This was just a little first-year patch on hard clay soil. I dug in some lawn clippings, as the only soil amendments. All the crops were of heritage varieties; the corn, beans and squash were varieties grown by my Indian ancestors. The native varieties of corn were bushier and shorter than the more familiar types. Someday it would be nice have my own yard, so be able to grow food, medicines, and have some chickens. Economics and lack of fulltime employment makes that unlikely for now. But you do what you can with what you have.
According to the 2001 Weather Almanac, Helena's growing season runs from April through September. (http://www.weatherexplained.com/Vol-4/2001-Helena-Montana-HLN.html)
The Montana Garden Guide (http://gardenguide.montana.edu/pdf/Montana_Climate_Summary.pdf) says:
May 2 through Oct 2: 153 days
Precipitation: 12.54 inches
May 14 through Sept 22: 131 days
Precipitation: 9.39 inches
These are approximations, with actual growing seasons varying from year to year by 2 week or so. And of course it also varies by site microclimate. The variations in the Garden Guide are also interesting, since East Helena and Helena are only 5 miles apart! It must have a lot to do with the actual site selection of the stations. Of course these are all figures for sites within the valley itself; the mountains' growing season will be much, much briefer!
Helena is in Zone 4 according to the USDA's Hardiness Zones system; the Sunset magazine system lists it in Zone 2. Yes, the systems are quite different; the Sunset system is more detailed and is considered more authoritative for gardening.
Comparison of USDA and Sunset: http://www.backyardgardener.com/zone/index.html
The Sunset system: http://www.sunset.com/garden/climate-zones/sunset-climate-zones-northern-rockies-00400000036338/