What Causes Rhododendron Leaves to Curl In?

8 years ago

I am testing two different soil mixes for Rhododendrons. Leaves of a plant grown in soil mix A is shown in the first photo. What I have noticed about these plants is the leaves are NOT curled in. Some of the plants have brown/dying leaf tips. So my conclusion is that they might be getting a little too much water.

Soil mix B is shown in the second photo. What I have noticed about these plants is all of the leaves have a slight curl inward. They don't want to flatten out. But none of these plants get brown leaf tips. The effect is subtle, but if you look carefully at each leaf you will see that curl inwards.

Would the leaf curling inwards be a sign of underwatering? Soil mix B does have an ingredient that absorbs more water and releases it slowly.

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Courtney Zone 9A Florida

8 years ago

last modified: 8 years ago

I was just reading the book, "How Plants Work" and she says Rhodys do this as a form of cold protection. She had a picture in the book and described them as looking like rolled cigar leaves when they curl in. Completely healthy.

But it is the transfer of water in the plant that allows the leaves to curl. If they have different absorption of water, one may not have enough water to curl in. I have noticed some of my houseplants folding up and in at night, the book described that as the same process - a different purpose though. I have noticed if they are dehydrated they will not curl up at night. Helps me remember to water them.

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Comments (6)

gardenprincethenetherlandsZ7/8
8 years ago
Are the rhododendrons you planted in mix A and B the same cultivars / hybrids?

If they are the same cultivars then it may indeed be about the soil you planted them in but it could also be about the amount of sun they get. Some rhododendron hybrids curl their leaves when they get too much (afternoon) sun.

If the rhododendrons are different cultivars / hybrids in A and B then it is dependant on the cultivar. Some species of rhododendrons have naturally curling leaves and when used for crossing with other species or hybrids this trait may be found in the new hybrid.
westes Zone 9b California SF Bay
Original Author
8 years ago
@gardenprincethenetherlandsZ7 yes they were sister plants purchased at the same time from the same nursery. They are side by side under the shade of the same tree, so I think they get similar lighting.
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westes Zone 9b California SF Bay
Original Author
8 years ago
Okay, I have further observations on these two plants. The plant whose leaves are flat has no leaves beneath the canopy. Basically, the leaves have fallen off the stems of the plant, except for the top canopy. But the leaves in that canopy look very healthy.

The plant with the curled leaves has leaves underneath its canopy. So it has retained most of its leaves all along the stem, but the leaves look a little less healthy because they have this curled-in feature.

I am not sure what to make of this. I am testing two different soil mixtures, and I am not seeing a clear winner. Each plant seems to have its own issues that make me think neither is optimal.
westes Zone 9b California SF Bay
Original Author
8 years ago
@Courtney I have concluded that the plant with the curled leaves is the healthier plant. It has denser canopy and underbrush. It has fewer leaves showing stress.
Courtney Zone 9A Florida
8 years ago
@westes Yeah, I wonder if something is troubling the roots and it can take up enough water or if the soil is more porous in the unhealthy one.
westes Zone 9b California SF Bay thanked Courtney Zone 9A Florida