There are a number of benefits to shaping tomato plants by pruning and trellising.

Shaping tomato plants will enhance air circulation and ventilation, optimise space and sunlight, improve growth balance between roots, leaves and fruit, and make the most of your working space.

PRUNING

• Pruning simply means the removal of side shoots or suckers that develop between the main stem and the leaf.
• This helps to maintain a balance between vegetative and reproductive growth.
• Generally speaking, if you don’t prune, or prune only a few side shoots, your plant will show excessive vegetative growth and could produce smaller fruit.
• Research conducted at South Africa’s Agricultural Research Council has shown that the fruit size of cherry tomatoes can be manipulated by pruning the stem.
• Plants with 2 to 3 stems reduced fruit size to a size more acceptable to the market.
• Generally, the retail market prefers small- to medium-sized fruits (20 mm to 30 mm).
• Take care not to prune the growing point of the main stem, as this will stop growth and fruit bearing.
• You can remove suckers by pulling outwards, using your thumb and forefinger.
• Remove them while they are young and succulent (2 cm to 5 cm long) as plants will heal faster.
• Large suckers are not easy to remove and can make a larger wound, which takes time to heal and can be an entry point for pathogens.
• Experimental evidence has shown that there is a large reduction in yield if side shoots are allowed to develop to 15 cm to 20 cm in length, because they use up nutrients that should go into fruit development.
• When you’re working with big suckers, it’s important to remove their growing points because doing so results in less shock to the plant.
• You may need a knife, shears or scissors to remove big suckers, and these should be disinfected after cutting to prevent diseases being spread from one plant to another.
• Don’t prune side shoots with your nails because the sap will stick to them and can pass diseases from one plant to another.
• Pruning suckers is known to increase the size of the fruit and promotes an early harvest.
• Although determinate cultivars should not be pruned, it will enhance air circulation if the leaves below the first truss are removed.
• In addition, pruning in this way doesn’t affect the fruit size or the vegetative growth of determinate cultivars.
• On the other hand, pruning suckers above the first truss will result in a lower yield.
• When the plant matures – especially once the first two trusses have been harvested – the lower leaves turn yellow.
• As a general rule, remove yellow leaves below the ripening fruit clusters, as they’re not actively photosynthesising.
• Snapping them off with your fingers will also enhance air circulation around the base of the plant, and help to reduce the build-up of fungal and bacterial diseases.
• To snap off the leaves, hold the main stem with one hand and use the other to remove the leaf where it’s attached to the main stem.
• It’s important not to remove green leaves which are a source of food for the fruit.
• Work far away from the production area and destroy the leaves you remove, to prevent the spread or build-up of diseases.
• Indeterminate cultivars grow very tall and, with time, the yield and fruit size become progressively smaller.
• Remember that, with low winter temperatures (and the possibility of frost) on the way, it is important to prune the growing points of all your plants.
• Tomatoes are sensitive to low temperatures, and if you remove the growth points, the plants will stop bearing fruit and ripening will be enhanced.

TRELLISING

• Trellising is the process of tying twine from the bag to the stay wire above the plant.
• The stem is then twisted loosely around the twine to give support.
• If you tie it too tightly the twine will cut into the stem as the plant grows.
• Trellising should take place no later than two weeks after transplanting.
• If not trellised early, transplants grow crooked and will break or be damaged if you try to trellis them later.
• Make sure that the trellising twine is always above the tomato flower truss, otherwise it will break the truss.
• A tomato plant usually grows 5 m to 6 m over a 6-month growing season, so it’s important to ensure that the stay wires are strong enough to carry the mass of a whole row of fruiting plants.
• The total weight of the plants and fruit in a 45 m row is more than 1 ton, so plants will sustain considerable damage if the stay wire breaks at the height of the production season.

ADVANTAGES OF SHAPING TOMATO PLANTS:

• Reduces the incidence of physiological disorders, such as fruit cracking and/or uneven ripening of fruit because of exposure to high solar radiation and temperatures.
• Reduces the incidence of fruit rot and soil-borne diseases.
• It maximises the efficiency of photosynthesis.
• Upright plants have fewer disease problems such as leaf spot and fruit rot because leaves stay drier and are not in contact with pathogen-laden soil.

DISADVANTAGES OF SHAPING TOMATO PLANTS:

• It requires expertise (good management and skilled workers).
• It’s labour-intensive as trellising and pruning need to be done regularly.
• Plants can be damaged during training and harvesting.

Also read:
Hydroponic farming: The basics – popular systems
Hydroponic farming: How to produce vegetable seedlings
Hydroponic farming: Growing lettuce in a closed system
Hydroponic farming: More on growing leafy vegetables

• This article was written by Martin Maboko and first appeared in Farming SA.