Hydroponics and growing cacti in aggregate

Types of hydroponic systems

In water culture, roots directly contact the solution. In inert or slightly reactive aggregate, the material supports the plant and creates pores, while the solution supplies water and minerals. A passive system uses capillary rise, while an active one may pump and aerate the nutrient solution. [6-WWW]

The boundary between hydroponics and ordinary mineral cultivation is not always sharp. A pot of pumice watered periodically with dilute fertilizer functions differently from roots permanently immersed in a reservoir. A method description should specify material, solution delivery, replacement frequency and the level remaining after drainage. [6-WWW]

Removing soil alone does not guarantee cleanliness or control. Aggregate may contain dust or soluble salts, the reservoir may accumulate deposits, and roots and microorganisms alter solution composition. The system needs a procedure as well as a different container. [6-WWW]

Supplying roots with oxygen

Roots respire. They consume oxygen in processes supplying energy needed for functions including ion transport. Water contains much less available oxygen than air, and oxygen solubility decreases as temperature rises. A warm, stagnant nutrient solution can therefore quickly become unfavourable. [6-WWW] [Dubrovsky and North 2002]

Aeration, solution movement and periodically exposing part of the root system manage oxygen, but do not justify removing plants daily. This damages delicate root hairs and increases infection risk. A better system provides gas exchange without constant root handling. [6-WWW] [Dubrovsky and North 2002]

Root browning and reduced water uptake may result from oxygen shortage, high temperature, salinity or infection. Colour alone does not resolve the cause. Check solution temperature, smell, conductivity, level, pump condition and changes made before symptoms appeared. [6-WWW] [Dubrovsky and North 2002]

Aggregate properties and selection

Assess support material by particle size, capillary rise, water retention, air space, durability and chemical reactivity. Pumice, expanded clay, perlite and lava are not interchangeable merely because they all look mineral. They differ in internal pores, density and behaviour after repeated wetting. [6-WWW] [6-WWW]

Before use, remove dust and check that the material does not release unwanted salts. Construction waste, slag, coke and arbitrary aggregates from older literature may have variable composition or contamination. They should not enter a collection without reliable characterization. [6-WWW] [6-WWW]

An excessively fine fraction restricts air space. A very coarse one may poorly draw water upwards in a passive system. Set solution level so part of the root zone remains aerated. There is no universal height because it depends on container, aggregate and root distribution. [6-WWW] [6-WWW]

Nutrient-solution composition and control

A plant needs a set of macro- and micronutrients, rather than one fertilizer described as good for cacti. Solution composition should account for ions already in the water. Calcium and magnesium supplied by the water source may alter the required recipe, just as high alkalinity affects pH stability. [7-WWW] [6-WWW]

Electrical conductivity indicates total dissolved-ion concentration. It does not show whether their proportions are appropriate. If the plant absorbs water faster than salts, reservoir conductivity may rise. Topping up only with full nutrient solution without measurement then gradually concentrates it. [7-WWW] [6-WWW]

pH affects nutrient availability, but continually adding acid or base to chase one value may cause major composition fluctuations. Distinguish pH from water alkalinity. Older chemical recipes should not be reproduced without water analysis, calculations and safe equipment. [7-WWW] [6-WWW]

System hygiene

Wash system components, remove root residues and limit material transfer between diseased and healthy plants. This does not mean an open home system will remain sterile. Microorganisms arrive with plants, water and air. The aim is hygiene and stable conditions, not sterility claimed after one disinfection. [6-WWW] [9-WWW]

Do not preventively add historical fungicides to the nutrient solution. Selecting any plant-protection product requires a current label and diagnosis. Sudden cloudiness, anaerobic smell or slimy roots primarily signal a need to stop the experiment, clean the system and assess the plant. [6-WWW] [9-WWW]

Root adaptation to a new environment

A root developed in fine substrate does not immediately become effective in solution or coarse aggregate. Water contact, oxygen diffusion and mechanical support change. Some older roots may die before new sections adapted to the system's conditions develop. [Dubrovsky and North 2002] [6-WWW]

Do not routinely remove the entire healthy root system. Gently remove loose substrate and assess tissues after rinsing. Wounds must heal before placement in a continuously moist system. A large specimen valuable to a collection is unsuitable as first trial material. [Dubrovsky and North 2002] [6-WWW]

Planning a comparative trial

Begin with several similar, readily replaceable plants. Keep some in the existing method as a reference. Record species or clone provenance, shoot mass or dimensions, root condition, aggregate type and particle size, water composition, fertilizer, conductivity, pH, temperature and solution-replacement rhythm. [6-WWW] [Woźniak n.d.]

Establish stopping criteria in advance. These include rapidly progressing root loss, collar softening, anaerobic smell and uncontrolled conductivity increase. A single increment of growth does not yet demonstrate method superiority. Assessment should include at least root health, new-growth habit, overwintering stability and repeatability in the next cycle. [6-WWW] [Woźniak n.d.]

The archival hydroponics text remains valuable as a record of a collector's experiment and a source of questions. Its author acknowledged his brief experience. A longer trial requires measurements, a comparison group and observation of at least one complete seasonal cycle. This assesses growth and root condition during growth slowdown. [6-WWW] [Woźniak n.d.]

Interpreting measurements

Conductivity may rise as water is lost even without fertilizer addition. Refilling the reservoir lowers it by dilution, which does not mean appropriate ion proportions have been restored. pH may change through nutrient uptake and microbial activity. A single measurement without date, temperature and top-up information therefore has limited value. [7-WWW] [6-WWW]

Take readings at similar times and after mixing the solution. Instruments require calibration and clean electrodes. Record values for fresh solution, the reservoir before refilling and after correction. If drainage is measured in an aggregate system, use a repeatable collection procedure. Otherwise differences may arise from the procedure rather than root-zone condition. [7-WWW] [6-WWW]

Plant mass, new-growth length and root appearance matter as much as chemical figures. Rapid growth of a soft, unnaturally elongated shoot is not success if light was insufficient. Assess the method through balanced structure, root-system health and the plant's ability to complete a full seasonal rhythm. [7-WWW] [6-WWW]

Interpreting the water-culture drawing

The drawing shows a suspended plant with some roots in liquid and the shoot base above its surface. This models water culture rather than instructing permanent immersion of the entire root system in stagnant water. Mineral nutrients and sufficient oxygen are needed. Oxygenation conditions follow the particular system's structure, nutrient-solution volume, temperature and gas exchange. [7-WWW] [6-WWW]

The transparent vessel makes roots visible in the illustration. In a real installation, light reaching the nutrient solution favours algae, so shield the reservoir appropriately for the system. Monitor liquid level, EC, pH, temperature, root condition and hygiene. Adding water alone does not automatically restore the solution's original composition. [7-WWW] [6-WWW]

Hydroponic production of young Opuntia cochenillifera segments was studied in an experiment discussed in the chapter on lighting. The historical experiments of Fleischer and Schütz remain separate material, situated in their system designs and nutrient-solution compositions. [Horibe et al. 2019] [Fleischer and Schütz 1978, pp. 103–126]