Choosing a tomato variety
Tomato growers are lucky: they have thousands of varieties to choose from. Likewise, they are unfortunate: with so many varieties, how is a good choice made? Read the gardening press, ask a fellow gardener, review the seed catalogues: all good starting points, but still, deciding on the right variety can be difficult. To make the choice easier, tomatoes must be broken down into their basic elements. And then, and only then, can an informed decision be made.
Plant growth habit
Tomato plants have two basic growth habits:
Tall growing, cordon types whose main stem and the side shoots they produce can grow on almost indefinitely. To keep the plants under control, the side shoots should be regularly pinched out, leaving only the main stem to develop. These in turn need staking or trellising to keep them upright and off the ground. Some authorities even suggest pinching out their growing tips to promote fruit ripening at the end of the season.
Indeterminate tomato plants: the main stem can grow almost indefinitely (left); pinching out a side shoot of an indeterminate tomato plant (right).
Bushy or shrubby plants whose growth is naturally restricted by self-stopping main stems and side shoots. Consequently, they need no pruning and are grown without support. They are often early maturing and are suitable candidates for growing outdoors and in hanging baskets.
Determinate tomato plants: in a growbag (left); in pots (right).
There are also some varieties that are defined as semi-determinate. These can grow quite large, and might benefit from some pruning and support to keep them off the ground, but the main shoot will eventually terminate.
To fully understand fruit colour in tomatoes both the colour of the internal flesh and the colour of the skin must be considered:
The colour of all immature tomato fruit is some shade of green, which is due to the presence of chlorophyll. As the fruit ripen, the colour of the flesh changes as the chlorophyll breaks down and various carotenoid pigments, including lycopene and beta-carotene, start to build up. Most varieties turn red, though other common colours are yellow and orange. In a small number of varieties, some of the chlorophyll is retained, and where no red pigment is produced the flesh remains green. If, however, there is an accumulation of red pigment, then the mixture of red and green produces flesh that is red-brown.
Left: A truss of tomatoes var. Apero showing ripe red fruit at the top, and green unripe fruit at the end of the truss.
The colour of the skin surrounding a tomato is either yellow or colourless. This is important since the skin interacts with the flesh to produce a range of colours on the surface of ripe, intact fruit. Some examples of the interactions and the colours they produce are as follows:
Tomato var. Green Zebra has green flesh and a colourless skin
- Red flesh + yellow skin = red tomato
- Red flesh + colourless skin = pink tomato
- Yellow flesh + yellow skin = yellow tomato
- Yellow flesh + colourless skin = white or ivory tomato
For more information on fruit colour, see: Carol Deppe (1993, 1st edition, though there is also a 2nd edition); Breed Your Own Vegetable Varieties. Little, Brown and Company. Pages 211-212.
Fruit shape and size
Other than colour, one of the most defining physical features of a tomato variety is the size and shape of its fruit. Fortunately, most varieties fit quite naturally into a manageable number of categories that are normally quite distinct from on another:
• Standard or classic
The type most commonly found in shops, it includes the varieties Ferline and Matina. Fruit are approximately 5 to 7cm in diameter and are round though normally slightly flattened. They have two or three locules, and their surface is generally smooth.
Small-fruited up to 32mm in diameter. The shape ranges from slightly flattened to slightly oval. The quintessential type for eating fresh, it includes the varieties Sungold and Apero.
• Mini or baby plum
Small, oval-shaped fruit with a diameter similar to that of a cherry tomato. Ideal for fresh eating, typical examples include the varieties Rosada and Golden Sweet.
Baby plum tomatoes var. Golden Sweet (left) and Rosada (right).
Size-wise, bridges the gap between the standard and cherry types.
The giant among tomatoes, fruit are about 7 cm or over in diameter. They are multilocular (with five or more locules), have a flattened shape, and are often strongly ribbed. Pruden’s Purple is a typical example.
Pruden's Purple beefsteak tomato
• Medium-sized, oval-shaped fruit that have a pasty texture due to a high level of dry matter. They are at their best when processed into sauces, and Nova and all varieties with ‘San Marzano’ in the name fall within this category.
Paste plum tomatoes var. Nova
A minority of tomatoes don’t fit neatly into the mould but are worth a look-at for their novelty value alone. They are often disguised as other objects, such as the larger-sized, somewhat heart- or top-shaped varieties Piriform and Cuor di Bue (oxheart). Likewise, there is also a small, pear-shaped type that comes in red and yellow; another one that is reminiscent of a bell pepper; and a variety that is similar (well, sort of) in shape, size and colour to a strawberry.
‘Earliness’ refers to the time it takes between planting and the first fruit to ripen. In this respect there are significant differences between varieties. For example, in our 2011 trial of 31 tunnel-grown indeterminate varieties, there was about four weeks difference between the earliest and latest ones to ripen.
Earliness is of the utmost importance for tomatoes grown outdoors, particularly in gardens where spraying is banned. Plants that ripen early avoid the late season onslaught of cool, wet weather and the inevitable blight it brings. And because determinate types are often early maturing, they are recommended for growing outdoors, though a few of the early maturing indeterminates, such as Sungold and Matina, might also be worth a try.
To a great extent, maximising yields is what gardening is about. After all, why put all the hard work into growing a crop unless there is a worthwhile harvest at the end? Yield in tomatoes is a product of the number and the size of fruit a plant produces, so varieties that produce a good number of large-sized fruits are bound to be the best yielders.
Tomatoes are the quintessential sweet-and-sour food, and the best-tasting fruits have high level of both sugar and acid. The balance is not always ideal, however, and high acid and low sugar levels result in tart fruits, while the reverse situation produces fruit that may be bland. The worst possible scenario is a combination of low sugar and low acidity, resulting in an insipidness that cannot be corrected by even a sprinkling of sugar and vinegar.
Choosing the right variety is an absolute must, but it is also essential to provide the right growing environment if optimum acid and sugar levels are to be achieved. Restricting water and growing the plants in full sunlight increases sweetness, while adding potassium fertiliser to the growing medium will give acidity a boost.
While sweetness and tartness are the dominant features of taste, volatile compounds contribute to both the aroma and flavour that make tomatoes what they are. Literally hundreds of these chemicals have been identified in the fruit, and though the roles of most remain obscure, others have been positively connected with the characteristic aroma found in fresh tomatoes.
OP vs hybrid
Most modern breeding has focused on the production of hybrids, and there is a preponderance of these available in the catalogues. Breeding open pollinated (OP) varieties, however, hasn’t been completely abandoned, though it must be said that most of the OPs currently available have been around for quite awhile.
Heirloom tomatoes are particularly old OP types that normally have an American origin. They consistently receive good reviews in the gardening press, though the hype is often undeserved. Many are quite late to mature; most have little of no disease resistance; and – the greatest insult of all – some varieties don’t even taste very good. That said, varieties well-worth growing do exist, such as the beefsteak Pruden’s Purple.
The term ‘heritage’, rather than ‘heirloom’, is reserved for older British varieties of vegetables, and seeds of a few heritage tomatoes are still around. Though they don’t come with the same romantic cachet as their American counterparts, varieties such as Moneymaker and Ailsa Craig remain surprisingly popular with amateur vegetable gardeners.
As a general rule, there is only one disease that is likely to be a problem in a well-managed crop of tomatoes grown by amateur gardeners. This is blight, and it tends to be more of an issue with tomatoes grown outdoors, especially if they aren’t sprayed with a fungicide.
Modern hybrids, at least the indeterminate ones bred for greenhouse production, are resistant to a host of diseases, including tobacco mosaic virus. The latest fashion is to breed for blight resistance, a characteristic that is occasionally found in determinate varieties destined for the outdoors.
This is not to say that OP varieties completely lack disease resistance – quite the contrary. For example, Red Alert, an older British variety, displayed some blight resistance in a Which? Gardening trial conducted in 2011, while Roma, a determinate plum tomato, has stated resistance to both verticillium and fusarium wilts.
Outdoor tomato crop: in early summer and late summer when devastated by blight.
© Michael Michaud