Hot-summer Mediterranean / Humid Subtropical
This is a Genovese type of basil, associated with the fertile western coastal regions of Italy around seaport cities like Genoa and Naples. Here are some regional climate factors to bear in mind, and how they compare to our local climate:
*Please note –
Bold = Regional climate info associated with ‘Italian Large Leaf’ basil
Italics = Las Vegas area climate info
The borderline Csa/Cfa climate is mild overall. The sea is a moderating influence, helping to keep the daily high and low temperatures within 11 degrees F of each other. (1,3)
Overall, the Las Vegas climate is anything but mild and stable. On the contrary, it is characterized by fluctuations. Temperatures often rise and fall dramatically in the course of a day. However, the weather can be quite “Mediterranean” during the warm transitional season of spring… a good time to grow basil! (4,6)
While the sea is a moderating influence in the Csa/Cfa climate, one influence that is both polarizing and moderating in Las Vegas’s hot desert climate is the lack of water. The relative absence of moisture or humidity helps to moderate the effects of summertime high temperatures. (4,6)
“Annual average relative humidity is 68%, ranging from 63% in February to 73% in May.” (1)
Las Vegas is much less humid than this. Average daily humidity is 30%, and sometimes remains below 10%. (4,6)
“Sunshine hours total above 2,200 per year, from an average 4 hours of sunshine duration per day in winter to average 9 hours in summer.” (1)
Las Vegas is significantly sunnier than this. Sunshine hours in Las Vegas total around 3,825 per year, with an average of around 9 hours of sunshine per day in winter to an average of nearly 13 hours in summer. (5)
This is one reason basil can be successfully grown on a Las Vegas windowsill in winter, when days are as long as Mediterranean summer days.
“Genoa is also a windy city, especially during winter…” (1)
Wind plays a major role in the Mojave Desert climate, too, all year long, especially in late winter and early spring. ‘Italian Large Leaf’ basil hails from a windy region, and may be fairly wind tolerant once established. (4,6)
Winters are cool but not cold, thanks to the marine influence. The coldest months are December through February, when the average temperature is around 54 F in the day and 43 F at night. Temperatures reach 32 F or below on only about 3 nights per year. (1)
LV area winters are generally cool, too, and winter daytime temperatures are very similar to this. However, LV area winter nights are chillier than Mediterranean winter nights. Temperatures can quickly drop by 15 degrees or more, and may fall below freezing. (4,6) Basil cannot tolerate freezing weather.
Winters are wet (1,3)
Likewise, winters are relatively “wet” in Las Vegas. Most of the annual precipitation falls during the winter months. However, this precipitation amounts to very little, with only four days of significant rainfall on average during even the wettest month of the year. (4,6)
“Snowfall is sporadic, but does occur almost every year, albeit big amounts in the city centre [of Genoa] are rare.” (1)
This is similar to–if heavier than– the typical snowfall pattern in Las Vegas. (4,6)
Summers are warm, with daily means of 73 F. (1,3)
This is similar to April-May weather in Las Vegas. (7)
The warmest months are July and August, when the average temperature is around 82 F in the day and 70 F at night. There are, on average, about 8 days each summer with temperatures rising to or above 86 F, in July and August. (1,3)
In Las Vegas, the summer months of June through September are much hotter. July is the hottest month, with an average daytime high of around 104 F. “On average, 134 days per year reach or exceed 90 °F, of which 74 days reach 100 °F and 7 days reach 110 F… During the peak intensity of summer, overnight lows frequently remain above 80 F and occasionally above 85 F.” (4,6)
‘Italian Large Leaf’ basil tolerates Las Vegas summers very well, considering that summer nights in the Mojave are generally warmer than summer days in the region where this basil is traditionally grown.
Summers are moderately dry, but only one summer month has less than 1.18-1.57 inches of rain. (1,3)
Rainfall is far scarcer than this in Las Vegas, with an average of around 4 inches of rain for the entire year, most of it falling in winter. Most summer days are hot and dry, but the North American Monsoon generally brings some thundershowers and increased humidity to the area around July and August. (4,6)
1 “Genoa” article, Wikipedia. https://en.wikipedia.org/wiki/Genoa#Climate
2 “Köppen climate classification” article, Wikipedia.
3 “Naples” article, Wikipedia. https://en.wikipedia.org/wiki/Naples#Climate
4 “Las Vegas article, Wikipedia. https://en.wikipedia.org/wiki/Las_Vegas#Climate
5 “Average Annual Sunshine in American Cities” page, Current Results: Weather and science facts website.
6 “Nevada” article, Wikipedia. https://en.wikipedia.org/wiki/Nevada#Climate
7 “Climate Las Vegas – Nevada” page, U.S. Climate Data website