Water

Water is a fundamental requirement for gardening that it is paradoxically often given little thought.

Water is a fundamental requirement for gardening that it is paradoxically often given little thought. As small children, we learn that plants need water to grow, but then it passes by without much in the way of further explanation. For those willing to look a little deeper, here is some of the rest of the story:

At sea level, water will freeze under 32 degrees Fahrenheit (0 degrees Celsius), and boil (at sea level) at 212 degrees Fahrenheit (100 degrees Celsius). Freezing water will cause it to expand, and become less dense than its liquid state, which is why ice will float on water. Frozen snow and ice are important for water storage that releases in summer months when plants need additional water for growth.

Water vapor is caused by evaporation or boiling water. The amount of water vapor in the air is recorded as humidity. High humidity gardens are prone to molds, and low humidity gardens are prone to spider mite and other insect infestations. 

Under normal circumstances and pressure, the temperature of liquid water will not exceed its boiling point. At sea level, water boils at 212 degrees Fahrenheit (100 degrees Celsius), and won’t get any hotter, since at that point it will turn into a gas and escape. Rice cookers use this principle to tell when the water has boiled off. As long as the bottom of the cooker doesn't exceed the boiling point of water, the device knows to continue cooking. When the temperature raises past the boiling point of water, it means that the water has boiled off, and cooking it done. At higher elevations, the boiling point of water is lower due to the drop in pressure. The higher the altitude, the lower the boiling point of water, and the longer food must be boiled to heat to a given temperature. For example, water boiling at 212 degrees will cook eggs faster than water boiling at 190 degrees. Pressure cookers use the other side of the same principle, water under pressure boils at a higher temperature, so immersed food heats faster.

While not technically a nutrient, but the transport agent for nutrients, water is an important requirement for growing healthy plants. Slight under watering is less detrimental than slight over watering, so if in doubt, run towards the dry side. The quality of the end solution is in part determined by the quality of the initial water used for the base liquid. If local water is of poor quality, reverse osmosis filters or other filtering systems can be used to clean it.

Distilled water has been boiled into steam, which has then been collected, and cooled back into a liquid. It is the purest form of water generally available. Pure water such as distilled water should be microwaved with care, because if heated in a clean smooth container it is possible for the water to become “superheated” which means that the temperature in its liquid state is above the normal boiling temperature. This can become dangerous when a contaminant or edge is introduced, such as dipping a spoon in it, as that can trigger a violent almost instantaneous boiling response. If the starting water is not pure (such as filtered or tap water), or if a contaminant is added (like coffee, tea, or sugar), then the water will boil normally.

Reverse osmosis water is also a very pure form of water, but incurs a high wastewater cost as part of the process. Neither distilled or reverse osmosis water contain nutritional elements in significant amounts. 

In contrast, as long as tap water is suitable for drinking, it should be suitable for growing plants in (the reverse is also true, if you can't grow a plant in your tap water, don't drink it). EC or ppm testing of available tap water will give an indication of suitability.  Two common contaminants for tap water are calcium carbonate salt, and magnesium, which are found in “Hard” water. Since this can be a source of calcium to plants, nutrients developed for hard water generally take this into account, and therefore contain little or no additional calcium. Another common contaminant in city water is chlorine, which plants do not need in very high quantities. To vent off chlorine from tap water, fill watering containers each time just after watering. Checking the quality of the source water will assist in fine tuning a garden, but tap water clean enough to drink will often work well enough. 

Water (H2O) is made of a collection of molecules having two hydrogen atoms, and one oxygen atom. It is particularly well suited as a solvent for many materials. Hydrophilic (water loving) materials like many of the salts dissolve easily in water, while hydrophobic (water fearing) substances such as oils do not. Because water molecules have a positive charge on the side with the two hydrogen (H) atoms, and a negative charge on the oxygen (O) side, they are attracted and attach easily to many other molecules. One reason that salts are so often used as nutrient sources, is that they also have a positive and negative side, but are held together with a weaker ionic bond. Water molecules attach themselves to either side of the salt molecule, and break them apart, dissolving the salt into the water, and releasing the nutrient element in the process. This is why many chemical hydroponic solutions make use of salts dissolved in water. Potassium nitrate for example, will seperate into both potassium and nitrate (NO3), which can allow it to provide two of the macronutrients (Nitrogen (N) and Potassium(K), heavy on the K). Organic nutrients are often less miscible, and should be shaken to create a suspension each time before use. 

Pure water has no electrical conductivity, so an EC or PPM meter will read zero conductivity. As the water becomes more contaminated with salts and other conductive materials from fertilizers, the nutrient solution will become more electrically conductive, and the meter will show higher values. The information gathered with a meter, coupled with the specific nutritional needs of the plant, can be invaluable to maintaining a suitable nutrient solution, but keep in mind, EC and PPM meters only display the total amount of electrically conductive contamination present, not specifically what the contamination is. These meters do not give the specific N-P-K values. A solution with a high Nitrogen (N) content may give the same reading as a solution with a high Phosphorus (P) content. 

Underwatering is a smaller error than overwatering. If plants are slightly underwatered, they will usually signal by getting droopy, and respond favorably within hours when watered. Overwatering is both more traumatic and has a longer recovery. If you do happen to drown your plants, don't give up, just try to learn from the experience, and try again. If your tap water is of a very poor quality, you may have to filter it before use, or use drinking water to hydrate your plants.

pH is a value between 0 and 14 to denote how acidic or basic a liquid is. Pure water has a pH of 7, solutions with a pH value lower than 7 are called acids, and solutions with a pH value higher than 7 are called alkaline or basic. Strong acids will corrode and dissolve many substances, and strong bases such as lye can cause deposits and damage to organic tissues.

The ideal range for nutrient solutions is around 6.0-6.2. If you are within a half point or so, don't bother adjusting it. Proper pH is more critical in hydroponic systems than soil gardens due to the additional buffering properties of soil. Radically incorrect pH can cause physical damage to plants due to the caustic properties of acids and bases, and less severe imbalances have an impact on the solubility of plant nutrients. Adjustments to pH are made by adding the opposite. Acids have positive hydrogen ions, and bases have a matching negatively charged acceptor. When the two combine, they combine to neutralize each other. If the solution has a pH value too low (is acidic), add a base to raise the pH. If the solution is too basic (pH too high), an acid is added to lower it.

Water is required for photosynthesis. Light energy is absorbed by the plant, which divides the water molecules into hydrogen and oxygen. The hydrogen is combined with carbon dioxide (CO2) to form glucose.

Water has a high surface tension, it sticks to itself very well (cohesion). Submerged molecules can attach on all sides to each other, but the molecules on the surface do not have water molecules above them to attach to, and so they hold tighter to their neighboring water molecules. This creates tension along the surface, allows water to “bead” into droplets, and allows for capillary action to force water to rise within a narrow tube. The water will “stick” to the walls (adhesion), and surface tension will pull to try to form a droplet (cohesion), supplying an upward force. This allows for both the transport of water up growing media to plant roots, and up the roots and along the rest of the plant as part of respiration.

A key component to plant health, particularly in hydroponic systems is a sufficient amount of available oxygen. While oxygen is a major component of water, the plant also requires oxygen in a more available form. The level of freely available oxygen in water is known as its dissolved oxygen (DO) content. Airstones and fountains are both used to increase DO. Since the amount of air that water will hold is dependent on temperature, the warmer the water, the less air it will hold, and the more important proper aeration becomes. Cool winter water tends to have higher DO than warm summer water. 

If the amount of dissolved oxygen drops too low, it creates conditions for anaerobic (air hating) bacteria to develop. Anaerobic bacteria are the rotting and spoilage bacteria responsible for the foul odors in stagnant water. Properly aerated water is conducive to aerobic (air loving) bacteria are the beneficial bacteria that assist in composting and healthy plant development. 

Water is an important part of gardening, and an improved understanding of its properties can help understand how many gardening concepts fit together. Like people, plants will die from lack of water faster than from a lack of nutrition, and also like people, drowning will kill faster than dehydration. This precious resource is one of the fundamental necessities of practically all life, but due to it's current abundance, is all too often treated without the respect it is due.

Peace, love and puka shells,

Grubbycup