Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001235
11/12/99
Rhododendron--Rhododendron, Azalea
Rhododendrons are ornamental, ericaceous, broad-leaved
evergreens. Azaleas belong to this genus, but many are
not evergreen. They tolerate shade or partial shade but a
sunny exposure increases the chance of winter injury to
evergreen types. Plant in an acid, moist, well-drained
soil with a pH between 4.5 and 6.5. The height and spread
depends on the type selected, but some are quite large.
The shallow root systems are easily injured by deep
cultivation but benefit from mulching. Remove the old
flower clusters as the flowers fade. Plants fail to
absorb iron and have yellow leaves with green veins, a
condition referred to as chlorosis, if the soil is not
sufficiently acid.
Several species of azalea and rhododendron are hardy in
northern climates. Prevent winter burn of evergreen types
by avoiding exposed planting sites and by shading during
winter. Some catalogs rate rhododendron hardiness with a
system using designators such as H-1, H-2, and H-3. These
equate to the following minimum temperatures and USDA
hardiness zones.
H-1 To -25 F Zone 4
H-2 To -15 F Zone 5
H-3 To -5 F Zone 6
The related cultivar lists will use the zone numbers to
designate cold hardiness.
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to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
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a commercial product or company.
This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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