Lime

Limes need very little pruning. In late winter, after the last hard freeze in your area and before new growth begins, take out dead wood, remove branches that cross or rub, and rub off any basal suckers coming from below the bud union. Avoid extensive pruning in the late fall and early winter. Shape only, and never remove more than a third of the canopy in one pass. Shoots below the bud union are rootstock, not lime, and if left they flourish at the expense of the grafted variety. Cutting before the freeze risk is over pushes a tender flush straight into cold weather, and a mature citrus that is pruned hard loses the canopy that shades its own fruit.

Watch the forecast through the cold months and act before the night arrives, not after it. 'Tahiti' lime leaves are damaged below 28F, and the tree takes severe damage or dies below 24F. Where those temperatures are realistic in your winter, grow the tree in a container you can carry indoors ahead of a freeze rather than in the ground. Lime has the narrowest cold margin of the common citrus, and the gap between leaf scorch and a dead tree is only about four degrees. A freeze that merely burns a lemon can take a lime out entirely.

Split the year's fertilizer into three applications as the crop builds: at early bud break, again at fruit swell, and again when the fruit reach about an inch in diameter. Use a complete fertilizer with micronutrients, 6-6-6 or 8-8-8 on young trees and 10-10-10 on mature ones, unless a soil test says otherwise. Lime pushes its heaviest growth and sizes its fruit across this stretch, and splitting the nitrogen across the three flushes feeds the crop steadily instead of dumping it all on the roots at once.

Only if canker is present in your area: begin copper sprays once the young fruit are about a quarter to a half inch across, and repeat at roughly 21-day intervals while the fruit expand. Fruit remain susceptible for about 60 to 90 days after petal fall; once past that, stop spraying, because later infections make only small inconspicuous pustules. The bacterium can only enter through stomates on the fruit surface while those stomates are still opening on expanding fruit. Copper is a short-lived physical barrier over that window and does essentially nothing outside it.

Inspect every new flush for psyllid nymphs and the waxy tubules they secrete on the tender tips - all stages feed on new growth, so the flush is the only place to look. On a dooryard tree, lean on biological control rather than sprays: the parasitoid Tamarixia radiata reaches up to 70 percent parasitism of nymphs where it is established, and it only persists where insecticide use stays low. Timing nitrogen and pruning for summer and winter, when psyllids are least active, keeps the tree from flushing into a psyllid peak. The psyllid vectors the bacterium behind huanglongbing, which has no cure and kills a lime tree within about five to eight years. The tender flush it breeds and feeds on is the whole of the problem and the whole of the scouting target.

On a young tree, spray horticultural oil as soon as new shoots begin to develop, repeating every 10 to 14 days and coating the expanding leaves. Stop once the leaves harden off. Mature bearing trees generally tolerate the mines and usually need no treatment, though a heavy infestation can reduce production. The moth lays only on soft, expanding leaves, so that flush is the entire control window - a hardened leaf cannot be mined and any spray after that is wasted. The mines matter mostly because the damage stunts young trees and makes them more susceptible to citrus canker where that pathogen is present, not because they starve the tree.

Harvest 'Tahiti' or Persian limes when they reach about 1 3/4 inches (45 mm) across and are dark to medium-dark green. The tree bears all year with a pronounced summer peak, so pick continuously rather than waiting for one date. A mature tree can carry 450 to 550 lbs of fruit. The rind runs from dark green to light yellow as the fruit passes maturity, and a lime picked at full green is at its peak of acidity and aroma. Yellow on the tree means the fruit is already past what you wanted from it.