Fertilizing the vegetable garden
We often think that the plants in our garden only need water and light to grow, however, despite these two factors being of significant importance, right nutrition is also important so that each individual plant can have the availability of elements it needs to develop and produce at its best, so we start talking about fertilization. But what exactly is meant by this term and above all, among the different products that we see on the shelves of our trusted nursery or garden center, which one should we choose?
Let’s proceed step by step to try to better understand.
Why fertilize?
The answer is immediate: to have healthy and strong plants! In fact, plants need 17 essential nutrients in variable quantities for normal growth, specifically carbon, hydrogen and oxygen provided by air and water while the remaining 14, including the three primary macronutrients (nitrogen, phosphorus and potassium), come from the soil but for which it may often be necessary to integrate with fertilizers.
Please note that the growth and health of the plant are not related to the total amount of nutrients available but to those present in smaller quantities because, as Liebig’s Law of the Minimum states, “growth is controlled by the scarcest resource which represents the real limiting factor for plant growth.”
During the growing cycle, therefore, we observe our young plants to recognize any nutritional deficiencies but also excesses in order to be able to act promptly. For example, plants lacking nitrogen can show yellowing of the older leaves, while too much nitrogen can cause excessive leaf development with a delay in fruiting, or a lack of phosphorus leads to stunted growth and reddening of the leaves, while browning of the plant can be related to a lack of potassium.
Where do we start?
Let’s start from the soil because if there are no nutrients in it, the plant can become more susceptible to attacks by fungal disease and other parasites. The availability of nutrients depends on various factors such as soil texture, organic matter content and pH but let’s understand better. Soils rich in organic matter have a greater capacity to retain nutrients than both sandy soils subject to nutrient losses, especially nitrogen, through leaching by the action of water and those with a finer texture, i.e. the most clayey ones, which retain the elements but do not make them available to the roots.
It depends on the cultivated species but in general the best soil condition is a medium textured soil defined by a correct proportion between the different granulometric classes, as well as having organic substance and well-draining.
Soil pH is the degree of alkalinity or acidity of soils, when the value is too low or too high chemical reactions can alter the availability of nutrients and biological activity in the soil; the ideal pH for many garden crops varies from slightly acidic to neutral, therefore from 5.5 to 7.0, but there are exceptions, so we recommend asking in advance for the optimum for the species that will be placed in your garden. If you then want to be sure of the chemical characteristics and therefore also of the availability of individual elements, you can always have a soil analysis performed at specialized laboratories of a sample taken from your soil.
A good practice also consists in adding organic matter to the soil, for example by adding a composted amendment, i.e. compost, to improve both the porosity and the capacity to filter rainwater and to guarantee a reserve of nutrients made available to plants through the decomposition process of the organic matter itself, carried out by the important microbial flora naturally present in the soil.
Which product to use?
The fertilizer we choose must meet the needs of our plants with an eye, even two, for what concerns the soil and environment protection.
On the market we find organic fertilizers and mineral fertilizers that differ in many aspects but mainly in the way they release nutrients, let’s try to understand better.
Organic fertilizers of animal and/or vegetable origin such as dried distiller’s residues, horn, guano, dried manure, liquid manure, poultry manure, residues of pressive olives, slowly and constantly release the nutrients, also improving the capacity to retain water in sandy soils and increasing drainage and aeration in clayey soils, while inorganic fertilizers, derived from minerals or industrial synthesis processes, often have a more rapid solubility; it is also true that there are inorganic fertilizers marketed as slow-release or modulated-release capable of releasing the nutritional elements in the medium term.
Mineral or inorganic fertilizers, derived from minerals or industrial synthesis processes, often have a more rapid solubility; it is also true that there are inorganic fertilizers marketed as slow-release or modulated-release capable of releasing the nutritional elements in the medium term.
Among the types of fertilizers, let’s not forget the organo-mineral ones, obtained by reaction or by mixing one or more organic fertilizers with one or more simple or compound fertilizers, often applied during the preparation of the garden soil for the so-called basic fertilization aimed to provide those nutritional elements that the plant needs in the early stages of growth just after transplanting. These fertilizers, in facts, in addition to releasing an organic matrix, thus preserving the microbial flora essential for mineralization, gradually and progressively release the elements.
Often when looking for information about fertilizers we read the term “formulation”, but what exactly does it mean? Fertilizers can come in different forms or formulated as slow-release granules (mineral fertilizers) to be distributed by scattering on the ground around the crown of the plant but not too close, taking care to cover them with a light layer of soil and irrigating afterwards, as well as pellets and powder form (organic fertilizers) to be incorporated into the ground before sowing or transplanting. There are also liquid fertilizers, both organic and mineral, absorbed by the roots more quickly and used through fertirrigation, that is, water soluble, diluted in the water used for irrigation and distributed on the soil. In some cases, leaf fertilization can also be useful, although most of the nutrient acquisition occurs through the roots of the plants.
How and when to fertilize?
In general, let’s remember to use the chosen fertilizer in the right quantity, according to the dosages and frequencies reported on the instructions on the relative label. Excessive use can damage the plants and the environment as well as being a waste of money.
The method of intervention and the product to be used strictly depends on the growth phase of our crop: in case of cultivation in flowerbeds or in open fields it is advisable to do a basic fertilization before transplanting by ploughing granular organo-mineral fertilizer with subsequent hoeing. We can then apply fertirrigation, specific liquid fertilizer for vegetable gardens diluted in the irrigation water.
Each fertilizer purchased has one label with very important information starting from the title indicating which and how many elements are present, in particular we will note the acronym N-P-K with the relative numbers corresponding to the percentage of nitrogen, phosphorus and potassium respectively, that is, the three macronutrients, for example if we read 20-20-10 it will mean that our fertilizer contains 20% nitrogen, 20% potassium and 10% potassium. Obviously in addition to the three elements mentioned above, it is necessary that our fertilizer also contains secondary macro elements and microelements important for a balanced growth of the plant.
It is also recommended to use fertilizers with different titles in relation to the phase of the crop cycle, for example for tomatoes, marrows or melons we can apply, always through fertirrigation, during the first phase of rooting and flowering a fertilizer with a title of 15-28-20, in the growth phase with a title of 27-10-15, finally in the last phase of maturation before harvesting a title of 18-12-26. But why we change the title? Because the plant’s needs vary in relation to the stage of development, for example nitrogen promotes vegetative growth but at the end of the season it can reduce or delay fruiting, furthermore this element is considered mobile and soluble therefore not available and for this reason it is preferable to administer it when the plants are ready to absorb it while phosphorus and potassium, having a lower mobility, can be applied in higher percentages during the basal fertilization.
Some tips and advice:
- Let’s choose the right fertilizer for our crop and, at the risk to be repetitive, let’s make sure to use it without exceeding the doses and frequencies but following what is on the relative label.
- Let’s apply organic or organo-mineral fertilizers directly to the soil before transplanting or sowing while for mineral fertilizers wait for the growing season.
- Let’s distribute the fertilizer evenly on the surface of the soil when it is quite humid, avoiding hard winter days or hot summer days. Furthermore, in the case of granular formulation, let’s make sure plough it lightly with the help of a hoe.
- Finally, let’s help our soil by adding compost, maybe produced by ourselves!