Courtesy of CSU Master Gardeners

Small Acreage: Hardiness zone ratings on plants, soil moisture and other topics

Q: I shopped for perennials recently and noticed a USDA hardiness zone rating on the plants. What does this mean?

A: The U.S. Department of Agriculture has established temperature zones based on 10-degree increments, which helps to predict the survivability of plants during the colder months. The higher the zone is, the warmer winter temperatures are required for plants to survive. These zones were updated in January 2012 to reflect local conditions and temperature trends based on 1976-2005 historical data. For example, Fort Collins is now Zone 5b, which means that winter temperatures can drop as low as -15 to -10 degrees allowing woody plants to survive. When buying plants, look for zones that rank lower than 5b (e.g. 4a, 4b, 5a) to insure that your new purchases are appropriate for our area. You can enter your zip code at the website to find your zone.

Q: With our warm spring, can I plant my tomato starts now?

A: This is not recommended, as our last frost date is still mid-May. In fact, there is some evidence that planting in late May actually allows your plants a better start and yield fruit more quickly. According to the climate summaries for our area, our ambient air temperature for May can still be a low of 43 and an extreme low of 32 degrees. Tomato, pepper and eggplant starts are considered warm season tender vegetables and can be stunted by air temperatures lower than 55 degrees. If you do plant early, use black plastic mulch and thermal water walls to keep seedlings warm. Refer to CSU Extension Garden Notes #720, Vegetable Planting Guide, and to Climate Summary #746 to find temperature trends for the Fort Collins, Greeley and Estes Park areas, based on 1970-99 data. These can be found at

Q: Is soil temperature important, and how do I determine this?

A: Yes, soil temperature is another consideration for plant survival. Measure your soil temperature at 8 a.m. with a probe such as a compost thermometer, to a depth of 4 inches. For bean planting later this spring, use a 6-inch depth.

Gardening Tips

■ Phenology is the study of how the biological world times natural events like the germination of seeds, flowering of plants, leaves of trees changing color and falling off or the emergence of insects. Three main non-biological factors that affect phenology are sunlight, temperature, and precipitation. Increasing average annual temperatures can disrupt the timing of natural events. If you would like to participate in recording data, go to, the USA National Phenology Network or Earthlink at

■ Move houseplants outdoors when night temperatures stay above 50 degrees. Place them in a shady location to avoid burning the foliage in our bright sunlight. Gradually move them to sunnier locations. If they are in clay pots they can be planted directly into the ground with the soil 1-2 inches below the rim. Moisture in the ground will transfer through the porous clay.

■ Buy bedding plants without blooms or pinch off the flowers and any buds when transplanting. This will give your plants a chance to develop better roots; pinching will give you a bushier plant with more blooms. ❖

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The Fence Post Updated May 21, 2014 11:37AM Published May 11, 2014 08:12PM Copyright 2014 The Fence Post. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.