We're almost ready and now for the moment we've all been waiting for! It's time to put your new knowledge to use and get started growing. In this chapter we will explore some of the more popular cultivars, and learn about their preferred growing environments. We'll also learn about starting from seed, and how to take and root cuttings. But before we get started, lets quickly recap a few more important plant requirements.
Temperature - The rate at which plants grow is controlled by the temperature of their environment. Usually as temperature rises, so does certain aspects of the plant's metabolism that may or may not be within optimal ranges either for genetic factors, or for other limiting factors as discussed below. In order to achieve the best growth, it is important to keep your garden within the temperature range your crop requires to avoid stress and prolonged maturation.
Humidity - The amount of water present in air is known as relative humidity. High levels of humidity prevent plants from transpiring water through their leaves, since the air is already full of water. High humidity can also prevent plants from cooling themselves through the same process of transpiration, and can hurt by providing the right climate for powdery mildew and botrytis to flourish.
Light - All light is not created equally, especially as far as plants are concerned. Light that falls within the range of color that stimulate photosynthesis is called PAR (Photosynthetically Active Radiation), and it's the only kind that will influence the growth rate of your crop. Many light meters don't measure PAR, which limits the meter's value in determining how fast your plants will grow. Even if they don't measure PAR, most meters are useful for determining if the lighting is even across your garden. PAR light is produced by the Sun, HPS, MH and now compact fluorescent lamps.
CO2 - In enclosed environments, the normal concentration of CO2 (325-425 PPM) can rapidly be depleted, resulting in slowed growth due to the lack of photosynthesis taking place. Providing plenty of fresh air or supplemental CO2 (in the range of 1000-1500 PPM) will keep chlorophyll activity constant and plants growing rapidly.
Dissolved Oxygen -Dissolved oxygen (DO) is the measure of available oxygen in your nutrient solution. Roots require oxygen to perform respiration, and will suffer if the proper amount of oxygen is not regularly available to them. Stagnant water in reservoirs and ponds must be agitated or oxygenated if plants are to be grown in them directly. A general rule of thumb is to maintain between 5 and 25 PPM of DO in solution that directly feeds and bathes plant roots. If the proper level of DO is not available to the plant, anaerobic respiration will result which will quickly cause the production of toxic levels of ethanol by the plants.
pH - The pH of a solution is the measure of the relative number of hydronium ions it contains. pH measurement ranges between 0 and 14, with a pH of 7 being neutral, 0 as extremely acidic, and 14 extremely alkaline (or basic). When the pH is neutral, there are equal numbers of hydrogen ions (H+) and hydroxide ions (OH-) in the solution to balance it out. A solution with a pH from 0 to 6.9 has a greater concentration of H+ ions that makes it acidic. A solution with a pH of 7.1 to 14 has a greater concentration of OH- ions and it is alkaline, or basic, as a result. The pH in a nutrient solution is critical because it controls the availability of elemental salts to the plant. At pH ranges outside of the norm, nutrient deficiencies may occur due to their unavailability to the plant.
Electrical Conductivity / Total Dissolved Solids (TDS)
Electrical conductivity (EC) is a measure of the total dissolved solids in a solution. As nutrients are taken up by a plant, the EC level is lowered since there are fewer salts in the solution. Alternately, the EC of a solution is increased when water evaporates from an open reservoir or is transpired by the plants.
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