Well, doesn't placing it in a shaded area mean your weather station is either 1) closer than four times the height of whatever structure is producing the shade, or 2) beneath vegetation like a tree that will act as an overall insulator. Both go against NWS standards when it comes to placing a weather station. You will get a temperature reading for a small spot in the garden, not anything close to what an official weather station would measure.
On a clear night with low dewpoints, radiational effects are so strong that there can be as much as a 3 to 5 degrees difference between an open area and an area under shade of a tree or structure.
Here are the NWS standards for the temperature sensor:
Temperature sensor siting:
The sensor should be mounted 5 feet +/- 1 foot above the ground.
The ground over which the [radiation] shelter is located should be typical of the surrounding area.
A level, open clearing is desirable so the thermometers are freely ventilated by air flow.
Do not install the sensor on a steep slope or in a sheltered hollow unless it is typical of the area or unless data from that type of site is desired.
The shelter should be no closer than four times the height of any obstruction (tree, fence, building, etc.)
The sensor should be at least 100 feet from any paved or concrete surface.
See
http://newa.cornell.edu/index.php?page=placement-guidelines.