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Avocado Fuerte
by Laurie Meadows

Summary: The Fuerte avocado tree is a cold resistant (for an avocado) selection from a cross of Mexican and Guatemalan type avocados. Fuerte is a very high eating quality winter and spring fruit, and flowers prodigiously from may to november (generally), but Fuerte has a high winter temperature requirement for fruit set. In cooler positions and cooler years it produces very few or even no fruit, although it may produce a number of tiny, poorly ripening seedless 'cukes'. It is a 'B' flower type. Early set fruit are much superior to Hass early set fruit in july, but its erratic fruit set in cool conditions makes it more suited for the warmest areas of New Zealand - and the very warmest aspects within those areas.
Up until very recently, we have had only one Fuerte tree here. The tree is over 20 years old, and is shaded by shelter trees to the north and east. Fuerte trees fruit poorly in cold conditions, so it is no surprise this Fuerte tree gives only a few fruit in most years, and in some years none. We have kept the tree because Fuerte is a very high quality avocado in the winter season. A new Fuerte tree has been planted in a warm situation with good shelter and cool air drainage. Fuerte is still a very important cultivar in some countries, but it is only being planted as a home garden fruit in New Zealand (if you can find a plant). These notes on Fuerte have been complied to help the home gardener.

Before Hass, Fuerte was the industry standard avocado in California. Fuerte is, like Hass, green when unripe. Unlike Hass, Fuerte is also green when it is fully mature and ripe. Prior to Hass, the major supply of avocados were green skinned.

Fuerte was first propagated in 1911. It was propagated by a Californian nursery, from imported buds of a seedling tree growing in a garden in Atlixco (1,874 meters above sea level), in Puebla State, Mexico. This tree was noted for its production of very good quality fruit. A particularly hard frost hit Southern California in the Northern Hemisphere winter of 1913 -1914, killing many of the grafted avocado trees in the local nurseries. However, the as yet un-named new import was relatively undamaged, so it was given the Spanish name 'Fuerte', which means 'strong'. Ironically, while the Fuerte tree is relatively cold hardy, it needs warm temperatures for the flowers to set fruit.

The Rodiles avocado groves in Atlixco had seed propagated the best local avocados for generations, and had thousands of bearing trees "of unusually high average quality". It is a mark of the generally high quality of these seedling trees that another variety, 'Puebla', was also selected from these groves at the same time as Fuerte. (Puebla is a Mexican type, about 170 - 450 grams, it has a large seed, the fruit is oblate, with a thick leathery purple red glossy skin and good flavored flesh. The American avocado explorer Popenoe wrote in 1918 that the parent trees of both Puebla and Hass are Mexican, but Fuerte, in particular does not resemble any part of the population of avocados in that orchard, and it distinctly different.)

Early USA work in attempting to cross Fuerte with other avocado varieties resulted in fruit roughly intermediate in character between the two parents. However, the crosses were done by hand, an extremely labor intensive process, so no further work was done on controlled cross pollination. Later, Dr. Bob Berg grew Fuerte trees in isolation blocks so that the seed had to have arisen from self pollination. Of the 470 seedling progeny, hardly any fruited, and of those that did, "a tiny portion of Fuerte seedlings had fruit of fair quality". There were many cukes, many elongated necks, and many with very large seeds. Interestingly "many produced warty fruit"

This was in contrast to Hass selfed seedlings grown in the same way, which produced many promising fruit, overall of high breeding worth. As a result, the breeding program accented Hass heavily, and Fuerte not at all. Fuerte, in America at least, had become yesterdays fruit. King.Hass now rules.

Fuerte is a hybrid of the Mexican and Guatemalan types (confirmed by Schnell et al. 2003, on satellite markers). The maternal parent tree was believed to be Mexican. Fuerte is cool temperature tolerant, has thin skin, and anise scented leaves (when crushed), all Mexican characteristics. The superior flesh quality is regarded as characteristic of Guatemalan avocados.

fuerte fruit shapefuerte fruit, flesh and seedThe fruit are obovate (bluntly oval shaped, not as wide at the stem end), although under some climatic conditions the neck can be quite narrow. The fruit weight ranges from about 250 to 450 grams (commercially, a 'large' grade Hass is 340 grams or more). This makes the fruit size range from small to large (relative to Hass).

The skin color is green with many tiny yellow dots, becoming a slightly duller green at maturity. The skin is relatively smooth, thin and pliable (although thicker than many Mexican varieties), and it doesn't adhere to the flesh underneath, so it peels well - an important attribute for the consumer. But because the skin is thin, it quite often splits around the basal end, mostly in the horizontal plane. The bottom part of the fruit is then often infected with rot fungi (Anthracnose), causing the skin to blacken and the flesh in that area to be "off". Very ripe fruit (those illustrated) may develop superficial black spots. If left, these will eventually affect the flesh immediately underneath the spot.

The seed is usually medium large, generally bluntly conic, but pointed-conic in longer, more 'necky' fruit (possibly more usual in warm growing conditions). The seed is tight in the fruit (it doesn't rattle when the fruit is shaken), but still separates cleanly from the flesh. The seed takes up about 15% of the total fruit volume.

The flesh is pale yellow, with a very good oil content. The oil content varies with maturity, but is around 12% to 22%. The flesh is smooth and buttery, with a rich flavor. The overall eating quality of a fully mature fruit is excellent. There is relatively little fiber in the flesh.

Sound fruit picked mature but hard don't bruise in handling and are generally not quite as subject to internal rots and the like as Hass is. This is an important reason for its former dominance as a commercial avocado cultivar in California - it could be shipped and arrive in good condition and ripen in the shops without too much spoilage. Fuerte has to be refrigerated at no lower temperature than 5oC, otherwise it develops brown or black cold-damage patches on the skin. (Most domestic refrigerators are probably set at about 4oC, and so cold damage can develop.) The flesh may also turn greyish when stored too cold. The greying of the  flesh doesn't usually affect the eating quality, but it is visually 'off-putting'. Mature fruit ripen at room temperatures about 7 - 14 days from picking from the tree.

When is Fuerte ripe?
The Fuerte ripening season in New Zealand's warmer parts is about august onward. In some years early-set larger fruit can be picked in july. However, the same comments can be applied to Hass, so Fuerte has no real advantage in most years (indeed, both Fuerte and Hass from Hohora in Northland appear in the shops in mid july in some years, and both cultivars are very good quality). The main season for Fuerte is about mid august to october (depending on yearly variations), but late set fruit can hang on the tree past october (unless the skin is damaged). We picked an excellent fruit on the 27th of november in one year - and there were other fruit holding nicely on the tree for even later picking.

Northern New Zealand has always ripened Fuerte fruit about 6 weeks ahead of the main producing region in the Bay of Plenty, and our experience demonstrates that is some (rare) particularly favorable seasons fruit can be size-picked in june and produce highest quality eating fruit - infinitely better than Hass at the same time. A few examples - in the 2004/2005 season, an exceptionally warm period resulted in a few good sized early-set Fuerte fruit by early june. A 290 gram fruit picked on the 3rd of june ripened by June 19th - 15 days - and was delicious. In the 1998/1999 season, the 1999 'Indian summer' helped a few winter/spring 1998 early-set fruit to mature by June 7th. A fruit picked on that date fruit took until the 21st to soften (14 days), when it was full flavored and excellent.

Conversely, fruit picked here in mid august 1997 did not ripen properly, and they had only acceptable but mediocre flavor, and there was moisture on the surface when cut, indicating the fruit was not really fully mature.

Fruit from the Bay of Plenty was, in the past, also picked too early, in an attempt to cash in on the early season prices being achieved by Fuerte fruit from the far north. These too were watery, sweetish, hard to ripen, and of very poor eating quality. Immature fruit often ripen the basal part of the fruit only, leaving the neck hard and unyielding. The true main season for quality Fuerte in the Bay of Plenty is probably about the end of september - competing with new season Hass.

How do you tell when a Fuerte fruit is ripe, given that, unlike Hass, it doesn't become purple-black when it is ripe? Well, a fruit picked off the tree is hard as a rock. When it has a little 'give' when a little gentle pressure is applied by the palm of the hand, it is ready to eat. In fact, it is easy to tell when it is ripe because it has a leathery, pliable skin - unlike Hass's thicker more 'brittle' skin. As always, a ripe apple or banana  put in a paper bag (a plastic bag 'sweats' too much) with the freshly picked fruit will speed up the ripening process.

The Fuerte tree is vigorous, wide and spreading, a distinct disadvantage. Fuerte is one of the most cold tolerant avocado trees, with some researchers stating it will withstand a 3oC airfrost for a few hours without "serious" damage.

Fuerte is a 'B' type flowerer, and flowers over a very long period, so it overlaps many other varieties. It is also noted as a very good pollenizer for other varieties, in climates where outcrossing is important. Sadly, its flowers require warmer temperatures than many other varieties to set. In cool winter and spring conditions it will set few fruit, and sometimes none. In some years it produces seedless tiny cucumber shaped fruits known as 'cukes'. These develop when the pollen grows enough to initiate fruit set, but not far enough to successfully fertilise the the egg and form a seed. I have always found it hard to ripen these tiny fruit, and consider them largely a waste of time. Paradoxically, in situations where it is warm enough for fruit set, it will often bear heavily, and then have a very small crop the next year. While in hot climates Fuerte set is improved by proximity to 'A' type pollenizer trees such as Hass, in New Zealand it is likely to set with its own pollen - given temperatures at flowering time are not limiting. The temperature range in which self pollination is known to occur is 25oC days and down to no lower than 10oC nights. Warmer is better.

An added dimension to Fuerte is that there seems to be a genetically determined interaction between the rootstock and the graft, such that some trees produce little or nothing, while other trees in the same grove produce well. Some overseas growers (mainly in Israel) now propagate the rootstock of productive trees to ensure the graft on top will in fact be productive. This is not justifiable in New Zealand, as the Fuerte variety is not grown commercially.

Fuerte is a spreading treeThe tree is spreading and relatively low. It doesn't  have a dominant main trunk, the side branches are relatively short, and the flushes of new shoots on the side branches produce laterals as they grow, adding to the spreading canopy effect. The heavily pruned tree in the photo on the left shows one of the the 45o angle major trunks and some of the major branches coming off the trunk at about head height. Sheep have browsed the foliage to about 1.6 metres - the canopy would otherwise go down to the grass. In a mature unpruned tree, the interior of the tree forms a 'room' devoid of branches, as it is heavily shaded by the outer canopy.

Left to itself, Fuerte has quite wide 'footprint'. It is not the cultivar you would want if you don't have much space. It may be possible to force it to grow as an upright central leader tree, but the strong growth flushes would have to be ruthlessly pinched back throughout the growing season, or it will revert to its spreading, multi-branch form. To my knowledge, no-one has attempted to grow Fuerte in this manner.

Like all avocados, Fuerte flushes whenever the temperatures are warm enough for growth, which means spring, perhaps also a summer and/or autumn flush. When the weather turn cold growth stops, and the bud just under the terminal bud becomes a dormant flower bud.


Fuerte starts flowering earlier than most avocado cultivars (about august here, but in some years it starts in early may, but nothing sets). The Fuerte flower season also continues for longer than most other varieties (august to november in our conditions). However, as warm temperatures at flowering are absolutely critical for Fuerte, it is really only the spring flowering that has the best chance of a good fruit set.

As early as 1951 workers in California observed that "When the maximum temperature did not exceed 70°F 21oC. and the minimum 53°F/11.6oC., Fuerte, a type B variety, either had no fully-expanded Stage I (female) flowers, or they appeared so late in the day that pollination was unlikely." That is, where the minimum temperature does not rise above 11.6oC and the daily maximum is 21oC or less, Fuerte flowers are either all male (female flowers simply don't open) or the female flowering is pushed so far into the afternoon that few or no pollinating insects are around..In mid october 2005 we had a period of warm settled weather, and the Fuerte tree produced large numbers of flowers that attracted very large numbers of pollinating insects - mainly blowflies, bees and other dipteran insects. There was an excellent fruit set, and very good crop matured in 2006 as a result. Exceptionally warm, calm weather at the right time in spring can bring very good results. But you wouldn't want to bet on the weather in New Zealand...

Fuerte flowers  produce copious amounts of pollen, and it is a good pollenizer variety for Hass, in those years when cross pollination for Hass and Gwen is useful (probably rarely the case in New Zealand). Fuerte also has ample pollen at the time the very earliest Hass and Gwen flowers open. Whether this is in any way useful for early Hass or Gwen fruit set is moot.