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Bitter orange is one of the toughest citrus you can put in open ground, and that toughness tempts people into careless siting. It takes several degrees more cold than a sweet orange and shrugs off wind that would bronze a lemon, but it opens its flowers in the same narrow spring window and still sulks in cold, saturated soil. Walk the garden on the coldest still night of the year before you dig. Cold air runs downhill and pools against walls and dense hedges, and a tree in one of those pools sits several degrees colder all winter than one on a slight rise.
The second thing to weigh is something no other fruit tree asks of you. The flowers of a bitter orange are the most powerfully scented of any citrus, carried in sheets for two or three weeks. That scent is worth siting for. Put the tree within a few paces of a path, a doorway or wherever you sit in the evening, and on a still warm night the perfume reaches you from thirty feet (9 m) away. A tree at the far end of the garden gives the same crop and almost none of the pleasure.
Drainage decides everything else. Citrus roots run wide and shallow and will not tolerate standing water; a tree in ground that stays saturated for two days after heavy rain declines slowly for years while you treat the yellow leaves as a feeding problem. Dig a hole a foot (30 cm) deep, fill it with water, let it drain, then fill it again. If the second filling has not gone within four hours, plant on a raised mound eight to twelve inches (20 to 30 cm) high, or choose another spot.
| Site check | What you want | What happens if you ignore it |
|---|---|---|
| Sunlight | Eight hours or more of direct sun through the growing season | Thin canopy, sparse flowering, fruit that stays small and stubbornly green |
| Drainage | A test hole that empties within four hours on the second filling | Slow yellowing from the base of the canopy upward, then root rot |
| Cold air | A rise or open ground, never a hollow or the base of a solid wall | Flower buds killed in a late frost, so a whole year with no crop |
| Wind | Shelter from the prevailing wind, especially cold dry winter wind | Scorched leaf margins and heavy flower drop before set |
| Room | Twelve to sixteen feet (3.5 to 5 m) clear in every direction | A thorny tree pressed against a path that you cannot prune safely |
Set the graft union high, and know what is below it
Bitter orange is the classic citrus rootstock, which makes the graft union on a bitter orange tree unusually easy to misread. Your tree may be a bitter orange scion worked onto another rootstock, or it may be on its own roots, and the two behave very differently when a shoot appears low on the trunk. Find the union before you plant. It is a swelling or a change of bark texture and angle, usually four to ten inches (10 to 25 cm) above the roots, and it must finish well clear of the soil and of any mulch you later pile against the trunk.
This matters more here than anywhere else in the citrus family, because the species sits underneath so many other citrus. If you see a vigorous, thorny, strongly upright shoot with large leaves coming from below a graft union anywhere in the garden, on a lemon, a mandarin or a sweet orange, that is bitter orange rootstock breaking out. It will never carry the fruit you bought the tree for, and left alone it outgrows and starves the scion within a few seasons. Cut it flush at its origin the day you see it.
- Find the union before the tree leaves the pot Wipe the lower trunk clean and look for the kink, bark change or slight swelling. Mark it with a loop of soft tie so you can still see it once the tree is in the hole.
- Measure the root ball, not the pot Slide the tree out and find the top of the actual roots, often an inch or two (3 to 5 cm) below the surface of the mix. That root line, not the mix, sits level with the finished soil.
- Dig wide and shallow Make the hole two to three times the width of the root ball and no deeper than the ball. Citrus roots spread sideways, and a hole dug deeper will settle and drop the tree an inch or two over the first winter.
- Check the height with a straight edge Lay a cane across the hole from undisturbed ground to undisturbed ground. The top of the root ball should sit level with the cane or an inch (2.5 cm) proud, leaving the union four to six inches (10 to 15 cm) clear.
- Keep mulch off the trunk forever Mulch out to the edge of the canopy but leave a clear ring six inches (15 cm) wide at the trunk. Mulch banked on bark rots it, and mulch burying the union invites the scion to root over the top.
Plant into the ground, not into a pit of compost
The instinct to backfill a citrus hole with bought compost does real harm. A rich, loose pocket surrounded by heavier native soil holds water like a bucket and encourages roots to circle inside it rather than push out into the ground they have to live in. Backfill with the soil you dug out, broken up and freed of stones. If that soil is genuinely poor, improve a wide area shallowly rather than one hole deeply.
Firm the soil in layers as you fill, pressing with your knuckles rather than stamping, then water in with five gallons (20 liters) delivered slowly. That first watering is less about moisture than about collapsing air pockets around the roots. Look at the tree afterwards: if it has sunk, lift it now while the soil is still loose. A tree that has settled two inches (5 cm) too deep will never recover on its own.
Through the first summer, water deeply every four to seven days in warm weather regardless of rain, because a new root ball dries faster than the ground around it and rain rarely penetrates a dense nursery mix. Do not feed at planting; a heavy nitrogen dose on a tree that cannot yet drink burns the fine roots you are trying to grow.
Rub off every flower the tree opens in its first spring in the ground. A newly planted bitter orange will try to fruit, and it will do so at the direct cost of the root system that has to carry it for the next thirty years. One year of deliberate barrenness buys a decade of steady crops.
Give the thorns the room they need
Bitter orange is thornier than almost any citrus you will have handled, and thorns on vigorous young wood run an inch and a half (4 cm) long, stiff enough to go through a glove. Plant accordingly. Twelve to sixteen feet (3.5 to 5 m) of clear space in every direction is the distance at which you can still walk past the tree and get a ladder in to prune it. A bitter orange squeezed against a path becomes a tree nobody maintains, and that very quickly becomes an impenetrable one.
Thorniness is worst on the strong upright water shoots a young tree throws in its first few years, and it moderates as the wood matures. Do not respond by shearing the young tree hard, which simply provokes more of the same growth. Let the framework build, keep the trunk clear to knee height, and accept that for three or four years this is a plant you approach with long-handled tools.
What to write down on planting day
Record the date you planted, the position in the garden, the height of the graft union above finished soil, and whether the tree is grafted or on its own roots. That last point decides how you treat every low shoot for the rest of the tree's life, and it is impossible to recover once the bark thickens and the union smooths over.
Add the drainage test result and how deep the workable soil went before clay or rock. Three years from now, when the tree drops leaves in a wet spring, you will want to know whether you planted into eighteen inches (45 cm) of good soil or six, and digging around a mature root system will not tell you.