Citrus in the home garden

Citrus trees are an important part of any edible garden, providing a fresh, tangy and nutritious addition to a sustainable kitchen, even in the depths of winter.  Once established, many citrus are easy to grow and can be cared for with a few simple skills and materials.

Course Notes
© Scott Hitchins

Varieties

There are hundreds of varieties of citrus available, many of which will do well in Melbourne’s climate. 

With the introduction of “Flying Dragon” rootstock, all varieties can be grown as miniatures in pots but if you want serious amounts of fruit, in-ground is the way to go.  The varieties named below are your best bets for this region but you will always find exceptions with local gardeners successfully growing varieties that are deemed unsuitable for our climate, so if a variety you love is not listed, pick your best, sunniest, frost-free spot and give it a go.

Lemons: Most nurseries will stock ‘Eureka’, ’Lisbon’ and Meyer lemons. If you often use lemon juice or zest in your cooking, then Eureka is the one for you. Plant it a good spot near the kitchen door so you can grab a lemon whenever you need one. Eureka will bear delicious lemony fruit for about ten months of the year. Lisbon is a hardy and delicious lemon but most of the crop will ripen at the same time: a good tree for lovers of marmalade or lemonade. Meyer is thought to be a lemon/orange hybrid loved by some for fresh eating but disappointing for its lack of lemon acidity in cooking.  Meyer is much better suited to (large) pots than the others.

Limes: Tahitian is a great small to medium tree that produces an abundance of delicious limes that will ripe across summer and autumn. The Kaffir lime produces a wrinkly fruit that many find too perfumed for drinks but it is the leaf used in South-east Asian dishes that it is valued for. Given how few leaves most of us use in a year, consider having a go at bud-grafting a branch onto another citrus to save apace for more productive trees.  The Mexican lime (aka West Indian lime) is much better suited to tropical areas but is still often sold in nurseries in Melbourne. Native Australian Finger Limes are best grown in pots and require a good warm spot to produce well.

Oranges: Your best choice for home grown oranges is the Navel orange, in particular; Washington Navel.  Valencia is rather harder to grow unless planted in just the right sunny spot, but it has the advantage of holding its fruit on the tree for a long time.

Mandarins: Good choices for tasty, sweet mandarins in Melbourne are the Satsuma or the orange/mandarin hybrid sold as Murcott or Honey Murcott.  Both are cold- hardy trees but the fruit is prone to frost damage.  Thin fruit very heavily to get decent sized sweet fruit instead of hundreds of dry, tasteless marbles.

Tangelo: One choice here: Minneola, which is partly self-fertile.  Other tangelos (a mandarin/grapefruit hybrid), unlike most citrus, require cross pollination.

Grapefruit: Either move further north or grow the variety Wheeny.

Cumquat: Great for marmalade and candying, look for the variety Marumi which is tastier than the commonly available Nagami.  Eat skin-and-all to get the best flavour.

 

Planting

Citrus are best planted or moved in winter when growth is slowed. When buying from a nursery, the trees will often have unripe fruit attached which should be removed: They are usually induced to fruit prematurely by temperature and light manipulation to make them more attractive to buyers but this can set-back establishment of good branch and root systems. Rather than waste your new tree’s energy on tasteless fruit, let it put it into sturdy growth that will pay you back in a couple years with an abundance of tasty fruit.

Citrus require a tricky combination of reliable moisture but good drainage, so plant into a raised mound of soil built up with plenty of well-rotted organic matter. Delay feeding until after frost has finished, avoiding delicate new growth being burnt off.  Water in well and stake until roots are well developed and the tree is firm. Your tree will require plenty of sun, so look for a north-ish facing position that is going to get sun even during winter when many varieties ripen.  This sort of spot is wasted on deciduous fruit trees like apples and stone fruit whose bare trunks can’t use winter sun. Water deeply, once a week (more often in hot weather). Build-up the edge of the mound to create a circular dam that will stop the water from running away before it soaks in. Most citrus have shallow feeder roots that are easily out-competed by grass, weeds and groundcovers or burnt by heatwaves, so maintaining a good layer of mulch is essential. Ensure this mulch is kept several centimetres from the trunk as citrus are very susceptible to Collar Rot.

Plant in a mound

 

Re-potting & root pruning

Growing in Pots

Citrus suitable for pots include Meyer Lemon, Tahitian & Kaffir Limes, cumquats and any of the miniature varieties now readily available. Other varieties listed above will survive in very large pots if you are prepared to do some regular heavy maintenance.  Young trees will probably have to be re-potted into a larger pot every year but, as the tree matures, this may be reduced to every two to five years until full size is reached. This is usually done in winter after the fruit is harvested.  When re-potting, examine the root ball for damage or disease, cutting away affected parts. If the plant is root-bound or the roots are spiralling in the pot, tease them out to fit the larger pot.

In addition to up-sizing, you will to do some yearly ‘refreshing’ of the potting mix. This is done by tapping the tree out of its pot, teasing out about a third of the potting mix and then re-planting with fresh, good quality potting mix. If the tree has grown too big for you to do this, just dig around the outer third of the pot, replacing the potting mix removed.  If the tree has reached full size and won’t be potted-on, you can also trim any roots in this outer third to ‘bonsai’ the tree.

 

Feeding

All citrus require regular feeding, but be cautious with artificially produced Citrus Feed: It is very easy to over-feed your tree with this highly soluble mixture, causing leaf & fruit drop and possibly killing the tree.  

A good organic feeding program for citrus is to mulch them 10cms deep with well-rotted compost out to the drip line in early spring. Supplement this with a generous sprinkling of composted chook poo or Organic Lifter and some Sulphate of Potash (follow directions on the pack) at the start of each season.

The heavy clay soils which we usually have on this side of Melbourne make iron and some other trace elements difficult for citrus trees to absorb, resulting in poor growth and yellowing of leaves in various patterns, depending on which of the nutrients are missing. Rather than trying to work out which mineral or combination of minerals is deficient, add Trace elements once or twice a year, as per directions on the packet. Particularly with Iron, this is the key to growing citrus in the West.

Pruning Citrus

Citrus require much less pruning than deciduous fruit trees and most of this, as with all pruning, involves first removing the ‘Three D’s”, that is anything that is Dead, Damaged or Diseased, including any rubbing or crossed branches which may cause damage that can allow entry of disease.   Pruning should be done in early spring but after the last frost has passed.

Citrus require much less pruning than deciduous fruit trees and most of this, as with all pruning, involves first removing the ‘Three D’s”, that is anything that is Dead, Damaged or Diseased, including any rubbing or crossed branches which may cause damage that can allow entry of disease.   Pruning should be done in early spring but after the last frost has passed.

 

In the first couple of years after planting your citrus tree, after the 3 D’s, your focus should be on developing its mature shape: A broad mound on a trunk rather than the hollow vase that most fruit trees are pruned to. Prune back to outward facing buds on outward growing branches that are evenly spaced and which are not going to grow into each other as they grow in thickness. Any branches which are too vertical (water shoots) should be cut back to a low outward facing bud or, if still young and flexible, tied down in a nearer-to-horizontal position to encourage fruiting. As with any grafted tree, remove any shoots from below the graft scar.

Once your tree has achieved its mature shape and size, it’s just a matter of the 3 D’s and keeping growth in check, particularly vertical growth. As with all fruit trees, don’t allow the height of the tree to get any higher than you can reach standing flat-footed. Any growth beyond this can’t be easily picked, pruned, sprayed or netted.

If you have an older tree that has got away from you, cut back about 1/4 to 1/3 of the runaway growth each spring so that you will get a decent crop while getting it down to size. You could do it in one hit if you are prepared to go a year or two without a crop as citrus respond well to levels of pruning that would kill many other trees. With these larger diameter branches, cuts should be sealed with grafting wax or a pruning sealant such as Steri-prune.

Alternatively, you could espalier a young citrus into a two dimensional fan shape against a wall or trellis by removing or tying back any branches growing towards you. The same rules apply as above but just think in one aspect.  This is particularly useful if you are trying to grow citrus with limited space or attempting to grow a variety that is not well suited to our climate:  A sun-soaked masonry wall will create a warm, frost-free micro-climate.

Pests and Diseases

The best defence against pest or disease attacks on any citrus is a well fed and watered tree. When this is done, disease rarely gets extensive enough to effect fruiting and insect pests just become part of your backyard ecosystem: eating and being eaten and doing no more than cosmetic damage to your tree.  If you notice a problem, act; don’t overreact.

Common Problems and Solutions

Citrus Gall wasp:  Caused by tiny wasps laying their eggs beneath the bark. As the larvae hatch and grow, part of the branch becomes swollen and disfigured. As the wood protects the larvae from any sprays (organic or conventional), the only option is to cut off the affected area and dispose of it. The wood must be binned or burnt as composting will allow the wasps to continue to hatch. If there are tiny pinholes in the branch, you are too late as the wasps have hatched.

Yellowing of leaves:  This is usually a result of nutrient deficiencies. While you can search books and the internet for specific needs, it is better to just apply Trace Elements as this will cover all your bases and avoid misdiagnosis. For a quicker result, apply the mixture as per the pack but as a foliar spray, allowing the excess to drip down to the soil. Note that in winter, it is normal for some older leaves to yellow and drop off.

Scale: These are small encrustations on the branches and sometimes on leaves. Most look like brown, black, white or red shields but some varieties are fluffy white.  One simple solution: Apply White Oil.

Ants:  Ants are not a problem, they are a symptom: They are usually only there to feed off the sugary secretions of scale or aphids. Remove the scale and the ants will leave also.  Think of them as a warning system.

Sooty Mould:  This is caused by the sugary excrement of scale growing mould. Check for scale and treat. Open up the tree with a bit of pruning for better air circulation. Spray the leaves with a solution of one tablespoon of ‘Carb soda’ (sodium bicarbonate) per litre of water.  This will temporarily make the pH of the leaf surface unsuitable for the mould to grow.

Brown leaf edges: Salt burn caused by artificial fertiliser, salty bore water or using grey water with high-salt products such as most fabric softeners. Flush well with clean water and check drainage is adequate.

Rotting, black and wilted leaves: Poor drainage or frost damage.  Check drainage, mulch with Casuarina leaves for silica and cover on frosty nights.

Sucking & piercing bugs: Don’t bother too much unless they are actually doing damage. If they are, White Oil them.

Holes chewed in leaves: Usually Citrus Butterfly caterpillars.  In the unlikely event that there are lots, pick them off. Otherwise leave them alone: The butterflies are really pretty and worth a few holes.

Silvery squiggles in leaf surface:  Citrus Leaf Miner; White Oil.

Fruit spotting: Various colours and causes some nutrient-based but most are caused by various citrus mites or fungal diseases. Feed the tree well and spray with White Oil that has a tablespoon of carb soda added per litre of spray.

Fruit distortion and cracking: Caused by fungal disease: Carb soda and Trace Elements.

Thick skin: Can be viral but is usually a copper deficiency. Trace elements and feeding.