What’s strong and upright with ample levels of fortitude, tenacity and vigor?
If you said dear old dad, move up to the bonus round, although the answer I have in mind is rhododendrons — this is a garden column, after all.
The name rhododendron comes from the Greek word rhodo, meaning rose, and dendron, meaning tree. There are more than 1,000 varieties out there, and right now, they’re blooming in magnificent colors across Michigan.
For those who’ve tried unsuccessfully to get grass — or much of anything — to grow in shady areas, consider the rhododendron. This evergreen shrub thrives in shady conditions with slightly acidic soil.
A few well-selected and well-placed plants can fill up an otherwise drab corner of the yard. They work well as a border or foundation planting with other shrubs, especially evergreen azaleas.
Rhododendrons look great when grouped together. The American Rhododendron Society recommends giving consideration to size, color and season of blooms. “Usually, the taller growing plants should be towards the back of the planting, medium-sized ones in front and low growing rhododendrons or other plants around the edges,” the ARS says.
Because rhododendrons come in all shapes and sizes, pay attention to the growth rate and ultimate size of each plant, as listed on plant labels. You don’t want the fast growers to shade out slower paced plants or aggressive varieties to crowd out smaller, more compact varieties.
Rhododendron roulette
The rhododendron family has early bloomers, late bloomers and many more that bloom in between. Flower colors include white, pink, orange, red, yellow, lavender and purple.
Some varieties max out at two feet in height while others top seven feet in 10 years.
Rhododendrons grown in the South will not tolerate temperatures below freezing, although there are scores of plants that can withstand Michigan winters, even taking temperature extremes to minus 20 degrees.
When searching for rhododendrons, check its rating for cold hardiness, which means the lowest temperature a plant can tolerate without damage. Most of Michigan is in Zone 5. Plants in this zone should be able to tolerate temperature extremes to minus 20 degrees, even though we haven’t experienced that degree of cold in many years.
Site selection
When selecting a planting site, check the pH level of the soil, which simply is a measure of acidity or alkalinity. A pH reading of 7.0 is neutral. Anything above that is considered on the alkaline side, while readings below 7.0 are considered acidic. Rhododendrons favor mildly acidic soil with a pH around 5.5.
When the soil tends on the alkaline side, rhododendrons can’t efficiently absorb key plant nutrients. Regions of the country with plentiful rainfall tend to have acidic soil.
The soil pH can be lowered by adding aluminum sulfate or ferrous sulfate to the soil. Though more expensive, ferrous sulfate also adds iron to the soil and is of most help to acidic-loving plants in poor health — especially those with yellowing leaves. A great long-term way to lower pH is to regularly add organic matter to the soil, such as compost and well-rotted manure.
Rhododendrons — like dads — are not invincible. Rhododendrons are vulnerable to attacks by weevils, specifically the black vine weevil.
The best defense is a good offense: keep plants properly watered and fed. To reduce weevil access to your rhododendron, prune off lower leaves that touch the ground, the side of the house or that are touching other plants.
For last-minute gifts for Dad, buy a bag or two of well-rotted manure and spread it around rhododendrons and other garden plants. He’ll appreciate the effort, and that’s no bull!
Robust Rhododendrons
Here are some tips from the American Rhododendron Society for keeping plants healthy. For more information, visit rhododendron.org
• Roots grow near the surface and can quickly dry. Plant in well-drained soil and keep moist, not water-logged.
• Keep soil on the acidic side. Rhododendrons prefer soil with a pH reading of between 4.5 and 5.5.
• Plants prefer organic fertilizer such as compost or well-rotted manure.
• If using synthetic fertilizer, feed more frequently with smaller amounts rather than with one large dose.
• Don't plant too deep or cover with too much mulch. Rhododendron roots grow just below the soil line; planting too deep or burying in mulch will smother them.
• Select plants that can withstand Michigan winters. There are more than 100 varieties able to withstand sub-zero temperatures.
• Protect from winter cold. Loosely wrap with burlap or spray leaves with an anti-transpirant such as Wilt Pruf.
• Spray with a fungicide in late spring and summer to protect from fungus diseases. Branches that suddenly turn brown and die in summer indicate a fungal disease is present.
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