How To Quick Plant and Grow Mandarin Orange Trees

In case you’re in any doubt about just how abundant a food-producing garden can be, plant and grow a mandarin orange trees. They’re the basket fillers of the citrus world, and while it’s common to see backyard trees literally dripping fruit, this kind of epic productivity comes at a price.

Food plants work hard. The trade-off for huge crops is the use of huge amounts of energy. If a plant is not able to continually replace this massive expenditure of energy, the consequence is stress and eventual problems with diseases and pests as well as lesser quality fruit. I’ve found that mandarin trees are a close second to lemons when it comes to suffering stress.

There’s a flipside to this. Mandarin trees that are well cared for produce crops of exquisite fruit that is large, juicy and blessed with that unmistakable mandy flavour combination of tangy and sweet. To get there you just have tick the right mandarin care boxes.

Climate and Cultivars

Cultivars

Some people claim mandarins are frost tolerant, but the terms "tolerance" and "mandarin", mean different things to different people. Regarding frost tolerance, there’s a big variance between -1°C and -10°C. Also, citrus trees have a habit of natural hybridisation, so while the mandarin is formally described as Citrus reticulata, it’s likely that various hybrids, cultivars and varieties are lumped under the mandarin banner.

The hardiest mandarin of the lot is reported to be ‘Jiouyuezao’, a Chinese cultivar that tolerates cold to about -12°C, but as far as I’m aware it isn’t available in Australia. The species Citrus unshiu, commonly known as the Satsuma (after being exported in the 1870s from the Japanese province bearing the same name), is available in Australia and will tolerate cold to roughly -10°C, which is the equivalent of the kumquat. Such hardiness makes Satsumas a possibility in the cold temperate climate zone.

As for the more traditional mandarins such as ‘Emperor’ and ‘Imperial’, it’s a case of light to moderate frosts only. These trees will suffer from leaf burn and fruit spoiling when exposed to temperatures below about -3°C. A deeper freeze may defoliate the tree, and a cold night that dips below -5°C may kill it outright. Stick to warm temperate, subtropical, tropical and semi-arid climates with these cultivars.

Heat isn’t an issue with mandarins. In fact, the trees can handle quite extreme heat as long as their roots are moist. A bigger issue is a lack of summer heat. While mandarins can theoretically be grown as far south as Hobart, the lack of consistent summer warmth may result in poor fruit development. If you’re in a cold climate and keen to give mandies a go, choose an early-ripener such as Satsuma and grow it in a microclimate sheltered from cold winds. A wide variety are available, especially late winter and spring, as potted grafted specimens.

Soil Conditions

The second key to mandarin success is to turbocharge the soil. You can do this by fertilising your mandarin at the start of each season with a complete organic fertiliser made from pelletised chook manure and other goodies. Better still, fertilise in addition to creating long-term nutrition in the soil.

Top-dress the soil below your tree in spring with compost or well-rotted manure (composted chook manure is ideal). Keep the soil covered with mulch to provide food for worms and micro-organisms, and ensure the tree can access nutrients by providing a steady supply of moisture. Take care not to let the soil dry out excessively during drought conditions. Drip irrigation is excellent.

A complete fertiliser will supply all the nutrients and minerals required for healthy growth, but at times (especially when heavy rains leach nutrients from well-drained soils) your tree might need extra trace elements to restore mineral balance in the soil. Do this by throwing on rock minerals (at recommended rates) in spring or by watering trees with seaweed solution once per fortnight until foliage is lush green. Aim for a neutral soil pH. Use lime to correct excessively acidic soil and sulphur to correct alkaline soil.

Thinning Your Crop

Key three to bumper mandies is to thin the crop. Few jobs are as unpopular, but heavy bearing trees benefit greatly from an hour or two spent by the gardener removing one-quarter to three-quarters of the fruit load. If this is done when the fruit are the size of a cherry tomato, the result is that the fruit remaining on the tree have less competition and are more likely to fatten up to an impressive size.

Thinning makes fruit juicier and more flavour some, and is one of the secrets commercial growers use to produce premium crops. Simply pinch off unwanted fruitlets in early summer and throw them in the compost.

Pests and Diseases

When it comes to pests and diseases, mandies are prone to all of the usual suspects affecting citrus trees, but a few problems affect them in particular. Citrus leafminer is a major issue. Control it, and any outbreak of scale insects infesting the branches and foliage, with horticultural oil sprays applied every couple of weeks until the problem is resolved. Borers tunnel holes into established wood and, if unchecked, cause dieback. Watch for their holes and insert wire to squash the grub inside.

Fungal diseases can be an issue because of the fruit’s thin skin. Copper hydroxide sprayed in spring can help prevent citrus scab, brown rot and anthracnose, but it’s also important to open the canopy of the tree up to air movement. Mandarins tend to form twiggy, bushy growth, so thin out closely spaced branches and remove dead or tired wood from within the shady canopy. Ensure leaves and fruit do not make contact with the soil and keep mulch away from the base of the trunk to prevent collar rot. This is a particular issue with seed-raised trees, but fortunately some grafted trees are on resistant rootstocks.

Harvesting

Knowing when to harvest your mandarins is an art in itself and keep in mind that they don’t continue to ripen once picked. My rule of thumb is to pick one and taste it. If it’s to your liking, go for it. In any case, most mandarins deteriorate if left on the tree for too long after ripening, so harvest fruit when it’s fully coloured and tasty. An exception is "Clementine" (a catch-all name for various cultivars). This can be left hanging on the tree for months, which makes it a good choice for extending the fruiting season. To avoid damaging the skin of your mandies, clip the fruit from the tree using secateurs.