(News article for July 18, 2019)
Making good plant choices is one of the most important aspects of gardening and landscaping. This includes choosing plants that are well-suited to our climate, including our temperatures and the amount of rainfall that we get. It also means appropriately matching plants to the conditions of particular spots on our property.
Over the next couple of weeks, we’ll be looking at how the right plant, right place principle can be applied to increase gardening success and reduce time and money spent on maintaining and replacing plants.
The focus this week is on temperatures and fruit plants.
Many gardeners are familiar with US Department of Agriculture (USDA) Plant Hardiness Zone map and the need to pick plants that tolerate the minimum temperatures that we expect. Most of Tangipahoa Parish is in USDA Hardiness Zone 8B, meaning that the average expected low temperature is between 15 and 20 °F. South of I-12, part of Tangipahoa Parish is in Zone 9B, meaning that the average minimum is expected to be 20 to 25 °F. These averages are based on minimum temperatures recorded from 1976 to 2005, and what we actually experience in a given year varies.
Kumquat is the most cold-hardy species among commonly cultivated citrus plants. Satsumas are next on the cold-hardiness spectrum, with ‘Owari’ and ‘Kimbrough’ being among the more cold-hardy. In winters like we had in 2017-2018, even these will likely need to be protected to avoid substantial damage.
Some plants can handle the minimum temperatures we experience but do not flourish in our heat. When teaching fruit classes, I often show a graph that demonstrates how temperatures like those we normally experience in the summer negatively affect the ability of raspberries to photosynthesize, or make food for themselves. ‘Dormanred’ raspberry is among the most heat tolerant and may be satisfactory if you’re looking for a raspberry to use to make jam or for other cooking purposes.
Besides tolerating our coldest temperatures and our heat, for some types of fruit plants, the number of “chilling hours” we experience is also important. Many plants need a certain amount of exposure to cool temperatures in order to break dormancy, flower, and produce fruit.
Chilling hours are calculated in different ways by different people, but two of the most common ways to calculate chill hours are hours below 45 °F and hours between 32 and 45 °F. In the Hammond area, we can expect to get at least 500 chilling hours in a typical year, by the below 45 °F model.
When shopping for fruit plants, it’s sometimes it’s hard to compare apples to apples (no pun intended) when it comes to chilling hours, since it’s not always clear on which model the stated chilling hour requirement of a particular variety is based. To make it easier for you, suitability to the amount of chilling we get is one factor that is accounted for in the recommendations found in, for example, our Louisiana Home Orchard publication.
For example, the ‘La Festival’ peach, which was bred in Louisiana, requires approximately 450 hours below 45 °F, while ‘Contender’, a variety that was popular where I used to work in North Carolina, requires approximately 1050 hours below 45 °F and is not recommended here.
Last year, someone saw ‘Belle of Georgia’ and ‘Elberta’ peach trees for sale for a low price and asked if those would be okay for Tickfaw. Both of these varieties require about 850 chilling hours, so the answer was no. While these may have been for sale for cheap, they would not have been a good deal for our area.
While it may seem that as long as fruit plants get the minimum number of chilling hours required, they should produce well here, this isn’t necessarily the case. As you know, temperatures are not consistently cold during the winter here. If plants get their required chilling hours, and we get a warm spell in January or February, they may start flowering. Then, when we get another freeze, those flowers – or the fruits that have developed from them – are likely to be killed.
Using another peach example, ‘Flordaprince’ requires approximately 150 chilling hours and would likely bloom too early here. Likewise, while ‘La Festival’ is likely to produce well in the Hammond area, now-retired LSU fruit crops professor Dr. Charlie Johnson once told me that it only produced fruit about half of the time in Calhoun, which is in northern Louisiana near Monroe.
Besides peaches, apples and blueberries are among the other fruit crops for which the chilling hour requirement is an important factor in determining which types grow well here.
Next week, we’ll look at other things to consider when choosing plants for our area.
Contact Mary Helen.
'Dormanred' is a heat-tolerant raspberry that can be used for cooking. (Photo by M.H. Ferguson)