“It always rains in Portland.” Not so. The Willamette Valley climate usually presents us with a dry summer and rainy fall, winter, and spring. But, of course, that is not always the case. A complex system of Pacific Ocean currents, mountain ranges to the west and east of us, and the east-to-west air flow of the Columbia Gorge influence our climate. Increasingly dry summers and the need to conserve water affect how we garden. Despite this weather pattern, we can garden enthusiastically with an amazing array of plants. But it requires a bit of planning, keeping in mind the plants’ relative need for water.
Soil preparation is very important. The ideal soil for growing plants drains but holds a moderate amount of water. The native soil in our neighborhood varies from the clay and river rock of the ridge area to the fertile delta soil closer to the Columbia River. The clay soil will need amending and removal of the largest rocks. All soil benefits from the addition of compost on a yearly basis, especially soil that is host to annual plants that need more nutrients to grow, flower, and produce vegetables or seed in one season. We have a compost pile and a worm bin. The rich soil produced is harvested at least yearly and placed where needed. Soil throughout the garden is amended with humus-rich material when planting to add nutrients and increase the ability to hold moisture. Clay soil that holds too much water and could drown plant roots is also amended with compost at planting time.
Consider growing annual flowers and vegetables in the same area, since they need more water than established perennials. We grew kale last season and left some to winter over and enjoyed eating the leaves throughout the winter. Now the plants are gorgeous with heavily blooming yellow flowers. If we leave some of them to grow on, we will harvest seed at the end of this summer. We plant annuals such as zinnias, feverfew, and marigolds in with the vegetables where they benefit from the added water and nutrients.
All annual and perennial plants need more water when newly planted. Once plants are established with a more mature root system, watering can be somewhat reduced. Be aware of plants’ water needs and consider grouping plants in your garden that need more or less moisture and light.
Lawns need a lot of water to stay green in the summer. Explore some approaches to lawn management to reduce water usage; for instance, plant less lawn, let the lawn go brown in the summer, or remove the lawn altogether.
Choose plants for your garden that require less water once established. Some research should go into selecting plants for your garden. Group together plants based on their water, light, and soil needs. An array of spring bulbs does well with less summer water, since after blooming they dry out and the foliage withers. Plants that require less water when established—such as small manzanita, mahonia repens (Oregon Grape), lavender, hebes, heuchera (coral bells), salvia, wild current (Ribes sanguineum), penstemon, and small pines such as Mugo pines—all work well in a drier garden. Several succulents are hardy and do well with less water, including several species of sedum, sempervivum, and yucca. These all are growing in my west-facing rock garden that is designed to need less water. Considering our dry summer garden needs, local plant growers have specifically selected smaller members of many of these shrubs for growing in our climate. A water-wise garden design can be very satisfying with many plants to choose from.
An interesting book that explores the issues of gardening in a dry climate is Gardening in Summer-Dry Climates by Nora Harlow and Saxon Holt (Timber Press, 2020).