Purple tomatoes are health enriching tomatoes developed through breeding or genetic engineering. They have a high level of anthocyanins, a pigment that brings about deep color in fruits and vegetables. There are true purple tomatoes and so-called purple tomatoes. So-called purple tomatoes have traces of green due to the green flesh gene which prevents chlorophyll breakdown.
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Where to buy purple tomato seeds
Purple Tomato seeds are available online for purchase as well as offline in gardening stores in many parts of the United States. Seeds are usually sold seasonally and often sell out. Popular online stockists of the seeds include Amazon and West Coast Seeds.
The Scientific Story of Purple Tomatoes
L.C. Marquart first used the term anthocyanins in 1835 in reference to the blue pigment found in flowers. Later in the 20th Century, Richard Willstatter isolated and chemically characterized plant pigments. By this time they consisted of red, purple and blue cutting across a variety of plants.
Today, anthocyanins are known to be in flowers, fruits, seeds, roots, and leaves. There are over 700 anthocyanins. These pigments have no odor and generally have no flavor. Anthocyanins are polyphenolic compounds belonging to the larger class of flavonoids. They are sometimes simply referred to as flavonoids.
Purple tomato breeding and genetic engineering
Tomatoes began in the wild. They carry the genetic capacity to produce anthocyanins. In the wild, mutations switch off the necessary biological pathways and regulatory elements. Anthocyanin-enriched tomatoes have thus been produced using breeding and genetic engineering. Tomatoes developed this way are what are referred to as true purple tomatoes.
On the other hand, so-called purple tomatoes have been available to home growers for many years. Examples are the heirloom Cherokee Purple tomato passed down generations. Although easily confused for the purple tomato, these tomato varieties are not true purple tomatoes. They are pseudo purple tomatoes. This is best illustrated by their traces of green even when ripe. The green flesh gene in the tomato prevents chlorophyll breakdown.
There is thus a marked difference, physically and scientifically speaking, between true purple tomatoes and so-called purple tomatoes.
The development of true purple tomatoes especially using genetic engineering has been resisted by GM Watch. The organisation argues that there are over 200 alternative fruits and vegetables with naturally occurring anthocyanins that are beneficial to human health. For this reason, GM Watch has argued that there is no justification to genetically modify the tomato for this purpose.
Nevertheless, purple tomatoes are intentionally developed with high concentration of anthocyanins. The development of true purple tomatoes has thus seemed to follow the less controversial breeding route especially in the United States. A good example is the Indigo Rose Purple Tomato which is discussed in detail later below.
Health benefits of Purple Tomatoes
Integration of purple tomatoes, and other fruits and vegetables with anthocyanins, in the human diet is thought to have preventative and controlling benefits against diabetes, cancer, cardiovascular diseases and obesity. This is supported by this 2004 study as published in the Journal of Biomedicine and Biotechnology.
Anthocyanins are increasingly generating interest in studies focused on the health benefits of phytochemicals in preventive medicine. Phytochemicals are chemicals originating from plants.
As stated earlier, anthocyanins are not only in tomatoes but also in a wide variety of edible fruits and vegetables. Examples include purple onion, purple potato, red cabbage, eggplant and pepper.
Their antioxidant and anti-inflammatory actions have been known to be beneficial to human health. Furthermore, high levels of anthocyanins in purple tomatoes may also have a neuroprotective benefit.
The pursuit of developing anthocyanins in tomatoes is directly linked to the widespread consumption of tomatoes in the human population across the world. This is in comparison to other anthocyanins-rich fruits and vegetables.
The Indigo Rose Purple Tomato
The Indigo Rose Purple tomato is an indeterminate deep purple tomato variety developed through many years of cross breeding work. The tomato can easily be mistaken for a plum in shape, size and color. It is a true purple tomato sought after by the American market of home gardeners.
The Indigo Rose has a purple exterior which when cut open exposes thick red interior flesh. It has a thick skin of flesh and a handful of seeds inside. Each fruit weighs between 70 and 80 grams.
Image source: OSU.
The story of the Indigo Rose Purple tomato started in the 1960s. Breeders cross-cultivated tomato varieties with wild species found in Chile and the Galapagos Islands. In 2012, the novelty type of true purple tomatoes was released to the home gardening market in the United States. The development of this tomato was done by the Oregon State University (OSU) under the leadership of Jim Myers (pictured). In 2021, OSU released another purple tomato, the Midnight Roma.
See below for discussion on how to grow the Indigo Rose.
How to grow Purple Tomatoes
Growing true purple tomatoes is in many ways similar to growing normal indeterminate garden tomatoes. See our full feature here on how to grow tomatoes. The steps in the feature are generally applicable to growing purple tomatoes, save perhaps for purple tomato exposure to sunlight and harvesting indicators which are explained below.
Soil for Purple Tomato
Purple tomato is planted and grown in loam or sandy loam soils which are nutrient rich. Native garden soil may also be used to grow these tomatoes with the necessary nutrient amendments. If the soil is magnesium deficient, Epsom Salt may be added to the soil at the time of planting.
Planting Purple Tomato
Purple tomatoes are lovers of warm weather. Seeds are started indoors some 6 to 8 weeks before the end of frost. Prior to outdoor transplanting into the garden, the seedlings are hardened off for 2 weeks. This is done by exposing the seedlings to outdoor elements for 2 hours a day. This amount of time is steadily increased in the following days to include direct sunlight.
Once the soil is warm, the seedlings are planted directly in the soil at a distance of 2 feet apart. The planting holes are dug to be 10cm in diameter and 10cm in depth. Manure or NPK is added to the hole before the seedlings are planted one per hole.
Watering Purple Tomato
Purple tomatoes require even watering. The soil in which they grow should not be let to dry. It must be be kept moist and this can be checked by dipping a finger into the soil. Mulch is also used to control moisture loss from the soil.
Exposure to sunlight
Purple tomato require at least 6 hours of sunlight per day. This is standard across most tomato varieties. However, purple anythocynin only produces when the tomato is exposed to sunlight. Sunlight is so vital such that if the fruit is shaded by a leaf the pigment will not develop.
The science to this behaviour is that sunlight triggers the production of anythociynns as means by which the tomato can protect itself from the sun’s UV light. Where there is no exposure to the sun there is therefore no need for the pigmentation to be produced.
Care and Maintenance
The purple tomato is an indeterminate tomato. This makes it a vining tomato which is available for fruiting all season. In a similar fashion as regular tomatoes, purple tomato is supported with stakes, trellises or cages.
The tomato plants are regularly pruned by removing suckers and excess foliage that is not beneficial to the plant. This promotes a higher yield and quality fruits.
Purple Tomato Diseases
The Indigo Rose in particular does not have resistance to some of the most popular tomato diseases – fusarium and verticillium wilt. Once the disease has caught on there is no effective treatment. Growers are advised to immediately remove the infected plants and properly dispose it. In some cases, infected soil is also removed. One effective way of helping purple tomatoes have a fighting chance against non-resistant diseases is through grafting.
Harvesting Purple Tomato
Days to maturity
Purple tomatoes are ready to harvest in 91 days from the day of transplant. This timeframe is based on the Indigo Rose which is widely sold in the United States. This harvest timing is generally later than other popular regular tomato varieties.
For example, the Indigo Rose purple tomato ripens some 8 days or one week after the popular Early Girl. Furthermore, it also ripens some 13 days after the Siletz variety. Fruit yield of this purple tomato variety is also lower than the foregoing two regular varieties.
How to tell when purple tomato is ripe
Purple tomatoes are ripe when their color changes from a shiny-blue purple to a dull-purple brown. This is not always obvious for first time growers. For its best taste, the Indigo Purple Tomato must first fully develop its sugars and acids. This is achieved when the fruit turns to dull-purple brown color.
Furthermore, when ripe, the purple tomato softens to the touch in a similar fashion as regular tomatoes. In addition the bottom section of the tomato changes from green to red. When the tomato fruit is picked before it is completely ripe, it can be ripen in a week by exposure to sunlight.
What to do with Purple Tomatoes
Purple tomatoes are primarily used in culinary applications. This ranges from salads to sandwiches and cooking. The tomatoes are best enjoyed raw and can be added to salads and other raw dishes alongside other colorful ingredients.
Most recipes made using the so-called purple tomato, Cherokee Heirloom, can easily be redone using true purple tomatoes. This includes heirloom tomato sauce (see video below) and homemade marinara sauce (spaghetti sauce) among others.
In this video, tomato sauce is made using heirloom tomato varieties. Purple tomatoes can easily be used to make the same tomato sauce.
Conclusion
Not all purple looking tomatoes are true purple tomatoes. True purple tomatoes with a high level of antioxidants are breed or genetically engineered. Due to activism, the cross-breed purple tomato is what is accessible to most home gardeners. The best known purple tomato in the United States is the Indigo Rose. Purple tomatoes are indeterminate tomatoes generally grown in the same way as regular tomatoes. However, they have a different growing timeframe and offer slightly different ripening indicators. Once harvested, purple tomatoes have a variety of applications which generally match that of regular tomatoes.
Jump to our in-depth feature on Indeterminate Tomatoes
Jump to our in-depth feature on How to Grow Tomatoes
