SCIENTIFIC NAME: Citrus species
FAMILY: Rutaceae

I garden in Raleigh, NC (a state on the Eastern seaboard of the US.), considered by the US. Dept. of Agriculture to be a Zone 7 region, which basically means that our winter-time temperature will dip down to 0 to 10 degrees F. Needless to say, this is not the ideal growing conditions for tropical plants. But with a greenhouse, a willingness to pay outrageous heating bills, and a rabid obsession for tropical plants, one can have a little piece of the garden of Eden.

Just before I graduated from college I began interviewing for jobs in the computer science field. Luckily, I received an offer to come down for an interview with the National Aeronautics and Space Administration at Cape Canaveral in Florida in November 1981. The interview went well and I was quite impressed with the space program and the potential job that I was going for. But what I remember most about that trip was the citrus trees growing in the surrounding area of Cape Canaveral. I thought to myself, how nice it must be to come out in the morning and pick a fresh grapefruit for breakfast. Once I returned home from that trip, I began the challenge of learning how I could possibly grow a citrus tree in my climate and most importantly, where I could get one. After several weeks of scanning every gardening magazine and book I could find, I located a mail-order nursery in California that sold citrus trees. And to my benefit they sold dwarf forms of citrus trees. I immediately ordered a lemon, orange, and grapefruit tree.

Now, 15 years later, my enthusiasm for tropical and exotic plants is still as strong as it was then. Until a couple of years ago, I had 122 different citrus cultivars. But sadly, I have had to find other homes for many of these trees. Even when grafted onto dwarfing rootstock, a citrus tree does require a significant amount of room in the greenhouse. Through a difficult and painful process, I have narrowed down my citrus collection to the blood oranges, citrus with variegated foliage and the potentially cold hardy citrus.

Currently I am testing 7 different citrus varieties for cold hardiness. They have all been grafted onto Poncirus trifoliata rootstock in an effort to enhance cold hardiness. Poncirus trifoliata is completely cold hardy in my climate and is sold in nurseries as an ornamental shrub. The following trees were set out in the garden in June 1996 and as I write this article they are currently sustaining temperatures of 12 degrees F.

Common nameLatin NameOrigin
Khasi PapedaCitrus latipesNE India
Ichang PapedaCitrus ichangensisSW China
Nanso DaidaiCitrus taiwanicaTaiwan
SanbokanCitrus sulcataJapan
Sinton Citrangequat(Poncirus trifoliata X C. sinensis) X C. fortunella)U.S.
US119(Poncirus trifoliata X C. sinensis 'Succari')U.S.

Although it will be several more weeks before I will know exactly how cold hardy these varieties will be, to date they seem to be tolerating the low temperatures quite well, with only partial leaf burning. The big test will be the month of March, when our spring will cause the buds to swell and night-time temperatures can, on occasion, drop down to 15 degrees F. I suspect such cold temperatures at this vulnerable time may prove fatal. Hopefully, in the coming months, I may be able to report that I have found a truly cold hardy citrus.

Although citrus is my passion, I grow quite a few tropical ornamentals that have proven hardy. The 'Pink-finger Banana', Musa velutina, is a real show-stopper in the garden. It has been cold-hardy in the ground for almost 10 years, never failing to produce a bountiful crop of fruit each year. This banana is extremely easy from seed, even if left on top of the ground through winter. A number of the flowering gingers are proving their perennial status. Among them, Zingiber mioga.

Alpina japonica, and a large number of the Hedychiums. One particular plant genus that I have recently gotten interested in is Amorphophallus, or commonly known in this country as the Voodoo lily, is also proving to be cold hardy.

For me, gardening is more than just a hobby, it is a lifelong passion. And when it comes to expanding one's gardening horizons, experimentation not only brings some disappointments, but splendid discoveries too.

Jim Wait, Cairns

DATE: November 1988

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