Growing in cracks between boulders

Leo A. Martin
Thu, 10 Oct 2013 09:57:00 PDT
Jim Waddick wrote

> Worsleya appears to grow in full sun on,
> in and among rocks on steep cliffs. As Lee
> said "they really do grow in large cracks
> in mountain-sized granite boulders."

I can't echo enough Jim's suggestion to find out what microclimate plants experience in
habitat. "Brazil", "Mexico" and "Madagascar" isn't much information. A lot of
non-temperate habitats just don't occur in temperate zones so we gardeners can't imagine
what they are like unless we see them and understand.

I haven't been to Worsleya habitat but I have seen this environment in other places.
Visitors to the American Southwest can find a similar habitat if they look under rock
overhangs here and there; ferns survive in some of the hottest and driest areas. Sedums
and a native prickly pear, Opuntia humifusa, in the east of the US, occur in similar
situations, though usually in flatter terrain.

All over the mountains of Mexico succulents like Echeveria, Graptopetalum, Sedum and
Villadia occur in similar conditions. In Brazil I have seen various cacti in this
habitat, along with a Hippeastrum and lithophytic Laelia orchids; I also saw but did not
recognize Sinningia tubers.

In Madagascar, the yellow-flowered Pachypodium grow in such habitats; also angraecoid
orchids like Jumella and several species of Aloe and Cynanchum. Also in Madagascar, many
Oeceoclades orchids grow on the forest floor in the layer of fallen leaves. This leaf
mat often is about a foot / 30cm thick but overlays large, jumbled boulders. It can be
treacherous walking since the surface seems smooth but is not. The orchids have a thick,
well-aerated layer of leaf mold with air underneath.

In the rock-face habitats rock cracks accumulate a little dust and a very small amount
of decaying leaves and moss. Mosses and ferns fill the cracks; frequently they are
"resurrection plants", green and growing with rain, and brown and shriveled during dry
seasons. Larger plants grow in these hummocks of moss and leaf litter.

Any plant living there will have lots of air at the roots even when soaked with rain for
many days on end. During dry spells the thin mat of organic matter holds moisture much
longer than expected. The decaying organic matter provides and acid environment. Water
runs off rapidly so minerals with a basic chemical reaction are not leached to the
surface as they are in arid environments.

Some of these habitats are wet to damp all year owing to nightly dews; others have
distinct dry spells. Some have cool weather and some warm. This needs to be taken into
account. Plants growing on high rock walls facing the sun will be accustomed to high
heat and insolation for at least some of the year. I was not able to grow some Brazilian
cacti well until I realized some grow on black rocks in full sun in places where daytime
temperatures may exceed 120 F / 50C.

John Lavranos taught me how to grow some of these plants in containers. He said to
choose a wide, shallow dish-type container with large drainage holes; fill it halfway
with pumice or something similar; top it with a 2-5 centimeters of crumbled fallen
leaves from my garden; and nestle the plant into the leaf mold. The leaf mold keeps in
the moisture, while the spaces between the pumice provide excellent aeration. I was able
to grow some lithophytic orchids for the first time with this method. It is the same
method Jim described in his message.

Leo Martin
Phoenix Arizona USA

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