OSU trial shows Ceanothus blooms profusely with little care

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In an evaluation, free-blooming Ceanothus like ‘Blue Jeans’ were found drought-tolerant and winter hardy. Photo by Neil Bell.
Last Updated: 
May 8, 2015

CORVALLIS, Ore. – Life is hard for plants when Neil Bell gets ahold of them.

Such was the case for wild lilac (Ceanothus) when Bell, a horticulturist for Oregon State University’s Extension Service, decided to evaluate the evergreen shrubs. He planted 45 cultivars at The Oregon Garden in full sun and poor soil with no water or fertilizer.

“We wanted to test their cold-hardiness and, to a lesser degree, the quality of their blooms and pest resistance,” said Bell of the plants he assessed from 2001-05 when the shrubs were not as readily available as they are today.

As Bell took on his evaluation about 80 percent of what was on the market were the very large C. ‘Victoria’ (syn. ‘Skylark’) that grow about nine feet tall and 12 feet wide, and C. gloriosus, a ground cover species. About a dozen or so – including ‘Blue Jeans,’ ‘Marie Simon,’ ‘Dark Star,’ ‘Julia Phelps’ and ‘Italian Skies’ – now show up in nurseries regularly.

All of the seven shrubs above scored high in Bell’s trial, proving cold-hardy in Willamette Valley’s Zone 8 (10 to 15 degrees) winters. They also produced more-than-ample flowers and showed little pest or disease damage. In fact, he said, Ceanothus as a group did well, though some showed a little leaf burn after particularly cold winters or when temperatures plummeted early in the season before plants had a chance to harden off.

“‘Blue Jeans’ is one of the best,” Bell said. “It was never winter-damaged and is one of the earliest to bloom. It’s a really cool plant.”

Ceanothus plants start blooming early in spring -- usually the first part of April – and continue until July, depending on the cultivar. ‘Skylark’ comes on a bit later than ‘Blue Jeans,’ which flowers in April. ‘Julia Phelps’ and ‘Dark Star’ bloom in late May through June.

“One of the things about Ceanothus,” he said, “is that it’s a reliable blue-flowered shrub. Getting blue into the landscape can be challenging. But when Ceanothus is in bloom, it’s solid glowing blue. That’s their biggest attribute.”

Not close behind, though, is the shrub’s drought-tolerance. In Bell’s evaluation, the test subjects received no water at all. In home gardens, once the plant’s roots are established after the first year, it should be treated same.

“Watering is the single worst thing you can do for these plants,” Bell cautioned.

Ceanothus demand well-drained soil, so at planting time add an organic material like compost to improve drainage. After that, no amendments or fertilizer are needed. The shrubs aren’t a particularly long-lived group, giving the gardener pleasure for between seven and 20 years.

“Sometimes they just peter out,” he noted.

Though most commonly associated with California and often called California lilac, Ceanothus is native to the entire West Coast from southern California up into British Columbia, as well as other parts of the U.S. Blue blossoms are by far the most common, but flowers also show up in white and pink.

Size and shape are variable, too.

“Because of  ‘Victoria,’ everyone thinks of Ceanothus as a gigantic shrub,” Bell said, “but there’s a great range of sizes, from ground covers on up.”

There are a lot of reasons to grow Ceanothus, Bell added.

“They’re tolerant of poor, dry soils,” he said. “They’re evergreen for the most part. You can get a long bloom season if you choose correctly. They have extraordinary flowers that attract swarms of beneficial insects so the plant as ecological value. And now we know most of them are hardy here in the Pacific Northwest. They’re pretty extraordinary plants.”

More of Bell’s research can be found on OSU’s Northwest Plant Evaluation Program website

Sizes and colors of commonly available Ceanothus

‘Blue Jeans,’ 5 feet tall and wide, violet blue

‘Marie Simon,’ 3 feet tall and wide, pink

 Dark Star,’ 8 feet tall and wide, cobalt blue

‘Julia Phelps,’ 5 feet tall and wide, dark lilac blue

‘Italian Skies,’ 6 feet tall and wide, dark blue

‘Victoria,’ 9 feet tall and 12 feet wide, cobalt blue

 C. gloriosus, 2 feet tall and 6 feet wide, deep purplish blue

 

Neil Bell’s list of plants that grow well alongside Ceanothus

Shrubs:

Barberry (Berberis)

Black elderberry (Sambucus nigra)

Flowering currant (Ribes sanguineum)

Manzanita (Arctostaphylos)

Oceanspray (Holodiscus discolor)

Rockrose (Cistus)

Rosemary

Smokebush (Cotinus)

 

Perennials:

Giant hyssop (Agastache)

Foxglove (Digitalis)

Hardy geranium

Jerusalem sage (Phlomis)

Russian sage (Perovskia)

Sedum

Spurge (Euphorbia)

Wild indigo (Baptisia)

Author: Kym Pokorny
Source: Neil Bell