Gadenin日本語Get the appPlan for a big tree, not a patio citrus
Kabosu grows away faster and larger than the small sour citrus most people compare it with. Left on its own roots and unpruned it will reach twelve to sixteen feet (3.6-5 m) tall with a canopy just as wide, and it gets there in eight to ten years rather than twenty. The wood is stiff, the branches are long and whippy while young, and the thorns on that young wood run one to two inches (3-5 cm) and sit at nearly every leaf base.
That combination is what decides the position. You need to be able to walk right around the tree at full size with a ladder and a picking bag, because the fruit is heavy and you will be reaching into the canopy for it every year. A tree jammed against a fence gets picked from one side only, and the unpicked half is the half that hangs on too long and goes yellow.
Set the trunk at least ten feet (3 m) from a wall or another tree, and keep a clear yard (90 cm) of dead space beside any path, tap, washing line or doorway. Thorn injuries almost always happen where somebody cuts a corner in the dark.
| Neighbor | Minimum distance from trunk | Why |
|---|---|---|
| Wall, fence or shed | 10 ft (3 m) | You must be able to get a ladder behind it to pick and prune |
| Another kabosu | 16 ft (5 m) | Mature canopies meet sooner than people expect |
| Path or lawn edge | 6 ft (1.8 m) | Fruiting branches sag a long way under a full crop |
| Doorway, tap, washing line | Do not plant there | Anywhere used in a hurry is the wrong place for these thorns |
| Overhead cable or eaves | 16 ft (5 m) clearance | Reducing height later means cutting into old thorned wood |
Take a grafted tree, and know your rootstock
A grafted plant carries adult wood and flowers three to four years after planting. A tree grown from a pip has to pass through its own juvenile phase first, which for this citrus runs ten years or more, and juvenile wood carries the longest and most vicious thorns of all. Nothing you do with feed or pruning shortens that wait, so raise seedlings only as rootstock.
The rootstock sets the final size and the cold tolerance more than the top does. A tree on a dwarfing stock stays around eight feet (2.4 m) and is far easier to pick; on a vigorous stock the same tree runs away to sixteen feet (5 m) and fruits a year later. Find the swollen graft union low on the trunk, note the leaf shape below it, and remember it: everything that ever grows from below that line is a sucker and must come off.
| Plant type | First fruit | Mature height | Use it for |
|---|---|---|---|
| Grafted, dwarfing stock | 3-4 years | 8-10 ft (2.4-3 m) | Small gardens and large containers |
| Grafted, vigorous stock | 4-5 years | 12-16 ft (3.6-5 m) | Open ground, biggest crops |
| Seedling from a pip | 10+ years | 16 ft (5 m) or more | Rootstock only |
| Rooted cutting | 5-6 years | 10-14 ft (3-4.2 m) | Workable, weaker root system |
Plant high and plant into the ground you have
The usual way to lose a young kabosu is not cold, it is a wet root. Citrus roots want air, and a planting hole dug in heavy ground and filled with rich compost behaves like a sump: water runs in from the surrounding clay and sits there all winter.
- Dig wide, not deep Make the hole three times the width of the rootball and no deeper than the rootball itself. Break up the sides with a fork so the roots can leave rather than circling in a smooth-walled pit.
- Mound on heavy soil If water stands anywhere on the site after rain, raise the whole planting position eight to twelve inches (20-30 cm) above the surrounding grade with the soil you dug out plus coarse grit. A raised position is worth more than any amount of drainage material in the bottom of a hole.
- Backfill plain Use the soil that came out, with no more than about a fifth grit or coarse bark added on clay. Do not enrich the backfill; save the compost for a surface mulch where it will feed the surface roots that citrus actually uses.
- Set the rootball proud The top of the rootball should finish one to two inches (3-5 cm) above the final soil level, and the graft union should sit at least four inches (10 cm) clear of the soil and of any mulch. It will settle. A tree planted an inch too deep sulks for years.
- Stake low, water in hard Use a short stake tied at about a third of the tree's height so the top can still flex and thicken the trunk. Water in with five gallons (20 liters) slowly, then mulch two inches (5 cm) deep in a wide ring, kept a hand's width clear of the bark.
The first season: no fruit, no strong feed
A newly planted tree will often try to flower in its first spring. Rub those flowers off. A crop set on a root system that has not yet reached out into the soil costs you a year of frame growth, and the frame is what carries every crop after this one.
Water is the whole job for the first twelve months. Give five gallons (20 liters) once a week in cool weather and twice a week once daytime temperatures pass 77F (25C), delivered slowly at the edge of the rootball rather than at the trunk. Little and often keeps the roots inside the original rootball and is the reason so many young citrus never establish.
Hold back nitrogen until you see the first new shoots extending, then feed lightly. A heavy feed on an unestablished tree pushes soft, extremely thorny growth that scorches in the first hot spell.
Write down the planting date, the rootstock, and where the graft union sits relative to the soil. Three years on, when you are trying to work out whether a shoot from the base is a sucker or a real branch, that one note settles it in seconds.