Ask Mr. Smarty Plants

This presents us with an interesting climatic problem. Canyon County is on the southwest border of Idaho with Oregon, and is in a USDA Hardiness Zone of 5b to 6a. That means that any plant there must be able to withstand pretty intense cold in the winter, with probably harsh winds on the northwest side of your house. Then, when summer comes along, a plant that is accustomed to part shade, which we consider to be 2 to 6 hours of sun a day, is suddenly confronted with blistering heat, including the heat reflected from the walls of the house.

We're thinking this should probably be some sort of shrub, if we can find one we think can take the two extremes of temperature it will be subjected to. Whatever we locate, you must be aware of that heat, and irrigate the plant accordingly. And don't spray water on the leaves during the sunny times of the day, as you will end up with scorched leaves. Water going into the soil early in the day, giving time for moisture to move through the limbs to the leaves and compensate for the transpiration from those leaves during the hot hours, will both cool the roots and support the rest of the plant. We will go to our Native Plant Database, select on Idaho, shrubs and part shade, and Combination Search. Then it will be necessary to read each page on the individual plants to see if it can adapt to the conditions you describe. We were surprised to find 8 good candidates for this spot, and checked the USDA Profile Map on each to determine that it grew natively either in Canyon County or nearby. Some, but not all, of these were described as tolerating sun (6 hours or more of sun), part shade (2 to 6 hours of sun) or shade (less than 2 hours of shade), which means they should be able to adapt to the space.

We would urge you to wait until Fall to plant these shrubs, because you don't want to put a small, newly transplanted bush into that sudden blast of heat every day. That is almost a guarantee for transplant shock. While you wait for Fall, we suggest you prepare the bed for the planned garden by working in a lot of compost and other organic material. This will build the bed up a little bit, greatly improve drainage so your frequent waterings won't leave the roots drowning, and will help the new little rootlets access the nutrients in the soil. When you actually put the plants in the ground, immediately mulch the area with 2 to 4 inches of a good shredded hardwood mulch. This will protect the roots from the intense temperatures at both ends of the scale that your bushes will be subjected to. Follow each link to the page on that plant to determine if the projected size, appearance and other considerations suit your purposes. 

From Our Native Plant Database: 

Amelanchier alnifolia (Saskatoon serviceberry)

Amorpha fruticosa (desert false indigo)

Arctostaphylos uva-ursi (kinnikinnick)

Ceanothus velutinus (snowbrush ceanothus)

Holodiscus discolor (oceanspray)

Lonicera involucrata (twinberry honeysuckle)

Mahonia aquifolium (hollyleaved barberry)

Mahonia repens (creeping barberry)

From our Native Plant Image Gallery:

Amelanchier alnifolia

Amorpha fruticosa

Arctostaphylos uva-ursi

Ceanothus velutinus

Holodiscus discolor

Lonicera involucrata

Mahonia aquifolium

Mahonia repens