Factors that complicate watering include type of plant, exposure (sun/shade, wind, etc.), growing conditions (in-ground versus container), soil type/planting media, how long it has been planted, and weather/season.
Get Off to a Good Start
Amend poor soil when necessary, plant at optimal times of year, dig hole in ground twice as wide as plant root ball, but no deeper, fill hole with water to ensure proper drainage, and pre-moisten the planting area. Pre-soak dry or root-bound plants in water, root stimulator, or compost tea, loosen up compacted roots, and plant at proper level in soil. Water plant again after covering roots with soil and apply mulch to cover root zone.
In-ground plantings: Newly planted items should be watered deeply every 2-3 days for the first week or two, then begin to gradually taper off to every 3-4 days, 4-5 days, etc. until you are able to provide deep watering weekly without the plant showing signs of stress (see later discussion on deep watering). Watering new plantings to establish healthy roots usually requires about 2-3 years before plants can be considered “established”; if drought tolerance is indicated, it will only be so once it is established. Although drip irrigation can provide deep watering, most sprinklers only wet a shallow layer of soil and are not enough for establishing new plants.
Container plantings: Container plantings often need more frequent watering when newly planted, but do not need to receive as much water as in-ground plantings since their roots do not extend far into the surrounding soil yet. The same plant, when more established, will have roots throughout the container to better utilize moisture near the bottom of the pot, so should be watered more thoroughly (until water comes out drainage holes).
Establishment Watering of Perennials, Trees & Shrubs: Deep Watering
Year 1 (Infancy): Depending on time of year of planting, begin watering regularly once it is no longer raining or anytime during periods of dry weather; often a light shower does not wet the soil deep enough to be considered as watering plant roots. Begin watering frequency at every 2 or 3 days for one to two weeks, then extend the break another day for another week or two until you are watering deeply once per week. Continue watering weekly until rainfall is reliable and significant.
Year 2 (Adolescence): Again, begin regular watering once dry weather has arrived and water deeply once each week, gradually skipping more days in between to get to watering about every 10 days or so.
Year 3 (College Years): A three-year-old plant should be fairly established, but will benefit from occasional deep watering every 2-3 weeks during hot, dry seasons (typically July to early September in Portland).
Mature Landscape Plants in the Ground
Without rain, trees benefit from a thorough watering once a month during the growth period and during hot, dry weather; shrubs every 3-4 weeks—water should penetrate the entire root zone (within the first 2 feet for most). Fall/winter blooming shrubs (especially Camellias) should be given supplemental water from July until rains begin since they are producing their flower buds at this time of year. Perennial garden watering depends on the types of plants and other growing conditions.
- Lawns: Need frequent, shallow watering to establish from seed or sod and once rooted can be watered at the rate of 1” per week (1/2-inch applied 2 times week).
- Container plantings, raised beds, and hanging baskets: Once or more per day during hot or windy weather. Container plantings will need to be regularly watered for the duration of their lives (even during winter if not in area that receives rainfall).
- Annual bedding plants: Should be kept moist, but never soggy and not dried out to wilting point.
- Perennials: Need more water when young and during growth and bloom times.
- Annual vegetables: Need different watering depending on crop and growing conditions; only container gardens and raised beds should be watered daily (with some exceptions of course).
Signs of Trouble
Wilting foliage is not always a sign that the plant is dry! Some plants partially wilt in mid-day in extreme heat and recover once the sun has become less intense. As long as plants have been properly hydrated earlier in the day, do not water in reaction to the mid-day wilt.
- When roots cannot take up water, the youngest foliage and new plant tissue are the first to suffer. The cause could be dry soil, curling or coiled roots, very poor drainage causing root-rot, or other issues.
- Smaller-than-average leaves and flowers are signs of long-term drought conditions or drought stress.
- Poor fruit yield, small fruit, and fruit lacking flavor can be caused by drought stress.
- Early red foliage color or extreme fall leaf color are signs of drought stress, as well as shriveled leaves with brown edges.
- Light green leaves, continued wilt even in moist soil, or yellowing of inner or bottom leaves is sign of overwatering and potential root rot.
- Blossom-end rot on tomatoes (dark patch on bottom of fruit) is often caused by inconsistent watering or from allowing plants to dry out too much between waterings. Lettuce or other tender salad greens can turn bitter when allowed to get too dry too often.
- Cucumbers and squash will often abort their flowers and not set fruit if not watered adequately during development.
Drought-Tolerant Plant Characteristics
Many drought tolerant plants share similar physical characteristics such as having silver, grey, or reddish foliage, fuzzy or “hairy” leaves, small leaf surface or needle-type leaves, or thick, fleshy foliage and stems.