Overfeeding tomato seedlings: the dangers and how to avoid it

Tomatoes are one of the most demanding garden crops, the most demanding when it comes to care, soil composition, and fertilizers. Too much fertilizer, too little nutrition, and even mature plants stop producing fruit, while seedlings die on the vine. You need to be very careful, applying all nutrients precisely and at the right time.

The dangers of overfeeding

Tomatoes become overfed when they are over-fertilized with organic or mineral fertilizers. Plants oversaturated with one element have difficulty absorbing other fertilizers. The results are similar to hypervitaminosis in humans—the unused micronutrient turns into a toxin, destroying fruit buds and branches.

Well, if you couldn’t avoid overfeeding, you’ll have to act according to the situation.

1. Nitrogen overload is a common problem for greenhouse tomatoes growing in soil overloaded with organic matter. Under these conditions, mature tomatoes begin to "grow fat," putting on green mass and turning the greenhouse into a tropical thicket of tomato plants—without a single vegetable. Seedlings with nitrogen overload grow at an indecent rate, but don't get your hopes up: they won't produce fruit.
2. Conversely, if there's too much phosphorus, the leaves will begin to wilt and fall off, becoming spotted. The plant will have trouble absorbing calcium and the copper and zinc ions needed for growth.
3. Excess potassium stunts seedling growth just as effectively as some herbicides. Leaves become covered in light spots. Potassium chokes out all other micronutrients, causing seedlings to wither and fail to thrive.

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In these three cases, the only way to correct the situation is to replant the plants in clean soil and avoid using "general-purpose" mineral fertilizers. Again, prevention is easier than cure: fertilize tomatoes only as needed, without panicking over "what if they don't grow?" With any fertilizer, seedlings require half the dose of active ingredient as an adult plant.

More exotic fertilizers, when overdosed, produce an equally harmful effect on the harvest:

1. Boron causes leaves to turn yellow and curl upward. Frequent watering and misting of the seedlings themselves can help prevent this (or correct it if they've already been overfed).
2. Manganese, which is more often used to kill pests on plants than as a fertilizer, can burn leaves and roots. Red and whitish scorch marks appear on plants. Veins contaminated with manganese turn red and die. Therefore, to combat pests, it's best to use gentler medications and substances that reduce the risk of herbicide shock.
3. An overdose of zinc, like manganese, is irreversibly harmful to plants. Veins, and later entire leaves, take on a dirty purple or brownish-red hue, and seedlings stunt and die.
4. Magnesium and calcium prevent tomatoes from growing even the minimum necessary green mass. Leaves become deformed, twisted, and take on asymmetrical and even bizarre shapes, while branches begin to die, and the entire plant dies.
5. Molybdenum doesn't have a noticeable effect on seedlings, even if it's present in much higher amounts in the fertilizer. However, those who later eat these tomatoes will feel the effects: in humans, molybdenum overdose causes a variety of interesting symptoms, from sudden weight loss and anemia to tachycardia and gout.

Adult plants can be saved from overfeeding by watering generously and stopping feeding altogether, or by adding other fertilizers as compensation. If the seedlings survive, simply transplant them into clean soil or directly into open ground and avoid feeding them, allowing them to digest the excess micronutrients.

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How to avoid overfeeding seedlings

Rather than trying to save plants that are overfed or wilting from an excess of micronutrients, it's easier to ensure their nutrition is balanced in advance. The first step in preventing overfeeding is choosing the right soil. Healthy seedlings grown in good store-bought soil won't need any additional feeding until they're planted in the ground. If you're saving on substrate and using pots from a previous planting or digging up soil from the garden, choose soil that previously contained cabbage, zucchini, or cucumbers—plants that require similar conditions to tomatoes. The second way to avoid this problem is choosing the right seedlings. Good seedlings won't need fertilizing before planting, which means they won't be overfed.

At this time, they will need much more warmth (a comfortable temperature for tomatoes is 24-26ºC) and bright, diffused light, which provides strength for photosynthesis and does not burn the delicate leaves.

Excessive fertilizer is harmful to seedlings and, in some cases, can even kill them. Maintain proper application rates and apply them according to the instructions.