Your rhododendron just croaked? Here's what to know.

By Steve Bender
June 08, 2020
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Large Pink Rhododendron
Credit: Steve Bender

I just returned from a family trip to Oregon and the rhododendrons there were spectacular. Huge trusses of red, pink, purple, lavender, and white blossoms decorated large, leathery, green leaves beneath them. I quickly developed a serious case of rhododendron envy.

Accomplished gardener that I am, I’ve never been able to keep a rhodie alive for more than a couple of years in my USDA Zone 8A garden in north-central Alabama. Why is that? To find out, let’s visit the mountains of western North Carolina, home to two native species used in breeding, Catawba rhododendron (Rhododendron catawbiense) and rosebay (Rhododendron maximum).

Rhododendrons love it here. They form forests of small trees up to 30 feet tall and bloom in July. The climate and soil here fit their needs to a “T.” Summer temps usually top out in the low 80s during the day and drop into the 50s at night. Clouds and fog coat the leaves with moisture. The acid, rocky soil drains quickly after a rain. Taller trees protect them from strong sun.

Light Pink Rhododendron Shrub
Credit: Ralph Anderson

It’s not like that where I live. It’s probably not like that where you live. So if you want to revel in rhododendrons for more than a year or two, you must do your best to give them what they want. Here’s your checklist.

Soil

As stated earlier, the soil must be acid (pH 5.5 or thereabouts), well-drained, and contain enough organic matter so that the soil holds necessary moisture. You can’t grow rhododendrons in heavy, clay soil. They’ll die from root rot. You can’t grow them in sand. They’ll die from thirst and starvation. And you can’t grow them in limy, alkaline soil. They’ll turn yellow and die.

Light

Provide dappled to light shade. Full sun burns the leaves. Deep shade eliminates blooming. You want that sweet spot in the middle.

Planting

Dig a hole three times as wide as the root ball, but no deeper. Plant so that the top of the root ball is slightly above the soil surface. Fill in around the ball with excavated soil. Then cover the top with a couple of inches of mulch. This allows the soil to hold necessary moisture, while letting excess water drain away.

Fertilizing

Rhododendrons don’t need much fertilizing, unless the soil isn’t acid enough and leaves turn yellow between the veins (a condition called chlorosis). In this case, increase acidity by applying garden sulfur, iron phosphate, or Espoma Holly-tone to the soil according to label directions.

Heat Tolerance

Don’t worry about winter cold in the South. Worry about how much summer heat a rhododendron will take. The following heat-tolerant selections will thrive as far south as USDA Zone 8: ‘Album Elegans’ (pale mauve), ‘Anna Rose Whitney’ (rose), ‘Caroline’ (orchid-pink), ‘Chionoides’ (white), ‘Lee’s Dark Purple’ (purple), ‘Nova Zembla’ (red), ‘Roseum Elegans’ (lavender-pink), ‘Vulcan’ (brick-red), and the Southgate hybrid series, members of our Southern Living Plant Collection.

You have your marching orders.