When choosing a site for your rhododendron dappled shade is best. To set buds, rhododendrons need light but require protection from the hot summer sun. Buds are set in the late summer for the following year. If you plant your rhododendron in deep shade, it will flower poorly and develop leggy growth.
Rhododendrons perform best when the soil is acidic (with a pH between 4.5 and 5.5).
Avoid planting rhododendrons and azaleas near concrete sidewalks, driveways or foundations that may leach out lime and raise the pH.
It’s important not to plant your rhododendron too deep. Find the point where the trunk flares and roots first extend from the plant. These should be set at the soil line. The American Rhododendron Society plant care section and the article by Nicholas Yarmoshuk listed below have helpful illustrations on how to plant and what pitfalls to avoid.
Because rhododendrons have a shallow root system and can’t tolerate wet soggy soil drainage is of critical importance. Your plant needs both oxygen and steady moisture for healthy root development. Add organic matter such as sphagnum peat moss, ground pine bark, or composted leaves to improve soil aeration.
You can prune your rhododendron after it blooms. Removing finished blooms by hand is best. If you want to fertilize your rhododendron use a fertilizer designed for acid loving plants and apply in the spring. Don’t apply any fertilizer after the end of June.
Protect your rhododendron from drying winter winds. Drying winds and frozen ground deprive plants of their natural ability to take up moisture. A good soaking in the late fall before freezing and a good mulch with pine needles or oak leaves will help your plant to survive harsh winter weather. If you don’t have a natural windbreak, consider creating one with a few stakes and burlap.
The North American Rhododendron Society provides a list of rhododendrons hardy to -25F or -32 C to help you select suitable varieties http://www.rhododendron.org/alphalist.asp?Hardy=-25&Genus=R. Some varieties that have done well in my parent’s Zone 6a garden on Lake Huron include: Rhododendron Nova Zembla, R. ‘Catawbiense Boursault’, R. ‘Catawbiense Album’, R. Cunningham’s White, R. Roseum Elegans, and PJM.
The North American Rhododendron Society https://www.rhododendron.org/index.htm
Daniel Robarts. Fine Gardening Magazine, How to kill a rhododendron https://www.finegardening.com/article/how-to-kill-a-rhododendron
Nicholas Yarmoshuk,. Growing Rhododendrons Successfully http://www.rhodoniagara.org/rhodos/2004_grow/
Growing Rhododendrons in Ontario https://localgardener.net/growing-rhododendrons-in-ontario/
Submitted by Nancy Burnett