"doug." wrote:

Rhododendrons, and Hydrangeas (Queens of the late-flowering shrubs), are
similar but are not the same. but their treatment is the same and they are
sometimes traditionally referred to as Azaleas. They are of the heather
family and will fail miserably in alkaline soil. . They may do reasonably
well in neutral soil but need an acid home if they are to flourish, and they
do better in partial shade.
Their's much more but the above is a guide and don't thank me. they are
straight out of a worthy book , - which by law I cannot mention.

Hi Doug, You better get you money back on that book.

Rhododendrons are kings of the early flowering shrubs of the Ericaceae
Family (so-called heather family). They are in the Dilleniidae Subclass
and the Ericales Order which includes heaths, heathers, mountain laurel,
and pieris.

Hydrangeas are mid-season bloomers of the Hydrangeaceae Family
(hydrangea family). They are in the Rosidae Subclass and the Rosales
Order which includes cannabis and roses.

The only thing they have in common is that they both have flowers and
produce seeds with two cotyledon leaves, dicots.

Rhododendrons and other Ericaceae are called acid loving plants since
they are usually found growing in acidic soils, though some members of
the family have adapted quite well to alkaline soils. That is the
reason that rhododendrons in Europe are grafted onto root stocks of
rhododendrons that are tolerant of a wide range of pH's. However they
are all sensative to soils containing aluminum and subject to aluminum
toxicity.

Hydrangeas are unique in that they have the ability to accumulate
aluminum. In acidic soils when aluminum is more available, it is taken
up by hydrangeas. Most hydrangeas have white flowers but some are
affected by the aluminum and produce flowers that are more blue in
acidic soils, flowers that are pink or purple in alkaline soils, and are
cream colored in neutral soils.

Some people mistakenly think that aluminum sulfate that is added to the
soil to make hydrangeas blue will help rhododendrons. It will help them
for a while by acidifying the soil, but will eventually kill the
rhododendrons which are killed by excess aluminum ions in the soil.
--
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Cheers, Steve Henning in Reading, PA USA Zone 6