soil temperature variation with depth in a bulb garden

Jane McGary
Fri, 22 Nov 2013 17:11:26 PST
Boyce wrote,
>To increase the probability of providing soil temperatures cool enough to
>perennialize some of the Mediterranean species of tulips try planting them
>on the north side of a structure and/or in the cracks between large paving
>stones.  Photo's taken of Tulipa species in the wild in Central Asia
>indicate a number of them grow in really rocky habitats.  I thought this
>was only to reduce predation by herbivores but there is a cooling component
>as well. Both microclimates (north side of a structure and use of large
>stones) are amazingly efficient at reducing the temperature of the soil.

A method I used with success in my former garden was as follows. 
After planting bulbs on a raised bed with a gritty soil incorporating 
coarse, sharp sand with the native gritty clay loam, I spread a 
single close layer of basalt rocks around the size of medium to small 
apples (I had an infinite supply of these in the rocky soil there). 
Then I spread a layer of the coarse sand over the rocks and 
top-dressed it with pea gravel. Low-growing rock plants and subjects 
such as Acantholimon went in as my seedlings got enough size. Many 
plants that I thought might not be cold-hardy there grew well for 
many years. I haven't done this in the new garden because I didn't 
bring small rocks (I brought a lot of large ones for rock garden 
construction), but it's a good way to use up a size of rocks that 
aren't good for visible construction.

Jane McGary
Portland, Oregon, USA

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