Growing in cracks between boulders

Jane McGary
Thu, 10 Oct 2013 17:46:32 PDT
Dylan wrote
>Plants that grow where nights are cool (about 55F) cannot properly process
>the food they have gathered via light during the day if nights are too
>warm. Their metabolism is interrupted and this can be fatal. Understanding
>the importance of nighttime temps, which is greater than daytime temps, is
>critical in growing certain bulbs.

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

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