Yuzu

If scale or mites built up last season, spray the trunk and limbs with a 2 percent horticultural oil solution, mixed to the dilution on your product's label, to the point of run-off. Do this before new spring growth starts, on a day when temperatures are above 45 degrees F. Oil kills by smothering, so it works on the armored scales and overwintering mite eggs that contact insecticides cannot reach. Hitting them before the flush breaks means the new leaves emerge onto a clean tree instead of into an established population.

Start feeding when growth begins in spring and repeat through midsummer, then stop. Use a balanced 8-8-8 at roughly half a pound per year of tree age for a bearing tree, spread out to the dripline and watered in. Young trees take smaller, more frequent doses: about a third of a pound at the first spring feeding in year one, working up to a pound by late summer of that year. Citrus pushes growth in flushes, and nitrogen applied late in the season forces a soft flush that has no time to harden before frost. That tender wood is the first thing a freeze kills, so a late feeding trades next year's fruit for this year's growth.

Wait until the spring flush has fully expanded and matured, then prune. Take out water sprouts, suckers from below the graft, dead or damaged limbs, and any branches crossing and rubbing. That is all yuzu needs. Cut back into living wood at a branch crotch, leaving no stubs. After a cold winter the true extent of freeze damage to branches may not be clear within the first few months. Pruning early means guessing at the line between live and dead wood and cutting twice. Waiting for the new spring flush to fully expand draws that line for you.

Through the growing season, turn leaves over and look for scale bumps, stippled bronzed foliage from citrus red mite, whitefly, mealybug or black citrus aphid. Sticky honeydew and the sooty mold that grows on it are the giveaway. If you find them, treat with insecticidal soap or a 1 percent horticultural oil on tender new growth, 2 percent on mature foliage. These are all sap feeders that build slowly and are cheap to stop early and hard to stop late. Catching them while the colony is small is the difference between one soap spray and a season of sooty mold shading out the leaves.

On trees under about four years old, watch each new flush after bloom for silvery serpentine mines and curled leaf tips. If young trees are being set back, spray spinosad while the new flush is still tender and egglaying moths are active. Residues are short lived, so repeat every 7 to 14 days while that flush is expanding. Mature trees more than four years old carry a dense canopy of older foliage, tolerate the damage with negligible effect, and rarely if ever need treating. The moth can only lay into tender, half-grown leaves; once foliage hardens it is immune. Spraying a fully expanded flush is spraying leaves the insect can no longer use. On a young tree the repeated mining genuinely slows growth, which is why the age cutoff matters.

Yuzu ripens in fall as the rough, pebbly rind breaks from green to yellow-green and then yellow. Cut fruit off with clippers rather than pulling, to avoid tearing the rind. You can also pick it green and hard earlier — yuzu is used for cooking primarily while still green, which falls in September to October. Begin harvesting as the first few fruits ripen, which stretches the picking period by a week or two, and get the whole crop off before a hard freeze is forecast. Yuzu is grown for the fragrant oily rind and the juice, not for fresh eating, so peel condition is the whole crop. Citrus fruit on the tree freezes easily at 26 to 28 degrees F, especially when those temperatures hold for several hours, and freeze-damaged fruit loses the aromatic oils that were the point.

Before the first freeze, bank clean soil around the trunk to a height of about 15 inches, or wrap the trunk with an insulating material such as fiberglass or foam rubber at least 6 inches thick, making good contact with the soil. Use clean mineral soil, not compost or other organic matter. Remove soil banks after the last chance of freeze in early spring. If you can run water, a microsprinkler is the most effective protection there is: at least 10 gallons per tree per hour, a 90-to-180-degree emitter placed within 12 inches of the trunk on the side facing the incoming wind with the spray focused on the graft union, run continuously for the entire duration of the freeze. Yuzu is among the hardiest edible citrus, but the graft union is the one part it cannot regrow from. If the trunk survives, a frozen top rebuilds itself. If the union dies, you are left with a trifoliate rootstock and no yuzu.