Tomato plants require a lot of sun and watering, good fertilizer, tutors and pinching out suckers. How to prevent diseases, insects and harvest red fruits

From sowing to outdoor planting, you have not been idle! If you now think you are resting on your laurels, think again: the tomato requires daily care and careful monitoring.

Plant care

Monitor and maintain your plants throughout the season to ensure an abundant harvest.

Watering

Tomato plants require a great deal of water to thrive. Rainy days aside, water every day, and container plants inn particular. Too much water is not good either, and avoid watering the leaves, since excessive moisture can lead to fungi developing. Watering early in the morning is preferable.

Fertilizers

Tomato plants remain in the earth for a long time and they are very nutrient-greedy. To satisfy their need for nutrients, add compost and a special tomato fertilizer around the base of the plant once or twice a month. You can also add liquid seaweed fertilizer to the water before watering, once every two weeks.

Staking

Determinate plants grow to approximately 1 metre. A tomato cage will provide sufficient support.

Indeterminate plants can grow to 2 m high. Use bamboo poles, stakes or straight branches at least 1.5 m long and insert them deep enough into the ground so they won’t bend under the weight of the fruit. Tie the plant to the stake with string or raffia every 30 cm throughout the growing period. To avoid impeding the grow-out of the stems or injuring the plant, make an 8 to secure the plant to the stake, leaving some slack around the stem. There are other “training” techniques, such as cages, gates, trellises or tipis. Learn as much as you can about each technique and choose the one best suited to your needs.

Pruning

Small tomato plants (cherry tomatoes, gooseberry tomatoes) and determinate tomato plants do not need to be pruned.
Pruning indeterminate plants consists mainly of pinching out the suckers that grow in the crotch between the main stem and the leaf branches, or side stems. They are called suckers because they suck out the sap of the plant. Removing them means the plant has more energy to devote to growing fruit. Also, remove leaves that are touching the ground, since they can be conduits to disease. Near the end of the season, prune back the head of the plant so no new flowers will grow which won’t have sufficient time to develop into fruit.
Some people claim that all pruning weakens the plant and that « wounds » on the plant open the door to disease. That’s a decision you’ll have to make!

Harvest

Let your tomatoes ripen on the plant. Harvest tomatoes when they are evenly coloured. Handle fruit carefully and without pulling to avoid damaging the plant. At the end of the season, collect all tomatoes even if they are still green and leave them to ripen in the sun on a window sill.

Insects and disease

Tomato plants are also susceptible to attacks from insects and disease. The heat and humidity tomatoes need to thrive also produce the conditions that lead to fungi and attract insect pests. Careful monitoring is essential. Below are the most common diseases that affect tomato plants.

Tomato: maintenance and fight against diseases and insects

Name Description Prevention Treatment
1 - Blight

Caused by a fungus.

Symptoms: black spots on lower leaves and stems.
  • Aeration is essential so leaves remain dry. Water the soil, not the plants, to prevent splashing.
  • Stake the plant to keep leaves and fruit from touching the ground.
  • Apply small doses of copper-based fungicide (Bordeaux mixture).
  • There is no treatment.
  • Remove and destroy affected parts of the plant. Sterilize pruning shears after each use.
2 - Powdery Mildew

Caused by a fungus.

Symptoms: white down under the leaves.
  • Aeration is essential so leaves remain dry. Since wet leaves allow fungi to spread, water the soil, not the plants, to prevent splashing.
  • Stake the plant to keep leaves and fruit from touching the ground. Apply small doses of copper-based fungicide (Bordeaux mixture).
  • There is no treatment.
  • Remove and destroy affected parts of the plant. Sterilize pruning shears after each use.
3 - Aphids

Tiny insects that feed on plant juices.

Symptoms: leaves curl inwards.
Companion planting with marigolds and lavender that naturally repel aphids, or plants that act as ‘traps,’ attracting aphids away from tomatoes, such as nasturtiums. Spray a soapy solution (1 teaspoon of dishwashing liquid for 1 litre water) or a natural plant purin (a blend of nettles, ferns, or rhubarb leaves).

Tomato: maintenance and fight against diseases and insects

Name Description Prevention Treatment
4 - Blossum-End Rot

Caused by a calcium imbalance.

Symptoms: water-soaked spot at the blossom end of the tomato. Spots turn brown and leathery.
  • Maintain consistent levels of moisture in the soil. Water regularly, particularly during heat waves.
  • Put straw around your plants to keep the soil moist and minimize evaporation.
 
5 - Whiteflies

Tiny insects (cousins of aphids) with white wings cluster under leaves, sucking out sap.

Symptoms: leaves become sticky with honeydew secreted by whiteflies, then turn yellow and die.

Introduce natural predators, such as ladybugs and dragonflies. Create a habitat favourable to hummingbirds, another predator.

Companion planting with nasturtiums, which whiteflies detest.

Try an anti-whitefly treatment or apply an insecticide every 3 days for 2 to 3 weeks.

Note: some commercial insecticides will not only kill whiteflies, but beneficial insects as well.
6 - Tomato Leafminer

The larval stage of a moth that hollows out tunnels on leaves, stems and tomatoes.

Symptoms: puncture marks, exit holes and rot.
  Destroy infested plants.

Applying a copper-based fungicide (Bordeaux mix) helps protect tomato plants from most disease and insect pests, but it must be used in moderation.

Do not throw plants or parts of plants infested with fungi or harmful insects into the compost; you will ruin the compost for future use. Instead, destroy plants by burning them.