Gadenin日本語Get the appWhat is actually happening
A yuzu sets the flower buds for next season during the current summer, while it is carrying this season's fruit. Developing fruit, and particularly the developing seeds inside it, produce hormones that suppress that bud formation. A tree loaded with a huge crop therefore builds very few flower buds, and the following spring it flowers thinly and gives almost nothing. With no crop to suppress it, that bare year builds an enormous number of buds, and the year after is another glut. The cycle then locks in and repeats.
Yuzu is more prone to this than most citrus for two reasons. It is naturally slow growing, so it has less spare capacity to carry a heavy crop and build buds at the same time. And it is heavily seeded, and it is the seeds that generate most of the suppressing hormone, so a given weight of yuzu suppresses harder than the same weight of a low-seeded fruit.
The years are usually described as an on year, the glut, and an off year, the bare one. Once you recognize which you are in, everything you do about it follows.
| Signal | On year (heavy) | Off year (bare) |
|---|---|---|
| Flowering | Sparse, scattered | Heavy, covering the tree |
| Fruit set | Light, then a big set the next spring | Very heavy |
| Shoot growth | Strong new growth | Weak, short shoots |
| Fruit size | Larger fruit, fewer of them | Small, crowded fruit |
| What to do | Feed and prune normally | Thin hard and early |
How the cycle usually starts
A tree does not drift into alternate bearing gradually. It is nearly always thrown into it by a single event that either wipes out one year's crop or produces an abnormally large one.
The usual triggers are a late frost that kills the flowers, a hard prune that removes most of the flowering wood, a drought during fruit development, or a first big crop on a young tree that nobody thinned. Any of these creates one extreme year, and the tree's own biology does the rest.
That is worth knowing because the fix at the start is trivial and the fix later is a multi-year project. If you know you have just had a frost-killed spring, expect an enormous set the following year and plan to thin it before it happens.
Breaking the cycle
You break alternate bearing in the on year, by removing fruit early enough that the tree still has the capacity to build buds. Thinning late, once the fruit is well grown, does very little, because the suppression has already happened. Timing is the whole technique.
- Wait for the natural drop, then look A yuzu sheds a large share of its fruitlets three to six weeks after flowering. Do not thin before that; you would be removing fruit the tree was going to shed anyway. Assess what is left once the drop has finished and the remaining fruitlets are marble sized.
- Thin while the fruit is still small Remove surplus fruit as soon as the natural drop ends, when fruitlets are around three quarters of an inch (2 cm). This is early enough that bud formation for next year has not been suppressed. Thinning after the fruit reaches full size will improve this year's fruit but does nothing for next year.
- Aim for one fruit per twenty to twenty-five leaves Rather than counting, work branch by branch: leave fruit spaced a hand's width apart along a branch, and take off every cluster of two or three touching fruit down to the single best one. Remove the small, misshapen and damaged fruit first.
- Take more off the inside and the branch tips Fruit deep in the canopy ripens poorly and fruit at the very ends of thin branches drags them down and breaks them. Clearing those two places does most of the thinning for you.
- Take a share of the crop green Picking part of the crop while it is still green, in late summer, removes load at the point in the season when bud formation is under way. On a heavily laden tree this is thinning that you actually get to use.
Removing fruit feels wrong when the tree is covered in it, and this is where most people fail. A yuzu carrying its full unthinned set gives you a mass of small poor fruit this year and effectively nothing next year. Thinning by half typically gives more usable fruit over two years, not less.
Support the tree through both halves of the cycle
Feeding and watering will not break the cycle on their own, but neglect will deepen it. Feed with a balanced citrus fertilizer from the start of growth in spring until late summer, then stop so the wood hardens before winter. A heavily cropping tree needs that feed most, and it is the year people most often forget, because the tree looks like it is doing fine.
Never let a yuzu dry out during fruit development. Drought while fruit is sizing causes a heavy secondary drop and, worse, shuts down bud formation for next year, which converts a normal season into an off year. Water deeply once a week in dry weather rather than lightly every day, and keep two to three inches (5-8 cm) of mulch over the root zone.
In an off year, resist the urge to compensate with extra nitrogen. There is no crop to support, and the excess simply produces soft growth. Prune lightly in an off year at most, because you have relatively little flowering wood and cannot afford to remove it.
The record that makes the pattern visible
Alternate bearing is invisible in any single year and obvious across four. Each season, write down three things: the date of full flowering and roughly how heavy it was on a scale of one to five, whether you thinned and when, and the final count or weight of fruit picked.
Add the two events that trigger the cycle: any frost that hit the flowers, and any pruning heavier than a normal winter tidy. Four years of that lets you see whether you are in a two-year cycle, which year is which, and whether the thinning you did actually flattened the swing. Without the numbers you will simply remember the last good year and the last bad one, which tells you nothing about what to do this spring.