Biome: Willamette Valley Natives

The Willamette Valley in its restored glory at the William Finley Wildlife Refuge. Native clumping grasses are interspersed with perennials and annuals in an open prairie.

The Willamette Valley is not only Oregons most populous region it is a landscape in flux. What was open grassland and oak woodland managed by fire by the initial residents was densely settled, farmed and logged by Europeans.  No where in the state are human pressures so close to fragile nature.

Xeric clay soils

The Willamette Valley is comprised of xeric clay soils. These soils are  dry in summer and biological activity ceases as the dry season sets in. These soils require diligent attempts to rehydrate once they have dried. Often the water just beads up and rolls along the surface of the soil (hydrophobic).  In soils like this mulch of any kind is paramount.

This still rare and endangered native Delphinium pavonaceum Pea Cock Larkspur is endemic to just a few sites in the Willamette Valley and it has been successfully reintroduced in Benton County. Not for Sale

A distinct dry season

This pronounced dry season is a hallmark of the valley biome. Beginning in June and progressing into early autumn  high pressure inhibits almost all precipitation.  The natives in this landscape including many annuals, perennials and bulbs that are native to California are also native in the Willamette Valley but not north of the Columbia River. Many plants are found and many are endangered only in the valley. The center of the genus Sidalcea finds a home and diversity no where else.

This restored Willamette Valley meadow is a matrix of the naturally widespreading Rosa nutkana and clumping grass species Festuca, Danthonia sp.. Accompanying those are native bulbs (Camassia- in this photo) and perennials and annuals.

Introduced exotics snuffed out many natives

Its important to remember that there were NO RUNNING or stoloniferous grasses native to the Willamette Valley. Only clumping grasses with space between for such things as native annuals and perennials.  When turf grasses were introduced for ornamental and commercial purposes they pretty much snuffed out most of the native habitat of many forbs (herbs). Wild flower habitat was destroyed.  Add to that rambunctious exotics such as Armenian/Himalayan Black Berry and Scot’s Broom and European pear and more exotics and the space for many of these natives is squashed. We include plants that are native adjacent to the valley too and perform wonderfully here.

Sidalcea malviflora ssp. virgata and the critically endangered Castilleja levisecta (not for sale) in Willamette Valley Oak Savanna.

Oregon’s most endangered biome

Most of the Willamette Valley was occupied by Oregon Oak Savanna. This is Oregon’s most endangered biome and attempts are being made to set aside the less than .06% that is left(!) We encourage local gardeners to welcome the wealth of wildflowers native to the Willamette Valley. They are in serious peril.

Three to four months of annual drought coincides with the heat of summer in the Willamette Valley. Oregon Oak Savanna near Eugene.  Photo credit: Angi Gass-Gilchrist

Climate adapted plants for gardeners in the PNW

Arbutus menziesii

Arbutus menziesii

Pacific Madrone, iconic tree of the Pacific Northwest. Famous for its glossy, russet orange sinuous trunks, exfoliating bark, and round, evergreen foliage. In spring, clusters of white flowers are showy and turn into vivid red berries by autumn. These are loved by birds- especially western tanagers who will quickly strip a tree as flocks move from one to the next. Must be grown from seed and it must be transplanted when small. Just the way it is. Plant it in average, well drained soil. Water lightly through the first summer in subsequent years leave it strictly alone. Full sun is best- tends to wander towards the sun in shade. Underplant with low water natives such as Arctostaphylos, Ceanothus, Vancouveria. Slow at first it picks up speed after about 4 years- then it can grow 2′-4′ a year. Somewhat messy tree- loses older leaves in summer and the bark exfoliates all over the place too. Know this and live with it. Ours are raised from seed of trees native to our wholesale nursery site- so its a local strain. Pacific madrone is native from the highest mountains of southern California to southern British Columbia. It is the northern-most broadleaved evergreen tree (native) in North America. Oregon native plant.

*Cultural note:  Pacific Madrone is best established with a little attention.  Remember that the first year is the most important.  Madrones are adaptable to a host of soil types, thats why you see them in such varied places but err on the side of good drainage, a slope etc.  If the soil is dry when you plant do this, dig a wide area and loosen the soil. This will add oxygen and allow the water to percolate and get to the roots. (If the soil is already moist plant as per your regular routine.) Water after planting to settle the soil.  Let the plant go dry and depending on aridity and heat- you may have to water more in hot weather, less in cool weather. This is only relevant in the first summer after planting.  To water give the Madrone seedling about 1/2 gallon of water. This will be just enough to wet the root ball and keep the seedling from wilting. It should grow a little bit too.  if the plant shows signs of wilting this amount of water will also revive it.  Stop watering when cooler weather arrives (September) and winter rains resume. In subsequent years you should not water your Madrone at all. Do not amend the soil at all, native unimproved soils are what they are adapted to.  Remember they are native right here and are perfectly adapted, trust this adaptation. Also, do not crowd your madrone immediately, mulch it  lightly with fine bark and give it good air circulation for its first several years.

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Arctostaphylos columbiana ‘Blue Point’

We’re intent on expanding our offerings of our cold hardy native Hairy Manzanita. This form we found in the Hood River Valley and it was conspicuous to us for several reasons. The plant which has long pointed blue leaves was exceptionally disease resistant. It also was tolerant of quite a bit of shade as well. Hairy Manzanita from this part of the state is exceptionally cold tolerant. It will happily live on both sides of the Cascades. The long blue/gray foliage is perpendicular to large stems. The bark becomes deep mahogany and glossy with age. Best in unimproved native soils. To establish water it regularly once a week until you see good new growth then set it free. Drought adapted. To 5′ x 6′ a large shrub that grows quickly to its ultimate size. Full sun to quite a bit of high overhead shade. Always good air circulation. The very early spring flowers are pure white and large on this cultivar. Russet berries that follow attract wildlife. Wonderful shrub, easier to grow than ‘Wolf Creek’.  Cold hardy well below 0ºF.  Oregon native plant.

Xera Plants Introduction

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Arctostaphylos columbiana ‘Mountain Blue’

This exceptional form of hairy manzanita we discovered on the north side of Mount Hood. The large foliage is distinctively blue and is held perpendicular to the stems. In very late winter to early spring pearl pink/white flowers decorate the branch tips and appeal to both hummingbirds and native bees. A large rounded shrub to 6′ x 8′ forming a wide dome. Its best attribute is its distinctive deep mahogany glossy bark which  contrasts with the blue foliage. Russst berries follow the flowers and are consumed by wild life. Full sun to very high overhead shade in average to poor unimproved soil. Water once a week to establish, when new growth begins taper off then drought adaptation is exceptional. Its also exceptionally hardy to cold to at least -15ºF and is as happy in the Willamette Valley as Central Oregon. Moderately fast growing. Disease resistant, Best to grow Arctostaphylos columbiana as lean as possible. Give it just enough water to establish and then only bark/chip mulch.  A very pretty cultivar that is one of our favorite manzanitas. Oregon native plant

Xera Plants Introduction

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Arctostaphylos columbiana ‘Pacific Coast’

This is a compact, dense growing form of Hairy Manzanita from the city of Manzanita on the coast. These are Greg’s collections. He chose several forms that had nice foliage, foliage color, habit, and resistance to disease. This form is one of the most compact of the three. Slightly smaller leaves are born densely on a more reserved growing plant. In late winter to spring clusters of white flowers  followed by drupes that turn distinctly red. Inland forms of this Manzanita have maroon to russet berries so this is a distinct difference. Beautiful dark, glossy maroon bark as for the species. To 6′ x 6′ in 7 years. Adapted to average to poor soils which will allow it to grow at a more reserved rate. Arctostaphylos columbiana reacts to richer soils, even clay soils with exuberant growth. Best in our native soils that are unimproved. Dig a large hole and provide regular water until you see good new growth then taper off. In subsequent years only what falls from the sky. Arctostaphylos columbiana (Hairy Manzanita) is a proto species one of the first and it is the most widespread Manzanita in Oregon and Washington.  Genetically it dominates and most of Calfiornia’s northern species are derived from ancient Hairy Manzanita. Provide full sun and good air circulation. Excellent underplanted with native annuals and Sedums. Good looking siver/ gray foliage year round. Extraordinarily drought adapted. Associated plants with the coastal species are Vaccinium ovatum, Pinus contorta ssp. contorta Garrya elliptica, Baccharis pilularis and Salal (Gaultheria shallon).  Often found with Festuca rubra on stabilized sand dunes.  Oregon native plant

Xera Plants Introduction

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Arctostaphylos columbiana ‘Wolf Creek’

Arctostaphylos columbiana ‘Wolf Creek’

Our native Hairy Manzanita is one of the most widespread species in the PNW. It is very susceptible to overwatering and overly enriched soils. .This can be avoided by strictly avoiding all irrigation once established and planting in average, unamended soil. Large-growing shrub with gray green leaves, the telltale hairy leaf petioles and white flowers in spring. Russet berries follow. Its best attribute is its smooth exfoliating mahogany bark. And in time you can remove the tired lower branches to reveal it as well as improve air circulation.  To 8′ x 8′ very quickly in average, well-drained soil. No summer water and little intervention from the gardener. Wild areas, dry hillsides. This form we selected from the southern Willamette Valley. It occurs in specific sites around the Valley and is common at the coast /coast range as well as the Cascades. Its populations are most stable on steep rocky slopes and sandy substrates at the coast where plants live longer in impoverished situations. During the warm interstadial (8000-4000 yr BP) when our climate was a bit milder but with a much more pronounced summer drought it was much more widespread- once found in the city limits of Portland at two sites those have been usurped by development. Excellent performance in hot dry urban sites.  Oregon native plant.

Xera Plants Introduction.

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Artemisia douglasiana

Many learn this plant as Douglas Mugwort but its more official common name is Douglas Sagewort.  This aromatic vigorous perennial is common throughout western Oregon. It happily inhabits everywhere from ditches to the headlands at the beach. The plant has medicinal qualities that were used by native Americans and they also used the pungent smoke to ward off the spirits of the dead. To 3′ tall and spreading underground by rhizomes. This is a very vigorous plant when established, give it room and the respect it requires. In improved situations it can swamp other plants so best to leave your patch of sagewort to its own devices. Mix with other plants of similar vigor- Spiraea x pyramidata or Rosa nutkana. Give it at least 5′  x  5′ feet to roam. In summer plumes of off-white flowers produce a haven for pollinators. This member of the daisy family brings them from long distances. Very long lived deciduous perennial with long indented leaves that are dark green on top with an underside of pure silver. This makes this almost woody perennial very easy to spot in breezy conditions  It appreciates average soil and light water to establish.. If it flags in drought you may give it a deep drink in summer to refresh. Loved by a host of butterflies. Doesn’t need much love to perform. Oregon native plant.

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Aruncus dioicus

Aruncus dioicus var. acuminatus

Goats Beard is a big bold and easy to grow perennial for part shade and perpetually wet sites. To 4′ tall and as wide with large fountains of pure white flowers in late spring to early summer. Native in seeps and along watercourses, mimic those conditions in your garden and you’ll have success. Long lived plant that develops a woody base. Completely winter deciduous. Excellent combined with other mesic water loving plants. Tolerates some inundation but not during the growing season. Often found on cliffs away from the browse of deer. Very large permanent perennial in time.  Fall color is often yellow. Widespread in the PNW. Native in the Portland City limits.  Oregon native plant.

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Asclepias fascicularis

Narrow leaved milkweed is an Oregonian butterfly weed that has a great wildflower demeanor and is just as attractive to pollinators as well as Lepidoptera (butterflies). Full sun and well drained soil, though it accepts clay soil on slopes that are strictly unwatered in summer , otherwise light consistent irrigation to establish- then natural rainfall alone. To 22″ tall and making a spreading plant. Mix with fine textured ornamental grasses,such as Tufted fairy grass – Deschampsia caespitosa and  tall spiky perennials such as simultaneously blooming Kniphofias. Light summer water when companion planted. Flower color is most often creamy white but ranges to light pink. Often seen on road cuts and in ditches in the Willamette Valley. Blends in with grasses and other plants but pollinators find it no matter what. Spreads to form colonies by underground stolons to  2′-3′ wide. Nice cutflower. Important food source for Fendler’s Blue Butterfly which is very endangered and locally indigenous. Winter deciduous. Blooms open in June and persist to August. The large seed heads are pointed and release their downy seeds on the wind in August-September.  Oregon native plant.

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Asclepias speciosa

Asclepias speciosa

This widespread species is native to the floor of the Willamette Valley and is locally common in the Columbia Gorge where it occupies dry rocky hillsides in full sun but tolerates heavy clay soil. In the best conditions (loam) it is huge spreading perennial that requires pre-planning and some real estate. Gray green stalks and leaves rise up to about 4’tall and bear deliciously fragrant pink orbicular flowers. These are irresistible to butterflies, including Monarchs, and if you want one to visit your garden this plant is good insurance. However, all butterflies find it irresistible. Spreads underground vigorously by stolons and can come up quite a way from the initial clump. Full sun and well drained soil. Completely winter deciduous and emerges relatively late in spring. Be patient. see video below. IMG 6323.  Oregon native plant.

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Baccharis pilularis ssp. consanguinea

This is the Willamette Valley form of coyote brush (bush)- also known as chaparral broom. A relatively short lived evergreen shrub in the aster family. Indeed this form blooms in autumn through winter with small brushes of white plumed flowers on female plants. Smaller yellow flowers on males. Typical of the steepest cliffs abutting the ocean and in the Willamette Valley it populates recent road cuts and fire zones. Often it will be seen all alone in the center of a Willamette Valley field. Native inland from northern Marion county to Douglas county. Very fast growing and drought adapted daisy bush for rough sites and poor soil. Improved soil will yield an enormous shrub so its difficult to pin point an exact size but everything from 4′ tall in poor soil with no summer water to 12′ x 12′ in rich soil with irrigation. I suggest no irrigation after planting. Excellent fodder for insects and birds. It may be pruned heavily in spring and will quickly regenerate. Foliage is deep glossy green but fine textured. Not bothered by deer. Excellent native companion for Manzanita, Grevilleas. VERY EASY to grow. average life span 10 years. Good instant plant for a native garden, but not long term. Native from N. Oregon coast south to Baja California. A prominent component of the California beach chaparral and on the Oregon coast as well. Common associated plants on the coast are Salal (Gaultheria shallon) and Mahonia nervosa. In the Willamette Valley its primary role has been ursurped by Scot’s Broom. Too bad.  Oregon native plant.

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