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
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
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.
The 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
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
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
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
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.
The 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.