How to Prune a Hassaku: Keeping a Vigorous Citrus Open and Reachable

The window is wide because the tree is empty

Hassaku is cleared in early winter and the fruit is then mellowed indoors, so unlike citrus that hang their crop into spring, the tree stands bare of fruit for months. That gives you a genuinely comfortable pruning window: from the end of hard frost in late winter until the buds begin to move in spring. Prune once the worst cold has passed, because fresh cuts and hard frost together cause dieback on cut ends.

Do not prune in autumn. Cutting then pushes a soft flush that has no time to harden, and on a tree as vigorous as this one the response is dramatic and entirely wasted. If you find yourself needing to remove something in autumn, limit it to genuinely broken or diseased wood and leave the shaping until spring.

One light corrective pass in early summer is acceptable and often useful on hassaku, purely to rub out or shorten the vertical water shoots that a spring pruning provokes. Doing that while the shoots are soft, before they harden into wood, saves you cutting thumb-thick suckers next spring.

Prune for light in the middle and for a canopy you can reach

Two objectives govern every cut on this tree. The first is light: hassaku builds a dense shell of foliage, and once the interior is dark the fruiting wood inside it dies back and the crop retreats to the outside of the canopy, where it is exposed to wind and hard to reach. The second is height: this is a big tree that keeps trying to get bigger, and a canopy you need a tall ladder to reach is a canopy you will not thin, will not inspect and will not pick properly.

Work towards an open center with three to five well-spaced main scaffolds, and keep the tree topped at a height you can work from a short step. Do that with reduction cuts back to a suitable side branch rather than by shearing across the top; shearing produces a thicket of vertical regrowth and makes the shading problem worse.

Be moderate. Hassaku responds to hard pruning with a wall of water shoots and a lost crop. Removing more than about a fifth of the canopy in one year sets off that response. If the tree has been neglected and needs major reduction, spread the work over three seasons and take one scaffold or one section per year.

Working through the tree

Do the work in this order and you will not overcut. Each stage removes wood that makes the next decision easier, and by the time you reach the shaping cuts, most of what needed to go is already on the ground.

1. Clean your tools first Wipe blades with alcohol before you start and between trees. Citrus wood carries disease easily and a dirty cut on a large scaffold is a wound you live with.
2. Take out the dead and the damaged Remove anything dead, broken, split at the crotch or obviously diseased, cutting back to sound wood. Do this before making any judgement about shape.
3. Clear the rootstock suckers and the skirt Pull off every shoot below the graft union, then lift the lowest branches until there is 18 to 24 inches (45 to 60 cm) of clear space beneath the canopy. That gap keeps fruit off the soil and cuts off the ant route into the tree.
4. Remove crossing and inward-growing branches Take out branches that rub, that cross the center, or that head back into the canopy. These are the branches that create the dark interior in the first place.
5. Thin the interior Standing under the tree and looking up, remove enough whole small branches that you can see dappled sky through the canopy. Remove complete branches at their origin rather than shortening many tips.
6. Reduce the height Cut any leader that has run above your working height back to a well-placed outward-facing side branch at least a third of the parent's thickness. That side branch takes over and the cut does not erupt in suckers.
7. Shorten the long, whippy outer shoots Trim back the longest slender shoots by about a third. A hassaku fruit is heavy and a whip that reaches the ground under one fruit is a branch that tears.
8. Step back and stop Walk twenty feet away and look at the whole tree. If more than a fifth of the canopy is gone, put the saw down and finish the job next year.

What not to cut

Do not remove the thin, twiggy growth on the outside of the canopy just because it looks untidy. That is where hassaku flowers and fruits. Beginners routinely tidy a citrus into barrenness by stripping the fine wood and leaving only the clean structural branches.

Do not leave stubs. Cut just outside the raised collar at the base of a branch, so the tree can seal the wound. A stub dies back, and the dieback travels into the branch behind it.

Do not strip the canopy so thoroughly that interior bark and major scaffolds are suddenly in full sun. Citrus bark sunburns, and a sunburnt scaffold splits and admits rot. If a big cut has exposed a limb, paint it with dilute white latex for the following summer.

Do not seal cuts with tar or wound paint. It traps moisture against the wound. A clean cut at the collar, left open, seals itself faster than any dressing will let it.

If your tree has become a tall, dark, bare-centered thicket, resist the temptation to fix it in one winter. Take a third of the excess height in each of three years. You will lose part of one crop rather than all of two, and you will not spend the next five years cutting out water shoots.

Record what you cut and where the fruit actually was

Before you prune, walk the tree and note which parts of the canopy carried good fruit last season and which carried none. Do it in the same notebook every year and after two seasons the pattern is obvious: the dark side of the tree stops producing long before you would have guessed from looking at it.

Afterwards, note the date, roughly how much you removed, and any large cut you made with its location. When a scaffold dies back two years later, knowing that it was reduced hard in a particular spring is the difference between diagnosing the cause and guessing at a disease.