Gardening: Basics

Select the following terms for more information:
PH | Electrical conductivity | | Salinity Fertigation | | drainage | bulk density Cation exchange capacity | Carbon/nitrogen ratio (C/N) | | wettability Total porous space | Water holding capacity | Available water holding capacity | Water holding capacity not available | | aeration Water readily available | Reserve water | Total water available | Water hardly available | | volume contraction Vapour pressure deficit (DPV) | Xylem and phloem | Meristematic tissues | Lignification | | stress Climacteric / non-climacteric fruits | Phytohormones | Apomixis | geotropism | Phototropism | Angiosperms | Gymnosperms | Genotype | Phenotype


  1. pH: it is a unit of measurement that indicates the level of acidity or alkalinity of a substance. It is expressed as -Log[H+], that is, the least logarithm in base 10 of the hydrogen ion concentration.

            El pH determinará la disponibilidad de los nutrientes para las plantas, y por ello, el tipo de planta que podremos cultivar según el tipo de sustrato que empleemos, así como el pH de entrada de nuestra solución de riego.

Electrical conductivity

2. In our case, we will define electrical conductivity as the amount of salts dissolved in a liquid. It is directly proportional to the temperature, increasing when it increases and vice versa. It will mainly give us an idea of the amount of cations dissolved in the water.


3. accumulation of salts in our substrate. They produce toxicity in the plant. The most frequent accumulations are given by sodium (Na+), chloride (Cl-), sulfates (SO4-2), magnesium (Mg+2) and calcium (Ca+2).

Fertigation solution

4. is the water along with the nutrients we bring to our plants.


5. It is called drainage fraction to the excess of nutrient solution that comes out of the lower part of our pots and that serves to control the accumulation of salts in the substrate.

Bulk density

6. dry mass per unit volume.
Cation exchange capacity
7. is defined as the ability of a soil or substrate to retain cations in an interchangeable state with the soil solution. This property is, above all, clays and organic matter. Substrate particles (peat, vermiculite, bark, coconut in pieces, calcined clay, etc.) also have electrical charges on their surface. If there is a negative charge on the surface of a substrate particle it is likely to attract a cation which can be transferred to the soil solution and be available to the plant. The binding force of the cations with the negative charges of the substrate particles depends on the charge of the cation (+1, +2…) and the type of the cation:

                                Stronger                                       Weaker


The anion exchange capacity is practically negligible.
Sandy frank
Franco 5-15
Clay loam
If we take a look at the table above we can see that the CIC of sphagno moss and vermiculite are higher than that of clay. This is true based on weight, as CIC is expressed in meq/100 grams. However, pots or substrate bags are filled by volume rather than the weight of the substrate. Expressing the CIC according to its volume is more accurate, since the plants in containers only have access to the nutrients of the substrate inside the container:
CIC (meq/100 g) 25 140
DA (g/cc) 1,3 0,1
Pot volume (cc)
1.000 1.000
CIC pot (meq/100 g) 260


As we can see, although substrates may have a reasonable CIC, they do not contribute much to nutrient retention or to preventing pH changes, unlike soils. If nutrients are needed, we must supply them through fertilization and not depend on cation exchange points. In the same way, the pH of a substrate can be manipulated by acting on the amount of limestone of the substrate, the potential for acidity or basicity of the fertilizer applied and the alkalinity (carbonate and bicarbonate content) of the water.
  1. Carbon/nitrogen ratio (C/N): in a soil it indicates the ratio of carbon skeletons / energy that that soil has to nourish the plant. A soil must have a C/N ratio between 8-12.
In the case of an inert substrate, it indicates the stability that this material will have over time against decomposition; the higher the C/N ratio, the more stable the material will be over time.
  1. Wettability: time in minutes necessary for a given substrate to absorb 10 ml of distilled water through its surface. The optimum is below 5 minutes.
  2. Total porous space: is the total volume of the growing substrate that is not occupied by organic or mineral particles. An ideal value is ≥85%.
There are micropores, which are those that retain water and macropores, which are those that drain water after irrigation and maintain the aeration of the substrate.
  1. Water Holding Capacity: The volume of water retained by a substrate after being saturated and having drained all the water by gravity.
  2. Available water retention capacity: percentage of water retained by the substrate and that is available to the roots of plants.
  3. Unavailable Water Holding Capacity: The portion of water that makes up the water holding capacity and is not available to plant roots.
  4. Aeration: The volume of air in a substrate after being saturated and having drained all the water by gravity. Its optimal value is estimated between 20-30%.
  5. Readily available water: it is the difference between water retained by a substrate between 10 and 50 centibars of suction.
  6. Reserve water: is the amount of water released by a substrate between 50 and 100 centibars of suction.
  7. Total water available: is the sum between the readily available water and the reserve water. Its optimal level is between 25-40% of the volume of the substrate.
  8. Water that is difficult to dispose of: it is water that is fixed in the substrate below 100 centibars of suction pressure.
  9. Volume contraction: it is the loss of volume that a substrate experiences when it is dried in a stove at 105ºC starting from a state of saturation and subsequent drainage at 10 centibars of suction pressure. The optimal level is below 30%.
  10. Vapor pressure deficit (DPV): it is the difference between the water vapor that the air has at a certain time and the one it would have if it were saturated.
  11. Xylem and phloem: are the vascular ducts through which the sap circulates in plants, communicating the root with the leaf structures through the stem. Xylem transports raw sap (water and ions absorbed by the root of the soil solution or substrate) from the root to the leaves for photosynthesis to take place. It is the central area of the stem. The phloem transports the processed sage (sugars and starch) from the leaves to all parts of the plant. It occupies the outer area of the stem.
  12. Meristematic tissues: meristematic tissues are, among the tissues that make up plants, those responsible for vegetative growth. It is characterized by always staying young and little differentiated. They have the capacity to divide and from these cells the other tissues appear. Plants, unlike animals, have an open system of growth; this means that the plant has more or less perennial productive areas, capable of periodically generating new tissues and organs. These regions are called meristems. We can classify them into:
  • Primary meristems are the first to appear during the vegetative growth of a plant. They are located at the apex of the stems and root.
  • Secondary meristems, or cambium, are responsible for radial growth, leading to the thickening of stems and roots through the formation of concentric layers of tissue.
  1. Lignification: process typical of the end of the cell growth period of higher plants by which lignin (complex organic polymer that forms important structural materials in the supporting tissues of vascular plants and some algae and insects) replaces most of the water of the cell membrane and produces the hardening of the same and its increase of 23. volume. It is the process of hardening wood.


  1. Stress: stress is defined as the consequence that results from the presence of a factor external to the plant, caused by the changing environment, and that exerts a negative influence on its optimal development.
  • Abiotic stress: We define abiotic stress as the negative impact that «non-living» factors cause on plants in a specific environment. They can be of physical or chemical type:
  • Physical abiotic stress
    • Drought
    • Heat
    • Cold
    • Freezing
    • Excess or lack of irradiation
    • Root anoxia due to lack or excess of water
    • Effects of a strong wind
    • Soil compaction
    • Wounds or injuries
  • Chemical abiotic stress; it is caused by salinity (in its ionic or toxic component) which results in a lack of mineral elements. It also involves the action that environmental pollutants such as sulfur dioxide (SO2), nitrogen oxides (NO), chlorofluorocarbon compounds (CFCs), ozone (O3) and metals exert on the metabolism of plants.


  • Biotic stress: We define abiotic stress as the negative impact that «living» factors cause on plants in a specific environment:
    • Animals large and small.
    • Other plants
    • Insects, mites and mollusks
    • Bacteria, fungi and viruses
    • Nematodes.
The effects of factors, whether biotic or abiotic, translate into greater oxidation of the plant which translates into a decrease in the growth and productivity of our plants. However, plants are able to, if environmental conditions become unfavorable, repress growth responses and trigger protection and defense mechanisms that compromise development but ensure the survival of the plant under adverse environmental conditions. The environmental conditions in which plants develop are perceived by the different organs, and this information is transmitted internally by modulating the synthesis of signals, mainly hormones that activate the responses of development and vegetative growth.
  1. Climacteric/non-climacteric fruits: Climacteric fruits are those that continue to ripen even after they have been harvested, which is because regardless of whether they are no longer in the plant, they increase their rate of respiration and endogenous production of ethylene. Among the climacteric fruits we find the apple, pear, nectarine, banana, mango, kiwi, peach, apricot, watermelon, melon, tomato, plum, avocado, papaya, custard apple, persimmon and fig.
The non-climacteric fruits are those that once cut from the plant, will only ripen a little more, being for many crops an almost negligible ripening. Non-climacteric fruits do not present significant variations in their respiration rate during the ripening stage, nor in ethylene synthesis. This implies that once cut, they do not improve their organoleptic characteristics (taste, aroma, color, etc.). Finally, it is important to mention that, for these fruits, the exogenous application of ethylene does not alter the characteristics of ripening, although it does increase respiration. We find orange, lemon, mandarin, grapefruit, grape, pineapple, strawberry, raspberry, cherry, olive and pepper,


Auxins: are a group of plant hormones that act as regulators of plant growth and development. Its function is related to the factors that stimulate plant growth, specifically cell division and elongation. These phytohormones are found throughout the plant kingdom, from bacteria, algae and fungi, to higher plants. The synthesis of auxins usually occurs in apical meristems, tender leaves and developing fruits. One of the essential characteristics of hormones is the ability to move from their place of biosynthesis to other parts of the plant, where they exert their action, but they can also exert a local action in the same cells in which their biosynthesis occurs. This biosynthesis can be stimulated by environmental factors All plant hormones can travel short distances by diffusion, and reach different organs through vascular tissues.  Among the auxins we highlight:
  • AIA or Indoleacetic Acid: phytohormone of natural origin, is the hormone that is found in greater quantity in the tissues of the plant. It is synthesized at the level of young tissues, in the leaves, meristems and terminal buds.
  • AIB or Indolpuityric acid: phytohormone of natural origin of broad spectrum. It contributes to the development of roots in vegetables and ornamental plants, likewise its use allows to obtain larger fruits.
  • ANA or Naphthaleneacetic Acid: hormonal product of synthetic origin, is widely used in agriculture. It provokes the growth of adventitious roots in cuttings, reduces the fall of fruits and stimulates flowering.
  • 2,4-D or Dichlorophenoxyacetic Acid: hormone of synthetic origin used as a herbicide with systemic action. Used at certain concentrations, it favors the appearance of adventitious roots.
  • 2,4,5-T or Acid 2, 4, 5- Trichlorophenoxyacetic: phytohormone of synthetic origin of pesticide application. Currently its use is restricted due to its lethal effects on the environment, plants, animals and man.
Cytokinins: A group of plant phytohormones that promote cell division and differentiation. They are synthesized in any plant tissue: stems, roots, leaves, flowers, fruits or seeds, but mainly in the root and can be transported both to the apex and to the base of the plant through the vascular bundles (xylem / phloem). The doses needed to obtain the desired response are very low due to their high activity. Its effects on the plant are:
  • Control of apical dominance: apical dominance is determined by a balance between auxins and cytokinins where auxins function as repressors and cytokinins as promoters of the budding of lateral buds on the stem and inversely in roots. In this way, cytokinins contribute to determining the architecture of a plant.
  • Delay of foliar senescence and therefore of leaf fall: cytokinins slow down the process of degradation of chlorophyll, RNA, lipids and proteins that occurs in the leaves in the fall or when they are separated from the plant.
  • Expansion of cotyledons: during seed germination cytokinins favor the elongation of cotyledon cells in response to light.
Gibberellins: Gibberellins are a type of phytohormone that affects a wide variety of developmental phenomena in plants. It was discovered by Japanese scientists in a fungus of the genus Gibberella. There are more than 110 different gibberellins, but for each plant species only a few are biologically active. Like auxin, gibberellins are synthesized in apical meristems, young leaves and embryos and are transported through the phloem and their main function is to stimulate growth:
  • Stimulates the elongation of the stem.
  • Promotes seed germination.
  • They induce parthenocarpy.
  • It reduces the needs of cold hours (vernalization) necessary for the flowering of certain plant species.
  • It induces the flowering of long-cycle species grown in the short cycle period.
  • Stops aging (senescence) of leaves and fruits in citrus fruits.
The most common active gibberellins in plants are GA1, GA3 and GA4.


Brassinosteroids: they are phytohormones that act as plant growth regulators and act in very low amounts. They are the only phytohormones with a steroidal-like chemical structure in plants and are considered to be the sixth class of plant hormones. The application of brassinosteroids causes an increase in the rate of stem elongation, increase in leaflet surface, pollen tube growth, and adaptation of the plant to biotic stress.
Abscisic acid (ABA): it is a phytohormone with important functions within the physiology of the plant. It participates in developmental and growth processes, as well as in the adaptive response to stress of both biotic and abiotic type. It participates in processes such as embryo maturation, seed dormancy, vegetative growth and processes related to stress tolerance, both biotic and abiotic.
Ethylene: it is the phytohormone responsible for the stress processes in plants, as well as the ripening of fruits, the senescence of leaves and flowers and the abscission of the fruit. Being a hydrocarbon, it is very different from other natural plant hormones. This gas is used artificially to ripen fruits that have been harvested in green. Ethylene appears to be produced by essentially all living parts of higher plants, and the rate varies with the specific organ and tissue and its state of growth and development. It is involved in processes such as ripening climacteric fruits, causing abscission of organs and fruits, stimulating seed germination, inducing flowering.


  1. Apomixis: we define apomixis or apomixia to the process by which certain plants reproduce by seeds without gamete fusion having occurred, so their descendants are genetically identical to the mother plant; it is therefore a type of asexual reproduction. Although from the evolutionary point of view apomictic plants lack the adaptive advantages offered by sexual reproduction, apomixis allows the indefinite fixation of genotypes highly adapted to their environment.
  2. Geotropism: movement of plant organs, especially the root, stem and leaves, which is influenced by gravity. If it is positive it goes in the direction of gravity (downward direction) and if it is negative it goes in the opposite direction (upward direction).
  3. Phototropism: movement of plant organs, especially the root, stem and leaves, which obeys the influence of light. If it is positive the organ moves towards the light and if it is negative it goes in the opposite direction.
  4. Cotyledons: Cotyledons are the first leaves that develop phanerogamous plants and that appear when the germination of the seeds occurs. They are modified leaves that absorb the nutritive material of the albumen to feed the plant during germination. It resembles neither in shape, nor size, nor coloration to true leaves. Its function is to nourish the plant in the early stages of its life so its life is short.
  5. Phanerogamous: phanerogamous plants are all those vascular plants that have visible flowers for sexual reproduction. Phanerogams are divided into 2 groups: angiosperms, whose eggs or seminal primordia are protected by the ovary of the flower and gymnosperms whose eggs are naked, free or not protected by the ovary of the flower.
  6. Cryptogamous: cryptogams are primitive plants, little evolved, that do not give seeds. They reproduce through the production of spores, and their plant body does not exhibit true tissue differentiation.
  7. Angiosperms: they form the largest group of terrestrial plants. They are vascular plants and spermatophytes, that is, they are produced from a seed.
All angiosperms have flowers (although they do not always correspond to the common idea that we all have of a flower), which produce seeds enclosed and protected by the wall of the ovary (carpels) that, subsequently, becomes fruit. They can be herbaceous, shrubby or arboreal plants. Depending on the number of cotyledons they present, they are classified into monocots (those that have only one cotyledon) or dicotyledons (their seeds have two cotyledons).
  1. Gymnosperms: they are vascular plants and spermatophytes, that is, they are produced from a seed, but unlike angiosperms the seed does not develop in an ovary, being plants without flowers or fruits. However, its flower can often be thought of as a branch of limited growth that can form cones or pineapples and that generate fertile leaves or sporophylls with an exposed seed. They are the oldest plants on the planet and date from the Carboniferous period (pines, cypresses, firs, larches, yews, etc.).
  2. Genotype: from the Greek genos (birth) and types (mark). Genetic makeup of an individual determined by the DNA sequence. It contains all the hereditary information of an individual. It is transmitted from the parents to their offspring.
  3. Phenotype: from the Greek phainein (show) and typos (mark). Detectable manifestation of the genotype. Observable traits such as, for example, hair color, bone size, etc. It depends on the genotype, the environment and nutrition.
  4. Pivoting root system: root system formed by a main root from which the lateral ones come out. The mature parts present secondary growth and the absorption of water is carried out at the ends, through the root hairs. It is typical of dicotyledonous angiosperms and gymnosperms.
  5. Fasciculated root system: it is formed by a bundle of adventitious roots originating at the base of the stem from which they can branch, but never have secondary growth. It is typical of monocotyledonous angiosperms.
  1. Achene: dried and indehiscent fruit (which does not open spontaneously when it reaches maturity to release the seeds), from an ovary with a single seed and whose pericarp (outer part of the fruit that surrounds the seed) is thin and not welded to said seed.
  2. Trichome: trichomes or plant hairs are appendages of the epidermis of plants. The functions they perform are varied: water absorption, temperature regulation, dispersal of seeds and fruits, protection against abrasive agents and perception of stimuli. Glandular trichomes also exude sticky compounds that trap insects or toxic substances that cause plant disease.
  3. Determined growth: vegetative growth of both the main and secondary stems ends once flowering has occurred.
  4. Indeterminate growth: Vegetative growth continues once flowering has occurred. Plants that present this type of growth have the phase of vegetative growth, flowering, fruit fattening and fruit ripening at the same time, only in different parts of the plant.
  5. Aporque: it is an agricultural work that consists of accumulating land at the base of the stem of a plant forming a small mound. To carry out this practice, the crop must have a certain height.
The benefits of the aporcado are:
  • Increases soil oxygenation.
  • Decreases damage to the base of the stem by frost or insolation.
  • Prevents the appearance of certain diseases.
  • It favors the development of roots in the soil.
  • Facilitates the fertigation of plants
  • Promotes vertical growth of plants.
  1. Adventitious roots: the adventitious root or aerial root is one that does not arise from the radicle of the embryo (that is, from the fertilized egg) but from any other part of the plant, such as from underground stems, old roots or from the foot or base of the trunk /stem.
They are the last to develop, appearing when plants have approximately 10 true leaves and originate from the two stem knots closest to the soil surface. Depending on the knot from which they originate, they can penetrate to depths between 5 and 15 cm. They basically fulfill a support function, allowing the plants a better anchorage; in addition, and although limited, they participate in the absorption of water and nutrients.
  1. Parthenocarpy: parthenocarpy is a phenomenon in which there is the formation of fruit without seeds even if there has been fertilization, that is, it is a fruit that has only vestiges of the seeds product of an abortion, or very few compared to the variety or non-parthenocarpic cultivar.
  2. Substrate washing; operation that consists of applying water to a substrate contained in a container in order to reduce the salt content of the same. It is usually done at night when the plants do not transpire so as not to cause any nutritional imbalance to the plant. Normally it is enough to apply 2 to 3 times the volume of the container in clean water, letting it drain. We will measure the electrical conductivity of the drain until it is the closest thing to inlet water. Once the substrate is washed, we will apply our nutrient solution.
  3. Tendril; in botany a tendril is a specialized stem, leaf or petiole that certain climbing plants are used to attach to a surface or other plants, since the morphology of their prostrate stems require it. There is a great variety of tendrils, the most important being those of caulinar and foliar type. Caulinares (like those of the vine) are modified stems without buds or knots; foliar (such as peas) derive from the modification of the limb of a leaf. In cucurbits tendrils come from the modification of the stem and leaf.
Tendrils can be right-handed if the turn in the direction of growth (like the hands of the clock), or levorotatory (counterclockwise).
  1. Ovary: it is the most important part of the gyneceo, formed by the lower part of the carpel that shelters the eggs. Some botanists define it as a fruit before its development. It has a generally rounded or oval shape and sits directly on the receptacle. It can be simple, if formed by a single carpel, and compound, when it results from the union of several carpels.
Plants have different types of ovary, depending on the position it adopts with respect to the place where the other whorls are born, as follows:
  1. Supero ovary: the ovary is located above the receptacle and at the insertion point of the other floral parts. It is a conical or convex receptacle, where the ovary will be the upper part of the flower. The sepals, petals, and stamens will be inserted to the base of the ovary. In this case the flower is defined hypogina.
  2. Inferous ovary: the ovary is located below the other whorls, on a well-concave receptacle where sepals, petals and stamens are inserted above the ovary. A flower with an inferous ovary is called an epigina.
  3. Semi-inferous or middle ovary: it is located in a middle position more or less surrounding the receptacle.
  4. Androceous: It is the male part of the flower. It is constituted by the stamens that are nothing more than some sheets modified in order to carry the pollen. Each stamen has two parts:
  • The filament, which ends in the anther.
  • The anther, which is the upper widening where the pollen grains are enclosed.
  1. Gyneceo: it is the feminine part of the flower. It consists of the following parts:
  • The stigma, which is located at the top in the form of a receptacle and whose function is to collect pollen.
  • The style, a kind of conductive tube that connects the stigma with the ovary
  • The ovary, widening at the bottom where the eggs that have to be fertilized by male pollen are located.
  1. Pepónide: fleshy fruit attached to the calyx, with an inferous ovary, with many seeds in a single compartment and attached to three placentas and whose cuticle is impermeable. It is the characteristic fruit of cucurbits.
  2. Hypocotyl: part of the axis of the embryo of a seed that is located below the insertion point of the cotyledons.
  3. Epicotile: part of the axis of the embryo of a seed that is located above the insertion point of the cotyledons. In the seedling of phanerogams, this name is given to the first internode that forms the plumula when it develops.
  4. Polar solvents: They are substances in whose molecules the distribution of the electronic cloud is asymmetrical, therefore, the molecule presents a positive and a negative pole separated by a certain distance. They are used to dissolve polar substances. The classic example of a polar solvent is water. Low molecular weight alcohols also belong to this type.
  5. Apolar solvents: they are substances in whose molecules the distribution of the electronic cloud is symmetrical, therefore, these substances lack a positive and negative pole in their molecules. They are capable of dissolving non-water-soluble substances. Some solvents of this type are: diethyl ether, chloroform, benzene, toluene, xylene, ketones, hexane, cyclohexane and carbon tetrachloride.