Pruning and staking tomatoes
THE AVAILABILITY of improved tomato varieties and the demand for quality fruits have encouraged farmers and agricultural researchers to investigate the technique of pruning and different staking methods to enhance crop production and supply the growing market demand for tomatoes both here and overseas.
Pruning is the removal of dead or unwanted branches or parts of a plant, thereby allowing it to regularize its size and crop-load. Unlike other plants, the tomato for the first month directs all the sugar it produces towards the production of new leaves. During this stage, tomato plants grow very rapidly, doubling their size every 12 to 15 days.
Eventually, the plants make more sugar than the single growing tip can use, which signals them to make new branches and to flower. This usually happens after 10 to 13 leaves have expanded, at which time the plant is 30 to 45cm tall.
In the next few weeks, the entire character of the tomato plant changes. If unsupported, the increasing weight of filling fruit and multiple side branches force the plant to lie on the ground. Once the main stem is horizontal, there is an increased tendency to branch. A vigorous, indeterminate tomato plant can easily cover a 1 by 1m area with as many as 10 stems, each 1 to 1.5m long. This creates a haven for disease and pest infestation, poor management of fruit production and low productivity.
If the plant is allowed to lie on the ground, or there is dense vegetation, many of the leaves are forced into permanent shade, significantly reducing the amount of sugar they produce.
If a leaf uses more sugar than it can produce, a layer of abscission cells develops between the main stem and the leaf petiole; eventually the leaves will yellow and drop.
Of course, sloughed-off leaves are replaced by new ones, but time will have been wasted. Prostrate plants get around to fruit production two or three weeks later than a pruned and staked plant. Most of the fruits they produce are on the small side, and tend to come in one big, late harvest.
Pruning
A properly pruned and supported single-stem tomato plant presents all of its leaves to the sun. Most of the sugar produced is directed to the developing fruit, since the only competition is a single growing tip. The result is a steady production of large fruits. If more stems are allowed to develop, some of the precious sugar production is diverted from fruit to multiple growing tips. Fruit production, although slowed, never stops. The result is a nearly continuous supply of fruits throughout the season. In general, more stems mean more but smaller fruits, which are produced increasingly later in the season.
Pruning also affects plant health. The leaves of a pruned and supported plant dry off faster, so bacterial and fungal pathogens have less opportunity to spread. Soil is less liable to splash up onto staked plants. The bottom line: Upright plants have fewer problems with leaf spots, and fruit rot because their leaves stay drier and free from pathogen-laden soil.
As a tomato grows, side shoots, or suckers, form in the crotches, or axils, between the leaves and the main stem. If left alone, these suckers will grow just like the main stem, producing flowers and fruit. Suckers appear sequentially, from the bottom of the plant up. The farther up on the plant a sucker develops, the weaker it is, because the sugar concentration gets lower as you move up the plant. On the other hand, side stems arising from below the first flower cluster, although stronger, compromise the strength of the main stem. For a multi-stemmed plant, your aim is to have all stems roughly the same size, although the main stem should always be stronger, because it has to feed the entire plant for the next five or six months.
The way you choose to train and prune your tomato plants will affect how you space your plants, as well as the best method of support. There are two ways to deal with a sucker that isn’t destined to
become a stem. The simplest is to pinch it off entirely; not surprisingly, this is called ‘simple pruning’. This should be done when the sucker is still small and succulent. Grab the base of it between your thumb and index fingers and bend it back and forth. The sucker should snap off, producing a small wound, which will heal quickly. Avoid cutting the sucker with a knife or scissors, because the resulting stump can become easily infected. Once a sucker becomes too tough and leathery to snap off, however, you’ll have to use a blade.
In Missouri pruning, you remove just the tip of the sucker by pinching, letting one or two leaves remain. The advantage is that the plant has more leaf area for photosynthesis and protecting developing fruits from sun-scald. The disadvantage however is that new suckers inevitably develop along the side stems, thereby adding to your future pruning chores.
Missouri pruning is necessary when things have gotten out of hand. When you’re dealing with large suckers, it’s better to pinch off just the tip than to cut off the whole thing close to the main stem. For one thing, if disease hits, it’s farther away from the main stem. And for another, removing just the growing tip is less of a shock to the plant than removing a foot or so of side stem.
Staking
Once flowering commences, all tomato vines must be tied to their supports. Although vigorous, the plants are also easily damaged. Take care how you tie them and what you use. Cloth strips work well, as long as they’re not too old and threadbare. Twine should be at least 1/8 inch thick, or else it can cut into the tomato stems.
There are two types of ties, namely training ties, which direct plant growth upwards, and supporting ties, which keep it there. The top 0.3m of a tomato stem, or leader, is very succulent and easily snapped; it needs to be directed upwards, gently. Wrap a short piece of twine around the middle of the leader, cross it over on itself, and loosely tie it to the support. The resulting figure-of-eight tie reduces the chance of the tender stem becoming bruised by rubbing against the support.
Fruit will form along this stem. If left to the devices of the loose training ties, the weight of the fruit will pull the ties down the stake. Eventually, the stem will bend over and crease. Luckily, as the stem matures, it toughens; by the time fruit develop, the stem can tolerate a tighter tie. To support a fruit cluster as it fills and gains weight, loop a longer piece of twine, 30to 45 cm, around the stem just above the fruit cluster, creating a sling. Then I gently pull it up to take the weight off the stem. I wrap the twine twice around the stake, and firmly tie it to the stake 15 to 25 cm higher than the point of attachment to the vine. To keep the tie from slipping, knot it underneath the point where the sling meets the stake.