Olive

Split the nitrogen: half at growth start, the rest before bloom

Give half the year's nitrogen in early spring as growth starts and the remainder before the tree flowers. Aim for 8 to 20 inches of new shoot growth a year and adjust the rate up or down from what the tree actually gives you. A mature dooryard olive in reasonable soil often needs nothing at all. Nitrogen applied after flowering pushes vegetative growth at the expense of the crop, and the soft growth it forces is also what reduces cold hardiness and dilutes oil quality. Getting it in before bloom feeds the flowers and the fruit set instead of the shoots.

⚠ Stop nitrogen well before fall - late-season applications force frost-tender new growth into winter on a tree that is already cold-sensitive. If you want to fertilize by numbers, sample leaves between June and early August, when leaf nutrient levels are most stable. Boron has a very narrow margin between deficiency and toxicity, so correct it only with small amounts.

Olive knot: do your pruning in dry summer weather

Take your annual pruning in dry summer weather, not in winter or spring. Open the canopy so light reaches the interior where next year's fruiting wood forms, and cut out any knotted, galled twigs well below the swelling. Wipe or dip your shears in a 10 percent bleach solution between cuts and between trees. Olive knot bacteria cannot enter intact bark - they need a fresh wound and rain to wash them into it. Pruning wounds made in the dry summer months are not susceptible to infection, while winter and spring cuts sit open through the rains and become new infection courts.

⚠ Bag the knotted prunings and remove them rather than chipping them back under the tree. Sterilize tools with a 10 percent bleach solution any time you must prune outside the dry season, because the bacteria ride on the blades from tree to tree.

Hang an olive fruit fly trap and read it weekly

Hang a yellow sticky trap baited with pheromone or ammonium bicarbonate, or a McPhail or Olipe trap baited with torula yeast, in the canopy and check it once a week through summer and fall. Replace yellow sticky traps about monthly, or sooner if they get wet, dusty, or clogged with other insects, and refresh McPhail lures on schedule. Olive fruit fly can finish a generation in as little as 30 to 35 days at optimum temperatures of 68 to 86 F, so a population builds fast and out of sight - the maggot is inside the fruit. The trap catch is the only thing that tells you whether to bait at all and when to start; by the time you can see stung fruit, the larvae are already in.

Peacock spot: copper on the leaves before the rains start

Spray a fixed copper fungicide, copper sulfate, or Bordeaux mixture to thorough coverage of the whole canopy in late fall, before the first sustained rains arrive where you are. Repeat in spring if wet weather keeps up. Peacock spot spores germinate and infect leaves between 35 and 80 F when about 48 hours of free moisture is present, so nearly all new infection happens during fall and winter rain. Untreated, it defoliates the tree, which weakens the following bloom and cuts the crop.

⚠ Copper is a protectant that works only on the leaf surface - it must be on the tree before the rain, not after, and it will not cure infections already inside the leaf. Copper is allowed with restrictions in organic production; confirm your specific product is listed.

Olive fruit fly: spinosad bait once your traps catch flies

Start spinosad bait (GF-120 NF Naturalyte Fruit Fly Bait) as soon as your traps are catching adult flies, or about 2 to 3 weeks before pit hardening, whichever comes first. Put it out as a coarse spray or stream of large droplets onto a small patch of foliage on part of the tree rather than covering the canopy, and repeat every 7 days as long as flies keep showing on traps. Apply pre-dawn or in the early evening so the droplets resist evaporation. This is a bait, not a contact insecticide - the adult fly has to find it and feed on it, so a few large wet droplets outperform a full-cover spray and an evaporated droplet does nothing. The point is to kill the females before they sting the fruit, which is why the trap catch, not the calendar, starts the program: once the maggot is inside the fruit no spray reaches it.

⚠ Spinosad has a 0-day preharvest interval on olive. This is a fruit-stage bait and must never be applied during bloom - no insecticide on a flowering tree. Spinosad is toxic to bees while the spray is still wet, so keep bait droplets off any open blossoms and apply outside foraging hours. Follow all label requirements.

Pick at the ripeness you want - then cure, always

Decide what you are making before you pick. Green-ripe olives come off while the fruit is still firm and has turned an even pale green to straw color. Naturally black-ripe olives stay on the tree until they reach dark red, purple, or black, which UC Davis puts at roughly 3 to 4 months past the green stage. Either way, every olive has to be cured in water, brine, dry salt, or lye before it is edible. Raw olives are loaded with oleuropein, a bitter compound most abundant in green fruit. Curing is what leaches or chemically breaks that bond - there is no ripeness at which an olive becomes good to eat straight off the tree. Ripeness is a choice about flavor and texture, not a deadline.

⚠ Use a tested curing recipe from a food-preservation source, not an improvised one - UF/IFAS FS469 (Fermented Foods: Olives) covers brine, lye, and dry-salt methods. Lye is caustic and demands eye and skin protection plus complete rinsing. Brine-cured olives carry a high salt load - a preservation requirement, not a nutrition feature.

Strip and destroy every leftover olive after you pick

Once you have harvested, go back and strip every olive still hanging in the tree, then rake up all the fruit on the ground. Bury it at least 4 inches deep or bag it for the landfill. Do not leave it in a pile, and do not compost it in place. Larvae in leftover fruit drop out, burrow into the soil, and pupate there - that carryover is exactly the population that stings next year's crop. Fruit left hanging on the tree keeps feeding fly generations right through the fall.

⚠ Mulching or mowing the dropped fruit also works if you can destroy it thoroughly; a shallow pile of culls just concentrates the next generation next to your tree.