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Re: USDA hardiness and heat maps and not enough info

A plant's tolerance of cold is only part of the necessary information a grower needs. From my experience in growing fruiting plants - the winter chilling requirement of a plant to break dormancy is just as important. Failure to consider this factor generally results in flowers being damaged by frost on a recurring basis. This information is not conveyed by the USDA hardiness map zone descriptions. Some fruit nurseries provide this information on the selections, but I have not seen any research of winter chilling requirements of other plants.
I have experienced a slow decline of cold hardy plants in my mild climate and the lack of chilling is the only cause I can attribute the lack of plant vigor in the second season. Note, dormant plants have usually been held in cold storage prior to shipment and thus grow vigorously after arrival. When electric rates were lower, I used to devote one refrigerator to holding bulbs, seeds, and dormant plants to provide what I felt was the needed chilling. I even used small control groups to provide a comparison. Cold storage did seem to solve the problem, but was very labor intensive. Not something many people would take the time and effort to follow to achieve success. They would more likely treat the plants as annuals and discard them at the end of the season.

Many fruiting plants also have to achieve a minimum number of heat units for the fruit to ripen properly. I don't see how the heat maps provide this information or I may not have seen the final version of the heat map.

Flowering plants may require a specific number of hours of light or absence of light to initiate flower bud development. The information of day length response and the time that must elapse for flowering to commence is not generally supplied. In climates with relative short growing seasons, the result can be frost damage in the fall prior to achieving peak bloom. Mums would be an excellent example of this problem.

Photoperiod response in vegetables also is a problem as noted in selecting the proper type of onion seed to insure the plants do not prematurely begin to form bulbs prior to achieving the necessary vegetative growth.

This type of cultural information is best provided from a local source. The more we try to simplify this data, the less useful it becomes and leads less experienced grows to choose a genus, species, and named cultivars that have a low percentage of success unless a very small micro climate exists on the site.

There is a problem of deciding just how much information to include in articles. It is even more difficult when nationally circulated information, such as these maps, provide a incomplete discussion of the factors a person should use when selecting plants. How do wwe as garden writers correct the omissions and please editors?

I would be interested in hear of the experience of others on this list.

Claude Sweet
San Diego, CA
located in a warm winter banana belt.

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