There are essentially three different types of tomatoes, Indeterminate, Semi-Determinate and Determinate. They are defined by their growth habits. In this article we are going to consider growing Indeterminate tomatoes on a non-commercial scale.
Indeterminate tomatoes are usually grown in the UK as cordons. A single stem is trained vertically upwards, either up a cane or strings, and all sideshoots taken off. There is no fundamental reason why Indeterminate tomatoes have to be grown as cordons and This article considers whether there are other ways of growing and the advantages and disadvantages of them.
When growing as a Cordon, the major disadvantage is that the quantity of fruit is limited by the number of trusses that can grow on the single stem and the number of tomatoes that grow on an individual truss. The number of trusses is limited by the height of the plants (which is set by the height of the greenhouse or polytunnel) and the separation of the trusses on the stem (which varies from cultivar to cultivar but is usually around 12 inches (30cm) but often more. So in an average greenhouse one can expect to get somewhere between four and six trusses per plant.
An alternative is to grow multiple stems from a single plant. Indeterminate tomatoes naturally grow sideshoots, usually at the leaf nodes and, the additional stems can be grown up separately. The advantage of growing in this manner is that these additional stems will create extra trusses of fruit (usually slightly later than the main stem) and therefore you will get extra trusses of fruit within the same height as the single Cordon that would be formed if the sideshoots were not removed.
So far, so good. Logically it would seem sensible to grow as many sideshoots as possible from the single plant but obviously this isn’t the case, otherwise the tradition of growing cordons would never have developed.
There are three disadvantages associated with growing multiple stems.
First, whilst the plant is growing strongly, it can see no reason to set large quantities of fruit. Indeterminate tomatoes are tender perennials. Given the right growing conditions of light and warmth, they will grow on indefinately. We want them to produce lots of fruit and less growth so we stress the plant by limiting its growth which makes it set fruit for seed so that it will survive to the next generation. Limiting the number of sideshoots and stems increases this stress and makes the plant fruit more quickly. At the same time, we feed it with potassium rather than nitrogen fertiliser so that it also tries to produce more fruit and less growth.
The next disadvantage of having lots of stems is light. The UK is not an ideal place to grow tomatoes. Its too cold in the autumn, winter and spring for the plants to survive without additional heat (tomatoes grow best between 20C and 30C) so we grow tomatoes as annuals setting fresh seed each year. Also, the sunlight is not very intense. Tomatoes are natives of Central America where the sunlight is stronger than in the UK. We therefore have to minimise the amount of shading that the plants experience by growing them in places that are not shaded by other plants or buildings and keeping the glass of the greenhouse clean.
The additional stems grow additional leaves and these shade the plants and have to be removed. But the leaves that create the most sugars to ripen the tomatoes are the two leaves above and below the truss, so we don’t want to remove these otherwise the truss of fruit will not ripen well. However, the additional stems on the single plant will have leaves at different heights to the main stem and these will shade the trusses on the main stem.
Finally, tomatoes are susceptible to airbourne diseases, in particular moulds and fungal diseases. Therefore we want to maintain a good airflow through the greenhouse to make sure that the leaves and plants are kept dry, even in the humid conditions that occur in the UK.
So, essentially, there is nothing that stops you growing multiple stems on a single plant. If you intend to do so, increase the spacing between plants so that the additional stems can be separated both from the main stem and the adjacent plants. You will increase the amount of fruit on the single plant but possibly not by as much as if you had grown more plants in the same space and grown them as Cordons. You will, however, have grown fewer plants in the first place and therefore perhaps been able to give them more care at the early part of their growth meaning that you have stronger plants which in themselves will grow more fruit.
A final advantage of growing multiple stems is that the single root can be grown in excellent soil and some of the greenhouse may not need to be as well tended, in other words (for example) you could grow a single plant with a number of stems with the additional stems supported over an area where it would not be possible to grow plants.