Tomatoes are quite easy to care for and still have certain demands on their environment: the right location, the right soil and the right care have a major influence on the harvest. To promote the growth of heavy feeders and make them more resistant to diseases – such as brown rot and powdery mildew – tomatoes should be fertilized regularly. The trick is to estimate the correct proportions, as too many of the nutrients they need (nitrogen, phosphorus, potassium, magnesium and sulfur) can lead to over-fertilization and harm the young plants. Below you will learn how and when you should fertilize tomatoes.
The most important nutrients for tomatoes are nitrogen (for growth), phosphorus (for root and flower support) and potassium (for fruit production). Since the nightshade plants are heavy feeders, i.e. crops with a large appetite, they quickly extract all the nutrients they need from the soil. For this reason, it is important to fertilize the soil and therefore the tomatoes regularly. The right time for this is autumn, to enrich the soil with nutrients for the next season, or spring: ideally in several stages – first when planting, then when the second pair of leaves forms (not always absolutely necessary) and again when the first flowers/fruits appear. From then on at regular intervals.
Keep in mind that solid fertilizer takes longer than liquid fertilizer to be absorbed into the soil. It also makes sense to use different fertilizers from sowing to harvest: when planting, horn shavings or organic long-term fertilizers are effective options. As soon as the heavy feeders produce their first fruits, a tomato and vegetable fertilizer can be used as it contains a lot of potassium and magnesium. Special garden fertilizers are often used to promote the growth of leaves and shoots – but they can have a negative impact on flower and fruit formation.
Important note: Please refer to the packaging to find out how to correctly use an organic fertilizer – whether liquid or solid. Depending on the manufacturer, the dosage can vary.
If there are too few nutrients in the soil, you can see it in the young plants. But even if the soil has been fertilized too much, the nightshade plants show the first signs of deficiency. The following signs indicate that your tomatoes are not doing well:
The leaves turn yellow. Healthy tomato plants have green leaves. If these suddenly turn yellow, this is a warning signal that the soil does not contain enough nitrogen. But don’t panic: you can make up for the deficiency by working a little tomato fertilizer or nettle manure into the soil.
The leaves are becoming darker and darker. If the tomato leaves suddenly turn dark green (almost black), this is a sure sign that there is too much nitrogen in the soil: In other words, the plants have most likely been over-fertilized. There’s not much you can do to counteract the deficiency symptoms except wait – and stop using fertilizer until the tomatoes have recovered.
The leaves curl up. Rolled leaves also indicate over-fertilization of tomato plants. Here, too, it is recommended to stop enriching the soil with new nutrients and to wait (and hope) for the nightshade plants to recover on their own. However, the curled leaves no longer recover.
The flower bases turn brownBrown spots around the flower bases (and therefore also brown fruits) are a typical sign of what is known as blossom end rot. This form of deficiency occurs when plants lack calcium – even if there is enough of it in the soil. Too little irrigation water or too much fertilizer with nitrogen is usually the trigger. The fruit can still be eaten, just cut off the brown parts later. To counteract the infestation, it is advisable to sprinkle some algae lime around the affected plants and then water the soil.
The leaves and stems turn brown. Brown spots appear on the leaves and stems of young tomato plants or they turn black and begin to wilt are the typical signs of late blight. This is a fungus (Phytophthora infestans) that particularly likes to add to outdoor tomatoes. In order to combat the infestation, the use of plant protection products such as “vegetable-fungus-free” or “special-fungus-free” should make sense.
Sources: My Beautiful Garden, My Harvest, Statista
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