The best way to water

'best practice' for managing garden irrigation

Young seedlings and new transplants have limited root systems and need a consistent supply of moisture, so they may need daily watering if the weather is sunny and hot. Established trees and shrubs, on the other hand, may need supplemental watering only during extended dry spells because they have more extensive root systems.

The best way to water most plants is by applying enough to moisten the plant's entire root system, and then letting the soil dry out slightly before watering again. Apply water slowly so it's absorbed by the soil rather than running off - a soaker hose is ideal.

Avoid daily light sprinklings, which encourage roots to grow near the soil surface where they're vulnerable to drying out.

Rather than relying on a schedule, water plants when they need it. Check soil moisture beneath the mulch

Try to avoid watering on sunny afternoons to minimize the amount of moisture lost to evaporation, but don't worry about leaf scorch. The myth that water droplets act like tiny magnifying glasses and burn plant leaves has no basis in fact.

Avoid overhead watering with a sprinkler. It's usually best to apply water directly to the soil around plants close to the stem so water can pass the mulch layer or around the drip line on larger shrubs and trees. Less water is lost to evaporation, especially on hot, sunny days. Foliage stays dry, minimizing disease problems.

Wilting is a sign that it's time to water. Plant roots need a fairly constant supply of both air and water. Too little water and the roots die from lack of moisture. Too much water and the spaces between soil particles remain filled with water, suffocating roots. Both situations reduce a plant's ability to deliver enough water to stems and leaves, resulting in wilting. Root diseases, physical damage (such as disturbing roots while you're hoeing) and soil-borne insects can also harm roots to the point that they can't fully hydrate the plant.

Things to remember...

  • Focus on the root zone. It's the roots that need access to water, not the leaves. Wetting the foliage is a waste of water and can promote the spread of disease.
  • Apply water only when needed. Automatic timers are  useful; just make sure to watch the weather, and reduce frequency when rainfall is abundant. Too much water can be just as damaging to plants as too little.
  • Water deeply and thoroughly. Lawns and annuals concentrate their roots in the top 150mm of soil; for perennials, shrubs and trees, it's the top 300mm. In heavy clay soil, it may take hours for water to percolate down 150-300mm. Use a fork poke deep holes into the ground to aid water infiltration.
  • Water in the morning. If you do get moisture on the leaves, this gives them time to dry out. It's much more difficult for plant diseases to get a foothold when the foliage is dry.
  • Mulch around plants. Mulch reduces competition for moisture, absorbs surface runoff and slows evaporation from the soil.
  • Use the right tool. For efficient watering at the root zone, use a soaker hose or an even more precise drip irrigation system instead of a sprinkler.



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