I would like to grow Azaleas in zone 5, eastern Washington. Can I get some advice on how I can overwinter these plants and where I can order them online?
First, there are evergreen azaleas which are typically more tender and require some protection, especially the first 2 or 3 winters.
Then there are deciduous azaleas which are typically hardier and shouldn't require any extra-ordinary efforts. A good mulch layer should be adequate.
Also, I assume by Eastern Washington you mean you have low rainfall and a more prairie-like climate with hot dry summers and cool nights. When you don't have rain, you will have to irrigate about once a week in summers and less often in winter, and not at all when the soil is frozen.
A good mulch layer will help you conserve soil moisture and keep the roots cools. Since you have cool nights, the mulch helps average the soil temperature.
With evergreen azaleas, first pick out a hardy variety and then protect it from winter sun and winter wind, especially the first 2 or 3 winter. Also, a spray-on antidesiccant will help if applied on before winter and again around mid-winter.
Some Gable evergreen azaleas that are good for hardiness: 'Herbert', purplish red; 'Purple Splendor', rich purple; and 'Stewartsonian', blood orange; hardy to Zone 5, -15 F.
Some Robin Hill evergreen azaleas that are good for hardiness: 'Conversation Piece', pink and white mix; 'Gwenda', pale pink; Nancy of Robin Hill, pastel-pink semi-double hose-in-hose flowers; 'Robin Hill Gillie' , large salmon flowers with red throats; and 'Watchett', creamy pink; hardy to Zone 5.
Some of the hardier Ghent deciduous azaleas include:
* Corneille : 6', -15F. It has soft double pink flowers.
* Daviesi : 4', -15F. It has white flower with yellow centers.
* Irene Koster : 6', -15F. It is late blooming pale rose pink flowers with a gold flare. Fragrant.
* Narcissiflora : 6', -15F. It has double light yellow flowers with pointed petals.
Some of the hardier Knapp Hill deciduous azaleas include:
* Cecile' (Exbury) : 6', -15F. It has red flowers with an orange-yellow blotch.
* Fireball' (Knap Hill) : 5', -20F. It has brilliant red flowers on an upright plant.
* Gibraltar (Exbury) : 5', -15F. It is brilliant orange, flushed with red, ball cluster, on a compact plant.
* King Red (Exbury) : 5', -15F. It has vivid red, slightly ruffled, large ball cluster, compact plant.
* Klondyke (Exbury) : 8', -15F. It has golden-yellow flowers. Striking bronze new foliage.
I highly recommend Gibraltar and Klondyke.
The Northern Lights are a new group of deciduous azaleas from the University of Minnesota for areas where winter temperatures are severe. They are a group of beautiful shrubs that are cold hardy to zone 3 and flower bud hardy to -40 F. Plants are fairly compact and can grow to about 6 feet in height and width. Some of the more notable Northern Lights azaleas are:
* Pink Lights Azalea : 3', -35F. Introduced in 1984. The flower has a light pink color with a sweet floral scent. Mature plants will have a height and spread of about eight feet. The plant is extremely floriferous.
* Rosy Lights Azalea. : 4', -35F. Introduced in 1984. The flower color is a deep rosy pink and plants are extremely floriferous. Plant height and spread is about eight feet.
* White Lights Azalea. : 5', -35F. White Lights is a hybrid of Rhododendron prinophyllum and a white flowered Exbury hybrid. The flower buds have a delicate pale pink cast but open to a white flower with a slight yellow blotch. This cultivar is extremely floriferous and has a flower bud hardiness rating of -35 degrees F. Plant height and spread is about five feet.
* Spicy Lights Azalea. : 3', -35F. Spicy Lights is a selection from hybrids having Rhododendron prinophyllum in their background. The flower has a salmon color with a slight fragrance. Flower bud hardiness is rated at -35 degrees F. Plant height is about six feet and spread is about eight feet.
* Orchid Lights Azalea. : 2', -35F. Introduced in 1986, Orchid Lights Azalea is a hybrid of Rhododendron canadense and Rhododendron x kosteranum. The orchid-colored flowers are 1-1/2 inches across and are sterile, so seed capsules are not produced. Flower bud hardiness is rated at -45 degrees F. The compact plants of Orchid Lights will mature at an average height of three feet and a spread of three to four feet.
* Golden Lights Azalea. : 5', -30F. Introduced in 1986, Golden Lights Azalea is a hybrid of an Exbury seedling and an unidentified azalea seedling. The golden flowers are 1-1/2 to 2 inches across and have a cold hardiness rating of -30 degrees F. The mature plants reach an average height and spread of four feet. Golden Lights has the added advantage of greater resistance to mildew than some other hybrid azalea cultivars.
* Northern Hi-Lights Azalea. : 3', -25F. Introduced in 1994, Northern Hi-Lights Azalea is a hybrid of an Exbury seedling and an unidentified azalea seedling. It is a hybrid with the same parents as "Golden Lights". The flowers are creamy white with a bright yellow upper petal and have a cold hardiness rating of -30 degrees F. Plants grow relatively slowly to four feet high and four to five feet wide. The dark green foliage has some resistance to mildew.
Here is a link that might be useful: How to raise Azaleas
My favorite is Karen's which is an extremely cold hardy Gable hybrid. I believe it is hardy to -25 degrees F. I has a great lavender bloom display and good to often EXCELLENT burgundy fall color. It will need watering in the summer like most azalea's.
Here is a link that might be useful: My blog
Karen and Karens are both very hardy. But the Gable plant is called Karen, not Karens.
The Gable hybrid 'Karen' (a kaempheri and poukhanense hybrid) has purplish-pink flowers and is hardy to -20F. It will bloom in the Fall occasionally. It is a great little azalea with a nice growth habit, heavy spring bloomer, great spring and fall leaf color.
The Pederson hybrid Karens' (Hinode Giri x R. yedoense var. poukhanense) is a hardy low growing azalea with reddish-purple flowers. It is stated to be hardy to -25 F. Leaves acquire copper tones in fall.