Gadenin日本語Get the appWater on soil moisture, not on a schedule
Kabosu carries a much larger fruit than the small sour citrus it is usually compared with: a good one weighs four to five ounces (110-140 g) against a bare ounce (30 g). Almost all of that extra weight is juice, and juice is water the tree pulled up in the eight weeks after the fruit set. Miss that window and you still get fruit, but thick-skinned, light, dry fruit that gives half of what it should.
Push a finger two inches (5 cm) into the soil at the edge of the canopy. If it comes out dry, water; if it comes out cool and damp, wait. In practice an established tree in open ground needs a deep soak every seven to ten days in mild weather and every three to four days once daytime temperatures sit above 86F (30C). A container tree in the same heat needs water daily.
When you do water, water properly. Ten to fifteen gallons (40-60 liters) delivered slowly over a mature tree's root zone will wet the soil to the depth the roots are in. Five minutes with a hose wets the mulch and nothing else, and it trains the roots up to the surface where they cook.
| Stage of the year | Watering interval | What is at stake |
|---|---|---|
| Before growth starts | Only if soil is dry 4 in (10 cm) down | Wet cold roots rot; the tree is using almost nothing |
| Flowering | Every 7-10 days, even soil | Swings between wet and dry drop flowers |
| Six weeks after set | Every 5-7 days, never let it dry | This is when fruit cells divide and set the final size |
| Peak summer swell | Every 3-4 days, deep | Every dry spell here costs juice |
| Approaching picking | Ease back slightly | Slightly firmer soil concentrates the flavor |
Feed three times, and stop feeding nitrogen in late summer
Citrus is a heavy feeder and kabosu, being a big vigorous tree, is heavier than most. Three feeds a year cover it: one as growth starts, one just after the fruit has set, and a third in mid summer to carry the swell. Use a balanced feed with magnesium and iron included, because citrus on limey soil runs short of both and shows it in the leaves long before it shows in the crop.
The one rule people break is the late feed. Nitrogen applied after mid summer pushes a flush of soft growth that will not harden before cold weather, and that soft thorned wood is exactly what dies back first and what aphids find first. If you want to give the tree something late in the year, give it potassium, which helps the fruit and the wood harden rather than driving new shoots.
| Feed | Timing | Type | Rate for a mature tree |
|---|---|---|---|
| First | As buds swell | Balanced with trace elements | Full rate |
| Second | Once fruitlets are pea sized | Balanced, higher nitrogen | Full rate |
| Third | Mid summer | Balanced or high potassium | Half rate |
| Late season | After mid summer | Potassium only, no nitrogen | Light |
Read the leaves
Citrus leaves are a decent diagnostic and worth two minutes every few weeks. Yellowing between the veins with the veins staying green on older leaves is magnesium; the same pattern on the newest leaves at the shoot tips is iron, and it usually means the soil is too alkaline for the tree to take up what is already there rather than that the iron is missing.
A uniform pale yellow across the whole tree is nitrogen or, far more often, a waterlogged root that cannot take nitrogen up. Check the drainage before you reach for feed. Leaves curling downward with the tips crisp is drought or salt build-up in a container; leaves that cup upward and look leathery are usually sun and wind stress on a tree that is short of water.
Leaf drop in itself is not an emergency. Citrus sheds a proportion of its oldest leaves whenever conditions change sharply, and a tree that loses a quarter of its leaves after a cold snap or a move will refoliate. It is continuous drop with no new growth that means the roots are in trouble.
Thin the crop if you want juice
A kabosu that has set well will carry more fruit than it can fill. The tree drops some of it naturally a few weeks after set, but on a good year it still holds too many, and the result is a heavy crop of small dry fruit followed by a light year as the tree recovers.
Once the natural drop has finished and the fruitlets are the size of a walnut, take off enough so that the ones left are roughly a hand's width apart along the branch. Remove the smallest, the misshapen, and anything hanging where a branch is clearly bending. On a young tree carrying its first crop, leave no more than a dozen fruit however many it set.
The trade is straightforward: fewer fruit, more juice in each, and a tree that crops properly again next year instead of taking a year off.
Note the date the natural fruit drop finishes and how many fruit you left on each tree. Compare that with the weight of juice you get. Two seasons of that record tells you your own tree's carrying capacity better than any general rule.
Container trees need a different rhythm
Kabosu will crop in a container, but only in a large one: twenty inches (50 cm) across is the working minimum for a fruiting tree, and it will need repotting or root pruning every second or third year. Use a free-draining mix with a real proportion of grit or bark, not a peat-based compost that turns to a wet block.
Watering is where container trees are won or lost. The mix should go from properly wet to just-damp between waterings, never to bone dry and never permanently saturated. Lift the pot or push a finger in; do not guess from the surface. Feed at every second watering through the growing season with a diluted citrus feed instead of relying on three heavy applications, because everything you apply washes out of a pot quickly.