Kabosu Growing Calendar: What to Do in Each Season and Why

The shape of the year

Everything on this tree hangs off one long fruit-filling period. Flowers open in late spring, the fruit sets, the surplus drops, and then the fruit spends roughly four to five months swelling. Picking happens while the fruit is still deep green, before the cool nights of autumn start turning it yellow. That gives four clear stages, and each has one job that matters more than the rest.

The stage most people underestimate is the swell. Kabosu is grown for juice volume, and the juice is put into the fruit during that summer stretch. A dry fortnight in mid summer costs you more than anything you can do in spring.

Late winter to spring: prune, feed, then leave it alone

Prune once the hard cold has gone and before the first flush extends. Take out suckers from below the graft, dead and crossing wood and the vertical water shoots, then hold the height. Follow with the first balanced feed as the buds swell, and mulch two inches (5 cm) deep in a wide ring kept clear of the trunk.

Once flowering starts, do very little. The mistakes at this stage are a heavy nitrogen feed, which makes the tree grow shoots instead of setting fruit, and letting the soil swing from dry to soaked, which drops flowers. Even moisture and no interference is the whole prescription.

Kabosu sets fruit on its own without another tree nearby, so a poor set is a weather or a watering problem, not a pollination one. A cold snap or heavy rain during the few days the flowers are open is the usual explanation for a light year.

Summer: the stage that decides your crop

Wait for the natural drop to finish, which is usually a few weeks after flowering, then thin what is left so the remaining fruit sit roughly a hand's width apart. Give the second feed when the fruitlets are pea sized and a lighter third feed in mid summer, then stop nitrogen entirely.

From then on the job is water. A deep soak every three to four days in hot weather, ten to fifteen gallons (40-60 liters) on a mature tree, applied slowly at the canopy edge. Keep the mulch topped up, because on a hot day the mulch is doing as much as the watering can is.

1. After the natural drop Thin to about a hand's width between fruit. Take off the smallest and any that are scratched or misshapen. On a young tree's first crop leave a dozen fruit at most.
2. Second feed Apply a balanced feed with trace elements once the fruitlets are pea sized. This is the last full-rate feed of the year.
3. Third feed, half rate In mid summer, half rate, and after this no more nitrogen. A late nitrogen feed produces soft thorned growth that will not harden before the cold.
4. Water through the swell Deep soak every three to four days above 86F (30C), every five to seven days below it. Never let the tree dry out and then flood it; that combination splits fruit and drops it.
5. Check the flush Turn over young leaves at the shoot tips each time you water. Aphids and leaf miner both arrive on the summer flush and are trivial to deal with in the first week.

Autumn: pick before the color goes

The fruit is at its best deep green, glossy and heavy. Once you see the first fruit at the top of the tree losing that green, the whole crop is on a clock: pick it all within a couple of weeks. Yellowing takes both the acidity and the skin aroma with it and neither comes back.

Cut each fruit with snips rather than pulling, cut the stalk flush to the button, and keep the fruit dry and unbruised. Sound green fruit stored somewhere cool, dark and out of a draft at 41-50F (5-10C) will keep four to six weeks and often longer, which means a single afternoon's picking supplies you for well over a month.

Once the tree is empty, do nothing more than tidy broken wood. Save the structural pruning for late winter.

Winter, and what to write down

In cold weather the tree is near dormant and its main enemy is wet roots. Water only if the soil is genuinely dry four inches (10 cm) down. Where frost is expected, protect the trunk and the graft union with a wrap and row cover the canopy of a young tree on the coldest nights; established trees on hardy rootstock in a sheltered spot generally need no more than the wrap.

This is also the right point to write the year up while it is still fresh. Four figures are worth more than any amount of description, and they compound: after three years they tell you whether your thinning is right, whether your watering held through the summer, and how long your storage spot really keeps fruit.