USDA Plant Hardiness Zone Map

A couple of weeks ago the USDA published the latest edition of the Plant Hardiness Zone Map.  This is the map that tells us what plants are most likely to thrive in a certain location.  The big news about the 2012 map is that the zones have changed by about a half a zone and the USDA has added two new zones—12 and 13.  The map is also interactive.  You can put in your zip code and it will tell you what zone you are in.

New hardiness zone map

This year’s map is based on weather data from 1976-2005.  Each zone represents the average extreme minimum temperature for that zone.  The previous map, published in 1990, was based on data from 1974-1986.  Of course, the media immediately jumped on this as proof of climate change and global warming.  The USDA cautions us not to read too much into these changes, that they are not a reliable indicator of climate change or global warming but that some of the change is simply due to better mapping technology that has greatly improved the accuracy of the map.

So what does all this mean for us folk here in Northern Illinois?  Well, don’t plan on planting crepe myrtle or camellias anytime soon.  We are still in Zone 5, though we are in subzone 5B.  We also should keep in mind that the zones are just a guideline.  Each individual garden has its own micro-climates.  The spot by the garage that is protected by the wind and gets radiant heat  off the exposed foundation might even be a Zone 6 while the low spot toward the back of the garden where cold are can sink could be a Zone 5A.   And  there are many more factors that impact how well a plant grows in our area including: light exposure, soil fertility and pH, temperatures at both ends of the thermometer, the duration of any particular cold snap (my rosemary held on until just last week in its whiskey barrel by the garage) and the general humidity level.  Many plants can adapt to varying conditions but it is important to have the proper conditions and the proper plant for those conditions. 

Cold hardiness zones only tell a part of the story.  Many plants, especially annuals, also have a hard time dealing with heat.  The American Horticultural Society publishes a Heat Zone Map and many plant tags are beginning to carry this designation.  The Zone tolerance measures a plant’s ability to withstand some number of “heat days,” or days the temperature goes above 86⁰.  According to the AHS we are in heat zone 5, which means we get between 30-45 days above 86⁰.

Birds In Winter

Birds at feeder in winter

Wow- We finally got some winter last week. As much as I hate shoveling snow it’s nice to get some insulating cover over our plants.. It really helps to protect them from the cold, drying winds and keeps moisture from evaporating from the ground. This is especially important for the broadleaf evergreens that don’t go dormant. If they dry out they will drop the buds that they set last fall and you won’t get any blooms this spring. I noticed that my climbing rose has finally dropped all its leaves and is fully dormant. It is now safe to prune as are any other trees or shrubs that need it.

There are lots of birds that stay around here over the winter including sparrows, nuthatches, chickadees, cardinals, juncos and even gold finches. Most people are surprised that the gold finches don’t migrate since they don’t see them. Actually you do see them its just that their plumage has turned from gold to brown, the better to blend into the environment and avoid predators.

Heated Bird Bath

If you are feeding the birds, make sure you are using a bird feed that is high in energy seeds. These would be black oil sunflower seeds and peanuts. Nyger thistle is also high in energy. Black oil sunflower also has thinner hulls and is easier for the birds to crack open in addition to being high in oil. Suet cakes are also very high in energy and good to put out in winter. 

Bird Bath Heater

With this cold weather, any open water has probably frozen over and is not available to the birds. In addition to feeding the birds, you should also put out fresh water.  My neighbor Dave has a bird bath out during the summer and the birds use it all summer long.  Water is equally important in the winter however.  Using a heated bird bath or a bird bath heater will keep the water from freezing in the bird bath.  The bird bath heater sits in your birdbath while the heated bird bath is all one unit-- heater and bird bath combined.