How to grow sweet orange

Line up your tree in the weeks before planting — a month or two ahead of the rains — so you have time to find a good grafted tree at a certified nursery rather than grabbing whatever is nearest on planting day.

Buy a grafted tree, not a seedling grown from a pip (a pip is an orange seed). A grafted tree is two joined plants: a tough rootstock — the bottom part, the roots and lower stem, chosen for strong, disease-beating roots — and a scion on top, which carries your orange variety and its fruit. You can see where they join: a knobbly bump low on the stem, the graft union.

Buy only from a certified, clean nursery. Certified stock is raised under cover to be free of citrus greening (HLB) and tristeza — two virus-like diseases that have no cure and slowly kill the tree. A cheap roadside seedling can carry them from its very first day.

Ask for a rootstock that suits your soil and your pests: one that stands up to root rot (a soil disease, Phytophthora, that rots the roots and collar on wet ground) and resists tristeza. Where tristeza is about, do not accept a tree grown on sour-orange rootstock — the tree collapses fast on that root.

Pick a healthy tree: dark green leaves with no blotchy yellow mottling, one straight stem, and a graft union that has healed cleanly. Leave behind any tree with yellow, mottled or twisted leaves — it may already be sick.

Plant at the start of the rains, so the young tree has months of steady moisture to settle in before any dry spell.

Choose deep, well-drained soil. Test it: fill a hole with water — if water still stands in it hours later, the spot is too wet. On wet ground, plant on a raised mound about a stride (1 m) across so the roots sit up out of the wet.

Dig a hole about 60 cm each way — roughly knee-deep — and mix the loosened topsoil with well-rotted manure or compost. Planting more than one tree? Leave about six strides (6 m) between trees each way, so every tree gets full sun and air.

Set the tree at the same depth it grew in the nursery bag — no deeper. The graft union (the knobbly join) must stand a hand-span (about 20 cm) clear of the soil. Bury that join and the scion roots into the ground, you lose the rootstock's protection, and rot sets in.

Firm the soil, drive a stake in beside the trunk and tie it loosely so wind can't rock the roots loose, then water it in well to settle the soil around the roots.

Keep a weed-free ring about a stride (1 m) across around the trunk and mulch it — but hold the mulch a hand-span (20 cm) clear of the bark so the trunk stays dry.

In the first year, choose 3–4 strong branches spread evenly around the trunk to become the tree's main arms, starting a little above knee height. Rub or cut off the rest while they are still small and soft.

Cut out any shoots growing from below the graft union (these come from the rootstock) the moment you see them — they are the wrong variety and steal the tree's strength. They often have different leaves or thorns, so they are easy to spot.

Aim for an open centre, like a cup or a hand held open: keep the middle clear so light reaches right inside, instead of one crowded ball of leaves.

Do this shaping little and often over the first few years, in the weeks after each season starts. Once the frame is built, the tree needs only a light yearly tidy.

Once a month, walk to each tree and look closely at the new leaves, the fruit and the trunk. Carry a bag for anything you cut off, so you don't drop diseased bits under the tree.

Citrus psyllid (the greening carrier): on the soft new leaves, look for a tiny brownish, aphid-like insect about the size of a rice grain that perches tail-up at an angle and jumps or flies off the moment you tap the shoot. Its surest sign is on the young leaves themselves — little cup- or crater-shaped bumps (pit galls) that make the flush look blistered and goose-bumped. It carries incurable greening, so even one is a warning to act.

Citrus greening (HLB): look for a blotchy yellow mottle that is NOT the same on both sides of the leaf's midrib (the midrib is the leaf's central vein). An even yellowing, matching on both sides, is usually just hunger — not greening. Also watch for odd yellow shoots standing out in the green canopy, and small, lopsided fruit that stay green at the bottom and taste bitter.

Root and collar rot (Phytophthora): at the base of the trunk, look for dark, wet, gummy patches oozing where the bark is dying, with the canopy above thinning and going pale. Keep soil and mulch pulled back off the trunk.

Black spot: on the rind of the fruit, look for small dark, sunken spots with pale grey centres, sometimes set in a ring — they blemish the fruit and make it drop early.

Leafminer: look for silvery, wiggly snail-trail tunnels just under the skin of young leaves, which then curl and twist. It rarely troubles a big tree, but the wounds open the door to worse disease.

Tristeza / aphids: look for clusters of soft black or brown aphids (small sap-sucking insects) on the new shoots, and whole trees that yellow and slowly go downhill for no clear reason.

As you go, rake up and carry away fallen leaves and fruit from under the tree — black spot survives in that litter and re-infects next year's fruit.

Once a year, around the start of the season, cut out any dead, broken or crossing branches, and the strong upright water shoots (fast, leafy shoots that spear straight up through the middle and carry no fruit).

Open the centre until you could almost toss a hat through it — sun and air must reach the inside of the tree.

Cut off any low branches dragging on the ground (fruit down there gets fungus and pests) and any suckers from below the graft union.

Use a clean, sharp saw or secateurs. Cut close to the branch without tearing the bark, then rake up and carry away the prunings and leaf litter.

Feed in several rounds across the growing year. Your recommendation gives the amount for your tree's age and size — a young tree needs far less than a big bearing one. Split it small and often so the rain can't carry it away.

Spread it in a ring under the outer edge of the leaves — the 'drip line', where rain drips off the canopy — because that is where the feeding roots are. Keep it a hand-span (20 cm) clear of the trunk; piled against the bark it burns the collar and invites rot.

Feed when the soil is moist (after rain or watering) and, if you can, lightly scratch it in or water it, so it soaks down to the roots instead of gassing off into the air.

Watch the leaves for hunger and fix it with a spray on the leaves (a 'foliar' spray): small, narrow leaves with yellow blotches between green veins mean the tree is short of zinc; older leaves yellowing from the base and edges, leaving a green V at the base, mean it is short of magnesium. A foliar zinc-and-magnesium spray on the fresh leaves fixes both.

In cool, higher areas the winter cold brings the bloom on its own — you need only be ready for it.

In the warm lowlands, hold back water for a few weeks until the leaves just begin to curl and look slightly stressed — but do not let the tree collapse. This short dry rest sets up the flower buds.

Then water heavily — or time it so the first rains arrive. The sudden moisture flushes out a strong, even bloom a few weeks later.

Give the zinc-and-boron spray before the flowers open (see the next task) to help the blossom set into fruit.

Mix a foliar zinc-and-boron spray (a foliar spray is one you spray straight onto the leaves). Your recommendation gives the product and the dose. Spray it in the two weeks before flowering, while the flower buds are still forming.

Spray to lightly wet the leaves and buds — do not overdose the boron. A little boron helps the fruit set; too much burns the leaves and fruit. Follow the label exactly and measure it.

Spray in the cool of early morning or late evening, with the wind at your back so the mist blows away from your face — never in hot midday sun.

Cover your skin, eyes, nose and mouth, keep the spray off food and drinking water, and wash yourself and the sprayer well when you finish.

Every week while the tree is pushing soft new leaves, check the flush (the tender new shoots) on several branches around each tree, turning the young leaves over to look underneath.

Psyllids: look for a tiny brownish, aphid-like insect about the size of a rice grain that perches tail-up at an angle to the leaf and jumps or flies off the moment you tap the shoot, like a miniature cicada. Its surest sign is on the young leaves: little cup- or crater-shaped bumps (pit galls) that make the flush look blistered and goose-bumped, with the leaves curling, puckering and yellowing. Turn a leaf over for yellow eggs standing on end along the leaf edge and flat, scale-like young ones sitting still in the pits, sometimes trailing fine white waxy threads; sticky honeydew (sugary droppings) may coat the leaves.

Mites: look for a fine bronzing or silvery dulling of the leaves and young fruit, worst in hot, dry, dusty spells. Tap a leaf over a sheet of white paper and you may see the tiny specks crawl.

Act on the first psyllids — spray them straight away (your recommendation gives the product). Even a few matter, because it is the disease they carry, not their feeding, that does the real damage.

When you spray, cover your skin, eyes and nose, spray in the cool with the wind behind you, keep it off any fruit you'll eat soon, and respect the pre-harvest interval — the number of days the label says to wait after spraying before the fruit is safe to pick. Wash afterwards.

About one to two months after flowering, once the petals have dropped and pea-sized green fruit show, pick out several typical shoots on different sides of the tree.

On each shoot, count the little fruit that are holding on and swelling, against the flowers that came to nothing. Some drop soon after bloom — a natural 'fruit drop' — so don't expect every flower to hold.

If a good number are holding and growing, you have a crop set — carry on with steady water and your pest watch.

If it fails — almost none are holding (a heavy drop, a poor set): keep the moisture steady from here on (jumpy watering causes drop), and next season give the zinc-and-boron spray before bloom and check for psyllids, greening and drought stress — those are the usual causes of a poor set.

Twice a week from fruit set right through to harvest, check the hanging fruit and the ground under the tree.

Fruit fly: look for tiny sting marks or soft, sunken rotten patches on the fruit, and fruit dropping early. Cut open a suspect fruit — small white maggots inside confirm it. Hang a bait or trap to catch the flies early.

False codling moth: look for a small hole with sawdust-like frass (grub droppings) on the fruit, and fruit that colours and drops too early with a grub inside.

Black spot: look again for the dark, sunken spots with pale grey centres on the rind.

Collect and bury or burn all fallen and stung fruit, twice a week — bury it deep enough that the maggots can't crawl back out. This starves the next generation and is the single most powerful thing you can do.

If fruit fly is building up, start protein-bait spots (your recommendation gives the bait). When you spray, cover up, spray in the cool with the wind behind you, keep it off fruit you'll eat soon, respect the pre-harvest interval (the wait after spraying before the fruit is safe to pick), and wash afterwards.

From fruit set through fruit fill, water every 1–2 weeks — more often in heat and on sandy soil that dries fast, less in cool or rainy spells.

Aim for even, steady moisture: never let the tree dry out hard and then flood it, because that swing is what splits the rind.

Water the ground out to the drip line (under the outer edge of the leaves, where the feeding roots are), not just at the trunk.

Check by pushing a finger or a stick into the soil under the canopy: water when it is dry a hand-span (20 cm) down, but never leave the roots standing in water.

Only in a heavy 'on' year, about 6–12 weeks after flowering once you can see the fruit load, judge whether the tree is carrying far more than it can size up.

Pick off the smallest, damaged and tightly-bunched fruit, leaving the healthy fruit spread out along the branches with room to grow.

Take off enough that the branches aren't bending under a solid mass of tiny fruit — you are swapping many small oranges for fewer large, sellable ones.

From about 8 months after flowering, start checking. Don't go by rind colour alone — in warm areas an orange can be fully ripe and sweet inside while its rind is still greenish.

Pick one sample fruit and taste it. It is ready when it is sweet and juicy with just a pleasant tang — the right balance of sugar to sourness. Still sharp and sour means not yet.

Look also for the 'colour break' — the rind just starting to turn from green toward orange — and for fruit that feels heavy and full for its size.

If it fails — still sour: leave the fruit on the tree and taste again in 2–3 weeks. It keeps sweetening on the tree, but remember it will not sweeten one bit once picked, so never pick early to 'ripen at home'.

If the inside tastes ripe but the rind is still green (common in the warm lowlands): it is ready — pick it, and the rind can be de-greened (brought to colour) after picking.

Clip, don't pull. Cut each fruit off with shears or a sharp knife, leaving a very short stalk flush with the fruit. Pull it and you tear out a plug of rind — and the fruit rots from that wound.

Pick over several passes, every 2–3 weeks, taking only the fruit that taste ripe each time — the rest keep ripening on the tree.

Handle gently — don't drop or throw the fruit into hard containers. Every knock is a bruise that becomes a rot spot in store.

Pick into a soft-lined basket or padded crate, and get the fruit out of the hot sun and into the shade straight away.

Sort (grade) the fruit as you pack: set aside any that are cut, stung, bruised or already rotting — one rotting orange spreads mould to the whole crate.

Handle gently and get the fruit into the cool and shade quickly — heat and knocks are what turn sound fruit rotten in store.

Where fruit is ripe inside but the rind is still green, it can be de-greened — held in a warm, airy place (or with ethylene gas where that is available) to bring out the orange colour for market. This changes only the skin colour, not the ripeness inside.

Store and move the graded fruit cool, dry and out of direct sun in clean crates, and sell the bruised or blemished fruit first — it won't keep.