Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

This process is called transpiration. Some of the water also returns manufactured sugars and starches to the roots.
    The roots support the plants, absorb nutrients, and provide the initial pathway into the vascular system. A close-up look at a root reveals the xylem and phloem core, vascular tissue that is enveloped by a cortex tissue or the layer between the internal vascular and the external epidermal tissue. The microscopic root hairs are located on the epidermal tissue cells. These tiny root hair follicles are extremely delicate and must remain moist. Root hairs must be protected from abrasions, drying out, extreme temperature fluctuations, and harsh chemical concentrations. Plant health and well-being is contingent upon strong, healthy roots.
    The nutrient absorption begins at the root hairs, and the flow continues throughout the plant via the vascular system. Absorption is sustained by diffusion. In the process of diffusion, water and nutrient ions are uniformly distributed throughout the plant. The intercellular spaces–apoplasts and connecting protoplasm, symplast–are the pathways that allow the water and nutrient ions and molecules to pass through the epidermis and the cortex to the xylem and phloem’s vascular bundles. The xylem channels the solution through the plant while phloem tissues distribute the food manufactured by the plant. Once the nutrients are transferred to the plant cells, each cell accumulates the nutrients it requires to perform its specific function.
    The solution that is transported through the vascular bundles or veins of a plant has many functions. This solution delivers nutrients and carries away the waste products. It provides pressure to help keep the plant structurally sound. The solution also cools the plant by evaporating the water via the leaves’ stomata.
Water Quality
    The concentration of calcium (Ca) and magnesium (Mg) indicate how “hard” the water is. Water containing 100 to 150 milligrams of calcium (CaC0 3 ) per liter is acceptable to grow marijuana. “Soft” water contains less than 50 milligrams of calcium per liter and should be supplemented with calcium and magnesium.

Look at a rooting clone. Check out the fine, fuzzy roots closely. You can see the minute hair-like feeder roots.

Roots on this clone have reached the wall of the container.
    Water with high levels of chloride frequently contains high levels of sodium, but the opposite is not true. Water with high levels of sodium does not necessarily contain excessive levels of chloride (chlorine).
    At low levels sodium appears to bolster yields, possibly acting as a partial substitute to compensate for potassium deficiencies. But when excessive, sodium is toxic and induces deficiencies of other nutrients, primarily potassium, calcium, and magnesium.
    Chloride (chlorine) is essential to the use of oxygen during photosynthesis, and it is necessary for root and leaf cell division. Chloride is vital to increase the cellular osmotic pressure, modify the stomata regulation, and augment the plant’s tissue and moisture content. A solution concentration of less than 140 parts per million (ppm) is usually safe for marijuana, but some varieties may show sensitivity when foliage turns pale green and wilts. Excessive chlorine causes the leaf tips and margins to burn and causes the leaves to turn a bronze color.
    Simple water filters do not clean dissolved solids from the water. Such filters remove only debris emulsified (suspended) in water; releasing dissolved solids from their chemical bond is more complex. A reverse-osmosis machine uses small polymer, semipermeable membranes that allow pure water to pass through and filter out the dissolved solids from the water. Reverse-osmosis machines are the easiest and most efficient means to clean raw water.

Check the pH of the irrigation water and adjust when

The drawing shows that pure water with no salts or dissolved solids migrates to the solution with more dissolved solids.
Osmosis
    The roots draw the nutrient solution up the plant by the process of osmosis. Osmosis is the tendency of the fluids to pass through a semipermeable membrane and mix with each other until the fluids are equally concentrated on both sides of the membrane. Semipermeable membranes located in the root hairs allow specific nutrients that are dissolved in the water to enter the plant while the other nutrients and impurities are excluded. Since salts and sugars are concentrated in the roots, the