Lemon

Use a fertilizer labelled for citrus and follow the bag rate. With a slow- or controlled-release product, two applications carry the year: one in February or March before bloom and one around September or October. If you use a dry soluble fertilizer instead, split it into four smaller feedings. Spread it in the root zone rather than piled against the trunk. A young tree needs about a quarter pound of a 6-6-6 type product every three to four months, stepping up as it grows; a mature bearing tree takes roughly 3 to 4 pounds per application, two to three times a year. Citrus is evergreen and pushes growth in flushes rather than one spring surge, so it draws nutrients across a long season - but nitrogen delivered right before bloom is what funds flowering and fruit set.

Once hard freezes are past and before the spring flush pushes, prune only lightly - enough to hold the tree near 7 to 10 feet tall and 10 to 15 feet wide and to take out dead, crossing, or damaged wood. Remove every sprout arising below the bud union at ground level, and cut out water sprouts in the canopy. Resist the urge to head the tree back hard. Lemons bear most of their fruit on the canopy periphery, so lightly pruned trees produce more fruit than heavily pruned ones - every branch you shorten is fruiting wood you removed. Suckers below the bud union come from the rootstock, not your variety, and will never make the lemon you planted; water sprouts are soft succulent growth that citrus leafminer moths prefer to lay eggs on.

Before cold arrives, mound clean, weed-free soil around the trunk as high as you reasonably can - up into the scaffold limbs if possible, but at minimum covering the graft union. Water early in the day ahead of a freeze so bare, moist soil can soak up heat and radiate it back overnight, and pull mulch away from under the tree for the winter because it blocks that heat. If you drape a cover, use cloth rather than plastic and take it all the way to the ground to trap the rising heat, then remove it as soon as the cold passes. Remove the soil bank once freeze danger ends, working carefully so the shovel never wounds the trunk. Lemon is the most cold-tender of the common citrus: flowers and young fruit die near 29F, leaves drop at 22 to 24F, and wood is damaged around 20F. Soil is a good insulator, so banking protects the graft union - even if the top is killed, the grafted variety can regrow rather than resprouting as worthless rootstock.

Starting with the spring flush and repeating monthly through fall, walk slowly around the tree and inspect the newest forming leaves. Look for twisted or notched leaves, adults feeding head-down with the body cocked up at a 45-degree angle, and nymphs excreting waxy tubules that look like a curly tube with a bulb on the end. Honeydew and black sooty mold are the giveaway from a distance. Report suspected psyllids or greening symptoms to your county agricultural commissioner or state agriculture department. The Asian citrus psyllid vectors huanglongbing, or citrus greening, which infects the tree's phloem, kills the tree in roughly 5 to 8 years, and has no cure. The psyllid can only lay eggs and develop on new flush, so the flush is the one place and time scouting actually finds it.

Water from flowering through fruit development, delivering it to the soil rather than over the canopy. A newly planted tree wants water every other day the first week, then once or twice weekly for a couple of months. A tree four years or older needs water only during prolonged dry periods. Flowering through fruit sizing is when the tree is actually building the crop and when a water deficit costs fruit, but wetting the foliage increases disease problems - and citrus roots resent staying wet, so over-watering an established tree causes decline rather than helping it.

As petals drop and the tiny fruit begins to size, apply one to two copper-based fungicide sprays at early fruit development. Cover the newly emerging leaves and young fruit, which are the tissues at risk. Citrus scab is the major fruit disease of lemon, raising corky wart-like formations on the rind. The fungus only infects tissue while it is young and expanding - once the fruit rind hardens it can no longer be infected, so a spray applied after the window closes protects nothing.

Expect silvery serpentine mines and curled leaves on summer and fall flush. On a mature tree, note it and do nothing - the damage is cosmetic and the tree carries the crop regardless. Instead, remove water sprouts that give the moths a place to lay, and hold off nitrogen that would force more tender flush. Only on a young tree, where leaf loss genuinely costs growth, consider spinosad. Leafminer infestations on mature trees rarely if ever require insecticide treatment, and the products available for backyard trees are not very effective. Many leave residues that kill the Cirrospilus and Pnigalio parasitic wasps already suppressing the leafminer, so spraying reliably makes next year's infestation worse than doing nothing.

Lemons are mature and worth picking once they reach about 1.5 to 2 inches in diameter, even while the peel is still light green. Picked at that stage, they cure at room temperature until the peel turns yellow and the juice content rises. If you would rather pick tree-ripe, wait for full yellow and a fruit that feels heavy for its size. Clip or twist gently rather than yanking. Peel color is a poor ripeness signal on lemon - a fruit can be fully juicy while still green, and lemons hold on the tree in overlapping flushes rather than ripening as one crop, so size and weight tell you more than color does.