Leaves play a vital role in tomato cultivation. However, having too many leaves can slow down plant growth and ripening of the tomatoes. Proper leaf management helps to improve efficient energy use and contributes to better yields. Marek Sowa, Product and Application Specialist at Cultilene, explains how to remove leaves correctly to get optimal fruit development.
The function of leaves in plant development
First of all, it's good to take a look at the function of leaves. Leaves act as the plant's energy factory, producing assimilates essential for growth and allowing for photosynthesis. They also regulate transpiration, affecting both plant hydration and the climate in the greenhouse.
However, having too many leaves can cause its own problems for the tomato plants. For example, leaves can shade the growing fruits and consume valuable energy through respiration. In addition, having too many leaves can increase disease risks due to higher humidity circumstances.
Therefore, the challenge for growers is to maintain enough foliage for healthy development of the fruit, while preventing unnecessary resource consumption.
Optimal leaf removal: when and how to remove leaves?
The goal of leaf removal is to support plant health and improve fruit development. Each cultivation phase requires its own approach.
Early stage: Before placing plants on the slabs, it's essential to remove all damaged or yellowing leaves, especially under suboptimal cultivation conditions like high humidity and lower air and substrate temperatures. Healthy leaves should stay on the plants, as in this phase plants are still establishing their root system. Premature leaf removal can cause plant movement, potentially hindering root development.
Growth phase: After the third cluster blooms, depending on the variety and type of tomato, it may be necessary to thin leaves between clusters. Practically, if you walk through the rows and see only leaves (but no visible clusters), remove one leaf between clusters. This will improve light penetration. The minimum number of leaves to retain at the start of cultivation and in extended production is 15 to 18 per plant, reducing to 10 after topping. It's not recommended to shorten leaves by cutting their tips.
Fruit development phase: As fruits mature, leaves below the cluster are gradually removed, leaving one or two beneath the lowest ripening cluster. This is done to improve air circulation and light exposure. Remove a maximum of 3 or 4 leaves per plant at a time, reducing this amount to 2 or 3 during prolonged sunny periods.
This gradual approach is necessary, since removing too many leaves at once can cause a variety of problems. Firstly, the plant's ability to regulate transpiration decreases. This leads to reduced evaporation, as fewer leaves are available for this process.
As a result, root pressure increases because the roots continue to take up water at the same rate as before. Since the water can no longer evaporate effectively through the leaves, it is redirected to other parts of the plant, such as the fruits. This increased internal pressure can weaken the fruit's cell structure, making it more prone to cracking, especially after harvesting.
In some cases, excessive water uptake can cause cell bursting, leading to discoloration of the fruits. Lastly, a possible consequence is guttation, pushing out excess liquid through the remaining leaves. This can make the plant more susceptible to diseases.
Note that the leaf removal procedure is performed when the tomatoes in the cluster are fully grown. Removing leaves too early can hinder fruit development. On the other hand, removing leaves accelerates ripening. Therefore, many growers opt to remove leaves below the first clusters earlier to hasten harvesting. Keep in mind that doing this comes at the expense of total yield.
Harvesting phase: During the harvesting period, lower fruiting clusters are uncovered by gradually removing leaves from the bottom, ensuring two clusters are leaf-free. This approach typically leaves 15-17 leaves per plant.
© CultileneMarek Sowa
Leaf Area Index: a practical formula
Upon entering the fruiting phase, you can use the Leaf Area Index (LAI). This formula helps accurately determine the number of leaves per square meter of the greenhouse. To calculate this, you need to measure leaf length and width. Remember to account for leaf shape to make sure you are calculating the numbers correctly.
So, what should the LAI value be? For vigorously growing tomatoes, an LAI value of 3 to 4 indicates that each square meter of cultivation area corresponds to 3 to 4 m² of leaves.
Since determining LAI is time-consuming, this formula is mainly used during methodical experiments and tests. In daily practice, growers often rely on counting the number of leaves per plant or per cultivation area. Routine observation is also effective. As long as you pay attention to plant condition, you can remove excess leaves as needed.
Fine-tuning leaf management
For optimal yield results, it's a good idea to adjust leaf removal to the specific needs of your crop and the greenhouse conditions. When in doubt, take a gradual approach, as removing too many leaves at once can do more harm than good. By fine-tuning your strategy throughout the season, you can maximize both fruit quality and overall yield.
For more information:
Cultilene
info.cultilene@saint-gobain.com
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