Gadenin日本語Get the appUnderstand what you are planting before you dig the hole
A citron is not a lemon with a thicker skin. The fruit is almost entirely rind and white pith, with a few dry segments and barely a spoonful of juice in a fruit that can weigh two pounds (900 g). Nobody grows it to squeeze. It is grown for candied peel, for zest, and for the scent, and every decision below follows from that: you are producing rind, so you are protecting the skin of the fruit and the branch that carries it.
The second thing to accept is the cold. Citron is the least hardy of the common citrus. It stops growing below about 55F (13C), leaves burn in the high 30s F (3-4C), and a night at 28F (-2C) kills wood outright. Unless your winter minimum genuinely stays above 40F (4C), plant it in a container that you can move under cover, not in the open ground.
If you are set on planting in the ground, the practical limit is a frost-free garden with a warm wall behind it. Everywhere else, a pot is not a compromise; it is the only method that reliably keeps the tree alive to fruiting age.
Pot size, and why weight decides it
Choose the pot by asking how you will move it in the autumn, not by how big the tree is now. A nursery tree with a rootball around eight inches (20 cm) across goes into a 12 to 14 inch (30-35 cm) pot. Step up two to four inches (5-10 cm) of diameter every second or third year until you reach a working ceiling of roughly 18 to 22 inches (45-55 cm), then hold that size and root prune instead.
Citron branches are long, thorny and comparatively slender, and the fruit is heavy enough to bend them to the ground. That makes the whole plant top-heavy and lopsided in wind. A wide, heavy-based pot beats a tall narrow one, and a wheeled caddy fitted before you fill the pot saves your back twice a year.
| Stage | Pot diameter | Approximate planted weight | How you move it |
|---|---|---|---|
| First year from the nursery | 12-14 in (30-35 cm) | 35-45 lb (16-20 kg) | Two hands |
| Third to fourth year | 16 in (40 cm) | 60-70 lb (27-32 kg) | Caddy, one person |
| Mature, final pot | 18-22 in (45-55 cm) | 100 lb (45 kg) and up | Caddy plus a second person |
A gritty mix that drains in seconds
Citron roots rot faster than they dry out. Do not use a bagged multipurpose or peat-based potting mix on its own; it holds water at the base of the pot all winter, exactly when the tree is not drinking. Mix roughly two parts of a loam-based potting mix, one part composted bark or coir, and one part coarse grit or perlite. Water poured onto the finished mix should run out of the drainage holes within about ten seconds.
Skip the layer of crocks or gravel at the bottom of the pot. It does not improve drainage; it raises the saturated zone and costs you root volume. Use pots with several large holes and stand them on feet so the holes stay clear.
Plant high, and keep the graft union in the air
Almost every citron sold is grafted, and the union is a visible swelling low on the trunk. Buried, it rots or throws rootstock shoots that overrun the tree. Set the top of the rootball about an inch (2-3 cm) above the finished soil line and let it settle down flush, never below.
- Water the tree before you unpot it A dry rootball crumbles and tears fine roots when you handle it. Water thoroughly and leave it an hour. Wear leather gauntlets from this point on: the thorns are long and are usually pointing at your forearm.
- Tease the outer roots, do not shred them If roots are circling the outside of the rootball, cut through the circling ones in three or four places with a knife and gently pull the ends outward. Leave the core of the rootball intact; citron sulks for a season if you bare-root it.
- Set the height with the pot empty Add mix to the bottom, sit the tree in, and check with a straight edge across the rim that the top of the rootball will finish about an inch (2-3 cm) proud. Adjust before you backfill, not after.
- Backfill and firm in stages Add mix in three or four lifts, tapping the pot on the ground between lifts rather than stamping it down. Leave a clear inch (2-3 cm) between the soil surface and the rim so water does not run over the side.
- Water in and then stop Soak until water runs from the base, then keep the tree in bright shade out of wind for two weeks and water only when the top two inches (5 cm) are dry. Do not feed for six weeks; a new root system pushed with fertilizer burns.
Where to stand it, and what to write down
Outdoors in the growing season, give it the warmest, brightest, most sheltered spot you have, ideally with a wall that holds heat behind it. Full sun is right, but not in combination with wind: moving air over a thorny, heavily laden branch tears leaves and rubs the rind of developing fruit, and rind damage is the whole crop on a citron.
Write down the date you potted it, the pot diameter, and the mix you used. In three years, when you are deciding whether it needs a bigger pot or a root prune, that one line tells you more than looking at the tree does. Note the position you stood it in and how it performed, too; the difference between a good corner and a windy one shows up as a doubled crop.