Fruit - Citrus in Tasmania

Introduction

Most Tasmanians believe that lemons are the only Citrus fruit that can be grown in our cool climate. However, a recent visit of our group to Ian and Jill’s garden in Sandy Bay, Hobart showed a garden in which eleven Citrus varieties are grown successfully. Ian and Jill showed that there is far more potential for Citrus in Tasmania than most Tasmanians think there is. They inspired me to write this blog post. It discusses how to look after Citrus trees and what Citrus varieties can be grown successfully in Tasmania.

General notes on Citrus

These notes apply to all Citrus varieties.

Buying a Citrus tree

Young Citrus trees are sold in pots because, unlike many other fruit trees, they do not go dormant and lose their leaves in winter. The best time to buy and plant a young Citrus fruit in Tasmania is October when soils begin to warm up.

Buy the earliest ripening variety of whatever Citrus you want to buy, as that will require fewer hours of heat, and hence be more suited to Tasmanian conditions.

All Citrus trees are grafted these days, so you get the benefit of good fruit and a rigorous root system. Inspect the graft before buying the tree. Make sure it is clean and healthy looking.

If you buy a compact Citrus variety or a Citrus tree that is grafted onto dwarfing rootstock, you could put it a half wine barrel or other very large pot. It means that in winter you can move the tree to a sunnier or more sheltered spot!

If the young tree bears any fruit at the time of buying, cut that off, as it will take away energy that is better spent getting established in your garden.

Planting a Citrus tree

In Tasmania only plant Citrus trees in Spring, as that gives them a long period to get established before growth stops in late Autumn.

Position all Citrus trees where they get the maximum amount of sun, light and heat. Soil needs to be well-draining, so do not plant a Citrus tree in clay. Soil does not need to be deep, as Citrus trees have shallow root systems. A spot sheltered from strong winds, along a north-facing brick or concrete wall with overhanging eves, while in front of the tree is a paved, concreted or pebbled area, is ideal. These materials store heat during the day, and keep soil and air temperature at night higher than they otherwise would be. A spot next to a pool or pond that reflects light and stores heat would also be great.

In gardens with clay soil, in order to get good drainage, consider planting your tree on top of a large mound of soil you create out of well-draining soil.

In Tasmania more compact Citrus varieties will do much better in a pot than in the cooler soil of your garden. Don’t choose a pot that is too small. A half wine barrel or a pot that is even bigger and deeper is your best choice. Feed the tree well twice a year, water it regularly, and it will be much happier than if it was planted in the garden!

Preparing the spot where you are going to plant your Citrus tree and planting it is done in the same way as for Peach and Nectarine trees. See the first section under Planting a Peach or Nectarine Tree in Food Garden Group blog post Fruit - Peaches and Nectarines.

Take care of its shallow roots

Citrus trees have shallow root systems. This means that weeds under Citrus trees will compete for water and nutrients with the tree roots. Keep the area inside the drip line weed free, the soil moist, but not wet, and mulch under the tree. Do not put fresh un-composted manures or fresh grass clippings under Citrus trees as shallow roots may get burned.

Water requirements

Regular watering and good drainage are a must for Citrus fruit. Irrigation is best done via drip lines under the canopy, rather than with overhead irrigation (see Food Garden Group blog post Improving your irrigation).

Split fruit on a Citrus tree is a sign of watering not being regular enough.

Mulching under Citrus fruit makes sure that the soil around their shallow roots is moist at all times. To avoid collar rot keep mulch away from the trunk of the tree.

Frost-tolerance

The Riverina is an agricultural region of South-Western New South Wales.  Its climate is hot and dry, ideal for Citrus. Occasionally frost hits the Riverina. Local Citrus farmers are very aware of the fact that  most orange varieties get less frost damage than most lemon varieties. This illustrates that to say that lemons are fine in Tasmania, but that most other Citrus varieties are marginal, is incorrect.

Frost can lead to leaves suddenly looking unhealthy, or worse falling off the tree.

Within the range of Citrus varieties that can be grown in Tasmania, some are more frost tolerant than others. A list in order of frost-tolerance (most frost-tolerant first) would look something like this:

Cumquat, Mandarin, Meyer Lemon, Grapefruit, Orange, Lemon, Tahitian Lime

One would expect the Lemon to be at the start of this list, but it isn’t!

Tasmanians living above sea level in areas that get some frost every winter might have no problems growing Cumquat, Mandarin and Meyer Lemon. In these areas consider covering young trees on frosty nights with hessian, shade cloth or thin clear plastic.

 

I was given the Tahitian Lime shown in the photos above with the question 'what has happened here?'. Apparently all the fruits on the bush were brown on the same side. It is a clear case of frost damage.

Frost-tolerance is not the only temperature factor that is important for Citrus.  Grapefruit is in the list above, ahead of lemon, but grapefruits need consistent heat over a period of time in order to become big and juicy.  This means that in Tasmania it is a lot easier to grow lemons than it is to grow grapefruits.

Fertilising a Citrus tree 

It is common for Citrus trees to produce a lot of fruit and therefore take a lot of nutrients out of the soil.  If you have a garden that gets frost, it is best not to feed Citrus trees in Autumn, as resulting new growth may die in frosty conditions in winter. Instead feed in early Spring when the chance of frost is over.

Citrus trees need plenty of nitrogen, so at least once a year feed the tree nitrogen-rich fertilisers such as Blood and Bone, Dynamic Lifter, other chicken-based fertiliser, fish emulsion, composted chicken manure, or other good quality compost. To avoid collar-rot make sure you keep it away from the trunk of the tree. Don't feed these fertilisers while the tree is flowering, because the flowers will fall off.  

Urine is high in nitrogen. Human urine comes free of charge, so you could certainly consider using it! Always dilute it with water, and apply it to the soil under the tree, not the leaves. Medical research has found no evidence that male urine is better than female urine (see under Recommended further reading).

Citrus trees perform best when a wide variety of trace elements are available in the soil. Spraying leaves regularly with seaweed extract is really good. The leaves of a Citrus tree will tell you whether the tree is happy or not. 

Yellow leaves with green veins is often caused by a lack of iron.  If every three months or so you mix a tablespoon of Epsom Salts (magnesium sulphate) plus a tablespoon of iron chelate (iron) in a watering can full of water, and spread this evenly around the drip line, your Citrus tree will be really grateful and its leaves will gradually begin to look healthy. 

Flowering and pollination

Flowering is on this season’s growth. Spring flowering is usually the heaviest, but trees flower at other times as well. Abundant flowering can be a symptom of a lack of water or nutrients. The best way to respond is to adjust irrigation and add nutrients. Many of these flowers will not result in fruit, so there is no need to remove them by hand. If you get too many fruits on a tree, then that is the moment to thin.

Most Citrus trees are self-fertile. You only need an insect to move pollen within the same flower. You will get fruit if you have just one tree. Cross pollination from other Citrus trees can with some varieties of Citrus increase the number of fruits.

Pests

Some people may not agree with this, but there is a simple approach to treating pests in Citrus fruit in Tasmania: if a Citrus tree is affected by a pest, solve the problem by realising that the tree is telling you that it is either in the wrong position (see above, reposition it in autumn or winter) or it needs more water or nutrients. 

In general, Citrus trees are robust and resilient. The simplest approach to prevent Citrus pests and diseases, or to get rid of a disease once a tree has one, is to water well, fertilise as described above, mulch, and foliar feed, as described above. If this is done, most Citrus trees will pull through and recover well over time, and spraying insecticides is not needed.

Thinning fruit

Fruits that form on young trees in their first two years are best removed to allow the tree to focus on establishing itself. Thinning of fruit is a good way to get larger fruit, avoid dropping of fruit in a heat wave, and to avoid large crops followed by small crops. It also avoids branches sagging too much when fruits increase in size. Fruits can take 7–14 months to ripen, depending on the variety. For a good article about thinning fruit see the Recommend Further Reading section at the end of this post.

Harvesting fruit

To make sure the skin of the fruit does not tear, don’t pull fruit from the tree, but cut it off with secateurs. Do not pick immediately after rain or irrigation, or when it is humid, as the skin will easily be damaged.

Storing fruit

In general Citrus fruit is best stored by leaving it on the tree until you need it. Ripe fruits can continue to hang on trees for months without any problems. An exception is Mandarins that go pithy and dry if left on the tree for a long time.

Citrus with thin skin, eg. Eureka lemons, can’t be stored for more than a few weeks off the tree.

To store Citrus fruit off the tree, pick fruit while still somewhat green. Store fruits in a cool position, making sure fruits don’t touch. They will keep for 2 to 3 months.

Pruning

Pruning a young Citrus tree to a vase-shape is not a must, but it won’t do the tree any harm either, if you prefer the tree to have that shape.

Compared to many other fruit trees, Citrus trees are relatively slow growing. Most Citrus trees don’t need more than a light pruning once a year to remove dead or old wood, branches that touch each other, or branches where there is too much wood in one part of the tree. The best time to prune is early Spring when there no longer is a chance of frost, so new growth will not be affected by it.

Flowers occur on the present season’s growth, so if you prune away too many new branches, you may not get many fruits this season.

Always remove branches that have formed below the graft, as they will not produce fruit you want. These branches use up vigour that is much better used further up the tree.

Above the graft water shoots will sometimes form. Water shoots are thick long vigorous vertical branches that come out of much thinner short horizontal branches. Remove most of these, especially if they grow into the centre of the tree, because most water shoots will only fruit at their tip.

Always remove or shorten branches that touch soil or will do so when fruits make them heavier.

Citrus trees are very tough, and rigorous pruning will rejuvenate a well-established tree. A Citrus tree that has not been pruned for years is best pruned back in stages over a number of years, so you continue to get some fruit. 

If you need to remove a whole large branch, leave its collar, that is the thicker area just before it meets the trunk.

Grafting

Citrus are not difficult to graft. All Citrus are compatible. It will save space to have multiple Citrus varieties on one tree! Give it a go! Methods are the same as for other fruit trees. See Food Garden Group blog post A Look at Grafting  for more info.

Citrus varieties suitable for Tasmanian conditions

There are many sub-tropical and tropical Citrus varieties for which Tasmania’s climate is simply too cold. The list below mentions Citrus varieties that grow in Ian and Jill's garden in Hobart plus ones that I have seen elsewhere in Tasmania, and that can be grown successfully if the circumstances are right.

Lemons

• Lemons will do best in full sun, but do not need all day sun to produce fruit.
• Lemons are frost-sensitive!
• Lemons flower and bear for most of the year, but heaviest flowering is after winter.
• Grown best in regions with mild winters and summers that are not hot. In these conditions Lemons bear fruit almost all year round. Lemons tolerate occasional light frost, but frost is the limiting factor for Lemons, not lack of heat.

The following lemon varieties that are suitable for Tasmanian conditions:

• Eureka – the least hardy of the three varieties mentioned here, medium to large tree, thick-skinned large fruit, open growth with sparse foliage, mostly thornless, thin-skinned fruit, has lemons nearly all year round.

• Lisbon – tolerates more cold than Eureka.  Lisbon is a vigorous large tree, upright, very thorny, and with thick leaves. Fruit is medium sized, thick-skinned and has a distinct nipple.

A young Lisbon in FGG member Max K's garden

• Meyer- is a hybrid between a Lemon and an Orange.  It is the most frost-tolerant of all Lemons.  The Meyer Lemon tree is smaller than the other two, and will grow well in a large pot,  It is thornless.  It Meyer Lemons have less bite than other lemons, but plenty of flavour. Not ideal where real lemon taste is needed, but great for drinks and light zests. Fruit is a bit rounder and smaller than other Lemons, orange-yellow coloured with thin smooth skin. Consider a Meyer Lemon where it is too cold to have ‘a true Lemon’. You will not find thin-skinned lemons like Meyer in shops, because off the tree they don’t keep well enough for commercial use. This is why it is great to have one yourself!

From left to right: Eureka, Lisbon, then Meyer

Limes

• Fruit is small, thin-skinned, stronger in taste than Lemon, and very aromatic
• Most limes are ripe while still green
• Limes need a warm sunny sheltered frost-free environment.

The following limes that are suitable for Tasmanian conditions:

• Tahitian Lime - fruit of this nearly thornless tree is oval, thin skinned, green, and almost the size of a lemon. The tree is almost as cold-tolerant as a lemon. Its flowers have a strong fragrance.  It will do well in a large pot.

Tahitian Lime

• Australian Lime – this is a native to Australia. Australian Limes fruits are green, round, small, and thin skinned. They are used as a food source by indigenous Australians, and are used in marmalade and sauces. Fine in a large pot when small, but ideally planted in the ground later on.

• Finger Lime – this is another Australian Lime. It is a thorny understorey shrub or small tree in rainforest regions of northern New South Wales and Southern Queensland. As the name suggests it has finger-shaped green to purple fruits that are is used to pep up drinks, in desserts, as a garnish and even to make marmalade.  A good article about Finger Lime can be found here.

Finger Lime - the fruits in the photo will grow to around 5 cms long

• Kaffir Lime – this Lime, native to tropical Southeast Asia and southern China, is mainly grown for its aromatic leaves that are widely used in stir fries, stews and drinks. The fruit is very strongly flavoured and sometimes used in curries. Kaffir Limes prefer hot summers and mild, dry winters. I have seen it grown successfully in Hobart. It can be done! Mature trees reach 3–4 metres high in optimal conditions. A good article on Kaffir Limes can be found in the Recommended further reading list.

Oranges

• Oranges root deeper than most Citrus, so soil should have good drainage further down. It is therefore not a good Citrus to have in a shallow pot.

The following orange is suitable for Tasmanian conditions:

• Valencia – this is a commercially grown sweet orange. It does not like frost. Fruits become sweeter as they hang longer on the tree.

Cumquats

• The most frost-hardy of Citrus varieties, but it is still best to choose a warm not-windy position in your garden.
• Will happily grown in a half wine barrel or other pot of similar size if well fed and watered.
• Quite a few Food Garden Group members grow Cumquats successfully
• Cumquats have an intense sour-orange flavour. Reportedly the best Citrus fruit for marmalade.

Mandarin

• Surprisingly, Mandarin is more frost tolerant than Lemon, but it is still best to put it in the warmest position in your garden (see notes under ‘planting’).
• If regularly fed and watered Mandarin trees are ideal for a half wine barrel or other large pot.
• Several Food Garden Group members grow Mandarins successfully
• Mandarins that are left on trees for a long time go pithy and dry.

Food Garden Group member Bernie lives at Lymington close to the water. She has a Mandarin tree (see photo above) in a sheltered position along the northern wall of her house. It is around 2.5 metres tall. It does not receive a lot of attention, but produces heaps of mandarins. The tree is in the ground and there are frosts in winter. She reports that the more water the tree gets, the bigger the mandarins become. Bernie also commented that ‘even though people think that mandarins need to be really orange before you pick them, mandarins which are mainly green with some orange colouring are the juiciest. If you leave them on the tree too long they become dry, not unlike the supermarket ones that are often a waste of money’.

Tangerine

• Tangerines are mandarin-orange hybrids
• The fruit got its name because it arrived in Europe from Tangier in Morocco
• Smaller than oranges, and sweeter than oranges
• Frost tolerant

Jill and Ian have a Tangerine in their garden at Hobart.  The photo above is of a fruit on their tree.

Grapefruit

Grapefruit trees are more frost tolerant than lemon trees, but need consistent heat over a period of time in order to produce big juicy fruit.  This means that growing grapefruits in Tasmania is much harder than growing lemons. It may explain why for a while I could not find anyone with a successful grapefruit tree.
When I asked readers to contact me if they knew of anyone with a successful grapefruit tree Fin M and Kate F (thank you!) responded, telling me that friends gave them home-grown grapefruits in the past.
This brought me in contact with Lynne M who has a grapefruit tree in her garden at West Hobart.  Thank you, Lynne, for your information and photos below!

Lynne reports that the tree is in a sheltered corner of her garden with a 6-foot paling fence on two sides. It produces ripe fruit for a good portion of the year. Because the tree was already there when she bought the property, Lynne does not know what variety it is.

Initially I could not find any Grapefruit trees in nurseries, so when I recently visited the garden section of Bunnings in Mornington I could not believe my eyes when I found two varieties of grapefruit:

Grapefruit Wheeny - Sweet flavour and good juice content. Heavy cropper. Matures early.
Grapefruit Marsh - Bears large fruit with pale flesh. Almost seedless. Crops for extended periods becoming sweeter with time. Prefers a warm sheltered position in rich well-drained soil.

Because of Tasmania's cool conditions I would always choose citrus varieties that mature early, so Wheeny would be my choice! Food Garden Group member Wendy P confirmed that the variety is a good choice for Tasmanian conditions. Her Wheeny produces large juicy sweet fruit in her garden at Sandy Bay!
I order to give a nice number of fruits the best chance to grow large and juicy I would thin quite a few fruits off any heavily-cropping citrus tree.

A mystery solved!

When this blog post was first published I ended it with the photo below of strange fruits on a Lisbon tree in Helen and David's garden at Acton, near Hobart.

Food Garden Group member Judith C, who previously lived in New South Wales, responded with the comment that this very much looks like the fruit of a Bush Lemon.  

Upon investigation it turned out that Bush Lemon (Citrus jambhiri) is a very tough imported lemon variety that managed to escape and 'go bush' in subtropical parts of Australia because it is one of the few kinds of citrus that self-seeds. Nurseries use it as rootstock. 

Helen and David explained that many years ago, before they had a chance to protect it from wildlife, their Lisbon was almost completely ring-barked by hungry rabbits.  We now know that the tree's root stock used that opportunity to take over!

Interesting!
David and Helen report that the tree is quite productive and that the sour fruits are quite edible.
We need to conclude that Bush Lemon can survive and do well in sheltered conditions in Tasmania, and that means that we need to make sure it does not 'go bush' here! 

Recommended Further Reading

• The Complete Book of Fruit Growing in Australia by Louis Glowinski is a seminal work on all fruits that can be grown in Australia. It has an excellent chapter on Citrus fruits.
• A good article on Kaffir Limes can be found here 
• The effect of male and female urine on Citrus growth is looked at here
• Thinning Citrus fruit is well covered here 

Thank you!

I would like to thank the Food Garden Group members who contributed to this blog post, especially Jill and Ian, but also Bernie, Helen, David, Tania and Max K!

If you feel that there is something needs correcting in this blog post, or if you have additional information on Citrus in Tasmania, please email foodgardengroup@gmail.com. I am interested in more info.

Have fun with Citrus!