Growing in cracks between boulders
Jane McGary (Thu, 10 Oct 2013 17:46:32 PDT)

Dylan wrote

This is a little-known but very important fact. Not only elevation
but also atmospheric humidity affects the difference between day and
night temperatures. In humid conditions temperature does not drop so
much at night. This is, I think, the main reason why some plants from
eastern North America don't grow well in western North America: the
east is humid in summer, and the west is dry, so the plants may be
triggered toward dormancy every night in the west. This is the
opposite of the phenomenon Dylan describes. In contrast, alpines
generally do better at low elevations in the west than in the east.

Also important is the "heat island" effect that occurs in urban areas
where buildings and pavement build up heat during the day and release
it at night, so that night temperatures stay higher than in the
nearby countryside. When I lived in the country in the Cascade
foothills, the day/night differential could be 40 degrees F; now I
live in a suburb, and it is more like 25 degrees F. (That would still
make our friends in the east happy.)

Alpine bulbs from the higher latitudes are in general difficult to
grow in mild climates. Tropical bulbs will probably do best in the
controlled atmosphere of the greenhouse. At high elevations in
equatorial South America, frost can occur at any time of year, but
the days will usually warm up. Some bulbs from regions with snowy
winters are adaptable, but others seem not to be; they must require a
long, cool, dry dormancy during winter. Some species I struggle with
in western Oregon include Fritillaria alburyana and Crocus
alatavicus, and I have never managed to keep Colchicum luteum.

Growing in rock crevices benefits plants in many ways: a lack of
temperature fluctuation (especially heating) in the root run;
trickling water from night-time condensation on the rock surface,
especially in foggy areas; and, of course, protection from predators.
However, if you see plants growing in such crevices, that doesn't
mean they have to be planted in that way; it might just be the only
place they can survive the voles, goats, or whatever. On Crete,
Tulipa cretica is seen in crevices, but I also saw that those that
had seeded down into disturbed soil below the rock formations were
more robust than their parents in the rocks. I grow it in an ordinary
sandy soil mix. Chasmophytes (cliff dwellers) may also be able to
grow early in spring when other areas are snow-covered. In contrast,
some plants prefer bowls or swales where the snow lies longest and
the soil stays moist longer (e.g., Oxalis adenophylla).

This topic is a lot of fun to investigate, and in fact I give a talk
called "Bulbs in their habitats" organized around photos taken in
various countries showing bulbs flowering on beaches, in scree, and
so on. I love books that illustrate this, such as Mary Gerritsen's
book on Calochortus, from which I have learned a lot.

Jane McGary
Portland, Oregon, USA