Botanical Name: Solanum lycopersicum
Plant Type: Tender perennial
Of all the vegetables grown in Australian gardens, the tomato is easily the king; in many cases it is the only vegetable that many people grow. Its popularity, no doubt, is due to the ease with which it is grown, its productivity, and the versatility of the tomato in the kitchen. Probably, because of its popularity, there are more misconceptions about growing tomatoes than any other vegetable, which for the beginner can be the cause of much confusion.
Recent research, at Digger’s Heritage Seed Farm and elsewhere, has affirmed the value of some established practices in the growing of tomatoes and rejected others. This will provide basic information to guide the novice through the steps of growing tomatoes, while the experienced gardener may find that some long-held myths are challenged.
Background
The tomato is classified by botanists as the species Solanum lycopersicum from the plant family Solanaceae. Its nearest relatives include peppers, eggplants, and the potato. A native of South America, it is an annual plant in cooler climates and a short-lived perennial in warmer climates, and in its wild form, it produces tiny pea-sized fruit, like the wild tomato now listed as ‘World’s Smallest’.
The natives of the region cultivated the tomato and through selective breeding developed some larger-fruited varieties. After the conquest of the Americas, tomatoes made their way to Europe.
Many people are surprised to learn that the first tomatoes grown in Europe were not red, in fact, but yellow. The association of tomatoes with being red is a relatively recent development.
After its arrival in Europe, the tomato spread through all countries of the region, and to colonies of those countries throughout the world. In different areas, people selected plants with the individual characteristics that suited their needs and personal tastes, so that over time a range of varieties were created. Some of the characteristics that growers developed revolved around the environmental conditions of their region.
In cold climates, people collected the seed from plants that prospered best under those conditions, and in hot climates, people saved seed from different plants. Where disease problems arose, seed was saved only from more tolerant or resistant plants.
In addition to selecting for growing traits, they also selected plants with fruit that suited their personal tastes and uses- some liking sweet fruit saved seed from plants producing such fruit, others saved seed from plants producing tart-flavoured fruit.
Colour was another characteristic: yellow, red, purple, orange, white, and even black-fruited varieties were developed.
Shape was another matter of personal choice. The end use was often a consideration, with firm fruit being desired for slicing, fibrous fruit for making sauces and hollow fruit for stuffing.
This process of selection and development occurred wherever the tomato was grown, so that by the dawn of the 20th century, it has been estimated that there were no fewer than 4000 varieties of tomato worldwide.
Here in Australia, with our relatively late European settlement and small population, there has been less opportunity for the development of uniquely Australian tomato varieties.
However, earlier this century seed catalogues listed a range of distinctive varieties. Probably the best-known variety in Australia today is Grosse Lisse (large and smooth), which, although having been developed in France, is far more widely cultivated here than in its homeland, almost to the point where it can be considered a gardening icon.
Tragically, many varieties of the tomato, and indeed other vegetables, have totally disappeared in this century, resulting in a huge loss of diversity. Several factors have contributed to the extinction of varieties. The first is the urbanisation of the population, with fewer people growing their own vegetables. Grandad’s variety of tomato grown on the farm was lost when his grandchildren moved to the city.
As farms amalgamated, fewer varieties were grown, and as farms became fewer, the markets of seed companies shrank; many folded while others merged. In effect, there was a rationalisation of the varieties listed.
With the ongoing decline of backyard growers, larger seed companies focused their attention on the commercial market. Varieties less suited to commercial production disappeared from the seed lists.
Exacerbating the decline was the development of broad- acre farming techniques in the United States, which relied on the machine harvesting of tomatoes. This practice involves the complete removal of the tomato plants from the ground; thus the characteristics of toughness of fruit and uniform ripening (see trials) became pre-eminent and other characteristics (including flavour) took a back seat.
Varieties not suited to machine harvesting, such as staked varieties preferred by gardeners, were dispensed with.
Another major factor causing loss of varieties was the development of hybrid varieties of tomato. A hybrid variety is produced when one type of tomato (or other vegetable) is crossed with another to produce a new variety with a mix of characteristics from its parents.
These characteristics are not stable, so that if seed is collected from such a hybrid, the offspring show a range of characters from their grandparents, much as we see in people.
Hybridisation may not directly reduce diversity, but indirectly, its use by seed companies has caused this reduction. All the old varieties of tomato are a common heritage of humanity, so that nobody owns them or has rights over them.
Hybrid varieties are also attractive from the point of view of market control by commercial companies. Due to the variation of the second generation the customer cannot collect his own seed and grow plants with the original combination of characters. The customer, therefore, must go back to the seed company each year to buy their seed.
The loss of vegetable varieties is of great concern to some people because part of society’s heritage is lost. As a consumer, there is less choice with fewer types offered, and varieties with distinctive and unique characteristics are lost. The home gardener can, however, help turn the tide in the loss of varieties and preserve genetic diversity.
One way is to purchase seed or plants from companies that offer old pre-1960s varieties (called heirlooms) and grow them at home. In effect, market demand will ensure their preservation. It can be great fun growing some of these obscure varieties with many surprises in store in terms of appearance and flavour. In time, you will have some personal favourites.
The other way home gardeners can help preserve them is to collect and save seed themselves.
Varieties
The rediscovery of the wonderful range of tomatoes that have managed to survive means that gardeners increasingly, as consumers, are demanding that these varieties are made available to them.
The majority of gardeners in this country are yet to grow any heirlooms, but with the knowledge spreading about the diversity of colours and intensity of flavours that exist, a steadily expanding range of varieties are being made available, both as seed and as seedlings.
For the newcomer, a long list of tomato varieties with exotic- sounding names can be most intimidating.
Tomatoes are described according to the size, shape and use of the fruit, the stage of the season that the fruit appears, and the growth habit of the plant. A range of terms is used to describe fruit shape.
Cherry tomatoes are the size of cherries or smaller, examples being Broad Ripple Yellow Currant. Beefsteak varieties have large symmetrical fruit, and include Mortgage Lifter, Brandy Wine, Yellow Delicious and Black Krim.
Oxhearts are pointed at the base and lobed at the top, similar to a heart. Paste tomatoes with physical characteristics that make them suitable for sauces and chutneys include Amish Paste and San Marzano.
Drying varieties tend to be cherry types, which have a minimum of moisture that dries rapidly, such as Principe Borghese.
Stuffing varieties like Mr Charlie and Green Bell Pepper contain large hollow cavities making them ideally suited for stuffing with your favourite filling.
Acid Tomato Myth
One myth that is continually perpetuated is the existence of ‘low acid’ tomatoes. Some people grow such tomatoes in the belief that the lower acidity will be less harsh on their stomach.
Research conducted in the United States has demonstrated that there is very little variation in the pH of tomatoes, with all types being acid, having a pH of about 4.3.
Some taste tart while others are sweet, this difference being determined by a variation in the sugar content rather than the pH. In effect, a high sugar level masks the acidity.
A similar situation existing in honey, which is actually more acid than tomatoes. Low-acid varieties are really high-sugar varieties.
A number of environmental factors can affect flavour. During overcast weather, photosynthetic processes in the plants are slowed, so the production of sugars and other components of flavour are reduced.
Tomato plants are often described as dwarf, determinate or indeterminate. Dwarf varieties tend to be small bushes that do not require support in the form of staking or trellising and require a smaller area of the garden than others.
However, their smaller size generally means that a lesser quantity of fruit is produced than the more vigorous varieties.
The words ‘determinate’ and ‘indeterminate’, ‘staking’ and ‘non-staking’ cause much confusion to the novice.
Determinate varieties have a growth pattern where the plant stops growing once a given number of nodes has been produced. In effect, a maximum plant size has been predetermined.
Indeterminate varieties do not have their growth limited by node production. In theory, this means that determinate varieties are compact (and almost always early) and indeterminate are sprawling. This largely holds in practice, though there are exceptions. Determinate varieties have won favour in recent times because they require less pruning, though, as will be discussed later, this may not be to the advantage of the gardener.
A common misconception is that determinate varieties do not require some form of support while indeterminates always do. While some of the smaller determinate varieties do not require staking, the larger versions certainly do. Similarly, the smaller indeterminate varieties can get by without staking.
Tomato varieties are classified as early-, mid- or late-season.
From Diggers trials, early varieties such as Ida Gold, Tommy Toe and Tigerella start producing fruit from 60 to 70 days after transplant.
Mid-season varieties, such as Green Zebra, produce ripe fruit after 90 days; and late-season tomatoes, such as Mortgage Lifter and Brandy Wine, produce fruit 110 to 120 days after transplant.
Some varieties, such as Ida Gold, are very early but cease fruiting well before others.
Once fruiting commences, many will continue to produce until frosts kill the plant.
Position
Some thought should go into selecting the site in the garden to grow tomatoes. Tomato plants love sun and heat, and where possible, they should be grown with full exposure. This is particularly important in the more southerly regions of the continent, where cool summers are not an infrequent occurrence.
Some gardeners plant their tomatoes in areas of partial shade, believing that too high a temperature inhibits fruiting. Extensive research has revealed the conditions under which tomato flowers will set fruit.
Low temperatures, particularly at night, are the principal cause of the failure of the flowers to set fruit. As temperatures fall below 15°C, flowers fail to set.
Extreme temperatures around 35°C to 40°C can result in the flowers falling off their buds. Therefore, in hot regions, protecting plants by partially shading them may be a consideration, but in our experience, full sun is usually a good rule to follow and may help produce tastier fruit.
Poor fruit set can also be caused by establishing tomato plants in sheltered sites.
Tomato flowers are self-pollinating; the flower contains both male and female organs. In most cases, tomato flowers are totally closed, so they are limited to self-pollination.
Transfer of pollen from male to female organs relies on some form of motion to dislodge pollen so that it falls onto the ovary, resulting in fertilisation. As a result, any form of disturbance or motion enhances the transfer of pollen, and the most common source of motion for the plant is wind.
Are Grafted Tomatoes Better?
Grafted tomato plants consist of the stem and leaves of one variety of tomato attached to the base and roots of a second variety called the rootstock.
The characteristics of the plant and fruit are determined not by the rootstock, but by the grafted variety. Grafting of tomato and other plants is a widely used practice to solve various problems in horticulture.
Most commonly, a variety of plant susceptible to some soil-borne disease is grafted on to the roots of another variety that shows resistance to the disease.
A well-known example is that of the wine grape, where the devastating disease, Phylloxera, is prevented by grafting susceptible varieties on to resistant rootstocks.
A number of soil-borne diseases affect tomatoes, including Fusariumand Verticilliumwilts, and nematodes. Individual tomato varieties are affected by these diseases to varying degrees; some being totally devastated, while others are unaffected.
Where such soil-borne diseases occur, one solution is to grow only resistant varieties, but this may greatly restrict one’s choice. The alternative is to grow grafted versions of the desired variety. Grafting requires a considerable amount of skill, and generally, most gardeners purchase grafted tomato plants rather than undertake it themselves. In this case, grafting is often a simple solution to a serious problem.
Recently, grafted tomatoes have increased in popularity, with gardeners believing that these plants are more vigorous than non- grafted plants and have improved productivity.
This idea was tested at the Digger’s Heritage Farm, where we grew, side by side, grafted and ungrafted plants of the traditional favourite, Grosse Lisse.
Admittedly, grafted plants appeared to be a little more vigorous or have brighter coloured leaves, but such judgements are subjective. When it came down to the fruit, grafted and ungrafted plants produced the same sized fruit, but yields were much lower for grafted tomatoes.
Sun: Full Sun
Pollination: self-fertile
Soil: tomatoes should never be planted in the same soil two years running. It is best to move your tomato patch each year, returning to the original bed, after a break of three seasons.
Tomatoes are best planted in beds that have been heavily manured for a previous crop, such as broccoli. A soil that is too rich in nutrients will produce prolific, but soft, sappy, disease-prone growth. Well- rotted com-post being high in organic matter, is the perfect addition to a tomato bed.
Growing from Seed
Sow: sow seed in trays, then transplant after germination into larger pots and left to grow before finally being planted into the garden after the last chance of frost has passed.
Ease of Germination: Easy
Germination Temperature: 15-29°C
Germination Time: 5-10 days
Spacing: 60-80cm
Harvest: 120-150 days
Yield: 3 kg–20 kg/plant over 3–4 months.
Transplanting, Maintenance and Additional Care
Plant out your seedlings when the soil reaches 15°C or more, after the risk of frost. Night temperatures over 30°C will cause blossoms to drop. If your seedlings are on the leggy side, don’t worry, they can be planted in a little deeper. Tomatoes form roots along their stems when they come into contact with the soil; so a good strong root system should result.
If the soil is warm enough and there are no frosts, the plants will grow and eventually produce flowers. Once again, climate influences the success of fruit set as described earlier, with low temperatures in particular inhibiting fruit set. In southern regions tomatoes are strictly a summer crop, and poor fruit set due to cold weather is a minor but unpredictable problem. As one moves farther north the extent of the growing season for plants broadens, and one trap is to transplant too late, so that vigorous plants produce fewer fruit because of the cooler nights of autumn. In subtropical regions, tomatoes fruit successfully in winter under the balmy night time conditions, and year-round fruiting is a reality.
We reiterate that the best advice to get on timing is from other gardeners in your area. As a guide, the optimum times for transplanting in different regions are: southern Victoria—late October to early November; South Australia, inland Victoria and the Riverina—early to mid-October, or mid to late September if plastic covers are used; Sydney and inland New South Wales—early to mid-September; southern Queensland—mid August. Note that these times are advice for low- lying areas and not for localities at higher altitudes.
Spacing of the transplants is partly determined by the management of the plant in terms of support and pruning. Generally, larger, more vigorous plants have larger root systems. If you are following the traditional method of staking, transplants can be as close as 60 cm. With trellises, it is advisable to transplant seedlings at least one metre apart. In one trial undertaken at Heritage Farm, tomato plants showed increases in productivity when separation increased up to a distance of 1.5 metres.
Once transplants are established the required management includes supporting and training the plants and appropriate watering. Unless you are growing one of the dwarf determinate varieties, your tomato plant should be supported in some way. Broad-acre farmers regularly grow tomato plants without any support, sprawled across the ground, as it is difficult to machine-harvest trellised plants. In the garden it is also possible to allow the plants to sprawl, but they will take up considerable space and look untidy. In addition, fruit and leaves in contact with the soil will be prone to various diseases, and difficulty will be experienced in harvesting without standing on other parts of the plant.
Where possible, trellis rather than stake tomato plants, because the increased area of plant will increase productivity. However, some thought must go into the trellis design in order to obtain the maximum benefit. Typically, a tomato trellis consists of some mesh-like material, such as wire fencing or concrete reinforcement, supported by posts at either end. Such a trellis, while being more productive than staking, will be labour intensive and unlikely to realise full plant potential. This is a result of the fact that such a trellis restricts the structure of the plant to two dimensions, limiting the total surface area, plus trellises requiring considerable effort in tying.
A more productive approach is a three- dimensional trellis: a simple concept is the use of two parallel trellises for the one plant so it can grow outwards as well as upwards. The plant will also tend to grow through such a trellis and support itself, so that much less tying is required. A similar effect can be achieved by parallel wires. Other novel ideas using locally available materials can be developed through one’s ingenuity. As a guide, a distance of about 60 cm between supports seems to be optimum.
Tying the plants to stakes or a trellis is another skill acquired with experience. A range of materials can be used for tying, such as twine, string or plastic-coated wire ties available from nurseries, though the latter are not very biodegradable. A novel form of recycling is to utilise old stockings or pantyhose, as their elastic properties allow some ‘give’ when plants move in the wind, and they are less inclined to cut the bark than narrow materials. Whatever material is used, plants should be tied to their support in a way that will not eventually constrict the stem. This is done by forming the tie into a figure eight which allows plenty of room for stem growth.
There is a commonly held view among gardeners that pruning tomato plants either increases fruit size or improves yields. These ideas were recently put to the test at Heritage Farm, where pruning trials were conducted on the traditional Grosse Lisse and the heirloom Tigerella. With both varieties, a number of plants were grown without pruning on a trellis, with moderate pruning on a trellis, and heavily pruned on a stake. Ripe fruit was collected regularly, counted and weighed for each trial.
The results were emphatic. With both varieties the greater the degree of pruning, the lower the yield of fruit per plant. With heavy pruning, yields were as low as 25 per cent in Tigerella and 33 per cent in Grosse Lisse of unpruned plants. This was not expected because logically, removing branches removes growing points for fruit. The unexpected result was that pruning had no effect whatsoever on the size of the fruit!
One interesting fact discovered was that late plantings tended to produce larger fruit but had a major effect on reducing total yield. This result has also been confirmed in a number of studies overseas. Some research conducted overseas has indicated that under commercial conditions of high plant density where there is excessive shading, light pruning can be beneficial. Such conditions are unlikely in the home garden. By all means, prune tomato plants for balance in the garden, but do not be mistaken in the belief that you will benefit from more or larger fruit.
Watering
Tomato plants should be well-watered during the establishment phase, with watering becoming less frequent with more established plants. In very hot weather it may be necessary to water daily, preferably in the morning, while under cooler conditions once a week may be sufficient. A good guide for watering is to watch the growing points of the plant. During the heat of the day, the young tips may wilt slightly, and this is acceptable.
Companion Planting
Good companions: amaranth, asparagus, basil, beans, borage, calendula, carrots, celery, chive, cleome, cosmos, cucumber, garlic, lemon balm, lettuce, marigold, mint, nasturtium, onion, parsley, sage and squash.
Bad companions: brassicas, corn, dill, fennel
Pests and Diseases
Tomatoes are prone to all sorts of diseases, some of them carried by pests.
The good news is that tomatoes are easy in long hot summers. If you use good organic principles of soil preparation and rotation, and have a sunny, airy and preferably biodiverse, garden to grow them in, you should not have too many problems. Hybrids growing in monocultures are far more disease prone, so breeders concentrate on disease resistance, which rarely affects biodiverse backyards.
Fungal diseases can occur in damp cool conditions, or when the leaves have been splashed with water. Target spot produces concentric spots on the leaves while bacterial speck manifests itself by leaving lots of tiny black-brown spots on the leaves. Sclerotina is a woolly fungus found on the leaves, that occurs in wet humid weather. Heirloom tomatoes are often resistant but move your tomato bed next season anyway.
These diseases will certainly reduce the vigour of the plant but are rarely life-threatening. Remove the badly affected of the leaves and improve air circulation. Perhaps thin some branches that are growing too close together – the problem can be solved by good observation and good husbandry, even if you can’t change the weather.
If disease is a recurring problem in your area each season, growing the vine-like indeterminate varieties, well-spaced on a trellis, could be the best solution, rather than the denser-foliaged determinate types.
More serious diseases are Fusarium and Verticillium wilts, and wilting caused by nematodes (organisms that attack the root system). These pests/diseases all come from the soil, hence the importance of good crop rotation. Sowing mustard in autumn can also alleviate this problem. Many heirloom varieties to these diseases, so changing the tomato you grow may solve the problem.
Blossom End Rot. The base of the tomato rotting. Is caused by lack of calcium.
Tomato Mosaic virus can also affect tomatoes- so smokers make sure you wash your hands well before handling your tomatoes. The heirloom, ‘Green Zebra’ seems to show resistance to this debilitating virus.
A good war to ‘clean’ beds that have harboured nematodes or Sclerotina fungi is to grow a resistant crop. Plant silver beet or beetroot to cope with the Sclerotina and brassicas to sort out the nematodes.
Growing in Containers
Tomatoes can be grown in containers. Bush tomatoes and the smaller determinate tomatoes are ideal. Use a good quality potting mix and liquid feed regularly. Mulch plants with pea straw or lucerne to insulate roots. Unless you choose small bush forms the plants will require staking.
Harvesting
Pick fruit when the skin is firm, and the colour has changed. Don't leave them on the vine for too long, otherwise they can over-ripen and split.
Seed Saving
Seed Longevity: 4-10 years
Isolation Distance: self-pollinating so no isolation distance
How to Save Seed
For slicing and paste tomatoes- pick and wash fully ripe tomatoes, and then cut fruit across the middle. Squeeze seed and surrounding gel into a bowl or bucket. For cherry and currant tomatoes, a similar process can be used how grinding the fruit in a food processor is far easier. You can mash your seeds with your hands or use a blender to make a pulp.
Each tomato seed is encased in a gelatinous sack. The gel in these sacks contain chemicals that inhibit germination. In nature, the ripe tomatoes fall and slowly rot. The rotting away of the fruits is a natural fermentation process n which the gel sacks are destroyed. Eventually the fruit totally rot away leaving the seeds on the surface of the soil. Ready to germinate when the conditions are right.
Artificially duplicating the tomato fruit’s fermentation process is a simple process. In addition to removing the gel sack, fermentation also kills many seed-borne tomato diseases. The container of the pulp (tomato seeds and gel) should be set aside to ferment for about 3 days. The mixture needs to be stirred twice daily.
After 3 days add water and mix. The good seeds will settle to the bottom, so the mold, debris and unviable seeds can easily be poured from the top. Add more water and continue the process until you only have clean seed.
Pour seeds into a strainer and then place on fine-wired rack to dry. Seeds need to be dried quickly as they can start to germinate quickly if moisture remains. In hot, humid weather, a fan will speed up the process.
