Plant Physiology




Water and Plants: What Makes Water So Special?

Understand the importance of water and you're well on your way to becoming a better grower. Good quality water is arguable the most important additive you can supply to your garden and plants. Find out why!

Water-we know it's important for plants, but how important? And why?

First take a look at this number: 100,000,000,000. Pretty impressive huh? It's one hundred billion-the sort of figure we typically only hear about when banks are being "bailed out" …. (Don't get me started on that!) But this huge number is also one that relates to reality… one hundred billion (tons) is the estimated amount of water that plants on our plant pump back into the atmosphere every year- equivalent to over 3,000 tons each second! Pause to consider that powerhouse for a moment!

Plants give up all this water during the process of photosynthesis. We call this process "transpiration" - it's a little bit like a human sweating. Of course, that water has got to come from somewhere. Plants first have to uptake this water via their root system, sucking it up from the soil.

The key concept here is to think of our plant friends as "water-cyclers" with water flowing through themrather than just water uptakers. Less than 5 percent of the water a plant uptakes from the soil is actually retained for growth purposes! This shift in perspective will really help you develop your understanding as a grower.

Water typically makes up about 70 percent by weight of most, softwood plants, continually moving around the branches, stems and leaves. Understanding the inseparable nature of plants and water should give you a clue as to how important good quality water is for your garden.Importantminerals required for plant nutrition dissolve very easilyin water making it the perfect conduit for bringing nutrients into the plant and moving them around to wherever they're needed. Water also acts as a cooling systemhelping plants not to overheat in the sunshine or under your grow lights.

Re-examining The Obvious: Some Wonderfully Useful Properties of Water!

  • Water remains a liquid in most regions of the planet allowing it to perform the tasks we just mentioned. (Compared with other substances of similar molecular mass (e.g. Ammonia) this is quite surprising!)
  • Water has high thermal conductivity. This means it redistributes heat energy well. If it didn't do this, plant tissues (which are made up primarily of water) would easily suffer from overheating.
  • As mentioned earlier, water helps to keeps plants cool. But water requires a relatively large amount of energy to change from a liquid to a gas (known as the 'heat of fusion'.) Because this energy must be absorbed from its surroundings, when water evaporates from the surface of a leaf (or your skin) it has a pronounced cooling effect-essential for all living things to survive in the sun!
  • The water molecule is highly "polar"-this means it can surround the molecules of a solute (the 'stuff' that we referred to as 'dissolved' in water) and shield it from other solute molecules-thus keeping it surrounded at the molecular level and preventing the solute from forming crystals (what we refer to as 'precipitate.')
  • Water diffuses solutes so that they are evenly distributed (the sugar you stir into your coffee makes all of your coffee sweeter, not just part of it.)
  • Plants contain special cellular membranes that allow water to pass through. However, they only allow small dissolved molecules called "ions" to get through too. Larger molecules that could potentially harm the plant or are unusable blocked. This forms an essential barrier between the living internal world of the plant and the external world.