Rock garden hardiness bulbs and perennials

My rock garden is sloped and about 25 ft long and about 9ft wide (sloping down). It is a full sun area. I can move rocks and allow for soil depths between 6" at the top and 16" in spots near the bottom and varying widths, usually about 6" -10".
My question is about hardiness. If I plant bulbs in about 8" of soil that is about 4" wide with stones around it from top to bottom, will those bulbs freeze as they are not in a regular bed insulated by soil, but rather stones? This questions extends beyond my concern for the hardiness of my bulbs to all the perennial plants I put in the rock garden. Does the stone and lack of soil depth surrounding the roots effect hardiness?
Thanks to all
Steph.
Abbotsford BC.

 

The simple answer is no, assuming you are growing plants and bulbs that are hardy to your zone... and you probably are.

 

Hi There, yes I am putting in hardy plants for my area. I was worried because the plants don't have much soil in the rock garden and I thought they'd freeze so it's good to know that they'll be okay.
Thanks for your help.
Steph.
P.S. You don't happen to know which plants will growing between the cracks of rock with minimal soil? I have put in some hens and chicks and stonecrop type succulents but I wondered about other types that thrive in the rocky low soil environment?

 

To be honest, pretty well any plant that is hardy to your zone and suited to the conditions (sun, moisture) will probably do just fine. Really, the hours of sun and expected moisture levels will be a great deal more influential on what will do well there than the thin soil and rocks.
We always underestimate the "resourcefulness" of plants - have you ever seen a tree growing out of a crack in a boulder? (I thought of this question last time I was out hiking and saw a good-sized saxifrage mat growing on top of a huge rock, in only a slight depression with no obvious fractures... but I didn't take a photo, unfortunately.)

 

Thank you.
Yes I see what you mean. I have found that snapdragons are a good buy as they seem to grow ina little soil, give great colour over a long period of time (April-Sept here in Zone 8) and then come back the next year. They also add such lovely colour to the rock garden. I have found trailing snapdragons to be great for rock gardens as they are not leggy but compact and trail a little. I worry about my minature rose in such little soil (about 10' wide by 7" deep (calle Cale) and I have some fuschias (Santa Claus) and a hydrangea in the bed at the front where it is about 14" deep by about 12" wide.
Thanks for your commentary. I appreciate all the feedback I can get. I am very much a keen amateur at gardening.
Steph.

 

Alternatively, you could use actual alpine plants (sempervivums and some sedums are actually alpine species)... a whole other subject.