Pushing the Limits of Your Planting Zone

By: Julie Day

“I live in Zone 10, and I wonder if it is wise to purchase plants whose labels state that they grow in ‘Zones 4-10’? I’ve lost some plants during our hot summers, and I wonder if it’s better to avoid plants if you live at the edge of the recommended zone range?” -Brenda

Your question brings up two important points when choosing plants for your climate:

  1. The USDA Hardiness Zone Map refers to the coldest temperature the plant can survive – it doesn’t take into account the summer heat. So, if you live in the warmer zones of the plant’s range, you can be reasonably sure that the plant will survive your winters, but what about the summers? The American Horticultural Society Heat Zone Map is a better guide for heat-tolerance, and some plant labels are beginning to include this information. It classifies plants based on the combination of average high temperatures and average number of days per year at that temperature. If possible, consider both “zones” when choosing plants.
  2. In addition to the general guidelines given by the zones, consider that gardens are made of microclimates. Depending on elevation, shade, exposure, drainage, and nearby structures, different areas of your yard have their own microclimates that can even put those areas into different planting zones.

If you are worried about the hardiness or heat tolerance of a plant, choose a location that increases its chances:

  • Plant cold-tender plants in sheltered, warmer spots.
  • Reduce heat damage by planting heat-sensitive plants in cooler spots with plenty of air circulation, water, and perhaps a little shade.
  • Keep all plants mulched to even out soil temperatures.

Get to know each area of your garden – if you choose locations wisely, you can push the limits of your hardiness and heat zones. For more information on planting zones, check out our article Hardiness and Heat Tolerance: Understanding Your Zone.

Julie

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