sets, and therefore more seeds and larger size.

Answer 4

Potassium is highly implicated in fruit size. I've used a lot of potassium for the last couple years, and I can say that it does seem to help for most varieties in my growing conditions (but not all; Omar's Lebanese, and Marianna's Peace are a couple examples that didn't seem to benefit in my growing conditions).

Potassium can help plants absorb water. Copper may also help fruit absorb water, but I don't know if it increases fruit size. Potassium may change the flavor and/or texture, however.

Extra nitrogen, however, may (in some situations) actually increase the number of fruits that set, while not increasing the total weight of the combined fruits, according to a study I read about (which seems to say that the fruits would be more plentiful, but smaller). Excess nitrogen in other conditions may lead to few fruits and excess foliage, as is more commonly thought.

It's not all about potassium and nitrogen, though. Clearly, from my experience, there are other factors, although it's difficult to pinpoint them all. I personally believe that acclimatization to the soil and growing conditions over both the season and generations can help. Sometimes, fruits that set later on are considerably larger than the first fruits (this may have to do with the plant maturity, and how acclimatized it is).

Some people have tricks that pertain to pruning, removing other fruits, and soil amendments to increase fruit production and/or size. This is especially true with some varieties.

I don't know about for tomatoes, but some people say that micorrhizae helps in growing giant watermelons.

Hybridization between two varieties can sometimes lead to fruits larger than either parent variety.

Container size can also influence fruit size.

Answer 5

No one has mentioned fertilizer. I guess because 'fertilizer' has somehow gotten a very bad reputation for being artificial no matter synthetically or organically produced.

Plants have to have very precise amounts of chemicals with which they use to make their own food, roots, photosynthetic growth that makes food for the plants, seed production and obviously fruit production. Soil does not come with these chemicals/fertilizers naturally. In self sustained ecosystems, there is little to none of these chemicals in the soil until something dies. That helps to maintain the system and limit population and subsequent needs of these chemicals.

The chemicals necessary for photosynthesis which makes the food for the plants to use as energy, also are responsible for the size and vigor of the plants and the size of the reproductive parts of plants; such as size of tomatoes.

The amounts of fertilizer necessary are found through soil tests and the ability to recognize the needs of your plants by how they look. And the sooner the better. When someone gets to the point of 'knowing' without soil tests what their plants need via experience and remembering the formulations already added, what kinds of organic material that has been added, what the symptoms look like by the plants showing deficit, excess of chemicals (nutrients) one is able to manage the chemistry of their soils to optimize vigor and larger fruits.

The manual process of taking reproductive growth off the plants; flowers and fruit/seeds is an important way to add more energy back into the plant and its vegetative growth. Cutting flowers off even before they open is excellent. You enable more energy into your plant to get larger, more vigorous, store more food/energy with which to produce even more flowers (especially annuals). To get more fruit/larger fruit you allow the flowers to grow into seed/fruit and select certain fruits you want to grow large. If you have a lot of flowers thus a lot of fruit you'll get smaller fruit if there isn't enough room to grow larger and if there isn't enough chemistry to put energy made by the plant into larger fruits. Taking off flowers and/or fruits will send that energy into the seed making/fruits and vegetative growth that are left.

If there are the proper chemicals, lighting and water to continue the photosynthesis you won't have to worry about pruning reproductive growth. Regular watering, regular temperatures, regular vigilance with chemicals will make fruits the size they were genetically designed to make.

The problem is, just a wee bit too much fertilizer will kill your plants. The pH of the soil has the ability to remove chemicals from access by your plants. The temperatures do the same thing. Some of the chemicals necessary if added in too large amounts or if deficient will also cause some chemicals to not be accessible to plants. If the soil has no life; mycorrhize, bacterias necessary for plant roots to up take chemicals that are in the soil, that will hamper plants as well to be able to access and up take necessary chemicals to make food/energy with which to make more vegetative growth or reproductive growth.

In addition, one of the most important concepts to produce reproductive growth versus vegetative growth is the proportions of chemicals added. If for instance you add a fertilizer with a formulation of 7-6-4, you will promote vegetative growth. If you add a fertilizer with a formulation of 10-12-14 you will enhance reproductive growth and the propensity to be able to get larger fruits. Too much Nitrogen in relation to the Phosphorus and Potassium percentages will enhance vegetative or leafy growth. Reproductive growth will suffer.

Great for salad greens, kale, rhubarb but if you want reproductive growth; raspberries, tomatoes, squash, cucumbers you need to watch carefully that the Nitrogen is less than the other two macro chemicals.

These are chemicals not nutrients or food. That is why I try to not use the word 'nutrient' as people think of nutrients in their own terms of food/fuel. Too much food for us just makes us fat not dead. For plants, there is an optimum amount of chemistry; a little too much of one chemical causes symptoms of excess, too little causes symptoms of deficiency and just a little too much of a few chemicals will most certainly kill plants.

Fertilizing is an important science we humans have to learn and understand. Stable ecosystems where we humans have not had the chance to disturb are so finely tuned there is just enough for the health of plants until something is allowed to die to be added back into the ecosystem for use by that ecosystem.

We humans go in and remove the biomass of these ecosystems and that soil will be deplete for the needs of plants we want to grow or for new plants in that ecosystem. The rainforest for instance. We burn and cut down the rainforest and that land is worthless for crops. Maybe the first year there might be enough chemistry to grow one crop but that is it. Most people have heard this but this is true every time we remove the forests and expect yummy soil to grow our crops. We humans are actually mining the chemistry of that soil by removing the biomass.

We have to learn how to add chemicals back into the soil so that we are able to grow crops for ourselves to eat. If we do not understand the chemistry in our soils and do not add fertilizer because some article says that fertilizer is bad we have misunderstood the entire biological/botanical/mineral parts of the system and we will not be able to grow anything with success...

Soils are an amazing science. The only way that has been found to improve our soil texture/structure/organics to enhance botanical growth is by the addition of already decomposed organic matter. To decompose organic matter organisms that are in charge of decomposition need lots of nitrogen. Once they have done their job by decomposing something newly dead, only then is that organic matter now decomposed available for use by micro and macro organisms in the soil to eat for energy. While organic material is being decomposed all the other organisms go to sleep, dormancy or die. Once the decomposers have decomposed organic matter there is then 'food' for the micro and macro organisms to wake up and reproduce. Plants need to have these micro and macro organisms to uptake chemicals they need for photosynthesis (to make food and seed). The decomposed organic matter is critical as well to improve the tilth of the soil for air, organisms and plant roots to thrive.

What is it that you are wanting to accomplish? Large tomatoes, more tomatoes, longer lasting tomato plants? What have you been using for management skills? What hasn't been working?

Hope this helps generate more questions...ask away!