The Organic Outdoor Tomato Project

We develop tomato cultivars for outdoor cultivation with participatory, organic breeding. Commercial horticulture, trade and processing, botanical and amateur gardens, extension services and research work together nationally and internationally. Results and materials are continuously made available at this site. Contact via Freiland-Tomatenprojekt[at]uni-kassel[dot]de

Project description

The Organic Outdoor Tomato Project led by Dr. Bernd Horneburg started in 1996 with observations on field resistance in several seed nurseries and in 2003 nationwide with up to 34 trials in Germany. Specific work is carried out internationally (e.g., Horneburg & Myers 2012, Miles et al. 2010, Steinschneider et al. 2017). The project is based on the free exchange of knowledge and seeds. The Open Source Seed Licence was introduced with the cultivar Sunviva (Kotschi & Horneburg 2018, Kotschi et al. 2017). The breeding program is based on great plant and human diversity and can therefore react quickly to new challenges.

Background: Globally and also in Germany, tomatoes are the number one vegetable. In Germany, only a small part of the demand is produced, although tomatoes are grown in almost every market garden. Processed tomatoes, the largest part of consumption, are almost 100% imported. A major limiting factor to the expansion of tomato production is the difficulty of growing tomatoes outdoors, which is much more resource-efficient and cost-effective than production in greenhouses and polytunnels. Production is severely limited by Phytophthora infestans, the fungal pathogen that causes late blight. In the 1990s, the pathogen had become so virulent that commercial cultivation in the open virtually came to a standstill (overview in Horneburg & Becker 2011). Even in protected cultivation, P. infestans can cause considerable damage if temperatures drop below the dew point.

Resistance breeding against P. infestans is the central pillar. Since infestation is not to be expected at every location in every year, breeding nurseries are established in the network at several locations. Research has been conducted to determine which resistances are effective (Miles et al. 2010, Raj 2019) and the selection methodology has been improved (Horneburg & Becker 2011). Potential sources of resistance are continuously included.

Fruit quality is on the tongue in tomato; it is given special consideration in the breeding program. The “Breeders’ Sensory Test”, an efficient method of testing a large number of small samples with a small team, was developed in the project, used with success (Eghbal 2015) and has now also been scientifically studied (Hagenguth et al. 2022). Quality testing plays a major role in parental selection (Mohammed et al. 2019 and 2012), as well as for selection and release of cultivars (Zörb et al. 2020). As a precaution against fungal toxins, resistance to Alternaria solani was investigated (Wojciechowska et al. 2014).

Cold tolerance, nutrient efficiency and drought tolerance as elements of general robustness are indirectly selected for. Robustness results in reduced dependence on irrigation and fertilisation, and plants can become productive again after periods of infestation. Most cultivars are also interesting for cultivation in containers. In protected cultivation, two or three shoots are usually required.

Bush tomatoes for container cultivation in urban gardening and processing for direct marketing and in community supported agriculture (see below: Scholz-Döbelin nursery) have been worked on since 2019.

The participation of active members of the value chain is possible and desired, from simple practical tests to extensive trials. In addition to commercial horticulture, we are currently looking in particular for:

  • seedling production for regional supply
  • school gardens
  • trials in allotment gardens
  • farms that want to test field cultivation for processing.

Funding: The project is made possible by personal commitment. Important sections were funded by the Rut- und Klaus-Bahlsen-Foundation, BÖL, BÖLN, Zukunftsstiftung Landwirtschaft, EFRE, Software AG-Foundation and the Lower Saxony Ministry of Food, Agriculture and Consumer Protection.

List of cultivars

Year of accreditation / Registration / Fruit weight

Resibella: 2019, by Culinaris, 50g
Rondobella: 2019, by Culinaris, 100g
Vivagrande: 2018, by Culinaris, 200g, Open source seeds licence
Sunviva: 2017, by Culinaris, 20g, Open source seeds licence
Primabella: 2012, by Culinaris, 30g
Clou: 2010, by Arche Noah, 35g
Dorada: 2010, by Arche Noah, 25g
Primavera: 2010, by Arche Noah, 25g
Resi: 2010, by Arche Noah, 20g

From the field

Please note text might be the result of semi-automated machine translation and is only intended as a working aid. Translated texts are indicated by an asterisk (*). No liability is accepted for any translation inaccuracies or errors. In any case, the German version is legally binding.

Culinaris produces and trades organic seeds with a focus on cultivation and use in home gardens and direct marketing. In addition to the most important crop, the tomato, Culinaris has a strong focus on fruiting vegetables (peppers, eggplant, etc.), but also from salads to cabbage a wide range has been created. All varieties are tested and selected under ecological low-input conditions (moderate fertilization, watering, etc.) in extensive variety comparisons before being included in the assortment. Culinaris thus hopes to contribute to horticultural success and more fun in gardening. The cultivation and breeding areas are located south of Göttingen on the edge of the fertile Leine valley with annual precipitation around 650 mm and an annual average temperature of just under 9°C.

Culinaris has been involved in the field tomato project from the very beginning. While Culinaris initially focused on providing seed for growers, gardeners and young plant companies, this role has evolved and expanded greatly into the area of active breeding. In the meantime, the Culinaris premises, together with those of the LohmannsHof nursery in Westen, are the main breeding sites. By distributing and selling the developed varieties to home and commercial growers, Culinaris also provides the funds needed for further breeding and has thus become an important interface between growers, breeders and end customers. To carry out this task, Culinaris, together with a network of seed growers, also takes care of the maintenance breeding of the varieties already developed, as well as the multiplication and quality control of the seeds. Variety registrations and market introduction are also the responsibility of Culinaris.

Culinaris is regularly looking for new people to carry out the valuable tasks in breeding and multiplication. Please apply to support our work!

Tomato Day 2021. From right: Matthias Stagge, Moritz Halekotte. Center: Dr. Bernd Horneburg
Tomato Day 2021, tasting and selection of breeding lines
Conservation breeding and propagation

Knofi & so has market stalls in the region that offer a wide variety of varieties. Outstanding is the praise of the varieties. Tomato seedlings can be offered in a very large variety, as a targeted cultivation is possible through advance orders. Detailed information is offered on the varieties.

If the harvest quantity is sufficient, tomatoes are offered in pure varieties. The cultivation of Primabella was particularly successful over several years and is awarded as "Sun Tomato - Open Field".

Young plants with detailed information
Trellis with straw mulch
Varietal marketing

LohmannsHof nursery has been growing field-grown tomatoes in the North German Plain since 2015. Farms that want to try out market crop cultivation or produce seed are advised.

Max Rehberg (3rd from left) and Dr. Bernd Horneburg (left) give an introduction to the organic breeding garden at Tomato Day 2020.

The end of a successful season

The Bioland nursery of the Magnuswerkstätten in 86859 Igling Holzhausen belongs to Regens Wagner Holzhausen and is located between Lech and Wertach on the edge of the foothills of the Alps at 600m above sea level with 1000 mm of annual precipitation and an average temperature of 7.5°C. Converted since 1986, 2400 m² are cultivated there under glass and foil, and fine and field vegetables are produced on 11 ha of sandy loam over lime marl. Our vegetables are mainly sold in direct marketing with farm store and markets. As part of our nursery we run a teaching garden with a 400 m² foil tunnel and a small outdoor area. In our training garden, we train young people with disabilities to become horticultural specialists (vegetable gardening). As part of this training, we have been participating in the outdoor tomato project for several years now.

Outdoor tomatoes are a challenge in themselves, but in our situation? We have a tomato trellis about 2m high, a support every 3m and a steel cable to hang the tomatoes. Planting is then every 50 cm, depending on the weather between mid and late May. Usually one plant is planted from about 30 varieties or genotypes and then the whole thing is repeated 3 to 4 times to reduce the influence of location. If hail and frost spare us, the harvest of the early varieties begins around mid-July. We first plant a so-called standard set of varieties with a wide range of characteristics. Among them are very early and very late, as well as disease-susceptible and highly resistant varieties. These are then joined by new varieties and genotypes that are also in the breeding process. Through the known standards with their known characteristics, new varieties can be put in relation to the location.

In our country, disease control traditionally begins with the first Alternaria wave and is then continued every 1 to 2 weeks, depending on the infection, until the plant dies. Towards the end of the season, we regularly have Phytophthora moving through our plant, which enables us to provide the network with information on late blight and blight resistance that is important for selection. Furthermore, we collect data on the first and last ripe fruit and conduct a mass harvest survey.

If the tomatoes end up looking like the photo, then for us it is

The end of a successful breeding season

Photo with Heinz Datzmann in autumn 2020
Heinz Datzmann in the fall of 2020

It all started with fruit in 1995.

The fruit farm Scholz-Döbelin GbR was founded in 1995 by Heike Scholz-Döbelin and Herwig Scholz on a small area as a sideline organic farm. The main focus was on the cultivation of apples, raspberries, currants and blackberries. Gradually, a small cidery was established, mainly for pome fruits. We produce in the Rhineland at about 60 m above zero with Atlantic climate on 80 soils in the middle of a large potato growing area with about 750 mm annual precipitation.

In addition to fruit and vegetable production, we offer plots in a garden project for private individuals to grow their own vegetables and soft fruits. Since spring 2019, we produce for the solidarity agriculture "Living Earth Krefeld". From Schwalmtal, we supply around 150 families with fresh vegetables and fruit every week.

Tomatoes, in abundance

It is hard to imagine our kitchen without tomatoes. They should taste as fresh as possible and be suitable for pasta and pizza. Outdoor cultivation offers special and intense taste experiences. First experiments started in 2015 with 'Philovita F1', one of the first varieties that showed a higher tolerance to late blight. As early as 2016, the trials were expanded to include varieties from the Organic Outdoor Tomato Project, offering a wider range of varieties that are particularly tolerant to late blight. Today, we grow outdoor tomatoes on a good 1,000 m².

Trials in the outdoor tomato project

In 2020, this was followed by a field trial with 18 varieties in the open, accompanied by the Plant Protection Service of the NRW Chamber of Agriculture. The aim is to test the cultivability in the Atlantic climate with a regionally high infection potential for late blight. In 2021, further sightings are planned for bush tomato varieties suitable for outdoor cultivation with comparative varieties in cultivation.

Processing Suitability

The majority of tomato cultivation in Central Europe is focused on varieties for the fresh market. However, even for solidarity farming and also in direct marketing, tomato cultivation in the unheated foil house and in the open field encounters a market saturation in summer that cannot be discussed away. In order to be able to offer regional tomatoes in sufficient quantities as early as possible at the end of June/mid-July, a larger scale of cultivation is required: at the beginning in the foil house and then expanded in the open field. At the end of July/beginning of August the yields increase, in the middle of the summer vacations. In the beginning, everyone is happy with 3-6 kg of tomatoes per week, but soon saturation sets in, even for enthusiastic solo growers. And by the middle/end of October at the latest, the regional supply comes to an end. Therefore, we process the "excess quantities" in the summer as strained tomatoes, whole cherrys in a jar or also concentrated. Soon perhaps also as ketchup.

Our interest is therefore to capture the summer also for the winter as long as possible in the jar. Our goal is to cover largely the entire annual demand of processed tomatoes of our solidarity harvest distributors through processing. Therefore, when we look at the assortment, we are not only concerned with supplying the fresh market, but also with qualities for processing.

Vine tomato sighting between the tomato trellis 2021
Vine tomato sighting between the tomato trellis 2021
Variety sighting 2020 in the trellis plant in late summer
Pasteur for preserving tomatoes in jar

Literature and the media

  • Erika, C., Ulrich, D., Naumann, M., Smit, I., Horneburg, B., Pawelzik, E. (2022) Flavor and Other Quality Traits of Tomato Cultivars Bred for Diverse Production Systems as Revealed in Organic Low-Input Management. Frontiers in Nutrition 9:916642. doi: 10.3389/fnut.2022.916642. [PDF]
  • Hagenguth, J., Kanski, L., Kahle, H., Naumann, M., Pawelzik, E., Becker, H. C., Horneburg, B. (2022): Breeders' Sensory Test: A new tool for early selection in breeding for tomato (Solanum lycopersicum) flavour. Plant Breeding, 141( 1), 96– 107. doi: 10.1111/pbr.12994.
  • Che, A., L, Erika, C., Naumann, M., Smit I., Horneburg, B., Pawelzik, E. (2021): Morphological, Leaf Nutrient, and Fruit Quality Characteristics of Diverse Tomato Cultivars under Organic Low-Input Management. Sustainability 2021, 13, 12326. doi: 10.3390/su132112326.
  • Horneburg, B., Volk, M. (2022): Anleitung zum Kreuzen von Tomaten [Instruction on crossing tomatoes]. Lehrvideo [Training video]. url:
  • Che, A., L, Erika, C., Naumann, M., Smit I., Horneburg, B., Pawelzik, E. (2021): Morphological, Leaf Nutrient, and Fruit Quality Characteristics of Diverse Tomato Cultivars under Organic Low-Input Management. Sustainability 2021, 13, 12326. doi: 10.3390/su132112326.
  • Zörb, C., Piepho, H.-P., Zikeli, S., Horneburg, B. (2020): Heritability and variability of quality parameters of tomatoes in outdoor production. Research, Bd. 2020, Artikel-ID: 6707529. doi: 10.34133/2020/6707529.
  • Mohammed, A.E., Smit, I., Pawelzik, E., Keutgen, A.J., Horneburg, B. (2019): Organically-grown outdoor tomato: fruit mineral nutrients, potential contribution to human diets and plant infection by Phytophthora infestans. Org. Agr. doi: 10.1007/s13165-019-00253-7.
  • Kotschi, J., Horneburg, B. (2018): The Open Source Seed Licence: A novel approach to safeguarding access to plant germplasm. PLoS Biol 16(10):e3000023. doi: 10.1371/journal.pbio.3000023.
  • Horneburg, B., Becker, H.C. (2018): Spontaneous outcrossing in tomato depends on cultivar and environment and varies between individual flowers. Plant Breed. 137:638–643. doi: 10.1111/pbr.12600.
  • Horneburg, B., Rehberg, M. (2017): Die Tomatensorte ‘Sunviva’ ist nicht patentierbar. Gemüse 11/2017:58.
  • Holzinger, A., Rehberg, M., Horneburg, B. (2017): Ökologisch produzierte Tomatenjungpflanzen für Hobbygärtner. Gemüse 9/2017:48–49.
  • Kotschi, J., Rehberg, M., Horneburg, B. (2017): Open-Source Seeds and the Tomato cultivar Sunviva. SAVE e-News 2/2017. url:
  • Kotschi, J., Rehberg, M., Horneburg, B. (2017): Open-Source Seeds und die Tomate Sunviva. SAVE e-News 2/2017. url:
  • Lerch, F., Horneburg, B. (2017): Paradeiser im Freiland. In: ARCHE NOAH Magazin (Hrsg.): S. 20–21
  • Steinschneider, C., Horneburg, B., Lerch, F. (2017): Freiland-Paradeiser in Österreich bei Befallsdruck durch Phytophthora infestans. In: Ländliches Fortbildungsinstitut Österreich (Hrsg.) Biogemüsefibel 2017:9–13. url:[tt_news]=374&cHash=9eaac78cb257eafc6abb04d4ef6c9e4e.
  • Hönigsberger, B., Antonelli, L., Samad, A., Horneburg, B., Trognitz, F. (2016): Genotype dependent microbiome of 60 different tomato cultivars. 67. Tagung der Vereinigung der Pflanzenzüchter und Saatgutkaufleute Österreichs 21.–23.11.2016, HBLFA Raumberg-Gumpenstein, Irdning, Österreich. url:
  • Wojciechowska, E., Weinert, C.H., Egert, B., Trierweiler, B., Schmidt-Heydt, M., Horneburg, B., Graeff-Hönninger, S., Kulling, S.E., Geisen, R. (2014): Chlorogenic acid, a metabolite identified by untargeted metabolome analysis in resistant tomatoes, inhibits the colonization by Alternaria alternata by inhibiting alternariol biosynthesis. Eur J Plant Pathol 139:735–747.
  • Klaedtke, S., Horneburg, B. (2012): Aromatische Tomatensorten trotz Krautfäule – auch in Luxemburg? Gaart an Heem Ausgabe Mai 2012: 132. Zeitschrift der "Ligue luxembourgeoise du Coin de Terre et du Foyer" (CTF).
  • Horneburg, B., Myers, J.R. (2012): Tomato: Breeding for improved disease resistance in fresh market and home garden varieties. In: Lammerts van Bueren, E.T., Myers, J.R. (Hrsg.). Organic Crop Breeding. S. 239–250. Wiley-Blackwell, Hoboken, NY, USA. ISBN: 978-0-470-95858-2.
  • Mohammed, A.E., Smit, I., Pawelzik, E., Keutgen, A.J., Horneburg, B. (2012): Organically grown tomato (Lycopersicon esculentum Mill.): Bioactive compounds in the fruit and infection by Phytophthora infestans. J Sci Food Agric 92:1424–1431.
  • Horneburg, B., Becker, H.C. (2011): Selection for Phytophthora field resistance in the F2 generation of organic outdoor tomatoes. Euphytica 180:357-367.
  • Horneburg, B., 2010: Participation, utilization and development of genetic resources in the Organic Outdoor Tomato Project. In: Goldringer I, Dawson J, Rey F, Vettoretti A (Hrsg.) Breeding for resilience: a strategy for organic and low-input farming systems? EUCARPIA 2nd Conference of the "Organic and Low-Input Agriculture" Section. S. 139–142.
  • Horneburg, B. (2010): Tomaten in menschlicher Gesellschaft. In: Brita Reimers (Hrsg.) Gärten und Politik. oekom verlag, München. S. 107–120.
  • Gladis, T., Horneburg, B., Suanjak, M. (2010): So was Krauses! ARCHE NOAH Magazin 4/2010:10–11.
  • Miles C, D. Inglis, B. Gundersen, P. Kreider, J. Roozen, B. Horneburg, D. Panthee (2010): Evaluation of late blight on tomato cultivars grown in the field, 2009. Plant Disease Management Reports 4:V126.
  • Horneburg, B. (2009): Chancen und Grenzen der Kulturpflanzenentwicklung im Praxisbetrieb - Tomaten im Freiland und Pastinaken. BIO AUSTRIA (Hrsg.): BIO AUSTRIA Bauerntage 26.–29.1.2009, Wels; Österreich: S. 77–79.
  • Horneburg, B., Watschong, L. (2005): Wildtomaten – mehr als eine Spielerei? Ludwig Watschong und Bernd Horneburg vom Dreschflegel e.V. sagen: Ja! Saaten & Taten 2006:94–9