Water
Marijuana Horticulture
by Jorge Cervantes
Clean rainwater is the best for irrigation. To make sure it is not too acidic and harmful to plants, take the pH and parts per million (ppm) reading from collected rainwater before using.
Sodium-heavy water builds up in the soil causing slow growth and shorter plants with smaller leaves. At low levels, sodium appears to benefit plants and may even make up for potassium deficiency, but too much leads to “sodium stress”. Roots lose the ability to absorb water and other nutrients and will dry out even with heavy watering. It is very important to test your water for sodium and other dissolved solids and take appropriate action if the reading reaches more than 50 ppm. Sodium is more of a problem when growing in containers than when growing in well drained soil.
Local farmers of the Department of Agriculture have information about water solids in your area, and many areas have low-cost, state-certified labs that can test your water for you.
Often, if the sodium content is below 300 ppm, a good flushing every month will keep sodium and other salts from building up to toxic levels.
There are several easy, inexpensive options to improve water quality. Irrigate seedlings, clones, and mother plants with rainwater to dilute dissolved solids.
Flush container gardens with three quarts of water for each dry quart of soil. Water once with tap water and always afterwards with tap water augmented with ammonium sulfate.
Clean tap water by filing barrels and setting 2-3 feet off the ground. Add ammonium sulfate to settle out the sodium, then siphon water from the top of the barrel, refilling after each watering to allow the chlorine to evaporate. Chlorine, like sodium, is beneficial in small amounts. It is essential to the use of oxygen during photosynthesis and is necessary for root and leaf cell division. But too much chlorine causes leaf tips and margins to burn and leaves to turn a bronze color.
Empty the barrel periodically, and scrub out residues and sediments. Clean rainwater is an excellent choice for irrigation. Collect runoff by placing a barrel under a downspout.Mix the rainwater with barrels of tap water to dilute the dissolved solids. Roofs and terraces can accumulate trash, which will pollute the otherwise clean rainwater. Covering you8r catch-barrel will prevent evaporation and keep out trash.
Sodium, calcium, and magnesium can be harmful in the soil, too. Excess calcium, for example, keeps the pH level too high and blocks uptake of several nutrients including iron and potassium. Fertilizer with chelated iron will counteract this problem. To much magnesium creates rapid uptake of trace elements but does not usually cause a problem.
The fertilizer comes in liquid or wettable crystal form and can also be used in soil to alleviate problems caused by bad weather. Several commercial hydroponic fertilizer formulations for “hard” water are available and work very well.
Check the garden daily, if possible, and water when soil is dry one inch below the surface. Irrigate plants in the ground until they are completely wet.
Many different types of receptacles and reservoirs can store irrigation water. Use the biggest storage unit that you can manage you will always need more water. One good option for storing a lot of water is to dig a nice big hole and line it with a pond liner.