Papaya

Start seed in sterile cells once the cold is done

Sow seed about half an inch deep into individual 2 x 2 inch cells filled with sterile, well drained potting media and set them in full sun. Expect germination in 10 to 21 days. Harden the seedlings off in the nursery and move them out at about 6 weeks old, when they are 4 to 8 inches tall, after all danger of frost has passed. In cold regions you can hold seedlings in a greenhouse over winter and plant them out in spring. Papaya needs a long, unbroken warm season to reach fruit, and a plant set out too early loses it to frost. The media has to be sterile because damping-off from Pythium, Phytophthora and Rhizoctonia is what kills papaya seedlings, and used media carries those fungi in with the seed.

Plant into full sun, sharp drainage, and soil that has never grown papaya

Pick the warmest, sunniest spot you have and dig a hole 3 to 4 times the diameter and 3 times as deep as the container the plant came in. Space plants 7 to 12 feet apart, and at least 7 to 10 feet from other plants. Staking is optional, but if you stake, never tie with wire or nylon rope, which will damage the trunk as it thickens; use a cotton or natural fiber string that degrades slowly. If papaya has grown on the ground before, add half a cubic foot of soil that has never grown papaya to each planting hole (the 'virgin soil' technique, CTAHR F&N-3). Papaya roots are killed by waterlogging in a matter of hours - CTAHR notes plants 'can be killed when subjected to puddled conditions for even a few hours'. Ground that has grown papaya before carries high levels of Phytophthora palmivora spores released as old fruit, trunk and root residue decomposes. The ring of clean soil lets the young roots get established in a fungus-free zone until they are old enough to withstand infection as they extend beyond it.

Step up to bearing rates as soon as it flowers

Up to about 7 months old, feed a quarter pound of a complete fertilizer carrying nitrogen, phosphate, potash and magnesium every 14 days. Once the plant flowers and starts setting fruit, shift to 1 to 2 pounds every other month, and add a micronutrient blend with manganese, zinc and boron up to once a month. On acid soils correct iron with iron sulfate; on high pH soils use chelated iron in the EDDHA form. A papaya has one terminal growing point that pushes leaves, flowers and fruit at the same time all year, so it feeds continuously rather than in flushes and runs down fast if starved. Boron shortage shows up specifically as bumpy, distorted fruit with latex weeping from the surface of developing fruit.

Read the first flowers and keep the hermaphrodite

Grow three seedlings together per spot and let them all flower, at roughly 6 months for most cultivars and about 8 months for Kapoho. When the buds open, look at the shape: a hermaphrodite flower is slender and of fairly uniform thickness, while a female flower is bulbous at the base and pointed at the tip. Keep one hermaphrodite and cut the rest off. For the UH Rainbow hybrid leave five plants per spot instead of three. Papaya seed segregates into female and hermaphrodite plants, and only the hermaphrodite carries pollen sacs and sets fruit on its own. A female left alone gives you gaps in production whenever no pollen is nearby. Standard solo cultivars segregate two hermaphrodites to one female, so keeping three seedlings gives a 97 percent chance at least one is hermaphrodite; Rainbow segregates 1:1, which is why it needs five.

Papaya ringspot virus: cut down infected plants, do not nurse them

Check plants through the whole growing year for yellow mottling in mosaic patterns between the veins on new leaves, leaves that are crinkled or deformed into narrow stringy lobes little wider than the veins, water-soaked or oily streaks on green stems and petioles, and ring-shaped spots on the fruit skin. Symptoms are most pronounced in cool weather and are suppressed in the heat, so do not read a clean-looking plant in midsummer as an all-clear. Destroy any plant showing these signs rather than leaving it standing, and do not let the stump regrow. Raise your own seedlings close to where they will be planted, and never carry papaya seedlings in from another region - seed is safe to move, seedlings are not. Do not plant cucurbits (watermelon, cucumber, squash, melon) near papaya. Papaya ringspot virus is the most severe papaya disease and is often the limiting factor in production worldwide. There is no cure, and an infected plant left in place is a permanent reservoir. It is spread by aphids - principally green peach aphid - which pick up the virus in seconds of feeding and carry it only a short distance for about half an hour, so nearby infected plants and nearby cucurbit hosts are what actually seed an outbreak; this is why removing the reservoir promptly and keeping alternate hosts away matters more than anything you could spray. The virus is not carried in seed, so a seedling moved from an infected area is the main way it arrives somewhere new.

⚠ CTAHR's commercial guidance is to kill aphids before roguing an infected plant so the vector does not disperse onto healthy neighbors. That is an insecticide application, and papaya flowers nearly continuously, so for a home planting it would put insecticide on open bloom - do not spray. Remove the infected plant promptly and keep cucurbit hosts away from the papaya instead.

Anthracnose: protectant cover sprays on the fruit column

Once fruit are setting, spray mancozeb over the fruit column on a regular interval, every 2 to 3 weeks in wet weather and every 3 to 4 weeks in dry weather. A copper product tank-mixed with the mancozeb increases efficacy, and a surfactant helps the spray spread and stick. Trim off only the leaves whose petioles angle below horizontal so the spray can reach the fruit, and keep trimming to a minimum in winter. Anthracnose infects the fruit while it is green and then sits latent, erupting as sunken black rot as the fruit ripens, so by the time you see a lesion the infection happened weeks ago. Fungicides on papaya are protectants with minimal impact once the disease is established, which is why coverage and interval matter more than the product.

⚠ Mancozeb registration and pre-harvest interval for papaya differ by state and product - read the label, confirm papaya is listed on it, and follow the stated pre-harvest interval before picking. Do not add an insecticide to this mix: papaya flowers nearly continuously, so a spray aimed at the fruit column is always going out over open bloom.

Bag young fruit against papaya fruit fly

While the fruit are still small and green, slip a paper bag or a piece of paint strainer cloth over each one and secure it at the stem. Leave the bags on as the fruit sizes up. The female papaya fruit fly lays her eggs through the wall of small green fruit, and the larvae feed inside the seed cavity where nothing can reach them. The fruit yellows in patches and drops before it ever ripens. Once the eggs are in there is no remedy, so the barrier has to be on the fruit before it is attractive to her.

Save the base of the trunk when a freeze is coming

When a freeze is forecast, cover small plants completely and wrap or bank insulation around the lower portion of the trunk on plants too big to cover. Container plants and dwarf types can be moved or covered outright. Do not prune cold-damaged tissue off until warm weather returns and you can see what actually died. Papaya is damaged or killed below 31F, but a plant killed to the ground will normally throw suckers from a protected lower trunk and bear again within a year, so the trunk base is the part worth defending. Papaya also stops flowering or sets misshapen cat-faced fruit when temperatures run below 59F, which is why zone 9a and colder growers get one season out of a plant and treat it as an annual.

Pick at color break, but the longer it hangs the sweeter it gets

Pick once yellow covers a tenth to a third of the skin, and ripen indoors at room temperature; ripe fruit then keeps 4 to 7 days. Where fruit flies and birds allow, leave fruit on longer for better flavor. Red-fleshed Sunset and UH SunUp build sugar slowly and should hang until a quarter to half ripe, and UH Rainbow is at its best at 70 to 90 percent yellow. Handle fruit gently and pick green if you want it as a vegetable. Sugar accumulates in the fruit while it is still attached to the plant, so a papaya cut at the first blush of yellow will soften and color indoors but stays noticeably flatter tasting than one left to color further on the plant. Fruit takes about 22 weeks to mature in summer heat and about 26 weeks in cool weather, so the calendar will not tell you when - the skin will.