How much water do plants need?Everyone knows that plants need to be watered, and indeed one of the most asked questions of a gardener is how much should my plants be watered? To answer this question you have to know why plants need water and how do they use the water. That’s what I’d like to talk about today.
Photosynthesis is the answer. Simply put; photosynthesis is the process that goes on within the leaves of plants that uses water plus carbon dioxide plus sunlight to create plant sugars that plants then use to produce growth. It was people like Jan van Helmont in the mid 1600’s and Nicolas-Theodore de Sussare in 1796 and many others who, through scientific experimentation proved that without water, sunlight and carbon dioxide plants would not grow. The exact chemical and physical processes are still being discovered as plant scientists today work down through the cellular and molecular levels into the atomic levels of plants.
How the water gets from your hose into and throughout the plant is another interesting question. The answer is xylem and phloem. Just under the bark or outer layer of the stem or trunk of a plant is the cambium layer of cells that is made up of phloem cells on the outside and xylem cells on the inside. This is where water from your hose, packed with nutrients from the soil, and after being absorbed by the roots flows up the xylem cells to the photosynthesis ‘factories’ in the leaves and then down through the phloem cells as sugar packed ‘sap’ to all the rest of the plant.
Carbon dioxide comes from the air, sunlight of course from the sun and water comes from either your hose or the clouds. We can’t really control how much carbon dioxide the plant gets and we can control sunlight only by providing shade for our plants, but we can control how much water our plants get, particularly in the summer time.
Photosynthesis is the answer. Simply put; photosynthesis is the process that goes on within the leaves of plants that uses water plus carbon dioxide plus sunlight to create plant sugars that plants then use to produce growth. It was people like Jan van Helmont in the mid 1600’s and Nicolas-Theodore de Sussare in 1796 and many others who, through scientific experimentation proved that without water, sunlight and carbon dioxide plants would not grow. The exact chemical and physical processes are still being discovered as plant scientists today work down through the cellular and molecular levels into the atomic levels of plants.
How the water gets from your hose into and throughout the plant is another interesting question. The answer is xylem and phloem. Just under the bark or outer layer of the stem or trunk of a plant is the cambium layer of cells that is made up of phloem cells on the outside and xylem cells on the inside. This is where water from your hose, packed with nutrients from the soil, and after being absorbed by the roots flows up the xylem cells to the photosynthesis ‘factories’ in the leaves and then down through the phloem cells as sugar packed ‘sap’ to all the rest of the plant.
Carbon dioxide comes from the air, sunlight of course from the sun and water comes from either your hose or the clouds. We can’t really control how much carbon dioxide the plant gets and we can control sunlight only by providing shade for our plants, but we can control how much water our plants get, particularly in the summer time.
Here's two photos of tomatoes, they all were planted at the same time, but the ones on the right haven't been watered nearly as much as the ones on the left. Wilted and even burned leaves, lack of growth and vigor, much lighter green coloring are all signs of the plant not getting enough water. The drought affected plants are sacrificing leaves, branches and color to produce tomatoes in a desperate effort to reproduce themselves. And when the season is over the healthy well hydrated tomatoes on the right will have produced a much larger crop of fruit.
Think of it this way, plants that produce a lot of growth during the summer, like tomatoes, corn, other vegetables, annual flowers, and plants that have just been planted and haven’t had time to grow lots of roots will need lots of water, at least an inch or even more of water a week. But trees and well established shrubs which have huge root systems that can get to large amounts of water deep underground will not need nearly as much additional water from your hose. And the hotter and drier it is the more water those shallow rooted, newly planted shrubs, veggies, and flowers will need.
Here's a trick you can use to tell when your flowers and veggies need water; poke a hole in the ground near the plant with your finger, down past the first knuckel, if the ground is dry all the way down it's time to water. For shrubs that have been in the ground more then a year; if the lawn around the shrub is dry, water the shrub as you water the lawn. For major trees; dont worry about it, you couldn't get the water down deep enough to do any good anyway.
So here it is deep summer and those veggies and flowers and newly planted shrubs will need all the water you can give them, and the well established shrubs should be all right as long as the lawn around them is alright and those big established trees,with their huge and deep root systems can fend for themselves.
See you next time.
Sedgewick
