Heavy feeders
Fertilizing tomatoes: How to strengthen the nightshade plants outdoors

There are different ways and means to fertilize tomatoes: In this case it is granulated fertilizer
© Zbynek Pospisil/Getty Images
According to Statista, an adult eats up to 28 kilograms of tomatoes per year. Growing the nightshade plants in your own garden is at least as popular as eating them. Tips for a bountiful harvest.
Tomatoes are relatively easy to care for and yet have certain demands on their environment: the right location, the right soil and the right care have a major impact on the harvest. Tomatoes should be fertilized regularly to encourage the growth of these heavy feeders and to make them more resistant to diseases such as brown rot and mildew. The trick is to estimate the right proportions, as too many of the nutrients they need (nitrogen, phosphorus, potassium, magnesium and sulfur) can lead to over-fertilization and damage the young plants. Below you will find out how and when you should fertilize tomatoes.
Which fertilizer is suitable for tomatoes?
- The best way to fertilize outdoor tomatoes is with garden compost. Ideally, you should add the soil to the beds in the fall to enrich the soil with nutrients until the following spring. Alternatively, you can also use horse manure, provided you know a farmer who would provide you with the natural fertilizer.
- If you cannot use either one, provide your plants with a organic long-term fertilizerIt is available in powder form or as granules. Both variants are also added to the soil and worked in – ideally before you sow or plant new tomatoes.
- Or you can make a kind of organic fertilizer yourself from natural ingredients: nettle manure. It not only supports the growth of the plants, but also strengthens them from the inside and makes the tomatoes more resistant to pests such as aphids. Read how you can make nettle manure here.
Fertilizing tomatoes correctly: How, when and how often?
The most important nutrients for tomatoes are nitrogen (for growth), phosphorus (to promote root and flower growth) and potassium (for fruit formation). However, as nightshades are heavy feeders, i.e. crops with a big 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 to do this is either in autumn, to enrich the soil with nutrients for the next season, or in 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/fruit appear. From then on, at regular intervals.
Bear in mind that solid fertilizer takes longer to be absorbed by the soil than liquid fertilizer. It is also a good idea to use different fertilizers from sowing to harvesting: When planting, horn shavings or organic long-term fertilizers As soon as the heavy feeders produce their first fruits, a Tomato and vegetable fertilizer because it contains a lot of potassium and magnesium. To promote the growth of leaves and shoots, special garden fertilizers are also often used – but they can have a negative impact on flower and fruit formation.
Important NOTE: Please refer to the packaging to find out how to use an organic fertilizer correctly, whether liquid or solid. The dosage can vary depending on the manufacturer.
How to recognize deficiency symptoms in tomatoes Yellow leaves are a typical sign of nutritional deficiencies in tomatoes © FotoDuets / Getty Images
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 will 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 sign that the soil contains too little nitrogen. But don’t panic: you can compensate for the deficiency by adding a little Tomato fertilizer or work nettle manure into the soil.
The leaves are getting 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 is not much you can do to counteract the deficiency symptoms other than wait – and stop using fertilizer until the tomatoes have recovered.
The leaves roll up
Rolled-up leaves are also a sign of over-fertilization of tomato plants. Here, too, it is recommended to stop adding new nutrients to the soil and wait (and hope) that the nightshade plants recover on their own. However, the rolled-up leaves will not return.
The flower buds turn brown
Brown spots around the flower buds (and therefore also brown fruits) are a typical sign of so-called blossom end rot. This form of deficiency occurs when the plants lack calcium – even if there is enough of it in the soil. Too little water or too much fertilizer with nitrogen is usually the cause. The fruits can still be eaten, you can simply cut off the brown spots later. To counteract the infestation, it is advisable to use something Algae lime to sprinkle the affected plants and then water the soil.
The leaves and stems turn brown
If brown spots spread on the leaves and stems of young tomato plants or if they turn black and begin to wilt, these are typical signs of late blight. This is a fungus (Phytophthora infestans) that particularly likes to attack outdoor tomatoes. To combat the infestation, the use of pesticides such as “Vegetable-fungus-free” or “Special fungus-free” make sense.
Sources: My beautiful garden, My harvest, Statista
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