Gadenin日本語Get the appThere is no dormant season, so prune little and often
The advice you will read for other citrus, to cut hard between the last harvest and the spring flush, does not transfer. A citron in good conditions has flowers or fruit on it in every season, so a hard cut always sacrifices a crop. Take the opposite approach: small, frequent cuts, a handful of branches at a time, so the tree is never asked to recover from a shock.
If you want one main session, take it after the largest wave of fruit comes off and before the strongest flush of new growth, which for most trees is the end of winter into early spring. Even then, keep the total to about a fifth of the canopy. Anything harder and the tree answers with a mass of vertical, viciously thorny water shoots that carry no fruit for years.
Never prune within a few weeks of moving the tree under cover or back outside. A tree adjusting to a big change in light and temperature is already dropping leaves; cutting it at the same time turns a normal adjustment into serious dieback.
The order of cuts
Work through the tree in a fixed order every time. Doing so means the cuts that matter get made even if you run out of daylight or patience, and with citron patience is the limiting factor because of the thorns.
- Rootstock suckers, on sight, at any time of year Anything growing from below the swollen graft union at the base of the trunk is rootstock. It is usually straighter, more vigorous and more thorny, with a different leaf. Rub it off with a thumb while it is soft, or cut flush if it has hardened. Left for a season it outgrows the citron and starves it.
- Dead, damaged and split wood Cut back to live green tissue under the bark. Pay particular attention to branches that have carried heavy fruit; look for splits at the crotch where the load pulled it open.
- Anything crossing or rubbing Remove the weaker of any two branches that touch. On a thorny tree, crossing branches also mean thorns dragging across neighboring fruit, which scars rind.
- Vertical water shoots in the center Take them off flush with the branch they rose from, leaving no stub, since a stub sprouts three shoots in place of one. Keep a shoot only if it fills a genuine hole in the canopy, and then shorten it by a third in early summer so it branches.
- Shorten branches that overreach Cut back to an outward-facing bud or side shoot, about a quarter inch (5 mm) above it. This is where you decide how far the tree will lean out over the pot, and therefore whether the fruit hangs over soil or over the path.
- Clear your own access last Stand back and find the branches whose thorns sit where your hands go when you water, feed and pick. Removing two or three of those is worth more to you over a year than any amount of shaping.
Working safely among the thorns
Citron thorns are longer and harder than lemon thorns and they sit at the base of every leaf on vigorous wood. Treat the tree as you would a rose you are lifting out of a bed. Leather gauntlets to the elbow, eye protection, and long-handled bypass loppers so your face is never inside the canopy.
Take out a thorny branch in two cuts rather than one. First shorten it to a stub you can hold, then cut that stub flush. Dragging a whole thorny branch out through the canopy tears leaves and rind on the way past and usually catches you as well.
You may safely snip thorns off branches that sit beside a path or a doorway; it does not harm the tree. Do not strip thorns from young growth across the whole plant in the hope of a comfortable tree. That is dozens of small wounds, each an entry point, and the wood becomes less thorny on its own as it matures.
Shaping for weight, not for looks
The shape you want is low, open and wide rather than tall. Keep the framework branches short enough that a two-pound (900 g) fruit near the tip does not bend the branch to the pot rim. In practice that means heading back the main limbs harder than feels natural, so they thicken instead of extending.
Open the middle enough that you can see daylight through the canopy in several places. Air moving through the center is the single most effective thing you can do against scale and the sooty mold that follows it, and it matters more on a citron than on other citrus because the tree spends part of the year in still indoor air.
| Job | When | How much |
|---|---|---|
| Rub off rootstock suckers | Any time, on sight | All of them |
| Remove dead, split or crossing wood | Any time | All of it |
| Thin water shoots | End of winter to early spring | Most; keep any filling a real gap |
| Shorten a kept water shoot | Early summer | By about a third |
| Head back overlong framework branches | End of winter to early spring | Up to a fifth of the canopy in total |
| Root prune and repot | Early spring, every 2-3 years | About 2 in (5 cm) off the rootball |
Root pruning, and keeping the dates
Once the tree is in its final pot, keeping it there means renewing the roots instead of the container. Every second or third year in early spring, lift the tree out, slice about two inches (5 cm) off the sides and base of the rootball with an old bread knife, and set it back into the same pot with fresh mix packed around the outside. Reduce the canopy by roughly the same proportion at the same time so the smaller root system is not asked to feed more leaf than it can.
Water it in, keep it out of direct sun for a fortnight, and do not feed for six weeks. Then write down the date. Root pruning on a two or three year cycle is impossible to judge by eye, and a tree that has quietly gone five years without it declines in a way that looks like a feeding problem and does not respond to feeding.