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Understanding what Plants, Shrubs & Trees really want

During times of drought, water purveyors (and horticulturists) all tell us to water deeply, once or twice per week to encourage the plant / tree to send its roots down as far as possible.

This is great advice, IF (and only if) there is not a regular water source.

What they dont tell you (and should know better) is that if the plants / trees were watered everyday, 30% less water would be  required.

This is because the plants cannot use this much moisture immediately, the soil is heavily watered, and a good 30% of the water goes down into the subsoil, and keeps going down, unused by your garden.

(Their concern is that most people would overwater if they watered everyday - especially if using a garden hose).

So if you want to save water - water more frequently, with lesser amounts, every day. But how does this relate to what plants need to grow?

What plants need to grow:

  • Room to Grow
  • Temperature
  • Light
  • Water
  • Air
  • Nutrients
  • Time

I can't do much for the room to grow, light, air or time requirements for your plants. But I can explain the interaction between water and nutrients.

The vast majority of plants and trees receive their water and nutrients via the root structure.

Nutrients:

Most nutrients are found in the top 3" of soil - the biologically active layer. The further down we go the less nutrients there are. In many soils there is little nutrient loading below 6".

It would make sense for a plant to grow most its root in this layer - right?

Water (moisture):

When a garden is irrigated daily (with a small amount of water), the top 3" of soil acts like a moisture blanket, the roots and organic matter, together with bacterria in the soil trap the moisture here, right where the roots are also looking for nutrients.

However, if the garden is only watered once or twice per week, the roots are trained by you to go as deep as possible, away from the nutrient supply.

Therefore the plant / tree is forced to spend more energy growing more roots than it ideally wants to.

There is a common misconception that the roots of a healthy tree extend out to the foliage line. The roots actually extend up to 3 times this distance if the ground has sufficient nutrients and water.

Think we are crazy?

We have installed over 1,000 graywater systems in Australia (and sold 5,000+ more), with many or our clients being horticulturists. All of our clients report garden health and growth far in excess of gardens being heavily watered (with a lot more water) once or twice per week.

But dont just take our word for it, visit Robert Kourik's website, he is the expert in obtaining better growth rates with less water. I stongly recommend his book, Roots Demystified, it explains how plants want to grow.

You could also research commercial growing locations where they are moving away from deep watering to watering with small amount every day (some cases every second day). It's why Netafim's (worldwide irrigation system manufacturer) motto is Grow More with Less.

Fertilizer and Soil Amendments:

If the existing soil is poor, and holds little organic matter in the first 3", soil amendment should be applied. However it is vital that the amendment is spread evenly over the entire garden area.

This is the opposite of what most people do when they buy a new tree or shrub.

  • First they dig a hole, a little large than the root ball of the plant.
  • Then they throw in some plant food / fertilizer in the hole, add lots of water and plop the plant in the hole.
  • If they have a potable irrigation system they then add an extra dripper right next to the plant.

This creates the following problems:

  • The roots of the plant quickly find an abundant source of food. Therefore they do not need to grow any more to find food.
  • The roots also have a water source that is wetter below the plant than the surrounding topsoil.

Rather than seeking out water and food, this plant will now need regular feeding, instead of using the soil for food.