What Zone are you in? It sounds like a bad pick-up line, but for gardeners it may well be one of the most important pieces of information you can have. Arvada has always been on the edge of a zone. It is not the foothills here and not the eastern plains. We sit higher than Denver proper at 5280 feet but not quite as high as Boulder at 5430 feet. Arvada is listed at 5344 feet. Most of these measurements are taken at city hall. Those of us that live here know that elevation of as much as 1000 foot difference is possible. That is the difference between rain and snow at times during the winter. It can also be the difference between a red tomato and a green one.
The newest hardiness map issued by the USDA has had some changes. There are warmer growing zones included numbered 12 and 13. The bigger news for those of us not affected by the new zones is that the hardiness map shows a warming trend. In General the United States seems to have warmed as much as 5 degrees. Some of this is due to better mapping and the additional zones. There has been the addition of 5 degree increments for the winter low temperatures. Check out the map to find out what the season is in your area.
Here in the Denver area we have always had the duel 5a and 5b zones. Arvada is now in the 6a zone which suggests a low of -10 to -5 degrees and a mid-May date for the last frost. Around Mother’s Day has often been a suggested planting time in this area. Remembering that these are based on seasonal averages, each year presents different cautions and opportunities in the garden.
This is just a guide. It is a way to plan if you decide to start seeds indoors. Remember that any May frost will affect the plants with foliage. You may need to cover the tender vegetation in the spring.
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