Tamarillos
Jason Goh – Pixabay.com

New Zealand horticulture has a reputation for turning obscure fruits into success stories.  From Chinese gooseberries (now recognised far and wide as kiwifruit) to feijoas, it seems we can take a species little-known outside of its native range, cultivate it successfully in our amenable climate, make it a domestic favourite, and then more often than not, turn it into star on the international stage.  The tamarillo, Cyphomandra betacea (syn. Solanum betaceum), formerly known as the tree tomato, or ‘arbol de tomate’ in Spanish, fits neatly into this category.  My first encounter with a tamarillo was at the age of about eight or nine years of age.  Every Thursday, I’d accompany my Mum on a trip to the (big smoke) of Blenheim after school – it entailed a music lesson and a swimming lesson for me, shopping for Mum, and then a trip to a small fruit and vege stall just south of town before heading northwards home.  I’d obviously been eyeing up the tamarillos for a few weeks, and who wouldn’t be fascinated by their exotic shape and ruby-red hue?  Mum was pretty good about letting me try new things (but always with the proviso “as long as you eat it”) but the lady who owned the stall very kindly nipped off up to her house, returning with a teaspoon and a little pile of raw sugar.  She sliced a tamarillo in half so I could eat it on the way home – it was great.  If somehow you’re reading this, Mrs Rainbird, I haven’t forgotten, and thank you.      

Tamarillos: a short family history

Tamarillos belong to the Solanaceae, or nightshade family, along with the familiar potatoes, tomatoes, capsicums and eggplant.  Close relatives in the edible fruit line also include pepinos, cape gooseberries, tomatillos, naranjilla and casana.  Many New Zealanders may also be familiar with the native poroporo (Solanum laciniatum or S. aviculare), definitely not recommended for consumption, but a fast-growing coloniser of cleared land, with conspicuous purple flowers followed by bright-yellow fruit that resemble miniature tamarillo fruit in shape.  Like many members of this family, the tamarillo originates from South America, and the New Zealand Tamarillo Growers’ Association reports they were actually introduced to New Zealand via Asia in the late 1800s, with commercial production beginning in the 1930s, albeit on a small scale.  Yellow and purple varieties arrived initially, then a red-fruited cultivar was bred at Māngere East in the 1920s.  The name tamarillo was coined by New Zealand Tree Tomato Promotions Council member W. (Bill) Thompson and was adopted on 1 February 1967, replacing ‘tree tomato’ to prevent confusion with actual tomatoes and to make the fruit sound more appealing in the export markets.  The name was chosen to blend Māori and Spanish elements, acknowledging the South American origins of the fruit and the culture of Aotearoa.  This versatile fruit plugs the hungry gap in the year-round fruit harvest schedule, ripening from late autumn right though until spring.  As tamarillos have become increasingly expensive to buy over the years (you’ll be lucky to find them selling for less than $10/kg), it is well worth giving a plant or two a go in the home garden if you are an aficionado and the climate is right.         

Suitable climates and growing conditions

Tamarillos are subtropicals, tolerating only light frosts, and are also sensitive to high heat environments and drought conditions.  They will not tolerate waterlogging or having wet feet either, and being large-leaved, smallish trees or shrubs with soft, semi-woody and fairly brittle stems, need protection from wind as well.  They are fast-growing but short-lived when compared with other fully-woody tree crops: you can expect a crop after 18 months, and a well-cared-for tree to produce reliably for seven to eight years, but no more than ten or twelve at most.  You can anticipate a harvest of between 10-30 kg of fruit per tree each season; cultivar, tree health and age depending.  Commercial growing regions are largely restricted to the northern North Island, but tamarillos do thrive in the mild climate of the South Island’s West Coast, especially in zones to the north such as Karamea.  Most commercial fruit is sold on the domestic market, with a small quantity exported to countries such as the USA.  Those further south may be able to produce fruit in a glasshouse or tunnelhouse – as the plants have a small, shallow root system, container culture is possible and even beneficial in cooler climates, as the trees can be moved inside for winter.  In the more marginal areas, but where outdoor culture is possible (e.g. the upper South Island) plants will do well tucked in a sheltered spot under the eaves of a house, or in a semi-enclosed courtyard. 

The plants are self-fertile and pollinated by wind and insects, with fruit set enhanced by planting more than one tree in close proximity.  Flowers appear from late spring through summer (cultivar dependent) and it is about eight months from flowering to harvest.      

Propagation

Tamarillos can be propagated readily from seed, or from cuttings. Growing from seed will give a degree of variation from the parent plant in the resultant generation of seedlings, whereas plants grown from cuttings will be clones of the parent plant.  Seedling-grown tamarillos grow straight up with little branching - it is recommended they are topped at a height of one metre to encourage branches to develop, and that the central growing tip is removed at about 1.5 m to promote side branching and overall growth.  Cutting-grown plants have a more shrub-like growth habit, with plenty of branches.  The disadvantage is that some of these branches may be too low-growing and require removal, so they don’t drag on the ground when heavy with fruit or detract from the formation of a proper tree structure.  If you lack the time, resources or inclination to raise your own tamarillo plants, most good garden centres will stock nursery-grown plants – look out for the ‘Incredible Edibles’ range.   

To grow from seed – wash the seeds to remove the fruit pulp.  You can add pectinase, a fruit flesh-degrading enzyme available from winemaking supply stores to help with this step – ¼ teaspoon to 200 ml water and soak the seeds in this solution for 48 hours.  If you want to prevent mould growth, rinse the clean seed in water with a few drops of Janola added.  Dry the seeds on plastic, and then stratify (chill) in the fridge for approximately 24 hours (these steps are not essential, but desirable for optimum germination). Sow in trays or pots of seed raising mix, and place in a propagation house or similar protected environment.  Germination takes approximately five days.  If you are not using all of your seed immediately, it can be frozen for later use, and this also takes care of the stratification step.    

To grow from cuttings – select healthy one to two year old wood and take cuttings 30-50 cm in length.  Cut the bottom of each piece just below a node, and remove most of the lower leaves.  Plant in pots or trays containing a free-draining propagation mix (the majority of which should comprise sand and pumice).  Place in a protective environment as for seedling germination, and don’t allow them to dry out or be overwatered.  Dipping the cuttings in a rooting hormone gel or powder prior to placing in the mix and/or placing the tray or pots on a heat pad may help increase your strike rate if you have access to these resources.

Site selection and planting

After the danger of frost has passed in the spring, choose a site which has a reasonably (but not overly) light soil type, with a decent amount of organic matter, and dig in a dressing of blood and bone or sheep pellets.  If waterlogging may be an issue, site your tamarillo in a sloping position to assist with drainage.  Allow at least a metre between plants.  The tamarillo’s large, soft leaves (which to me smell strongly of popcorn when crushed or brushed against) are easily battered by wind, as is the brittle wood, so install a sturdy stake and some windbreak cloth if there is no natural shelter present.  Frost cloth may also help nurse plants through the colder months and help protect the new growth of older plants in early spring. 

Culture and care

Side dress the tree with compost in early spring and again in mid-summer – an organic mulch will help supress weeds around the base of the tree as well as help conserve soil moisture, just remember to keep any mulch material clear of the trunk itself.  A seaweed-based foliar spray can also be beneficial for optimum plant health and nutrition, and may assist with fungal diseases.    Tamarillos are shallow-rooted, so when you are weeding around the base of the tree, do not cultivate the soil too deeply.  You can apply a general NPK fertiliser regularly in the spring to maintain new growth and assist with fruit development; the total quantity should not exceed 1 kg per mature tree, split into at least three applications about a month apart.  Ensure adequate water is provided, especially in dry conditions in the heat of summer, but take care not to overwater either. 

Pruning

Tamarillos produce their fruit on the current season’s growth.  Mature plants should be pruned in spring, once the danger of frosts has passed – this will stimulate new fruiting growth.  The earlier you prune your tree, the earlier it will produce fruit, so this is good to keep in mind, especially if you have several trees and wish to stagger the harvesting of your crop.  Follow the general pruning guidelines of pruning out any dead, damaged or diseased branches, as well as those crossing over others or crowding the structure of the tree.  In frost-prone areas, you may find that the frost does some preliminary pruning for you!  On mature trees, cut back lateral branches once they have fruited.  Left unpruned, unchecked growth will extend the branches unnecessarily, pushing the fruiting zone further away from the centre of the tree.  Because the wood is so soft and brittle, having overly long branches with fruit right at the tip can cause them to snap.  Remove the suckers from young trees, and low-growing branches on shrubby, cutting-grown plants.  

Pests, diseases and what to do about them

The most significant insect pests affecting tamarillos in New Zealand were traditionally aphids, whitefly and green looper caterpillars.  In 2006, the tomato potato psyllid, Bactericera cockerelli (TPP), entered the country and had a devastating impact on all crops from the Solanaceae.  Tamarillos were hit especially hard, given that they are perennials, not annual crops that are able to be replanted afresh each growing season.  TPP not only cause mechanical feeding damage, but also transmit a bacterium, Candidatus Liberibacter solanacearum (CLso) which causes an additional set of damaging symptoms within the plant.  Look out for leaf yellowing, leaf curling, plants with generally stunted growth and misshapen fruit.  The insects themselves look like tiny black cicadas with a white stripe on the abdomen and will jump if disturbed.  They excrete a sugary exudate covered in wax, known as ‘sugars’ as it resembles tiny grains of sugar.  Bright orange eggs are laid on stalks on the upper and lower surfaces of leaves, and particularly around the leaf margin, where they look like tiny Christmas lights.  Nymphs (light green to orange-brown and dorsoventrally flattened, favouring the undersides of leaves) hatch from these eggs and grow through five instars before the adult insect emerges.  Commercial growers now must implement a fortnightly, year-round insecticide spray programme to remain commercially viable, but can still end up replacing 5-30% of their plants annually due to the effects of TPP and CLso – in years with warmer winters which allow extra generations of the TPP lifecycle, even with a spray programme the plant losses will tend towards the higher end of the scale.  In the home garden, insect pests on tamarillos can be kept in check with a neem oil spray early in the season, follow-up mineral or vegetable-based oil sprays (which have a smothering effect), or a combination pyrethrum and oil-type product.  In areas where TPP are a particular issue, Yates produce an insecticide concentrate designed for home garden use called Success Ultra, derived from a soil bacterium, which is effective against TPP.  With any of these applications, take care to target the undersides of leaves in particular, as this is where these small beasts like to shelter.       

In New Zealand, tamarillos are affected by a number of plant viruses, many vectored by pest insects such as aphids.  The viruses cause a range of symptoms, including interveinal yellowing on leaves, and chlorotic (bleached white) patterning on leaves and fruit.  Growing plants from clean seed helps eliminate viruses at the propagation stage, whereas any infected plants used for clonal propagation via cuttings will transfer the virus to their offspring. 

In terms of fungal diseases, powdery mildew is the main problem for tamarillos.  Ensure good air movement around your trees by maintaining a minimum of 1-1.5 m spacing between plants, and avoid overwatering, to encourage environmental conditions unsuitable for the pathogen. You can try treating any outbreaks using a spray made by diluting milk 1:10 with water, baking soda and water (1 tsp per litre of water), a mixture of the latter, or a commercial sulphur preparation (e.g. flowers of sulphur) applied according to the label directions.       

Varieties: My top picks

The most common tamarillo varieties available in New Zealand are either red or yellow-skinned.  The red varieties are generally sharper and more acidic, with yellow-orange flesh and black seeds (and some say a superior flavour).  Cultivars include Red Beau (an early variety developed by the government research programme and licensed for commercial growers), Ted’s Red, Tango, Mulligan, Laird’s Large, and Oratia Red.  Laird’s Large was developed by grower Allan Laird over a number of years and generously shared amongst the tamarillo-growing community.  It is a lower-acid, sweet, large fruit which grows on a larger, rangy tree.  The gold or yellow-skinned varieties are somewhat milder in flavour, with the skin, flesh and seed pulp all being yellow.  My tamarillo-growing friends caution that the latter can have a small, hard, stony growth about the same size as a seed in them, and tamarillo connoisseurs with dental work should be aware of this!  Cultivars include Goldmine and Bold Gold.  There are also a few amber-coloured cultivars which bridge the flavour profile gap and form a happy medium between the tart red and mild yellow cultivars, so keep an eye out.  

When harvesting tamarillos, make sure to leave the long stalks intact to ensure they store soundly.  Harvested fruit will keep for about two to four weeks in a cool storage area, and longer under refrigeration.  

What to do with your crop

I’ve always preferred to eat tamarillos fresh, simply scooped with a teaspoon, with or without a sprinkle of sugar.  Any fruit that gets away on me and becomes overripe is mashed up, mixed with stewed apple (try 50:50 to start) and dehydrated on solid trays to give an interesting, almost savoury fruit leather.  The pulp freezes well if intended for this purpose. 

I’m not really a fan of cooked tamarillos, but I know people rave about tamarillo chutney and recipes abound for using the fruit in cooked dishes, not only desserts such as crumble but also in meat dishes in place of actual tomatoes.  I’m yet to try them in a sandwich but I hear this is also an acceptable use! 

Browne, Leach and Tichborne’s excellent “The Cook’s Garden – For cooks who garden and gardeners who cook” (Reed, 1980) offers many excellent New Zealand-centric suggestions for preparing and using tamarillos, among them serving the fruit simply peeled and sliced as an accompaniment to curries. They also recommend serving the uncooked fruit as a breakfast or dessert item after slicing and layering with sugar, then leaving to macerate for eight hours so a syrupy juice forms.  They also provide an ingenious technique for peeling: pour boiling water over whole fruit, leave them to stand for a few minutes, then impale each on a fork and use a knife to help peel off the softened skin. 

In the process of researching this article, I also found many references to traditional South American uses for the fruit, one in particular that piqued my interest, and that is using the fruit to prepare various types of salsa.  The Peruvian method involves grilling the fruit first to aid skin removal, then mixing the chopped flesh with diced green capsicum, salt and pepper.  Once Ecuadorian recipe uses fresh, uncooked tamarillos with the more familiar additions of lime juice, coriander, chilli and onion.  Recipes also abound for a type of hot sauce made with tamarillos, chilli and occasionally the addition of ‘lupini’ beans – literally the prepared seeds of certain species of lupin, popular as a snack food in Latin America and Africa.  I can see that I’m going to have to branch out and change my tamarillo-eating habits and I hope you do too!     

The New Zealand Tamarillo Growers’ Association has a wealth of information available on its website: https://www.tamarillo.com/   

Anna-Marie Barnes is an active member of the New Zealand Tree Crops Association who endeavours to grow and preserve as much of her own fresh produce as possible.  When the weather’s no good for gardening, she can usually be found inside working on a batch of homemade cheese or soap.    

The New Zealand Tree Crops Association is a voluntary organisation promoting interest in useful trees, such as those producing fruit, nuts, timber, fuel, wood, stock fodder, bee forage and other productive crops.  Find out more about the NZTCA here: https://treecrops.org.nz/