Father Haskell wrote:

Best soil for rooting cuttings? Sand works better than potting soil
(Miracle Gro), but is there something better still?

The classic medium for woody cuttings is Cornell mix. It is composed of:
50% sphagnum peat moss and 50% horticultural pearlite or vermiculite.

Most evergreen rhododendron and azaleas may be propagated from stem
cuttings. Cuttings are usually taken in the early fall from new growth
that is just hardening off. Cuttings are taken in the morning when full
of moisture. The cuttings are usually terminal cuttings with one whirl
of leaves with the leaves cut in half (to reduce the leaf area) and any
flower buds removed. The cutting has the end cut off just before placing
in hormone powder (containing a fungicide). Then the cuttings are placed
in a flat of sterile media containing a mix of 50% peat moss, and 50%
horticultural perlite or vermiculite. The flat is placed in a
polyethylene bag with struts to keep bag away from the foliage and
placed in a light area with no direct sunlight. The flat is rotated once
or twice a week to compensate variations in light and temperature.
Usually bottom warmth of 75?F is used to encourage root growth. Rooting
usually takes about 6 weeks for evergreen azaleas and 3 to 4 months for
large-leaf rhododendron. Once the cuttings have rooted, pot or
transplant them to flats containing a sterile mix of 60% peat moss and
40% perlite. Fertilize once a month with an acid-based azalea plant food
like Peters. Removing terminal buds promotes sturdy well branched
plants.

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