When To Water?
When it comes to watering, there are no hard or fast rules. It's a judgment call that depends on the type of plant, the soil, the weather and the time of year.
Watering is of no value if the water runs down the outside of the root ball, leaving the roots at the core of the plant dry. This can happen if you water too quickly or apply too much water at once. Slower watering is usually more effective. The key is to ensure that water gets to the root zone — whether you are tending seedlings, watering houseplants, watering a row of tomatoes or soaking thirsty shrubs and trees.
The Best Way to Water
Focus on the root zone. Remember that 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.
Water only when needed. Automatic timers are especially 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 6" of soil; for perennials, shrubs and trees, it's the top 12". In heavy soil, it may take hours for water to percolate down 6-12". Use your finger or a shovel to check the progress.
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 everything. Mulch reduces 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.