1.  The garden site should get a least 8 hours of sunlight daily.  Most vegetables need maximum sunlight to succeed.

2.  The slope of the land should face south or, second best, west so the garden will get maximum sun light and heats up during the day.

3.  The garden site should not be in a "bottom".  i.e. Cold air should be allowed to "drain" from the site unimpeded by hedges or other obstructions.

4.  Taller plants such as corn or staked tomatoes should be placed north of other shorter vegetables so the shorter vegetables are not shaded during the day.

I placed my vegetable garden in the larger of our meadows.  The land sloped south and received about 7 hours of sun a day.  The meadow lies in an area lower then the land to the north, east, and west (where our house sits) and continues south down to Elk Creek, about 3/4 mile away, allowing for good "air drainage".  With a very long hose (125 feet), I can get water to the garden  The soil seemed to be the best possible on our property which is mostly forested. 

However, while a high altitude garden does share some growing conditions with a "northern" garden (such as a short growing season), they encounter vastly different growing environments.  A high altitude garden has, in general, much less moisture available to it.  The sun is much stronger at high altitude and, for many crops, 8 hours of sun a day causes wilting and desiccation.  The soil depth is shallow allowing the sun to dry the top 4 to 6 inches in a few hours.

Some crops have grown wonderfully in my garden such as potatoes and peas.  Other crops do not grow so well such as cabbage and other cole crops which wilt every afternoon in the hot, drying sun.  Lettuce grows thick and tough  Spinach grows well but bolts quickly.  I have learned the following about gardening at a high altitude:

1.  A land sloping east is best, followed by a northerly sloping land, for most crops.  I noticed when I first moved to Colorado that many foothills and mountains did not have trees or bushes on the south and southeast slopes while the north slopes were fully forested.  I now know that the sun is so hot and intense on the south and southwest slopes that seeds do not easily germinate and the organic matter is quickly decomposed leaving very poor soil.

2.  Most vegetables cannot tolerate 8 hours of sun a day.  Shade, at high altitudes, can protect many vegetables.  I plant lettuce in the shade of my pea fences.  Corn provides welcome shade for spinach.  I plant the tallest vegetables directly south of more sun sensitive crops.

3.  Areas that receive shade most of the day tend to hold moisture best.  For example, the land on the north side of our house had the greenest, most healthy looking grasses,  This grass stays green much longer into the summer and into the dry fall days.  I plan to plant lettuce and some other sun sensitive vegetables in a small patch behind the house this summer to see if they will grow better in the full shade.

4.  Wind is a major factor at high altitude.  Since the air is already dry, even a slight wind can dehydrate the garden. 

5.  Unimpeded air drainage is important at high altitudes about the same as in northern latitudes.  The cooler air should not be trapped in the garden area.