Top 10 Tips for Watering the Garden & Landscape

Watering the Garden
Since plants are 90 – 95% water they can quickly wilt if they get too dry. Good gardeners monitor the water available to their plants (rain) and avoid this stressful wilting with extra irrigation. Some plants (thinking Hydrangeas here) wilt every day on hot afternoons but come back by evening. Others (Rosemary) are less tolerant and quickly turn yellow when water stressed.

But too much water isn’t good either. Plants require a balance of both water and oxygen around their roots. Overwatering excludes the necessary oxygen from the soil causing roots to rot and die and resulting in yellow or wilted tops. On the other hand, too little water does not allow the roots to replace water lost by the plant through transpiration from its leaf surfaces. In this case, tender roots shrivel and die, and again we get wilting. In both cases, either too much or too little water, the plant suffers from lack of moisture in its tissues.

I have long been uncomfortably amused by the dark concept of “PWP”. The Permanent Wilting Point is a technical term for “bye, bye baby”, the point of no return when the plant is DEAD.

So I’ve assembled my Top 10 Tips for Watering the Garden and Landscape Plantings.

1. How often to water depends on how often it rains. As a rule of thumb, most plants thrive with about an inch of water a week. Visualize a short, 10-minute downpour every two or three days. Keeping the soil lightly moist prevents it from drying out completely. It’s the fluctuation that is damaging to most plants.

2. How often to water also depends on the soil type. Clay soils hold water a long time, while sandy soils are like a sieve, letting the water quickly drain away below the root zone. Both types of soil can be improved with the addition of organic matter. Organic matter adds lightness and air to clay soils; it acts as “tiny sponges” holding the water in sandy soils.

3. The very best time to water is in the cool of the morning, when the wind is calmed, evaporative water loss is minimal and the rising sun quickly dries off the leaves.

4. Water the soil, not the leaves. When water sits on plant foliage for hours (e.g. overnight), fungus spores can germinate and attack leaves, buds, flowers, and fruit. Plants susceptible to leaf spots, fruit rots, and flower blights are best watered in the morning, when the warming sun will quickly evaporates the water and discourage fungus development. Avoid watering disease-susceptible plants in the evening.

5. Wind and air movement increase water loss from the pores (stomata) on the leaf surfaces, called transpiration. That’s why fuzzy or felted plants like lavender or silvery artemesia do well in hot, stressed situations. Anti-desiccant sprays are available for houseplants or for broad leaf evergreens when the soil freezes up north, but I don’t have much experience with them. Consider microclimates when planting.

6. Plants need more water on hot, bright days when the relative humidity is low, and evaporation is high. An insulating layer of organic mulch is good at reducing the evaporation.

7. Water needs vary with the type and maturity of the plant. Some vegetables and bulbs are tolerant of low soil moisture.

8. Set a rain gauge or two in an open area of the garden to learn how much water the garden receives each week and judge the need for supplemental irrigation accordingly. Use a straight-sided can or purchase a calibrated, easy to read gauge at a garden center.

9. Stand-alone containers or hanging baskets tend to dry out more quickly due to the combination of crowded, intensive planting and increased surface area along the sides of a porous pot, so they depend on careful monitoring. The smaller the container, the more frequently it needs water.

10. Sometimes a wilting plant does NOT need more water. This is true if plants are growing fast and the leaves get ahead of the roots' ability to provide them with water, and is easily corrected. Unfortunately it is also true if the roots are rotted from TOO MUCH water, which brings us back to the PWP.

Notably, young plants and new transplants require more moisture more often at the soil surface to help their root systems take hold. Water lightly but more frequently to accommodate their growth needs. Mature plantings with large root systems are best watered heavily but much less frequently than younger plants. The moisture soaks deep into the soil and encourages the roots to thrive. Follow watering guidelines in your municipality and happy gardening!