The kumquat is the hardiest of the popular citrus, but not much hardier than oranges—perhaps ten degrees at most—while the fruits are uniformly small and sour. They are another ingredient capable of mixing into the hardy citrus recipe.

My first crosses of kumquat were undertaken not for the purpose of creating hardy seedlings, but to test the longevity of pollen in storage. I made crosses on one small Nagami plant in a tub: a third to old P. trifoliata pollen, a third to new P. trifoliata pollen, and a third to Meiwa. There were no takes from six-week-old pollen, six from new pollen, and twelve from Meiwa.

Of this last cross, I grew out the seedlings, which were called NaMeiwa. One of these was seedless, but with sterile pollen, and seeds appeared no more often than once in ten fruits. Its progeny, in turn, seemed to show no variation, and must be a stable nucellar type, uninfluenced by any of several different pollens.

Another of the progeny produced one long, rose-colored but wooden fruit, had high flower and fruit production, and was a potentially good ornamental—but the least cold-hardy kumquat ever seen, and gone fifteen or more years ago.

Four others were intermediate in characteristics between Nagami and Meiwa, and one came to be called Nameiwa #1, being quite seedy like Meiwa, with a more peppery peel than either parent, but producing a fair number of hybrids as a female.

One of the more memorable of these was by Glen Citrangedin, itself a citrange × calamondin hybrid. The Nameiwa #1 × Glen hybrid showed enough trifoliate leaves at an early stage to identify it as progeny of Glen pollen. It produced calamondin-like fruits; the tree was hardier and the fruit prettier and larger than calamondin, but less hardy than Glen. It came to be called Clusterquat because of its heavy fruiting in clusters. Bill Chapman, who has survivors growing in the Rio Grande Valley, calls it Clustermondin. Mine was lost in December 1989.

The obvious first choice of work with kumquat is the cross with P. trifoliata. Six seedlings were obtained, and all died out the first year or so, except one grafted on Severinia, which merely hung on for possibly six or seven years. I do not recall why it never got onto a P. trifoliata rootstock. One graft on Meiwa kumquat grew like a storm one summer, but was killed back by the first cold of winter.

One ‘Ruby Red’ grapefruit grafted high up in a Yuzu tree did the same thing once, and from the two experiences I still cannot isolate the cause—whether weather, scion, or stock.

Dr. Olson showed me a trifoliate Hong Kong kumquat (Fortunella hindsii), which I was unsuccessful at establishing by grafting here. We did produce one plant of Nagami × F. hindsii, which grew beautiful dark-green leaves and was quite prolific of Nagami-sized fruit, with flavor dominated by F. hindsii. The F2 seedlings were quite similar but variable in vigor, and no F2 ever fruited.

At the same time I became reacquainted with the Meyerquat, a hybrid between the fruit known as Meyer lemon in California and a kumquat. The Meyer lemon itself is a probable kumquat × lemon, so this makes the Meyerquat an F2 kumquat backcross. The Meyerquat is a juice fruit for blending—a sweet-sour blend of its own—with a sweet albedo (the white underpeel) like the other kumquats and Yuzu.

Like its kumquat parent, the Meyerquat is relatively seedy and extremely polyembryonic. When backcrossed again, either to Nameiwa or Nagami, the resulting NameiMQ and NagamiMQ give bushes yielding seedless fruits when not pollinated by other citrus. If the fruits are the result of selfing, they are somewhat sweet. The NameiMQ will produce seedy, woody fruits if pollinated by P. trifoliata. Such seeds will all be nucellar.

The most successful, and most widely propagated, hardy hybrid of kumquat is the citrangequat. While the direct hybrids of kumquat and P. trifoliata were not viable, those using the P. trifoliata derivative citrange have been worth making over and over.

Thomasville Citrangequat was another early hardy hybrid of Dr. Swingle’s from Florida and has stood the test of time. It is the workhorse— as hardy as any here—and we grow it still for its own sake and as a parent. It is one, if not the only, quarter-progeny of P. trifoliata which can be eaten peel and all. Even this is an acquired taste, however, and Thomasville is still by no means a dessert fruit. Any kumquat has a thicker, softer, and sweeter albedo.

If frost should knock it out of early spring flowering, it will usually rebloom a little later, and those fruits will ripen in their normal season.

We used Thomasville citrangequat as pollen parent with Clementine tangerine. The few seedbox survivors were planted at William Chapman’s in League City about 1970 and fruited sometime in the early 1980s. The flavor was worse than Thomasville, and though it made some early indications of being hardier, it was erased from the list by the December 1989 freeze.

We also used it as pollen onto Nagami kumquat, in a backcross. Three plants were produced, and one—grafted onto P. trifoliata root in a favorable location—shot straight up eight to ten feet and produced kumquat-like leaves and very Nagami-like fruit. Our original plans were to backcross again to Thomasville for analytical purposes, but that did not happen before a frost in December 1983 cut the experiment short. We could have expected some seedless progeny of crosses to Meiwa or Meyerquat.

Two siblings left in a less favorable corner lasted until December 1989. This freeze was our century’s worst in East Texas, and spread temperatures from zero in Franklin to five above in Houston. It did, understandably, prove a watershed in the history of my hardy citrus hybridizing.

The Chinotto is a peculiar citrus, long believed to be a form of the sour orange (C. aurantium), but more likely a hybrid. The chinotto is better known in Italy than in the United States, but it may fairly be described as a small, flattened, sour orange midway in size between calamondin and tangerine. The flavor is sweet, but the peel is decidedly bitter, and it is used in various tonics in the Old World.

It has two advantages: chinotto is the hardiest of oranges, and the tree is naturally dwarfed. The leaves are crowded together, with very short internodes. It is not, however, so hardy as to be able to stand on its own here at Franklin, or even at Westfield or League City, so we may conclude that it confers slight hardiness, if any.

Chinotto produces some hybrids as a female. The Citradia, also called CiChinotto or Chinottotri, is a hybrid with P. trifoliata. It is fully hardy and produces flowers prodigiously and in flurries. One such event Chapman and I caught at the old place on Shady Nook in mid-July 1990, and we pollinated it to NameiYuzquat and Murami kumquat.

It is of great hardiness and productivity, and very bad flavor. This survivor, which we call ‘Large-leaf’ (sometimes ‘Purple-flower’) Citradia, bears annual crops of undesirable fruit and becomes ever less promising as a female parent, especially as we examine the most recent season’s progeny.

The other CiChinotto was dwarf, with small trifoliate leaves crowded on short internodes. It was kept for a while on a P. trifoliata rootstock, and there was no improvement in vigor after grafting onto sour orange stock. Eventually, this dwarf disappeared from sight.

The Changsha is a hardy citrus from the middle latitudes of China. Since its introduction to the United States, it has been identified as a form of mandarin. It seems considerably hardier than either the conventional mandarins or Satsuma, so it must have an admixture of hardy exotic ancestry somewhere. Its origins are lost in Oriental antiquity, but it is certainly older than Yuzu.

Following the freeze of January 1961, we made some crosses of Changsha. This was at the Boyle orchard at Friendswood. His Clementine tree was about the only thing available to receive pollen, so we dosed it with Changsha pollen from College Station. A single tree came out of it, which was a worthwhile upgrade of Changsha for fruit quality, and of comparable Changsha hardiness.

The two ChangshaYuzu are hardy progeny of Changsha. They were identifiable at the embryonic stage as two white cotyledons among green (nucellar) polyembryos. Both were hardy enough to survive the Decembers of 1989 and 1990.

ChangshaYuzu #1 is vigorous and productive in alternate years, but quite sour, with many rather dry fruits, and no fruit at all after the last two years of freeze. Its counterpart, ChangshaYuzu #2, is a much less vigorous, willow-leafed tree, but produced sour, juicy fruit instead, and made one fruit after the severe freeze of December 1989.

ChangshaGlen was Changsha × Glen citrangedin. Its progeny was of reasonable vigor and hardiness and was as sharply sour as any calamondin descendant; its size was about half that of Changsha.

A Changsha × grapefruit was also produced about the same time. It lived from 1964 to 1984 in the Boyle orchard at Friendswood, but never showed a sign of flowering or fruiting.

Changsha × Thomasville citrangequat survived with me for some twenty years, from Boone Prairie and back to Westfield, in reasonable vigor, but never once flowered or fruited. It was wiped out completely in December 1989 on both P. trifoliata and Namei-Meyerquat rootstocks.

We also hybridized Sanford citrummelo × Changsha, analogous to those made with Bloomsweet pollen mentioned under citrange. Twelve of sixty seedlings reached maturity in the backyard hedgerow at Houston, and ten of them fruited.

The resulting SanCitChang fruits were paradoxically larger than SanCitBloomsweets, all orange to bright orange in color except one progeny which was yellow. This one had the tightest, thinnest, smoothest, and brightest peel; it was the earliest to come to fruit and the most prolific, but it was tinged unmistakably with P. trifoliata flavor.

All were sour, even the one I could eat in the manner of a grapefruit. This one was quite large, but short of grapefruit size because of the thickness of its peel, and it was the most prone to winter damage. It did withstand 5°F (-15°C) in 1989, surviving to within three feet of the ground.

Another, SanCitChang #1, the largest and prettiest, but also the most seedy and least productive, did not survive that freeze.

A third sibling, SanCitChang #9, one of the best for size, color, and flavor but inferior for excessive seeds and segmentation, had large, round leaves quite unlike the others out of this cross.

The specimen growing at Westfield with SanCitBloomsweet #9 and Siam pummelo × Ichang lemon were intercrossed in all directions in the spring of 1988. The seeds of these were planted rather late that fall, and because of cold weather, only one possible hybrid—looking like ‘Round Leaf’—has survived to date, regrowing from the ground each year with three obvious Yuzus.

The mystery species Citrus ichangensis is likewise an ancient Chinese fruit, and is known only in cultivation—or at least trees found in the Szechuan countryside cannot be proven not to be abandoned dooryard trees from long ago. The species has been spread during centuries past to the northern limits of citrus culture, and is a common courtyard plant in China, usually grown in containers. It is the supposed parent of Yuzu, and the source of Yuzu hardiness.

A single plant grew in Franklin on its own roots without fruiting or flowering from the early 1960s until struck down by the freeze of December 1989. A graft of it on P. trifoliata in the 1960s grew like a storm, and flowered and fruited within four years of grafting. After two seasons, it had to be removed from the tree to give other grafts a chance to grow.

C. ichangensis, like Yuzu, does not flower or fruit for us on its own roots—only on P. trifoliata, in my experience. Seed for C. ichangensis, Yuzu, and Ichang lemon were supplied to us about 1960 by Lynn Lowry from his old home place in Sulphur, Louisiana.

There were a number of C. ichangensis hybrids besides Citemple, described earlier. C. ichangensis pollen produces sweeter hybrids from Changsha than does Yuzu, though only two of each have grown so far.

Changsha × C. ichangensis survived until December 1989, after having been killed to the ground in 1983. One selection produced leaves resembling the C. ichangensis parent, and was very productive in alternate years of small, thin-peeled, orange-colored fruit, bright orange inside, with two to four very large seeds—juicy and sweet but with a slight off-flavor of Yuzu.

Another selection, with leaves like Yuzu, fruited for the first time in summer 1989, with fruits a bit larger and sweet, thus prompting thoughts of further work with it—but it froze out that December.

There were hybrids between C. ichangensis and Bloomsweet. I had grafted a P. trifoliata rootstock to C. ichangensis at Houston, and it was in flower three years later. I wet one flower with saliva, blew it dry, and applied Bloomsweet pollen. Eight young trees were produced of this cross. They grew at Westfield, froze to the ground in 1983 but regrew, and two produced fruit in 1988.

The fruit were small but sweet, with russet spots on their thin peel that hot, dry August and September. The fruits will be remembered fondly by a number of tasters who had spent too many long years sampling P. trifoliata hybrids.

One Clementine tangerine × C. ichangensis produced perfect flowers during the years from the mid-1970s until it froze to the ground in December 1989. But the tree never set a single fruit. One switch of regrowth has appeared from the ground this year.

In 1987, I moved from Houston to Franklin. Many or most trees had been moved or repropagated in advance, either to my sister’s place in Franklin, or to the old Mitchell place on Boone Prairie ten miles north. Some few others were restarted after the move at the Luther Cole orchard a mile south of Franklin (his children had grown up eating Changsha mandarins planted in a protected space by his house until about 1979). Some trees too large to move, or just coming into fruiting, were left behind in the Houston area.

The move north had the incidental result of making my hardiness trials rather more rigorous. But the cold in December 1985 (to zero at Franklin, five above at Houston) resulted in about the same losses at both locations. It has reminded me what a fool I am.

The Yuzu is an age-old hybrid of Citrus ichangensis × mandarin, one which has been popular in Japan since before the arrival of Commodore Perry, so we may never know how far back it goes. It is grown on most of the islands of Japan, and is famous for its ability to burst into bloom at the moment of snowmelt. The Japanese count it as an edible citrus, but probably for culinary purposes rather than for eating out of hand. It is encountered more frequently now in the United States at the northern limits of citrus culture.

My first Yuzu hybrids were produced at the College Farm at Texas A&M, College Station. The big freeze of January 1961—of three days around the eleventh, I believe—dropped temperatures at College Station into the twenties by day and ten to twelve degrees at night. The experiment station lost one of two Changsha mandarins, their only Satsuma and only grapefruit, but merely defoliated the adjacent rows of Yuzu and one other which I recalled as Savage citrange but which Bill Chapman much later decided was a Sacaton citrummelo.

While working the Yuzu the following spring, I ran out of the pollen I had been using, and seeing the flowers on the neighboring citrange, I reached for one and used it. Out of the fruit formed of that Yuzu flower came the seed that produced two hybrid seedlings displaying P. trifoliata characteristics, doubtless from the Savage pollen.

In fact, the more vigorous of the two was unmistakably trifoliate all the way, and upon fruiting gave the impression that Yuzu can cancel the bad flavor of P. trifoliata. The other seedling, much the less vigorous, soon turned unifoliate (these things happen), and the one or two fruits we ever had from it are remembered as up to tangerine standards, but I no longer have it.

The YuSavange could instead be YuSacaton if Yuzu was pollinated by Sacaton citrummelo instead of Savage. The YuSavange has withstood one degree above zero at Franklin, being more than “twig-bit.” The original tree fruited at Friendswood before 1967, was eliminated at Tomball by cold in 1989; we await fruits at Franklin.

Meanwhile, at the Bales orchard in Friendswood, the January 1961 freeze eliminated five of thirty Satsumas; five were essentially uninjured and later bloomed but set no fruit, and the remainder were intermediate in degree of damage. The one Temple tangor and both Ponkan mandarins were killed; the Bloomsweet grapefruit and Nagami kumquats were injured, and I believe the various oranges also, as well as the single Clementine tangerine in the neighboring Boyle orchard.

It took a year for the Clementine to return to blooming condition, and when it did, it was pollinated to Yuzu. There must have been a great deal of seed produced, as I soon had two tubs of Clementine × Yuzu seedlings, later to be called ClemYuzu.

One selection, ClemYuzu 2-2, survives in fair condition as a mature tree in Houston, though its seedlings freeze to the ground repeatedly up here, and only about ten percent resprout from the ground. If it were only more consistent in producing its best every time, it would be our sweetest, best hardy hybrid citrus. However, it is prone to producing dried-out, juiceless fruit, overloading one year and producing none the next, in alternate bearing.

Another promising seedling of that group, ClemYuzu 1-5, did not survive the cold of December 1989. A third sibling, ClemYuzu 3-3, is in the possession of Stewart Nagle. The same clone, or one much like it, has received from us the self-explanatory name ‘Tingletongue’, a reference to the tingletongue or toothache tree—the “Hercules’ Club” of East Texas.

Selections of these ClemYuzu siblings were grafted onto a mother tree rootstock of P. trifoliata: ClemYuzu 1-1 through 1-6, along with ClemYuzu 2-1 and 2-2, and a limb of Satsuma monoembryonic for good measure, not to mention all five or six surviving Nagami × Meiwa kumquats, the YuSavanges, ClemYuzu 3-3, and Tingletongue on a neighboring multiple-grafted P. trifoliata in the Bales orchard.

The various branches bloomed and set fruit, and the resulting seeds from these were therefore open-pollinated. Some of those from ClemYuzu were saved and grown by Dr. Bricker, a friend of Bill Chapman. The progeny produced fruits that varied from typical tangerines to the “Kat” type of tangerine, like Tim Kat and Chou Chow Tien Kat, and the trees were hardy to about Satsuma level. These tend to be polyembryonic, and hopeless as female parents.

ClemYuzu 2-2 has produced large, sweet fruits with a minimal detergent taint of Yuzu, and survived perhaps five degrees above zero with only slight damage, but produced no crop the following year.

The basic hybrid of P. trifoliata × Yuzu, known as TriYuz, produced fruit that was a bland piece of wood, and though they were presumed perfectly hardy, December 1989 proved them otherwise—at least for older trees in Houston. Here in Franklin, seedling trees were only “twig-bit” at the edges, and flowered and fruited for the first time this year.

Other Yuzu hybrids have already been described under Sanford citrange. We also had, until December 1983, Yuzuquat, from Nagami × Yuzu. Another, called Nameiyuz, is Yuzu × Nameiwa #1, and produced a large, smooth, pretty lemon on one of our most vigorous and hardy trees. It is known elsewhere as ‘J-Lemon’.

It was a good juicer, though quite seedy, with sourness to the lime level and some Yuzu off-flavor when fully ripe, with the soft, non-bitter albedo of both parents. It was quite productive, with intermittent flowering year-round, like kumquats.

Professor Randall at the University of Houston had a trifoliate seedling from one of these Nameiyuz, which has always appeared structurally monoembryonic for most of its nearly twenty years of fruiting, but has never produced a verified hybrid.

Attempts at Yuzu × Bloomsweet grapefruit have not been brought to fruition.

Yuzu × Thomasville citrangequat was a promising hybrid, with which we may conclude. Among some twenty seeds to come out of the Yuzu fruit in this cross, there were only three variant seedlings: two of them rather less vigorous and less deep-green of foliage, but otherwise typical of Yuzu; the third bore trifoliate leaves and was of reasonable vigor.

The latter was distinctly less hardy than the Yuzu look-alikes—this suggests that hardiness and trifoliateness are not inseparably linked. We still cannot conclude anything about linkage of quality factors to either trifoliateness or hardiness, of course.

The trifoliate seedling was never brought to fruit before being laid low by cold. One of the less vigorous but more Yuzu-like forms was eventually worked onto P. trifoliata rootstock and brought to fruit in 1987. By that time I had moved to Franklin, and the new owner blindly mowed it down with a bush-hog tractor mower in the tall grass of August and September. Its fruits never reached maturity.

One not-too-distant summer, the third seedling succumbed to drought, having been missed one time too many outside the reach of the irrigation setup.