Our western Oregon climate is usually warm and dry from late spring to fall. Native plants have adapted to the lack of water during the growing season. In a natural area you will see a colorful late winter and spring, followed by fewer flowers and some dormant plants during the summer. Dormancy is a survival strategy that serves native plants well.
As gardeners, we can work with this by using a variety of native plants for a succession of bloom from winter through fall. Evergreen trees and shrubs provide a backbone of structure and are appreciated by birds for warmth and foraging places. Some plants have attractive twigs in winter, and grasses are interesting most of the year.
Watering some plants a little during their dormant season will prolong bloom or create a second bloom in the fall as they begin to push out new growth in the cooling weather.
When you survey your garden, take note of sun, shade, wet, and dry areas. Then, make a list of plants that are evergreen, early blooming, and late blooming so you can have functional and interesting plants at all seasons. This diagram from Oregon State University Extension is useful for visualizing how this works.
Remember to use groups of plants of the same species to create attractive blocks for pollinators. Groupings are also more pleasing to look at. Remember too, vertical space gives you a lot to work with to create a natural layered look from the high canopy, through mid-canopy and shrub layers to ground level. This will moderate the micro-climate in the immediate area and make watering more efficient.
How much water?
After the initial establishment period of about three years, native plants need very little if any irrigation when sited properly. The first few years are very important to grow a strong plant that will age well. During the early period you may need to water once or twice a week during the dry months (Late May – Late October approximately). A good deep soak is essential. Make sure water reaches the root zone, and then wait until it dries a little before watering again. A rule of thumb is one inch per week; and this might be applied in two waterings of ½ to ¾ inch, or you may find that a sandy soil needs more frequent but less water, and a clay soil is good with one good soaking. The condition of the plants, whether in sun or shade, and other factors all make this just a rule of thumb so you will need to learn your own site to make it work.
After plants are mature, or on their way to self-sufficiency, consider watering only as needed to keep them looking fresh. In a garden, it might be necessary to water a couple of times per month when the hot weather arrives to keep plants from going fully dormant. Remember to soak deeply to get enough water where it is useful to the roots. Plants send their roots deep and wide, to find soil moisture.